Environment Environnement Canada Canada How Much Habitat is Enough? Third Edition About the Canadian Wildlife Service Environment Canada’s Canadian Wildlife Service is responsible for wildlife matters that are related to species of federal concern. This includes protection and management of migratory birds as well as nationally significant wildlife habitat, endangered species, control of international trade in endangered species and applied science on wildlife issues of national importance.    Executive Summary An important challenge for Canadian society in addressing the natural environment, one of the three elements of sustainability along with society and economy, is to ensure that there is adequate wetland, riparian, forest and grassland habitat to sustain minimum viable wildlife populations and help maintain selected ecosystem functions and attributes. The goal of the How Much Habitat is Enough? series is to provide science-based information and guidelines related to these natural systems and the biodiversity for which we all are the stewards. The information is tailored to be of use to government and non-government restoration practitioners, planners and others involved in natural heritage planning, conservation and preservation. The guidelines concentrated on providing information to assist decision makers in Great Lakes Areas of Concern in the setting and achievement of delisting criteria concerning fish and wildlife habitat beneficial-use impairments, and for post-delisting to provide further guidance on habitat restoration. An assessment of the guidelines (First Edition) in 2002 demonstrated that they were well-used within, but also outside of, Areas of Concern. The assessment indicated that they were indeed used as originally envisioned—as a guide to set restoration targets and restoration project locations, and also as a sciencebased reference for natural heritage practitioners. A Second Edition was prepared and released in 2004. Regular updates are necessary to ensure that current research and scientific literature is incorporated and to provide an opportunity to expose new ways of considering old problems. This has also provided Environment Canada with an opportunity to invite contributions from a wider selection of topic experts. In this, the Third Edition, there are 21 wetland, riparian, forest and grassland habitat guidelines and accompanying rationales. These are typically supported with a discussion addressing additional potential guidelines or issues. The grassland section is a new chapter that represents a first attempt at addressing these complex habitats. More than any other habitat type, grasslands are very dependent on human activity. This section is sure to evolve in the future as many of the newly listed species of conservation concern are found within grassland habitats. In the forest section, there has been an important shift toward a risk-based approach, one that is likely to be applied in other habitats in future years. Overall, the guidelines have expanded significantly both in terms of the supporting discussions within each topic and the base of scientific literature that has been reviewed. The framework of guidelines and supporting text that comprise How Much Habitat is Enough? are effectively an “open file” meant to be built upon and to be adapted according to historical and current local conditions. This framework will hopefully continue to serve as a starting point to develop strategies to conserve habitat, develop natural heritage systems and discuss research needs around those habitats. This is in the spirit of keeping common species common, while restoring ecosystems for those species most at risk—the sensitive, the endangered, the threatened and the rare. How Much Habitat is Enough? 1 Acknowledgements for the Third Edition How Much Habitat is Enough? (A Framework for Guiding Habitat Rehabilitation in Great Lakes Areas of Concern) (1998) was initially guided and championed by the Ontario Ministry of the Environment, the Canadian Wildlife Service of Environment Canada and the Ontario Ministry of Natural Resources. Subsequently, it has evolved into a living document in response to challenges, questions, experience and information brought forward by an active cross-section of individuals, agencies and organizations. These numerous contributions are greatly appreciated and acknowledged with this third edition. This new edition further adds to the extensive list of individuals who have worked on this publication since its beginning in 1995 and on the first and second editions (1998, 2004). There have been many authors, contributors and reviewers over the past 18 years drawing from private consultants, federal and provincial agencies, Conservation Authorities, academia, and conservation organizations. Funding support has come from the Great Lakes Sustainability Fund of Environment Canada, the Ontario Ministry of the Environment and the Canadian Wildlife Service of Environment Canada as well as much support in the form of many in-kind reviews and advice. For the Third Edition: Editors: Graham Bryan and Brian Henshaw Nancy Patterson provides guidance, direction and editorial oversight for the How Much Habitat is Enough? series. Lesley Davy has provided coordination, additional review, and research and editing of the third edition. Reviewers and additional contributors include: Aquila Conservation & Environment Consulting – David Kirk; Beacon Environmental – Margot Ursic; Bird Studies Canada – Debbie Badzinski, Audrey Heagy, Jon McCracken; Canadian Wildlife Service – John Brett, Mike Cadman, Lesley Dunn, Christian Friis, Kevin Hannah, Nancy Patterson, Daniel Rokitnicki-Wojcik; Central Lake Ontario Conservation Authority – Heather Brooks, Kathy Luttrell, Jackie Scott; Conservation Ontario – Bonnie Fox, Don Pearson, Leslie Rich, Jo-Anne Rzadki; Couchiching Conservancy – Ron Reid; Credit Valley Conservation – Dan Banks, Paul Biscaia, Kirk Bowers, Mark Eastman, Kate Hayes, Rod Krick, Liam Marray, Bob Morris, Judi Orendorff, Aviva Patel, Kamal Paudel, Yvette Roy, Saleh Sebti, Scott Sampson, Paul Tripodo, Christine Zimmer; Environment Canada – Anie Cyr, Kathy Lindsay; Ganaraska Region Conservation Authority – Ken Towle; Gray Owl Environmental Inc. – Al Sandilands; Kilgour and Associates – Anthony Francis; Ontario Ministry of Agriculture, Food and Rural Affairs – Paul Smith; Ontario Ministry of Natural Resources – Mike McMurtry, Angus Norman, Brian Potter, Danijela Puric-Mladenovic, Les Stanfield, Allen Woodliffe; Nature Conservancy of Canada – Dan Kraus; Ontario Power Generation – Steve Hounsell; Paul Keddy; Toronto Region Conservation – Dan Clayton, Noah Gaetz, Dave Lawrie, Ryan Ness, Lionel Normand, Paul Prior, Christine Tu, Ron Wu-Winter; Trent University – Tom Whillans; and Upper Thames River Conservation Authority – Cathy Quinlan. 2 How Much Habitat is Enough? Table of Contents 1. How Much Habitat is Enough? Third Edition Introduction ..................................................................... 4 2. Habitat Guidelines .......................................................................................................................................... 16 2.1 2.1.1 Percent Wetlands in the Watershed and Subwatersheds .............................................................. 20 2.1.2 Wetland Location ................................................................................................................................ 22 2.1.3 Amount of Natural Vegetation Adjacent to the Wetland .............................................................. 24 2.1.4 Wetland Area, Shape and Diversity ................................................................................................. 34 2.1.5 Wetland Proximity .............................................................................................................................. 37 2.1.6 Wetland Restoration ........................................................................................................................... 40 2.2 Riparian and Watershed Habitat Guidelines ............................................................................................. 43 2.2.1 Width of Natural Vegetation Adjacent to Stream ........................................................................... 48 2.2.2 Percent of Stream Length Naturally Vegetated .............................................................................. 51 2.2.3 Percent of an Urbanizing Watershed that Is Impervious .............................................................. 53 2.2.4 Additional Riparian and Watershed Considerations ..................................................................... 57 2.2.5 Fish Community Targets .................................................................................................................... 58 2.3 Forest Habitat Guidelines........................................................................................................................... 59 2.3.1 Percent Forest Cover ........................................................................................................................... 61 2.3.2 Area of Largest Forest Patch .............................................................................................................. 66 2.3.3 Percent of Watershed that Is Forest Cover 100 Metres from Edge ............................................... 69 2.3.4 Forest Shape ......................................................................................................................................... 72 2.3.5 Proximity to Other Forested Patches ................................................................................................ 73 2.3.6 Fragmented Landscapes and the Role of Corridors ....................................................................... 76 2.3.7 Forest Quality: Species Composition and Age Structure............................................................... 79 2.4 3. Wetland Habitat Guidelines ....................................................................................................................... 16 Grassland Habitat Guidelines .................................................................................................................... 81 2.4.1 Where to Protect and Restore ............................................................................................................ 84 2.4.2 Habitat Type and Area ....................................................................................................................... 85 2.4.3 Landscape Configuration, Heterogeneity and Connectivity ........................................................ 88 2.4.4 Patch Size.............................................................................................................................................. 92 2.4.5 Landscape Heterogeneity................................................................................................................... 93 2.4.6 Additional Grassland Considerations .............................................................................................. 96 Cited References .............................................................................................................................................. 98 How Much Habitat is Enough? 3 1. How Much Habitat is Enough? Third Edition Introduction How Much Habitat is Enough? provides science- complexity of life and the multiple and often based guidance to conserve and restore habitat unknown linkages that allow species to flourish. for migratory birds, species at risk and other wildlife species within the settled landscapes of The Third Edition of How Much Habitat is the lower Great Lakes and Mixedwood Plains. Enough? contains new and updated science that This biophysical area crosses provincial and has been used to provide new guidance or international borders: in southern Ontario revise existing guidelines. This edition builds on it forms an area south and east of the previous versions, combining and removing Canadian Shield. some guidelines to reflect better the current body of knowledge. And where there is now The landscape of much of the world has a sufficient amount of supporting science, irreversibly changed with increasing requests for guidance on topics such as competition for land and resources. In many grassland habitat have been addressed. areas, the sustainable management of landscapes that considers the natural environment, society and economy is now commonly accepted as the goal in both land How to use this guide: Principles and considerations use planning and policy (North-South How Much Habitat is Enough? was developed Environmental 2010). How Much Habitat is through the 1990s and published in 1998 as A Enough? plays a role in that discussion by Framework for Guiding Habitat Rehabilitation in providing guidance for the restoration and Great Lakes Areas of Concern. This framework, conservation of wildlife habitat: in particular comprised of guidelines and supporting habitat of wildlife species under Environment information, has been used extensively for land Canada’s mandate. In order to contribute best, use, habitat restoration and land securement general guidance is provided at the scale of planning as well as for policy development, habitat patches, watersheds and subwatersheds, as a post-secondary classroom resource and reflecting the scale at which land use planning as a general conservation primer. The basic occurs in the settled landscapes of southern principles the framework was built upon have Ontario. The guidelines in this report are a non- endured and lessons have been learned over the exclusive contribution as to how that landscape years. It is essential to consider these principles could look, reflecting one approach at a and lessons before applying the guidelines. particular scale. The guidelines address the size and configuration of habitat patches and the overall quantity of habitat across a landscape for multiple species. It is an inclusive approach that allows for increased conservation of ecosystems. Such a systematic approach better captures the 4 How Much Habitat is Enough? The basics of migratory birds and other species of federal There are four habitat categories addressed by the guidelines: wetlands, riparian and watershed, forests, and grasslands. In reality these habitats overlap and are separated only to provide clear guiding principles. For example, a concern, such as species at risk, and that the guidelines also reflect the limits of existing scientific knowledge. To help bridge knowledge gaps regarding species of federal concern, science on species that are not specifically under the federal mandate has also swamp could simultaneously been used to help formulate provide forest- and wetland- the guidelines. related ecological functions and can be considered as forest and as Regardless, restoring and conserving wetland under these guidelines. habitat using the guidelines will contribute to the maintenance of Also, the individual guidelines multiple ecological functions and and principles should not be health across various mandates, applied separately but as a suite along with associated derived goods of interacting and interdependent and services for humans. This is guidance. For example, guidance on grassland patch size is best addressed in context of the overarching suggestion to target existing and potential grassland discussed further in the text box Figure 1. A conservation science primer from the Canadian Wildlife Service landscapes. Where habitats are not defined, please refer to the community class descriptions found within Lee et al. (1998). Science The guidelines are based on scientific “Why birds?” Additional general guidance regarding conservation biology and landscape ecology is provided by sources such as Environment Canada’s Beyond Islands of Green report (www.ec.gc.ca/Publications/ default.asp?lang=En& xml=1 CEC82DE-8E6C4A51-A0A5-48A2A6FD078D), and information on the needs of migratory birds is provided in Bird Conservation Region (BCR) Strategies (www.ec.gc.ca/mbc-com/default.asp? lang=En&n=1D15657A-1). literature with an emphasis on published and unpublished studies from eastern North America, south of the Boreal Shield, and in particular the lower Great Lakes region. Supporting information and references are provided with each guideline, and the reader is urged to refer to the original studies and to adapt, and not necessarily adopt, the guidelines. Before applying the guidelines, consider that the advice provided emphasizes the habitat needs How Much Habitat is Enough? 5 Guidelines are not binding targets The framework is not legislative and should be viewed as a means to guide, not dictate, local decisions, by providing planners, rehabilitation teams and other decision makers with the best natural heritage system in degraded landscapes, but protecting existing habitat is far more efficient and more effective. The guidelines are minimums available information. Direction regarding The How Much Habitat is Enough? guidelines are habitat for specific species at specific locations is intended as minimum ecological requirements provided through various provincial and federal with the objective to maintain wildlife policies and statutes including the federal populations at levels that would prevent local Species at Risk Act and Migratory Birds Convention extirpations of species. However, the preference Act, 1994 and Ontario’s Endangered Species Act, is to maintain population levels to provide 2007, Fish and Wildlife Conservation Act and better for long-term species persistence: this Planning Act. The general guidance provided preference is reflected in the Third Edition in the within How Much Habitat is Enough? is “percent forest cover” guideline, which has been secondary to direction provided under rewritten to address risk associated with such statutes. different forest cover amounts. Generally, a greater diversity and amount of habitat than the Conserve it first The conservation of existing habitat must remain the most important ecological planning activity in any jurisdiction. Restoration will always be necessary to have a fully functioning minimum will almost always be more beneficial in terms of supporting healthy species populations and a wider range of ecological functions. It should be noted that How Much Habitat is Enough? should not be used to set lower habitat targets for landscapes that Why birds? An example of the limits of scientific knowledge and the value of focal species Forest birds are often used as indicators of the quality of the landscape because they are more easily surveyed, and more is known about their habitat requirements and distribution than other wildlife groups. Likewise, the protection and regulation of migratory birds is a major part of the Canadian Wildlife Service’s mandate. The guidelines in How Much Habitat is Enough? reflect the general minimum habitat requirements of the different bird pillars or guilds, encompassing priority species within the Ontario portion of BCR 13. Where there are specialized habitat requirements for individual species, these needs are noted in the Bird Conservation Strategy for Ontario’s Bird Conservation Region 13: Lower Great Lakes/St. Lawrence Plain (Environment Canada 2012) or within relevant recovery strategies or action plans (see the SARA registry: www.sararegistry.gc.ca). Less is known about the sensitivity of invertebrates, amphibians, reptiles, plants and small mammals to, for example, forest fragmentation, although amphibians and reptiles have been receiving more research attention over the past decade or so. In the absence of this knowledge, forest birds serve as a useful indicator of forest and ecosystem health. They can be seen as “umbrella species,” a term debated within the field of conservation science that refers to species with requirements that overlap requirements for many other species. 6 How Much Habitat is Enough? currently have habitat in excess of the guideline Coalition’s “Big Picture” illustrate the need to minimums, as often irreversible ecological look at larger ecosystems and landscapes. damage will occur. Removing or degrading habitat, for example moving from 50 to 30% forest cover, will result in reduced wildlife populations, reduced capacity to provide ecological goods and services, and generally lower ecological integrity. The guidelines should be a starting point: where local decisionmaking can provide more habitat than the minimum, then a greater robustness in natural heritage systems can be anticipated. Consider landscape context If a planning unit spans across different ecoregions, then consider representing the full range of natural communities that occur in those ecoregions. For example, concentrating habitat conservation and restoration in only one part of a large watershed may result in an underrepresentation of communities and species in other ecoregions within that watershed. Adapt first, adopt second The guidelines are general and not landscape- or watershed-specific. They should be viewed as ecological principles that detailed local scientific and other knowledge, including traditional knowledge, will build upon and inform where appropriate. Local ecological differences such as the location of historic grasslands or original extent of wetlands, and whether precedence will be given to forest, wetland or grassland habitats, need to be considered where appropriate. Look beyond local boundaries Habitat within a planning unit, such as a watershed or municipality, is often ecologically connected with features beyond that unit. In order to promote linkages of habitat between watersheds and across landscapes, surviving habitat corridors and geographic features should be carefully considered. Likewise, local Figure 2. Multiple ecoregions in one watershed jurisdiction efforts should consider larger-scale planning efforts, such as conservation blueprints and conservation action plans, unique biogeographic features such as the Oak Ridges Moraine, and the role the local landscape plays in the overall diversity and integrity of larger ecoregions and ecozones, such as the Mixedwood Plains. Projects such as the Carolinian Canada How Much Habitat is Enough? 7 Acknowledge stressors beyond habitat There are additional stressors that affect fish and wildlife populations beyond the loss of habitat, including toxins, nutrient enrichment, disease are at risk not because of direct habitat loss but because of other stressors such as invasive pathogens or species (e.g., Butternut, American Chestnut and ash trees). and invasive species. In several cases, species The importance of the matrix The “matrix” in landscape ecology typically refers to land cover or land covers that dominate a landscape. In the Mixedwood Plains, the rural areas outside of large cities and towns are predominantly agricultural, dominated by open farmland and interspersed with natural features and small towns and villages. The farmland may be active, lying fallow or regenerating to forest, wetland or other “natural” land covers. In large cities and towns, a built-up urban matrix dominates. In the Mixedwood Plains and other settled landscapes, protected natural areas, natural heritage features (such as forest patches) or natural heritage systems (interconnected or linked natural features) are embedded within these urban and agricultural matrices. Earlier scientific literature largely disregarded the influence of the matrix on species within natural areas in fragmented landscapes. However, there is a mounting body of evidence suggesting the nature of the matrix can have a profound effect on habitat use by different species, particularly in highly fragmented landscapes. It can do this by (a) directly influencing the dynamics within the natural habitat patch itself, and (b) influencing the ability of species to move between patches (Ewers and Didham 2006). Studies to date in fragmented landscapes have shown that effects are generally greater in urban than in rural areas (Borgmann and Rodewald 2004; Dunford and Freemark 2004; Hansen et al. 2005), and that successional habitats in rural landscapes can provide important supporting habitats for forest species (Gibbs et al. 2005; Milne and Bennett 2007). This means that in much of the Mixedwoods Plains Ecozone, the attributes of the matrix can be as important in influencing species composition and abundance as the attributes of the natural habitat patches themselves. 8 How Much Habitat is Enough? The Third Edition: Emerging considerations Some of the following emerging concepts were protect and conserve species at risk by restoring noted during the preparation of the Third ecosystems upon which those species rely. Edition. Acknowledge the limits of land use planning, restoration and protection Reference points, populations and change The current settled landscapes of northeastern The guidance in this report is aimed at a North America have undergone great change common framework of conservation measures since before European contact. After the retreat that include land use planning, habitat of the great ice sheets and prior to European restoration and protecting natural areas. contact, southern Ontario was a forest biome However, there are forces, such as commodity with vast swamps and abundant marshes that markets, that influence the landscape and do not supported extensive stream systems and easily fit within this conservation framework. abundant populations of forest and wetland For example, agricultural practices create habitat species. There was an unknown extent of for grassland birds in the form of hay or pasture. grassland habitats, many of which were created These practices are driven by factors such as by the activities of First Nations. Subsequent market forces and consumer demand. Land use to settlement by Europeans and with land planning can allow uses such as planting hay clearance in the 19th century, an open country and grazing, but generally it cannot force land matrix arose. Today, the landscape continues to to be used in a particular way. change along with species populations. How Much Habitat is Enough? looks to the dominant Species at risk The guidelines are intended to help keep common species common, and the general guidance provided should not be seen as a substitute for identifying specific species-atrisk habitat under the Species at Risk Act (Government of Canada 2002) or regulated habitat under the Endangered Species Act, 2007 (Government of Ontario 2007). It is intended that the guidance in this report will help to habitats associated with these time periods as multiple reference points for restoration efforts. The goal is to incorporate habitat requirements for a diverse suite of species into the current landscape, while factors such as climate change and invasive species continue to challenge and change ecosystems. The guidelines work on the principle that efforts to conserve and restore the extent and integrity of natural and surrogate habitats will increase ecosystem resilience and better allow species to adapt to evolving conditions. How Much Habitat is Enough? 9 A note about scales and planning units The guidelines operate at different scales and are applied to different features to reflect specific ecological functions. The wetland and riparian guidelines tend to address the health of aquatic habitat within a watershed; therefore, watersheds are the unit and scale used within these guidelines. The forest and grassland guidelines tend to address terrestrial species needs. These needs are independent of watershed boundaries and are instead described in units such as patches and landscapes, as those are the units where ecological effects will be realized. In addition, many of the guidelines are often described in terms of a watershed or municipal scale, regardless of ecological function, because watersheds and municipalities are common conservation planning units. An example of using units independently of function can be seen in one of the forest guidelines. The guideline calling for 30 to 50% forest cover applies to an area under 500 to 1000 square kilometres. This happens to be roughly the size of two major land use planning units: most rural Ontario municipalities and smaller fourth-order (quaternary) watersheds. While the guideline refers to terrestrial habitat independent of watershed function or municipal boundaries, a watershed or municipality is a similar-sized unit that is useful for planning purposes. 1000 Km 2 watershed municipality Figure 3. Similar-sized land units that can be used for planning purposes There is also a hierarchy to some of the guidelines. In terms of the forest guidelines, when regional forest cover is below 30 to 50%, then guidelines addressing patch size and configuration gain importance. When forest cover is above 30 to 50%, then the configuration of the habitat is less important for maintaining species richness. 10 How Much Habitat is Enough? Urban areas mean temperature increase of 2.5 to 3°C as well How Much Habitat is Enough? assumes a predominantly non-urban context. In some of these watersheds, changes to ecosystems have not been so drastic as to preclude rehabilitation of these systems. However, in many urbanized areas, ecosystems have shifted to an entirely new, and often irreversible, ecological state. It will therefore be impossible to fully implement these guidelines in urban areas. For example, a built-up environment will generally not be suitable for many area-sensitive forest birds. The most effective conservation approach would be as an increase in annual levels of precipitation in the order of 10% (Expert Panel on Climate Change for Ontario 2009). Habitats in North America and the species they support are already beginning to show responses to climate change. Documented responses include range shifts in some species, earlier calling for some amphibians, and longer stays on their breeding grounds by some wetland birds (2degreesC 2007; Crick 2004; Niven et al. 2009; Varrin et al. 2009). to identify and protect habitat However, for some of the above minimum levels before Mixedwood Plains habitats the urbanization occurs. However, this net impact upon extent and does not preclude increasing composition remains unclear. For habitat cover in urban areas. example, some wetland species that Wetlands, forests, grasslands and are sensitive to small changes in riparian zones provide many vital hydrologic regimes may be affected. ecological services both for wildlife It is possible that some wetland and humans. Even partial species will expand their range or implementation of the guidelines populations due to a generally will yield ecological benefits. It may be far more appropriate to consider new baselines and targets for habitat in urban areas. There Figure 4. A guide addressing habitat needs in urban areas warmer and wetter climate. The full effects of climate change remain to be determined, and as the climate may also be discussions as to the need to change models become more refined it will be compensate elsewhere in a region for habitat possible to better predict anticipated effects on a loss due to urbanization within that region, regional scale, and for different habitats. which would affect habitat targets set outside urban areas. A precautionary approach is to strive toward protecting and restoring more complete Climate change Although there are many models and predictions, current data suggest that over the next 40 or so years there will be an average ecosystems with greater integrity that will be more resilient to change. This requires venturing beyond the minimum amounts of forests, wetlands, grasslands and riparian areas required to maintain species populations above extinction thresholds. How Much Habitat is Enough? 11 What about the Canadian Shield? The environment of the Canadian Shield contrasts greatly with the settled landscapes of the Mixedwood Plains of southern and eastern Ontario. The Shield’s complex terrain is characterized by rocky outcrops, relatively thin soils covering Precambrian bedrock, and an abundance of lakes and wetlands. It remains largely forested. In this rugged landscape, with relatively low agricultural potential, the human population density never reached that of areas further to the south. Today, the Shield is in many regards an opposite of the Mixedwood Plains—cleared land and human settlements form patches within the forested matrix. In such an environment the approach taken and presented in How Much Habitat is Enough?—based as it is on science from the settled agricultural landscapes—does not transfer well to the Shield. An area of particular interest to planners and ecologists alike is the southern part of the Shield. South of the French River and Algonquin Park is a distinct transition area bordering the Mixedwood Plains and the Great Lakes. This is an area of growing human influence with many growing urban areas and second homes and other residential and related development adding to existing land uses and activities such as forestry, mining and recreation. In this region, a reasonable approach might be to consider how much the landscape can be disturbed before there are substantive ecological effects. This contrasts with the “How Much” approach used in settled landscapes that considers the minimum natural land cover that may be required to conserve biodiversity. This different approach was outlined in the unpublished report How Much Disturbance is too Much?: Habitat Conservation Guidance for the Southern Canadian Shield available from Environment Canada (Beacon Environmental 2012). The report does not provide specific guidelines; rather, it assesses the available science and provides an initial review of the topic along with the introduction of general principles and concepts. As a foundation, How Much Disturbance is too Much? stresses the importance of identifying local and regional “habitat mosaics.” In these defined areas, restricting most types of development should be considered. These areas would consist largely of forested areas with components of diverse wetlands (e.g., swamps and marshes, as well as fens) interspersed with open, shrub and treed rock barrens. These areas could be based on landscapes having relatively high levels of the following characteristics: diversity, naturalness and habitat extent. They could be identified at two levels: (1) Regional Habitat Mosaics and (2) Local Habitat Mosaics. Regional Habitat Mosaics could include blocks of habitat identified as important on a regional scale (e.g., within an ecodistrict or ecoregion) and would likely include many of the Crown Lands in the southern Canadian Shield. Local Habitat Mosaics could include blocks of habitat identified as important on a local scale (e.g., within a county or township) but similarly capture concentrations of diverse natural areas that are largely undisturbed. Local mosaics would contain one or more large blocks of habitat. Planning could be coordinated at both regional and local jurisdictional levels to identify opportunities for ensuring that Regional and Local Habitat Mosaics are complementary or in proximity to each other where possible, and where it makes sense within the given biophysical and land use context. These areas should cover 50 to 60% of a jurisdiction and be connected to one another. Disturbances within the mosaics should be avoided, especially disturbances created by roads of any kind. 12 How Much Habitat is Enough? Table 1. Summary of Wetland, Riparian, Forest and Grassland Habitat Guidelines Parameter Guideline Wetland Habitat Percent wetlands in the watershed and subwatersheds Wetland location in the watershed Ensure no net loss of wetland area, and focus on maintaining and restoring wetland functions at a watershed and subwatershed scale based on historic reference conditions. At a minimum, the greater of (a) 10% of each major watershed and 6% of each subwatershed, or (b) 40% of the historic watershed wetland coverage, should be protected and restored. Wetlands can provide benefits anywhere in a watershed, but particular wetland functions can be achieved by rehabilitating wetlands in key locations, such as headwater areas (for groundwater discharge and recharge), floodplains and coastal wetlands. Consideration should also be given to protecting networks of isolated wetlands in both urban and rural settings. Critical Function Zones should be established around wetlands based on knowledge of species present and their use of habitat types. Amount of natural vegetation adjacent to the wetland Protection Zones should protect the wetland attributes from stressors. Recommended widths should consider sensitivities of the wetland and the species that depend upon it, as well as local environmental conditions (e.g., slopes, soils and drainage), vegetative structure of the Protection Zone, and nature of the changes in adjacent land uses. Stressors need to be identified and mitigated through Protection Zone design. Wetland proximity Wetlands that are in close proximity to each other, based on their functions, or that are in close proximity to other natural features, should be given a high priority in terms of landscape planning. Wetland area, shape and diversity Capture the full range of wetland types, areas and hydroperiods that occurred historically within the watershed. Swamps and marshes of sufficient size to support habitat heterogeneity are particularly important, as are extensive swamps with minimum edge and maximum interior habitat to support area-sensitive species. Focus on restoring marshes and swamps. Restore fens under certain conditions. For effective restoration, consider local site conditions, have local sources to Wetland restoration propagate new vegetation, and wherever possible refer to historic wetland locations or conditions. Prioritize headwater areas, floodplains and coastal wetlands as restoration locations. Riparian Habitat Width of natural vegetation adjacent to stream Both sides of streams should have a minimum 30-metre-wide naturally vegetated riparian area to provide and protect aquatic habitat. The provision of highly functional wildlife habitat may require total vegetated riparian widths greater than 30 metres. Percent of stream length naturally vegetated 75% of stream length should be naturally vegetated. How Much Habitat is Enough? 13 Parameter Percent of an urbanizing watershed that is impervious Guideline Urbanizing watersheds should maintain less than 10% impervious land cover in order to preserve the abundance and biodiversity of aquatic species. Significant impairment in stream water quality and quantity is highly likely above 10% impervious land cover and can often begin before this threshold is reached. In urban systems that are already degraded, a second threshold is likely reached at the 25 to 30% level. Forest Habitat 30% forest cover at the watershed scale is the minimum forest cover threshold. This equates to a high-risk approach that may only support less than one half of the potential species richness, and marginally healthy aquatic systems; Percent forest cover 40% forest cover at the watershed scale equates to a medium-risk approach that is is likely to support more than one half of the potential species richness, and moderately healthy aquatic systems; 50% forest cover or more at the watershed scale equates to a low-risk approach that is likely to support most of the potential species, and healthy aquatic systems. Area of largest forest patch A watershed or other land unit should have at least one, and preferably several, 200-hectare forest patches (measured as forest area that is more than 100 metres from an edge). Forest shape To be of maximum use to species such as forest breeding birds that are intolerant of edge habitat, forest patches should be circular or square in shape. Percent of watershed that is forest cover 100 m from forest edge The proportion of the watershed that is forest cover and 100 metres or further from the forest edge should be greater than 10%. Proximity to other forested patches Fragmented landscapes and the role of corridors To be of maximum use to species such as forest birds and other wildlife that require large areas of forest habitat, forest patches should be within two kilometres of one another or other supporting habitat features. “Big Woods” areas, representing concentrations of smaller forest patches as well as larger forest patches, should be a cornerstone of protection and enhancement within each watershed or land unit. Connectivity width will vary depending on the objectives of the project and the attributes of the forest nodes that will be connected. Corridors designed to facilitate species movement should be a minimum of 50 to 100 metres in width. Corridors designed to accommodate breeding habitat for specialist species need to meet the habitat requirements of those target species and account for the effects of the intervening lands (the matrix). Forest quality – Watershed forest cover should be representative of the full diversity of naturally species composition occurring forest communities found within the ecoregion. This should include and age structure components of mature and old growth forest. 14 How Much Habitat is Enough? Parameter Guideline Grassland Habitats Where to protect and restore Focus on restoring and creating grassland habitat in existing and potential grassland landscapes. Habitat type and area Maintain, restore and create native grassland patches to their historic extent and type at a county, municipal and/or watershed scale considering past presence and current conditions. Landscape configuration, heterogeneity and connectivity Grassland habitat patches should be clustered or aggregated, and any intervening land cover should be open or semi-open in order to be permeable to species movement. Patch size Maintain and create small and large grassland patches in existing and potential local grassland landscapes, with an average grassland patch area of greater than or equal to 50 hectares and at least one 100-hectare patch. Landscape heterogeneity Some grassland habitat should be located adjacent to hedgerows, riparian and wetland habitats for species that require different habitat types in close proximity. How Much Habitat is Enough? 15 2. Habitat Guidelines 2.1 Wetland Habitat Guidelines Wetlands are defined here following the Ontario typically have acidic organic soils, and often Wetland Evaluation System of the Ontario contain Sphagnum mosses and ericaceous shrubs Ministry of Natural Resources. Essentially, these (Ericaceae, a family of plants commonly found are areas where hydrophytic (water-adapted) in acidic and infertile conditions). plants comprise 50% or more, by cover, of the vegetation in a given area, and when standing Fens are peat-accumulating wetlands with water is present, it is less than 2 metres deep. groundwater as the dominant water source, which support a variety of plant species, Wetlands can provide valuable ecological and including orchids, sedges and grasses. hydrological functions at both site-specific and watershed scales. Many of southern Ontario’s Swamps are wetlands dominated by trees and flora and fauna inhabit wetlands during part or shrubs, with periodic standing water, limited all of their life cycle, including many species at drainage, and often neutral or slightly acidic risk. Wetlands are known to be biologically organic soils. diverse habitats, tending to support a wider range of flora and fauna than either temperate Marshes are wetlands that are almost always upland forests or grasslands, particularly on a flooded and are characterized by a mixture of species per area basis (Comer et al. 2005; emergent, floating and submerged aquatic Gibbons et al. 2006; Meyer et al. 2003). vegetation such as reeds, sedges, pondweeds and water lilies. Wetland types Understanding the diversity of different wetlands is important for conservation planning and restoration because of their differing hydrologic regimes and vegetative structures, each supporting unique assemblages of species and combinations of ecological functions. The wetland classification system for southern Ontario, which is the standard that has been in place since the 1980s, divides wetlands in the Mixedwood Plains into four types: bogs, fens, swamps and marshes. Figure 5. Derryville Bog, Durham Region, Ontario: one of very few true bogs in southern Ontario © Beacon Environmental Bogs and fens Bogs are peat-accumulating wetlands that trap precipitation as the major water source. They 16 How Much Habitat is Enough? Bogs are highly specialized environments, and true bogs are rare in the southern part of the Great Lakes basin. They receive almost all of seasonal habitat attributes, with the understorey their water and nutrients from precipitation, being dominated by wetland species early in the are acidic, have very low productivity and are growing season, and plants adapted to drier dominated by plants that are adapted to low conditions playing a greater role later in the nutrient levels. Fens receive most of their water year. In addition, spring flooding creates and nutrients from groundwater, and they may ephemeral ponds that are used for breeding be either nutrient-rich or nutrient-poor, with by frogs, toads and salamanders. These same nutrient-rich fens having a greater diversity of pools are also important breeding areas for species while the nutrient-poor share many invertebrates such as some caddisflies and characteristics with bogs. midges, and these, in turn, are important food for bats and many bird species. While they play major roles in the hydrology and ecology of the Boreal Shield Hudson Plains Ecozone, bogs and nutrient-poor fens are relatively rare and unique in the south and play less of a role in providing wildlife habitat than the larger, more extensive, and more diverse swamps and marshes of the Mixedwood Plains. Swamps Swamps have more than 25% tree or shrub cover; swamps are a major natural landscape feature because of their sheer extent (they comprise almost 90% of the remaining wetland area in southern Ontario). Swamps make significant contributions to forest cover and to watershed hydrology and aquatic health. They also disproportionately contribute to biodiversity because of the variety of cover types they provide. This includes providing mammal wintering areas, sources for a high proportion of cold-water streams, habitat for Figure 6. Flooded swamp at Minesing wetland © Graham Bryan Hydrologically, swamps shape the characteristics and health of lower-order streams; they moderate stream hydrology and help maintain water quality. This affects wildlife habitat all the way downstream to the receiving waters of species-rich coastal wetlands. forest-interior or area-sensitive species, and Marshes habitat for many wildlife species, including Marshes are typically associated with the word numerous species at risk, often all simultaneously. The diversity of swamps goes beyond their extent and cover types, and includes a temporal element that is key to the life cycle of many wildlife species. The plant communities of many swamps are dynamic and provide a variety of “wetland”; however, they represent only about 10% of the area of wetlands in southern Ontario, and about 5% of all of the province’s wetlands (Riley 1988). Today, extensive marshes are rare in the landscape relative to historic conditions, so species that require this habitat are also restricted in their distribution. Several fish How Much Habitat is Enough? 17 and wildlife species are totally dependent on resulting in the maintenance of downstream marshes, and a high proportion of these are of wildlife habitat. Marsh vegetation also stabilizes provincial and federal concern. Some examples shorelines and reduces the risk of erosion, of obligate marsh species include Spotted Gar, protecting and stabilizing in-situ and adjacent Spotted Sucker, Banded Killifish, Bullfrog, habitat, along with reducing sediment delivery Pied-billed Grebe, Red-necked Grebe, Least to water bodies (Sheldon et al. 2005). Marshes Bittern, Ruddy Duck, King Rail, Virginia Rail, are also the primary building block for wetland Sora, Common Gallinule, American Coot, restoration; establishing a marsh is often the Forster’s Tern, Black Tern, Marsh Wren and initial step in the long-term process of Muskrat. establishing swamps and more complex and diverse wetland communities. The noteworthy ecological role of marshes is illustrated by Jude and Pappas (1992), who The following series of wetland habitat found that of 113 fish species occurring in guidelines relate to the amount of wetlands and the Great Lakes, 41.6% were coastal marsh wetland location in a watershed, the amount of species and 31% used coastal marshes for vegetation adjacent to a wetland, representation nursery habitat or feeding. In Lake Ontario of wetland area and type, and wetland marshes, 63.9% of species present used marshes restoration, as summarized in Table 2. for spawning and 86% of species used marshes as nursery habitat. The importance of marshes to the fish of the Great Lakes and also inland water bodies cannot be overemphasized. Approximately 90% of the fish biomass in Lake Erie is forage fish (also called prey or bait fish), and most of this is produced in wetlands (Keast et al. 1978; Stephenson 1990). Likewise, marshes are key to waterfowl nesting and stopover. As with swamps, inland marshes help shape stream hydrology and aquatic ecosystem health, including playing a major role in improving and maintaining water quality, Figure 7. Long Point – a Great Lakes Coastal Marsh © Environment Canada Wet meadow marshes – a specialized wetland type Wet meadows provide habitat for a high diversity of plants and wildlife in southern Ontario. Rare species known to inhabit wet meadows include Henslow’s Sparrow and Yellow Rail. Wet meadows are habitats subject to temporary flooding dominated by herbaceous plants typical of moist soils, and can be easily overlooked as upland habitats if seen during a dry period. These types of wetlands occur predominantly along shorelines of large lakes and rivers where invasion by woody species is also prevented by ice scouring and waves. 18 How Much Habitat is Enough? Table 2. Summary of Wetland Habitat Guidelines Parameter Percent wetlands in the watershed and subwatersheds Wetland location in the watershed Guideline Ensure no net loss of wetland area, and focus on maintaining and restoring wetland functions at a watershed and subwatershed scale based on historic reference conditions. At a minimum, the greater of (a) 10% of each major watershed and 6% of each subwatershed, or (b) 40% of the historic watershed wetland coverage, should be protected and restored. Wetlands can provide benefits anywhere in a watershed, but particular wetland functions can be achieved by rehabilitating wetlands in key locations, such as headwater areas (for groundwater discharge and recharge), floodplains and coastal wetlands. Consideration should also be given to protecting networks of isolated wetlands in both urban and rural settings. Critical Function Zones should be established around wetlands based on knowledge of species present and their use of habitat types. Amount of natural vegetation adjacent to the wetland Wetland proximity Protection Zones should protect the wetland attributes from stressors. Recommended widths should consider sensitivities of the wetland and the species that depend upon it, as well as local environmental conditions (e.g., slopes, soils and drainage), vegetative structure of the Protection Zone, and nature of the changes in adjacent land uses. Stressors need to be identified and mitigated through Protection Zone design. Wetlands that are in close proximity to each other, based on their functions, or that are in close proximity to other natural features, should be given a high priority in terms of landscape planning. Capture the full range of wetland types, areas and hydroperiods that occurred historically within the watershed. Swamps and marshes of sufficient size to Wetland area, shape support habitat heterogeneity are particularly important, as are extensive and diversity swamps with minimum edge and maximum interior habitat to support areasensitive species. Focus on restoring marshes and swamps. Restore fens under certain conditions. Wetland restoration For effective restoration, consider local site conditions, have local sources to propagate new vegetation, and wherever possible refer to historic wetland locations or conditions. Prioritize headwater areas, floodplains and coastal wetlands as restoration locations. How Much Habitat is Enough? 19 2.1.1 Percent Wetlands in the Watershed and Subwatersheds > Guideline Ensure no net loss of wetland area, and focus on maintaining and restoring wetland functions at a watershed and subwatershed scale based on historic reference conditions. At a minimum, the greater of (a) 10% of each major watershed and 6% of each subwatershed, or (b) 40% of the historic watershed wetland coverage, should be protected and restored. > Rationale All watersheds in southern Ontario currently have less wetland cover than they did prior to extensive European settlement (c. 1800), with losses exceeding 70% in many jurisdictions (Ducks Unlimited Canada 2010; Snell 1987). The guideline addresses basic minimal generic ecological functions and does not address the overall loss of unique wetland ecosystems that dominated portions of southern Ontario. Any investment in wetland restoration beyond the minimum guideline toward the historical wetland baseline will result in enhanced wetland functions and contributions to ecological goods and services. Maintenance of wetland cover across a watershed provides many ecological and hydrologic benefits. The extent of these benefits varies depending on a variety of biophysical factors including predominant landforms and soils, wetland locations, types of wetland, and predominant land uses (Flanaghan and Richardson 2010; Keddy 2010; Zedler 2003). Historically the overall wetland coverage within the Great Lakes basin exceeded 10% (Detenbeck et al. 1999), but there was significant variability among watersheds and jurisdictions. For example, recent studies of three watersheds in the Lake Simcoe Watershed (i.e., Whites Creek, Maskinonge River and Innisfil Creek) have 20 How Much Habitat is Enough? resulted in wetland cover estimates of 68, 52 and 59% respectively (A. Norman, OMNR, London, pers. comm. 2011), while analyses by Ducks Unlimited Canada (2010) indicate that presettlement wetland cover in some counties such as Peel was as low as 7.6%, and as high as 83.4% in others such as Essex. Using historical reference points can be useful for helping to determine an appropriate level of wetland cover at the watershed or jurisdictional scale (e.g., Bedford 1999; Puric-Mladenovic and Strobl 2006). More recent historical mapping (c. 1930–1980) can also be used to help target former wetland areas that may be suitable for restoration. One of the real challenges for maintaining key ecological and hydrological functions is in estimating the critical threshold for wetland cover in a watershed (or jurisdiction). Not surprisingly, the science on this topic shows variation among watersheds, and focuses on protection of hydrologic functions. In Wisconsin, Hey and Wickencamp (1996) examined nine watersheds and found that increasing the amount of wetland in a watershed resulted in reduced yields of water downstream, reduced flooding, higher base flows and reduced occurrence of high flows. However, these responses flattened very rapidly beyond 10% wetland cover. Zedler (2003) scales can be used to ensure that a minimum determined that flood abatement, water quality level of wetlands are distributed throughout improvement and biodiversity support declined the watershed. significantly when about 60% of the Upper Midwest’s historical wetland area was drained, While the maintenance of wetland functions is suggesting retention of about 40% of that area’s as or more important than the maintenance of wetland cover would continue to support those wetland area, given the limited nature of our key functions. A study conducted by the current understanding of wetland functions, University of Minnesota (Johnston et al. 1990) particularly at the watershed scale, wetland area found that watersheds in the southern United serves as a useful surrogate measure. States containing less than 10% wetlands were more susceptible to incremental losses of In many watersheds in southern Ontario, wetland functions than watersheds with more particularly urbanized watersheds, it is not wetlands. This condition was found to be possible to return to historical or pre- particularly true for flood control and urbanization levels of wetland cover or function suspended solids loadings. because of the degree and nature of alteration that has already occurred. Nonetheless, given These studies support the importance of the known extent of wetland losses in this part considering watershed-specific differences in of the province and the critical hydrological and historical wetland cover, information that is ecological functions provided by these habitats, readily available to jurisdictions in southern a “no net loss” approach combined with a Ontario, in older as well as in updated reports commitment to work towards at least 40% of (i.e., Ducks Unlimited Canada 2010; Snell 1987). historical levels of coverage where it does not In applying this guideline, current wetland already exist is recommended to yield tangible cover, topography, soils and extent of benefits for communities and wildlife. The impervious surfaces in a specific watershed guideline can be achieved, in order of priority, must also be considered. In the absence of such through: (1) protection of extant wetlands; information, the guideline of 10% cover at the (2) enhancement of extant wetlands; (3) watershed and 6% cover at the subwatershed restoration of wetlands in historical locations; and (4) creation of wetlands in suitable areas. How Much Habitat is Enough? 21 2.1.2 Wetland Location > Guideline Wetlands can provide benefits anywhere in a watershed, but particular wetland functions can be achieved by rehabilitating wetlands in key locations, such as headwater areas (for groundwater discharge and recharge), floodplains and coastal wetlands. Consideration should also be given to protecting networks of isolated wetlands in both urban and rural settings. > Rationale Wetlands anywhere within a watershed will provide both ecological and hydrological benefits, but are increasingly being understood to provide different functions depending on their location in the watershed, as well as the characteristics of the watershed itself. The extent to which wetlands can provide water quality benefits has been linked to the biophysical characteristics of the watershed (Norton and Fisher 2000) as well as the land use context (Mitsch and Gosselink 2000; Zedler 2003). Model-based analyses indicate that water quantity and quality benefits are derived from protection of a range of wetland sizes throughout the watershed, with small (i.e., 0.2 hectares) headwater wetlands being important for sediment removal, medium-sized (i.e., 10 hectares) mid-reach wetlands retaining significant amounts of phosphorus, and large (i.e., 250 hectares) floodplain wetlands effectively storing and attenuating long-period hydrologic flows (Cohen and Brown 2007). Earlier literature has also shown that wetlands can perform different functions depending on flow levels. For example, Johnston et al. (1990) found in their watershed-scale study in Minnesota that wetlands adjacent to streams were more effective at attenuating suspended solids, total phosphorus and ammonia during periods of high flow, and more effective at 22 How Much Habitat is Enough? removing nitrates in periods of low flow. These results support the need for wetlands of various sizes and in various locations in the watershed, at least for provision of a more full range of water quality benefits. In headwater areas, wetlands can provide beneficial functions. For swamps, these include protection of the quality of groundwater (discharge or recharge or both), introduction of leaves and woody debris that are essential to providing habitat for fish and macroinvertebrates downstream (Gurnell et al. 1995 cited in Detenbeck et al. 1999), and reducing the warming of streams at the source. In turn, good water-quality conditions in higher portions of watersheds are likely to benefit downstream coastal wetland ecosystems (e.g., Crosbie and Chow-Fraser 1999). Janisch et al. (2011) speak to the benefits of headwater wetlands in influencing headwater surface area processes, including improving resilience of streams following disturbances. Further downstream, palustrine and riverine wetlands are important in reducing and asynchronizing peak flows, improving water quality, and providing habitat for aquatic invertebrates, fish and other wildlife. Richardson et al. (2011) were able to demonstrate, through a multi-phased restoration project of a stream and riparian wetland area located within the lower portion of maintenance of amphibian and reptile a watershed in North Carolina, that wetlands in biodiversity (Comer et al. 2005). A study lower reaches associated with riparian areas undertaken by Russell et al. (2002) in managed can also provide significant benefits. They young-growth forests in the Coastal Plain of documented reduced downstream water pulses, South Carolina found that isolated wetlands nutrients, coliform bacteria and stream erosion; were focal points of amphibian and reptile a substantial attenuation of nitrogen and richness and abundance and contributed more phosphorus; and an increase in wetland plant to regional biodiversity than would be expected abundance and diversity within the floodplain. based on their size and ephemeral hydrology. McKinney and Charpentier (2009) found that In coastal areas such as the Great Lakes, geographically isolated wetlands contribute to marshes are crucial habitat for fish. Wetland stormwater retention, flood prevention and habitats in lakes tend to support more fish maintenance of water quality. biomass than open parts of the lake, and are important in supporting fish production and Wetlands can also provide benefits that address species diversity (Petzold 1996; Trebitz et al. specific objectives or problems at a watershed or 2009). Petzold (1996) found about 60% of Lake more site-specific scale. Wetlands located within Superior’s fish biomass was associated with urban or agricultural settings act to improve wetlands and concluded that these habitats are water quality by retaining nutrients and critical for the fisheries of the entire lake. This is sediments, and providing stormwater supported by observations that changes in the management (Flanagan and Richardson 2010; amount and type of wetlands at Long Point McKinney and Charpentier 2009). Flanagan and have affected the fish assemblages populating Richardson (2010) found that former wetland all of Lake Erie (T. Whillans, Trent University, areas converted to agricultural uses were linked Peterborough, pers. comm. 2011). to higher levels of phosphorus in nearby water bodies and recommended restoration of at least Recent literature indicates that geographically some of these areas to wetland to address this isolated wetlands also provide water quality issue. Some of these more localized benefits are and flow regulation services, as well as discussed in the following section. How Much Habitat is Enough? 23 2.1.3 Amount of Natural Vegetation Adjacent to the Wetland > Guideline Critical Function Zones should be established around wetlands based on knowledge of species present and their use of habitat types. Protection Zones should protect the wetland attributes from stressors. Recommended widths should consider sensitivities of the wetland and the species that depend upon it, as well as local environmental conditions (e.g., slopes, soils and drainage), vegetative structure of the Protection Zone, and nature of the changes in adjacent land uses. Stressors need to be identified and mitigated through Protection Zone design. > Rationale The amount of natural habitat that is located adjacent to wetlands can be important to the maintenance of wetland functions and attributes, particularly for wetland-dependent species that rely on these adjacent natural areas for portions of their life cycle. In cases where these adjacent natural areas form an intrinsic part of the wetland ecosystem, providing a variety of habitat functions for wetlandassociated fauna that extend beyond the wetland limit, these lands can be described as Critical Function Zones (CFZs). Beyond habitat functions, adjacent natural and semi-natural areas can also provide what are 24 How Much Habitat is Enough? often called “buffer” functions by protecting the wetland (and its associated CFZs) from external stressors. These stressors are typically associated with human-induced changes in land use and include sedimentation, contaminants, noise, light, physical disturbances (e.g., trampling or garbage dumping), and the introduction and spread of invasive species. These adjacent areas that serve primarily a protective function are best described as Protection Zones (PZs). Determining the appropriate amount of natural area adjacent to a wetland requires independent consideration of the CFZ and the PZ, and the functions of the two should not be confused. Critical Function Zones and Protection Zones defined The term Critical Function Zone (CFZ) describes non-wetland areas within which biophysical functions or attributes directly related to the wetland occur. This could, for example, be adjacent upland grassland nesting habitat for waterfowl (that use the wetland to raise their broods). The CFZ could also encompass upland nesting habitat for turtles that otherwise occupy the wetland, foraging areas for frogs and dragonflies, or nesting habitat for birds that straddle the wetland-upland ecozone (e.g., Yellow Warbler). A groundwater recharge area that is important for the function of a wetland but located in the adjacent lands could also be considered part of the CFZ. Effectively, the CFZ is a functional extension of the wetland into the upland. It is not a buffer for the Critical Function Zone Waterfowl nesting 200 m wetland. See Figure 8, The Critical Function and Protection Zones. Once identified, the CFZ Wetland (along with the wetland Painted turtle nesting 60-90 m itself) needs to be protected from adverse effects that originate from external sources by a Dragonfly occurrence 160 m Protection Zone (PZ). The PZ’s primary function is to protect the wetland and its associated functions from stressors associated with activities in, or changes to, the Protection Zone lands external to the wetland. The PZ acts as a buffer in response Figure 8. The Critical Function and Protection Zones to stressors on wetland water quality, water quantity (including the timing and degree of changes in water levels), habitat functions, or all three. PZs are analogous to filter strips and are typically vegetated areas for intercepting stormwater runoff and attenuating and transforming associated nutrients or other contaminants. They also provide physical separation from one or more stressors such as noises or visual disturbances. And they protect against direct human-associated intrusions into the wetland. Such functions are well-established in the literature (e.g., Kennedy et al. 2003; Lowrance et al. 2002; Passeport et al. 2010; Sheldon et al. 2005; Thompson et al. 2004; Woodard and Rock 1995). Depending on the nature of the stressors and the sensitivities of the wetland, alternative PZ design features such as a fence can be effective. Fundamentally, the PZ is aimed at reducing impacts on wetland functions that originate from the upland side. How Much Habitat is Enough? 25 A word about buffers and adjacent land The term “buffer” is a common term used for lands adjacent to wetlands and watercourses. In How Much Habitat is Enough?, the term “adjacent lands” is commonly used and is meant to be interpreted literally as the lands immediately adjacent to a wetland. This is because adjacent lands may have buffer functions, important non-buffer habitat functions, or both. These distinctions are important. For example, an area that serves a CFZ for one species may also act as a buffering PZ for another species’ CFZ, or as a wetland or stream buffer. In land use planning in Ontario, the term “adjacent lands” is used specifically to refer to “those lands contiguous to a specific natural heritage feature or area where it is likely that development or site alteration would have a negative impact on the feature or area” (MMAH 2005). These are typically prescribed as a set distance (e.g., between 50 and 120 m) from the boundary of the natural feature. The combined CFZ and its PZ may range Guidance regarding non-wetland habitat in total width from a few metres to hundreds requirements for wildlife is increasingly of metres. Management objectives, individual available, and some of this current information characteristics of the wetland, ecological is summarized in Table 3. interactions with upland areas, and the source, magnitude and frequency of potential stressors For wildlife, the variability in ranges of CFZs is and engineering options all contribute to the great because of both inter- and intra-species design of effective CFZ and PZ areas. variability in documented distances travelled for feeding and overwintering, as well as variability For CFZ determination, a good understanding among breeding sites (e.g., Nichols et al. 2008). of the local biophysical context, hydrologic In time, more data will become available as regime and the species using the given wetland, further research (e.g., ongoing radio-telemetry as well as the nature and extent of their non- studies) will lead to a more complete wetland habitat requirements, is required (e.g., understanding of various species’ habitat Guerry and Hunter 2002; Pope et al. 2000). requirements. 26 How Much Habitat is Enough? Table 3. Selected Critical Function Zone Data for Wetlands Species Extent of Critical Function Zone from Wetland Edge Reference Notes Maximum 600 m, mean 60 m; range 1 to 164 m; mean 90 m, range 1 to 621 m Semlitsch and Bodie 2003 Review of three studies 1 to 620 m, mean 90 m for nesting Christens and Bider 1987 85 m for nesting, 54 m for dormancy Joyal et al. 2001 75 to 312 m for nesting; dormancy up to 412 m Milam and Melvin 2001 Maximum 150 m; range 3 to 265 m; range 60 to 250 m Semlitsch and Bodie 2003 Review of three studies 380 m for nesting, 18 m for basking and 114 m for dormancy Joyal et al. 2001 Distances are mean plus standard deviation Mean 815 m, range 650 to 900 m; mean 135 m, range 2 to 1115 m; mean 168 m Semlitsch and Bodie 2003 Review of three studies Spiny Softshell Mean 3 m; range 2 to 3 m; mean 0.3 m; mean 5 m Semlitsch and Bodie 2003 Review of four studies; latter two studies single individuals Snapping Turtle Mean 94 m, range 38 to 141 m; mean 37 m, range 1 to 183 m; mode 25 m, maximum 100 m; mean 27 m, range 1 to 89 m Semlitsch and Bodie 2003 Review of four studies Wood Turtle Mean 27 m, range 0 to 500 m; maximum 600 m; mean 60 m, maximum 200 m Semlitsch and Bodie 2003 Review of four studies Northern Map Turtle Mean 2 m, range 2 to 3 m Semlitsch and Bodie 2003 Review of one study Eastern Musk Turtle Mean 7 m, range 3 to 11 m Semlitsch and Bodie 2003 Review of one study No adjacent lands area recommended Attum et al. 2007 Species fairly sedentary and generally does not require upland habitat Reptiles Midland Painted Turtle Spotted Turtle Blanding’s Turtle Northern Watersnake Maximum 6 m Semlitsch and Bodie 2003 Distances are mean plus standard deviation Review of one study How Much Habitat is Enough? 27 Species Western Chorus Frog Wood Frog Green Frog Bullfrog Extent of Critical Function Zone from Wetland Edge Frogs Reference Notes Maximum 213 m, mean 75 m Semlitsch and Bodie 2003 Review of one study Post-breeding movements ranged from 102 m to 340 m, median 169 m Baldwin et al. 2006a Recommends conservation of network connected habitats 30 m inadequate to support viable populations Harper et al. 2008 Did not test beyond 30 m 11 to 35 m partially mitigates timber harvest impacts Perkins and Hunter 2006 Study is in forested landscape where the nonbuffered area is logged 40% of individuals wintered further than 100 m from breeding pond Regosin et al. 2003 Recommends maintenance of suitable terrestrial habitat beyond 100 m Mean 36 ± 25 m for foraging Lamoureux et al. 2002 Mean 137 m, maximum 457 m; mean 121 m, maximum 360 m; mean 485 m , range 321 to 570 m Semlitsch and Bodie 2003 Review of three studies Mean 406 m Semlitsch and Bodie 2003 Review of one study Salamanders Spotted Salamander Mean maximum 106 m Veysey et al. 2009 Salamanders used clearcut areas to some degree 30 m inadequate to support viable populations Harper et al. 2008 Did not test beyond 30 m 60% of individuals wintered further than 100 m from breeding pond Regosin et al. 2003 Recommend maintenance of suitable terrestrial habitat beyond 100 m Mean 67 m, range 26 to 108 m; mean 103 m, range 15 to 200 m; mean 64 m, range 0 to 125 m; mean 150 m, range 6 to 220 m; mean 192 m, range 157 to 249 m, mean 118 m, range 15 to 210 m Semlitsch and Bodie 2003 Review of six studies Faccio 2003 Recommended “life zone” to encompass 95% of population was 175 m Range 3 to 219 m, mean 112.8 m for overwintering 28 How Much Habitat is Enough? Species Extent of Critical Function Zone from Wetland Edge Reference Notes Ambystoma salamanders Mean 125 m for adults, 70 m for juveniles Semlitsch 1998 Recommended “life zone” to encompass 90% of population was 164 m Range 3 to 219 m, mean 112.8 m for overwintering Faccio 2003 Recommended “life zone” to encompass 95% of population was 175 m Mean 39 m, range 22 to 108 m; mean 92 m, range 15 to 231 m; mean 252 m, range 20 to 625 m: mean 250 m Semlitsch and Bodie 2003 Review of four studies 52% of individuals wintered more than 100 m from breeding pond Regosin et al. 2003 Recommend maintenance of suitable terrestrial habitat beyond 100 m No distances given Roe and Grayson 2008 Newts are wide-ranging and active in the terrestrial habitat No distances given Rinehart et al. 2009 Proximity to developed land cover essentially precluded newt occupancy Jefferson Salamander Blue-spotted Salamander Eastern Newt Nesting Waterfowl Various species in Ontario 0 to more than 400 m; 90% were within 200 m. About 20% of nests were inside or within 25 m of wetlands Henshaw and Leadbeater 1998 Based on data from 102 nests at coastal marshes over two years. May be applicable where suitable waterfowl nesting habitat is present. Dragonflies and Damselflies Various species Dragonflies, especially Halloween Pennant, found 10 to 160 m from wetland edge Bried and Ervin 2006 Study in Mississippi. There was a different sex balance at different distances. Bogs with natural habitat around them had a higher dragonfly and damselfly abundance than those with peat mining in adjacent lands Bonifait and Villard 2010 Study in bogs in New Brunswick How Much Habitat is Enough? 29 Like CFZs, optimal PZ widths also vary development is proposed close to wetlands. For depending on a number of site-specific factors example, an appropriately sized and designed as well as the land use context. Of primary PZ can accommodate trails that support importance is understanding the desired opportunities for hiking and cycling, as well as function(s) that the PZ is expected to perform. nature interpretation and appreciation, or Key parameters that need to be considered in urban infrastructure such as stormwater determining PZ widths include local hydrologic management facilities. dynamics, slope, soil type(s), the vegetative composition of the buffer, and the extent and Based on current knowledge, the literature nature of the anticipated stressors (Ducros and increasingly indicates that the habitat Joyce 2003; Hawes and Smith 2005; Johnson and requirements for wildlife tend to result in the Buffler 2008; Polyakov et al. 2005). Examples of widest and most varied CFZs (e.g., in the order recommended PZ (buffer) widths for wetlands of 100 metres or more). In contrast, maintaining are provided in Table 4. water quality and aquatic habitat functions in streams and wetlands can often be achieved PZ width can also vary depending on its with zones of approximately only 30 metres anticipated uses. How Much Habitat is Enough? (although there is a fair amount of site-specific encourages a shift towards the development of variability). There are no known studies that multicriteria evaluation approaches for PZs (or actually test the ability of different buffer types buffers) (van der Merwe and Lohrentz 2001). or widths to protect wetland habitats (whether This approach encourages the identification and for plants or wildlife or both). Therefore, PZ prioritization of various criteria that are selected recommendations related to wildlife, where on a site-specific basis. This could result, for provided, are typically extrapolated from example, in the encouragement of some land measurements of impacts to various wetland uses or activities within the PZs (e.g., trails), but species. Such recommendations may not within the CFZs. The use of distinct “bands” overestimate or underestimate the actual buffer within the adjacent lands area can help resolve widths required, and more research is required some land use challenges when urban to address this knowledge gap. 30 How Much Habitat is Enough? Table 4. Examples of Recommended Protection Zones or Buffers to Wetlands Suggested Extent of Protective Zone Reference Notes 6m Hook 2003 High attenuation rate regardless of slope (0 to 20%) 10 to 60 m Skagen et al. 2008 Range based on literature review Herbicide drift from agricultural lands Strip at edge of cultivated fields (data indicate > 6 to 9 m) Boutin and Jobin 1998 Cites other studies suggesting 5 to 10 m Non-point source agricultural pollutants 16.3 m grass/woody strip (riparian) Lee et al. 2003 Removed > 97% of sediment, narrower (7 m) grass provided some benefits Residential stormwater 15 m; 23 to 30 m on slopes greater than 12% Woodard and Rock 1995 Groundcover type also very important Human disturbance, landscaping (e.g., wood piles, composting) 19 to 38 m Matlack 1993 Fencing may achieve same results in less width Nitrate 16 to 104 m Basnyat et al. 1999 Objective was > 90% nitrate removal Based on a flush distances* of approximately 45 to 80 m for Great Lakes species (no waterfowl) Stressor Sediment Human disturbance by watercraft More than 80 m Rodgers and Schwikert 2002 Human disturbance, recreation-related (e.g., camping, hacked trees) 67 to 130 m Matlack 1993 100 m Erwin 1989; Rodgers and Smith 1995 Flush distance* was 32 m ± 5.5 m; 40 m added to mitigate antagonistic behaviour 190 m Haspel and Calhoon 1991 Measured distance predation rates on wildlife extended into adjacent natural area Human disturbance (on nesting Great Blue Herons) Urban cats * Flush distance = proximity of disturbance that will cause bird to leave nest How Much Habitat is Enough? 31 Useful guidance is also available from review wildlife habitat functions of wetland-dependent papers that summarize data from a wide range species (with some studies recommending of sources. Several review papers that have larger widths). The comprehensive review of examined the available data on recommended temperate freshwater wetlands by Sheldon et al. adjacent natural areas for wetlands are (2005) concludes that there is no one effective summarized in Table 5. Notably, these reviews buffer width, and recommends three possible tend not to distinguish between CFZs and PZs, ranges for both wildlife functions (i.e., CFZs) and instead include all adjacent land and buffers (i.e., PZs) combined depending on requirements into the category of “buffers.” (a) the wetland’s level of habitat function, and The Planner’s Guide to Wetland Buffers for Local (b) the intensity of adjacent land uses ranging Governments (Nichols et al. 2008) concludes from 8 metres to more than 92 metres. that, on average, between 30 and 91 metres of adjacent natural areas are required to support Table 5. Selected Reviews or Guidelines that Consider Areas of Land Adjacent to Wetlands Reference Recommendations for Adjacent Lands* 30 to 168 m for groundwater protection; 23 to 114 m for Brown et al. 1990 sedimentation; 98 to 223 m for wildlife habitat Notes Study in Florida (with a particular geology). Recommendations based on consideration of landscape conditions and information from literature review. Castelle et al. 1994 Minimum of 15 to 30 m under most circumstances, but sitespecific Based on U.S. studies. Literature review encompasses sediment removal, nutrient removal, stormwater runoff, moderation of temperature, habitat diversity and habitat protection functions. Lowrance et al. 2002 Range from 1 to 30 m Based on U.S. studies. Focus on water quality functions (sedimentation and erosion, nutrient management, and pathogens and pesticides). Norman 1996 Baseline adjacent lands area of 50 m, then subject to site-specific considerations (e.g., waterfowl production or sensitive hydrology) Southern Ontario context. Focus on water quality functions (erosion control and reduced contamination transportation) in agricultural settings. Cautions against very narrow buffer strips. Kennedy et al. 2003 Recommended minimums:  25 m for nutrient and pollution removal  30 m for microclimate regulation and sediment removal  50 m for detrital input and bank stabilization  100 m for wildlife habitat functions Based on U.S. studies between 1990 and 2001 32 How Much Habitat is Enough? Reference Recommendations for Adjacent Lands*   Sheldon et al. 2005  8 to 23 m for wetlands with minimal habitat functions and low-intensity land uses adjacent to the wetland 15 to 46 m for wetlands with moderate habitat functions and moderate or highintensity land uses adjacent to the wetland 46 to 92+ m for wetlands with high habitat functions, regardless of the intensity of the land uses adjacent to the wetland Notes Focus on freshwater wetlands in Washington State Synthesis documents generally recommend adjacent land area widths of between 15 to 100 m, but no one width can be recommended Recommended principles: Bentrup 2008 For Critical Function Zones – larger species require larger widths, width should increase with length and in human dominated areas, and Critical Function Zones that need to function for a longer time should be wider  For Protection Zones – width can be variable if variable runoff, but should be wider on steeper slopes and on soils with lower infiltration capacities No distances recommended  Nichols et al. 2008    9 m to 30 m for sediment and phosphorus removal 30 m to 49 m for nitrogen removal 30 m to 91 m for wildlife protection (with some studies showing more) Review based on 50 U.S. ordinances, hundreds of scientific papers, and analyses of wetland adjacent land area performance * Includes Critical Function Zones and Protection Zones (buffers) Notably, even protection of wetlands and (Sheldon et al. 2005), which can be more heavily their functions through the identification and influenced by changes in land use in the broader implementation of CFZs and PZs will not fully landscape than by localized habitat protection conserve the habitat functions of wetlands on a efforts, and for wildlife such as amphibians landscape scale. Implementation of these site- and plants that rely on successful dispersal specific measures must be considered in the and migration in the broader landscape for broader context of natural heritage protection on population maintenance (Bauer et al. 2010; a watershed or regional scale. This is well Keddy 2010; Semlitsch 2008). recognized for water quality and quantity How Much Habitat is Enough? 33 2.1.4 Wetland Area, Shape and Diversity > Guideline Capture the full range of wetland types, areas and hydroperiods that occurred historically within the watershed. Swamps and marshes of sufficient size to support habitat heterogeneity are particularly important, as are extensive swamps with minimum edge and maximum interior habitat to support area-sensitive species. > Rationale Extensive, heterogeneous wetlands as well as less extensive, isolated wetlands both make significant contributions to supporting biodiversity at the local and watershed scales. The presence of larger, contiguous swamps and marshes (e.g., more than 30 hectares) are important for area-sensitive species such as Prothonatory Warbler and Black Tern. However, the presence of complexes of smaller, more isolated wetlands in the landscape are also important in that they provide habitat for many wetland-dependent amphibians and reptiles. Swamps have the potential to support areasensitive wildlife species (i.e., those that require larger areas of continuous habitat in which to be productive) or edge-intolerant species (i.e., those that prefer to use habitat away from the influence of habitat edges, also sometimes referred to as “interior” habitat species). In some watersheds with many land use pressures, treed swamps may be the only remaining significant contributors to interior-forest habitat, and the discussion on forest size and species that may be expected (see Section 2.3) applies here as well. However, treed swamps provide interior habitat for a different suite of specialist area-sensitive forest species compared to large patches of upland forest. Larger marshes also have the ability to support area-sensitive wildlife species (Smith and ChowFraser 2010). Area-sensitive birds may include species such as Marsh Wren, Black Tern and Forster’s Tern. Black Tern will nest in smaller marshes if larger feeding areas are located nearby. Some other species, such as Least Bittern and King Rail, occasionally occur in smaller marshes, but long-term viable populations are associated with extensive marshes. Extensive swamps and marshes also tend to have greater habitat heterogeneity (i.e., the habitat is more varied within them), which in turn tends to support more species of wildlife (e.g., Golet et al. 2001). In marshes, this is called “interspersion” or the juxtaposition of different marsh communities. High levels of habitat interspersion (e.g., the presence of open water/submerged vegetation, emergent vegetation and in some cases shrubs) within a marsh provide higher-quality habitat for a wider variety of species than, for example, a narrow band of cattails around the shoreline. For example, some species require extensive stands of emergent plants with few or no openings (e.g., Northern Harrier), while others seem to prefer areas dominated by emergent plants but with small, isolated openings (e.g., Least Bittern). The ratio of open water/submerged vegetation to emergent vegetation and the interspersion pattern may 34 How Much Habitat is Enough? vary considerably from year to year because reason that the Ontario Wetland Evaluation marshes are dynamic systems. However, area System recognizes the concept of wetland remains a key factor, and more extensive complexes (OMNR 1994). marshes are more likely to be used as productive habitat by more species of wildlife The presence of coarse woody debris in many (e.g., Attum et al. 2007; Webb et al. 2010). wetland types—particularly swamps, but also riparian areas and terrestrial areas associated Relatively isolated (i.e., not coastal or riparian), with wetland pockets—is important to many smaller wetlands can also be important for species. The functions of this debris include local or regional biodiversity. For example, providing cover and nutrients for fish and other amphibians such as Wood Frog and Spotted aquatic organisms, and providing important Salamander have been documented in wetlands cover and overwintering habitat for pond- ranging in size from 0.1 to 5.2 hectares (Babbitt breeding amphibians that spend the bulk 2005; Lehtinen and Galatowitsch 2001). These of their life cycle in associated uplands wetlands can have variable hydroperiods, may (Keddy 2010). be permanently wet (i.e., year-round) or only seasonally wet (typically in the spring and part Maintenance of the full range of wetland of the summer), and can be “hot spots” for some vegetation community types that occur in a groups of amphibians, particularly when they watershed is also key to sustaining biodiversity. do not support predatory or competing fish Meyer et al. (2010) found that at Long Point on (Snodgrass et al. 2000; Werner et al. 2007). Lake Erie, while the overall abundance and Interestingly, current research indicates that diversity of birds was greater in Common hydroperiod may be a more important factor Reed habitat, the abundance of marsh-nesting than wetland size in determining the diversity birds was greater in meadow marsh habitat, that can be supported by isolated wetlands supporting the need to protect these types of (Baldwin et al. 2006b; Hermann et al. 2005; more specialized habitats. Paton and Crouch 2002; Snodgrass et al. 2000). The role of wetland shape in supporting habitat Complexes of relatively isolated wetlands also and species diversity is difficult to discuss tend to be more supportive of biodiversity than independently because it is so closely related to, single, isolated ponds. Amphibians and reptiles and in the literature is often confounded with, are known to use multiple local ponds, habitat area and fragmentation in the landscape sometimes over the same season (Joyal et al. (Ewers and Didham 2006). The limited available 2001; Semlitsch 2008). Waterbirds are also data indicate that the optimum shape of a known to use complexes of small wetlands, wetland varies by wetland type. Swamps, which especially for springtime pairing and feeding, are a type of forest, are better able to support and have been documented using isolated area-sensitive and edge-intolerant species when wetlands in urban and peri-urban landscapes they are relatively compact and regularly in London, Ontario (Pearce et al. 2007). Some shaped (e.g., circular or squarish) (see Figure 13, birds have specifically adapted to use wetland on forest shape determining amount of core complexes in the landscape and will readily habitat, in the Forest Habitat Guidelines). move between them to forage (e.g., Northern However, some other wetland-dependent Harriers, herons, dabbling ducks). This is the species require ecotonal or edge habitat (e.g., How Much Habitat is Enough? 35 transitional areas between open water and abundance, and the presence of wetlands, has adjacent uplands) and thrive where there is been made repeatedly for amphibians. Specific more “edge” (Attum et al. 2007; Stevens et al. research on hydroperiods of seasonally 2002). Long, narrow marshes may also provide inundated wetlands in forests has shown that more water quality benefits since they maximize wetlands with longer hydroperiods (but not water contact with vegetation that is responsible permanent water) support a higher diversity for the uptake and transformation of many of amphibians, irrespective of wetland size nutrients and other contaminants. The link (Babbitt 2005; Baldwin et al. 2006b; Herrmann between wildlife species diversity and et al. 2005). 36 How Much Habitat is Enough? 2.1.5 Wetland Proximity > Guideline Wetlands that are in close proximity to each other, based on their functions, or that are in close proximity to other natural features, should be given a high priority in terms of landscape planning. > Rationale Fragmentation of wetland habitats degrades their functions by reducing habitat for species that are less tolerant of disturbances, that require more contiguous habitat, or both, compromising the ability of individuals of a species to effectively disperse and mate with individuals from other populations, and increasing habitat for opportunistic species (such as exotic invasive species and pests). Some of these negative impacts of fragmentation can be offset, at least for some species, by maintaining concentrations of natural habitat fragments within relatively close proximity in a given landscape. This approach is wellrecognized through the approach of the Ontario Ministry of Natural Resources to complexing wetlands that are within 750 metres’ distance of each other. The benefits of this type of land use planning may be further enhanced by minimizing the scale and extent of built-up land uses (e.g., road size and density) in the lands within such areas. Fragmentation of marshes within lakes can result in depletion of zooplankton and the fish species that depend on them. Even in systems where zooplankton is not a concern, small marsh patches may be ecological traps. They attract fry of many fish species as nursery habitat, but predation rates by common piscivorous (fish eating) fish such as Rock Bass may be very high. Small marshes—especially high concentrations of small marshes in a landscape—have traditionally been conserved and restored for waterfowl production. Increasingly, the importance of adjacent natural areas, as well as proximity between patches of wetland, has become recognized for a number of other wildlife species. Attum et al. (2008) in a study conducted in Ohio and Michigan found that both Copper-bellied Watersnake and Blanding’s Turtle were more likely to occur in wetlands with more surrounding forest, while Attum et al. (2007) conclude that protection of wetland complexes with a range of wetland patch sizes is needed to support Northern Watersnake foraging and mating habits. Stevens et al. (2002) found that occurrence of calling Green Frogs in restored wetlands was positively correlated with proximity to other wetlands (but provided no specific distances), while Houlahan and Findlay (2003) found in their study of 74 Ontario wetlands that amphibian richness was positively correlated with forest cover in adjacent lands, and also identified this trend in previous studies. In terms of numerical distances for proximity, examples from the current literature are summarized in Table 6, and show a great range. How Much Habitat is Enough? 37 Table 6. Examples of Distances in Which Positive Relationships to Other Wetlands or Other Habitats Was Documented Wildlife Group or Species Distance Within Which a Positive Response Was Documented to Wetlands or Other Natural Habitats Reference Notes Amphibians Strong positive response to the proportion of wetlands within 750 to 3000 m of breeding pools Houlahan and Findlay 2003 Studied 74 wetlands in southeastern Ontario Amphibians Distance to natural wetlands was an important factor in predicting amphibian diversity in the restored wetlands, particularly within the first 1000 m Lehtinen and Galatowitsch 2001 Turtles Movement was concentrated within 375 m from the edge of the breeding wetland Roe and Georges 2007 Green Frog Occurrence increased with the percent forest cover within 1000 m of ponds Mazerolle et al. 2005 Spotted Salamanders At least 100 m (range: 1.6 to 427.6 m) around seasonally inundated vernal pools was required for upland migration Veysey et al. 2009 Wood Frog and Spotted Salamander Positive association with the area of upland forest within 1 km of the pond edge Skidds et al. 2007 Birds Diversity and richness increased with the extent of forest and wetland within 500 m of the wetland edge Mensing et al. 1998 Birds Presence and abundance of some species linked to the amount of wetland within a 3 km radius Fairbairn and Dinsmore 2001 38 How Much Habitat is Enough? Study based in Australia Studied presence of egg masses in ponds Study set in prairie marsh habitats Additional considerations, as pointed out by alternate or “redundant” habitats in the Sheldon et al. (2005), include their observations landscape can provide critical refuges for that amphibians are not randomly distributed in amphibians when one breeding pond is potential habitats in the landscape but tend to be disturbed or dries up. concentrated in suitable habitats that While most of the are better connected available research on upland forest habitat to each other, and the effects of wetland breeding pool that the presence of fragmentation is terrestrial habitats focused on birds and between wetlands amphibians, it is can be an important intuitive that factor in waterfowl distribution. maintaining wetland hydrologic Semlitsch (2008) also connections between points out that nearby wetlands 1 km periodic drying of temporary wetlands is an important part of (where they exist), as Figure 9. Wetlands in close proximity with adjacent natural areas their natural cycle that helps reduce amphibian well as wetlands and other nearby natural areas, could also be critical to maintaining their functions. predation by fish and invertebrates, and that How Much Habitat is Enough? 39 2.1.6 Wetland Restoration > Guideline Focus on restoring marshes and swamps. Restore fens under certain conditions. For effective restoration, consider local site conditions, have local sources to propagate new vegetation, and wherever possible refer to historic wetland locations or conditions. Prioritize headwater areas, floodplains and coastal wetlands as restoration locations. > Rationale Defining restoration The terms “rehabilitation,” “creation” and “restoration” apply to distinct activities associated with habitat management and conservation. The term “restoration” in the general context of How Much Habitat is Enough? encompasses all these activities and refers primarily to the recreation, enhancement or improvement of habitat functions in locations or areas where the habitat had been historically present, but may also capture creation of habitats in alternate locations where conditions are suitable. In the current land use context of southern of amphibian colonization of 12 restored open Ontario, it is simply not possible for many water wetlands in Minnesota, found that watersheds and jurisdictions to return to restored sites were colonized by up to 75% of estimated historical levels of wetland cover. the species occurring in the nearby reference Also, the ability to restore the diversity and sites within a year. Stevens et al. (2002) found complexity of wetlands, and their wildlife amphibian species diversity was the same functions, remains questionable, and where between restored and reference sites, and possible even partial restoration of a wetland species abundances of amphibians (Northern can take many years. Therefore, wetland Leopard Frogs, Green Frogs and Spring restoration should only be considered after Peepers) were higher in restored than in alternatives for protection have been examined reference sites. Using historical data and and discarded, as a means to rectify anticipated reference sites as a starting point for setting losses, or when the objective is to increase realistic targets and identifying appropriate wetland cover (see Clewell et al. 2004). locations for wetland restoration is an ecologically sound approach. Regardless, where necessary, targeted and wellplanned wetland restoration can help priority restoration areas meet water quality and wildlife habitat targets at watershed-wide and ecozone scales. Despite the limitations, restored wetlands can provide habitat for a range of species. Lehtinen and Galatowitsch (2001), in their study 40 How Much Habitat is Enough? Restoration by wetland type Only two wetland types—marshes and, to a more limited extent, swamps—may be restored with some confidence. Currently, limited information is available on organic matter, lower plant species diversity the science of rehabilitating fens and bogs, and and structural complexity, and lower diversity the best management strategy (as for all of other groups of wildlife (e.g., amphibians) wetlands) is to protect them by protecting their than their reference sites (Kettlewell et al. 2008; water sources and not altering their watersheds. Sheldon et al. 2005). There have even been documented differences in levels of success In some cases, abandoned pits and quarries that between different types of marshes, with open are connected to the water table may offer water wetlands being most successful, shallow unique opportunities for fen creation (Hough marsh and scrub-shrub wetland restoration Woodland Naylor Dance Limited and Gore and being quite successful, and wet meadow Storrie Limited 1995). A current review of the restorations being relatively unsuccessful state of pit and quarry rehabilitation in Ontario (Sheldon et al. 2005). Common problems (Skelton Brumwell & Associates Inc. and included failure of wetland vegetation to Savanta Inc. 2009) identifies a number establish throughout the site, and lower levels of of locations in southern Ontario where vegetation and wildlife diversity compared to rehabilitation of former pits and quarries has reference sites. involved areas of wetland creation, including a few examples where fen vegetation has The relatively low level of documented success become established. provides a good rationale for working towards replacement ratios of more than one to one. Although there is also little published research Another argument for wetland replacement on successful reproduction of mature forested ratio of more than one to one is presented by wetlands, these wetlands are considered less Gutrich and Hitzhusen (2004), who found time complex (from a restoration perspective) than lags for restored wetlands to attain the floristic bogs or fens, and are generally considered and soil equivalency of reference wetlands to reasonable candidates for restoration given the range from 8 to 50 years. right conditions and sufficient time for trees and tall shrubs to grow. Marshes are considered the most readily restored type of wetland and can be at least partially functional within a few years. As a result, marsh restoration has been widely implemented. Despite this, restoration has often been unsuccessful. Available data for regulated wetland restoration from the United States, from hundreds of projects evaluated over five different states, indicate that less than a third to a quarter were considered successful in terms of area of wetland replaced for area lost. Furthermore, when specific wetland functions Restoration considerations Successful wetland restoration requires technical expertise. Key variables that need to be considered include soil conditions and fertility (including the presence of organic matter), water level fluctuations, and plant competition and structure (as determined by gradients along wetland edges). The presence of rare species is also important, not just for intrinsic value, but because they indicate the presence of rare habitat conditions that may also be valuable to other species (Keddy 2010; Keddy and Fraser 2002). were compared between reference and restored wetlands, most restored or created sites had less How Much Habitat is Enough? 41 Recommendations for improving the success of copied across southern Ontario (A. Norman, wetland restoration include using a watershed OMNR, London, pers. comm. 2011). approach to target and prioritize site selection, having a good understanding of the local biophysical conditions (especially hydrology, soils, slopes and potential sources for plant propagation), accepting that the restored wetland may not return to its former state or reference condition, maintaining and referring to existing hydrologic (and if possible terrestrial) linkages in the landscape, adding “ecological insurance” (e.g., try to restore more area, introduce more native diversity and incorporate a greater range of natural gradients), and where possible, undertake large-scale projects where different restoration approaches can be tested (Keddy 2010; Keddy and Fraser 2000; Keddy and Reznicek 1986; Palmer 2008; Sheldon et al. 2005; Verhoeven et al. 2008; Wagner et al. 2008; Zedler 2000). It should also be remembered that humans are not the only mammals playing a role in wetland creation: Muskrats and Beavers influence many wetland functions, and are often active participants in restoration (e.g., Gurnell 1998; Johnston and Naiman 1990; Naiman et al. 1988). A practical process of implementing headwater wetland restoration in agricultural southern Ontario has been developed in Aylmer District of the Ontario Ministry of Natural Resources in southwestern Ontario. The process involves local biologists, drainage superintendents, landowners and others. The methodology incorporates current science, land use considerations, landowner interests and hydrological and biodiversity benefits. A guide book has been produced. This is a valuable strategy for wetland restoration that can be 42 How Much Habitat is Enough? Restoration by location Wetlands restored anywhere within a watershed will provide an array of benefits including regulation of peak water flows and increases in biodiversity, provided that they are in suitable sites. However, the scientific literature is increasingly demonstrating that restoration of wetlands in some areas can be more beneficial than in others. Some guidance for determining the best locations for wetland restoration projects is available (Almendinger 1999; Bedford 1999; DeLaney 1995; Griener and Hershner 1998). Restoration of some major wetland areas such as Great Lakes coastal wetlands can result in extremely valuable ecological benefits; however, these projects can be technically challenging due to their size and complexity. In considering wetland location (see Section 2.1.2), restoration is best targeted to the following areas:  Headwater wetlands, particularly swamps, should be restored where they previously existed;  On-line or flood plain marshes and swamps should be rehabilitated or restored on second- and third-order streams;  Rehabilitation of wetlands in lakes is a high priority because of their extreme importance to fish as well as other wildlife species; and  Rehabilitation of wetlands in known historic locations is encouraged, where still feasible. 2.2 Riparian and Watershed Habitat Guidelines Lands adjacent to streams and rivers are possibly diminished) by both the aquatic system referred to as riparian. The riparian zone is an on one side and the broader terrestrial systems area where terrestrial and aquatic systems on the other side. Watershed attributes beyond influence each other (Knutson and Naef 1997), the riparian zone, such as land cover and land and it functions as an ecotone and ecosystem use, will also have an influence on stream (Naiman and Decamps 1997). Riparian habitat habitat quality. contains vegetation communities and soils with attributes of both wetland and upland areas, The habitat guidelines presented here relate and provides the transition between forest and to the tributaries of the Great Lakes and St. Lawrence River. The term “stream” is used here to describe any natural flowing watercourse, though unnatural (i.e., constructed or altered) watercourses may merit similar consideration depending on their function and importance within a watershed. The focus of this section is principally on Figure 10. The riparian zone stream, hillside and valley, as well as terrestrial and aquatic ecosystems (Everett et al. 1994, as in Knutson and Naef 1997). The extent of the riparian zone is defined here as the area where vegetation may be influenced by flooding or elevated water tables (Naiman and Decamps 1997), by its related ecological functions, or both. Riparian zones provide two broad types of ecological function. They provide essential services to aquatic habitats as both a buffer between aquatic ecosystems and terrestrial systems, and as contributors of resources including woody structure, nutrients and shade. Riparian zones also provide habitat in their own right, which may be moderated or enhanced (or terrestrial habitat and its relation to watercourses and wetlands. As such, it does not include in-stream habitat guidance. There is a large and growing body of knowledge on in-stream habitat and hydraulic parameters that should be considered when specifically assessing stream health and considering stream rehabilitation. The width of the riparian zone and the percent vegetated stream length guidelines directly address the amount of riparian area present to provide both direct terrestrial habitat and ecological services to aquatic habitat. It is important to recognize that this entire complex environment requires overarching general protection. This is a complex zone because How Much Habitat is Enough? 43 riverine floodplains are species-rich systems Finally, measures of water quality and of containing ecotones at various scales between fish communities provide feedback on the multiple habitat types (Ward et al. 1999). Fluvial effectiveness of the riparian zone—in processes in the form of floods and regular conjunction with the surrounding watershed variations in water levels also contribute to land cover—in protecting and maintaining the functional and species diversity within the aquatic environment. Fish communities may be floodplain (Ward and Tockner 2001). In order to affected by direct influences on aquatic habitat best address stream quality as well as terrestrial such as point source and upstream tributary and aquatic habitat functions, the area of natural inputs, or by other in-stream disturbances riparian vegetation should encompass the (human-induced or otherwise), or both. floodplain and upland transition zone or However, the quantity and quality of riparian ecotone. Where there is a strong physical habitat can help to directly mitigate watershed disjunct between the stream and upland, such as landscape effects on both water quality and a bluff, riparian vegetation may have less direct aquatic life. habitat value, although it may have strong value in terms of erosion control and some habitat attributes. Widths necessary to provide effective buffering capability may also be influenced by the sensitivity of the receiving watercourse and its ability to assimilate any stressors. The width and percent vegetation guidelines represent a generic riparian zone that is applicable under the greatest range of geographic, biotic and abiotic conditions. Impervious land cover within the broader watershed will have significant impacts on the quality of aquatic habitat within streams. These impacts may be mitigated to some degree by riparian zones. Relatively narrow riparian zones may be adequate when the broader area is in good condition (i.e., dense, native vegetation on undisturbed soils), and the adjacent land use has low to medium impact potential (i.e., parkland or low density residential). Wider riparian zones may be required to provide sufficient habitat and/or buffering functions for biologically sensitive systems, where the area is in poor condition, where soils are less permeable or highly erodible and slopes are steep, or where the adjacent land use is intense (e.g., intensive row-crop agriculture or urban centres). 44 How Much Habitat is Enough? Contributions of the riparian zone to aquatic and terrestrial habitat Stream size and physical characteristics associated with stream order are the products of fundamental biophysical factors (Imhoff et al. 1996; Kilgour and Stanfield 2001; Kilgour and Stanfield 2006; Stanfield and Kilgour 2006). Seelbach et al. (1997) stated that upstream catchment area, geology and slope are the primary determinants of stream size and physical conditions and, allowing for the normal distribution of plants and animals, stream biota. Modifying factors beyond land use such as instream barriers (including dams), channel modifications and point-source discharges will have a significant effect on stream and aquatic community qualities (Stantec 2007). Table 7 shows stream response to human alteration based on underlying conditions. Studies where the effect of adjacent vegetation has been separated from overall catchment vegetation cover show a positive relationship between the overall forest cover and stream health (Wang et al. 2006). Small headwater systems are highly dependent upon vegetative cover for moderation of stream temperature (Broadmeadow and Nisbet 2004) Drawing from studies on a small shaded stream, and flow (Swanston 1985) as well as sediment Nakano and Murakami (2001) found biomass load buffering (Dosskey et al. 2007; Dosskey et fluxes between stream and forest accounted for al. 2010). Additionally, these systems receive 25.6 and 44.0% of the annual total energy budget and transport large volumes of beneficial of bird and fish assemblages respectively when organic matter (e.g., falling leaves and insects), terrestrial and aquatic ecosystems are intact. that are processed by fish and benthos In addition, England and Rosemond (2004) downstream (Wipfli 2005). Headwater streams suggest that relatively low levels of riparian are significantly more efficient at retaining deforestation along headwater streams can and transforming organic matter than larger weaken terrestrial-aquatic linkages. In turn, streams. The retention and transformation of diversity of life in first- and second-order, as organic matter upstream affects downstream well as intermittent, streams contributes to the water quality and the survival and condition of diversity of life within the entire river and its organisms reliant on in-stream food sources riparian zone (Meyer et al. 2007). (Cappelia and Fraley-McNeal 2007). Table 7. General Overview of the Sensitivity of Streams to Human Alteration of Land Cover (based on Stantec 2007) Response Variable Permeable Soil Impermeable Soil Small Catchment Large Catchment Small Catchment Large Catchment Mid-summer water temperature Significant increase Modest increase Modest increase Minor increase Energy supply from inputs Significant decrease Minor decrease Significant decrease Minor decrease Energy supply formed within Significant increase Minor increase Significant increase Minor increase Dissolved oxygen concentration Significant decrease Minor decrease Significant decrease Minor decrease Benthic invertebrates Significant change to more cool and warm water, tolerant forms Minor change to more warm water, tolerant forms Minor change to more warm water, tolerant forms Minor change to more warm water, tolerant forms Fish communities Significant change to more cool and warm water, tolerant forms Minor change to more warm water, tolerant forms Minor change to more warm water, tolerant forms Minor change to more warm water, tolerant forms From a watershed perspective, effective through three—both directly and indirectly, and management practices must consider how how they provide terrestrial habitat in their own riparian zones contribute to conditions within right. The discussions presented below provide local streams—especially for stream orders one scientifically supported guidance for the How Much Habitat is Enough? 45 minimum habitat parameters under which aggregation of urban land use. The potential riparian zones can function as aquatic buffers, influence of these and/or other similar wildlife corridors and in situ habitats. The measures demonstrate the importance of definition of the riparian zone within a monitoring other aspects of urbanization in management context should be flexible enough addition to impervious surface. to encompass these functions as well as address the need for enhanced functions to mitigate Fitzpatrick et al. (2001) found fish communities potential future impacts. Within watersheds in good condition with watershed-wide where targets higher than these guidelines can agricultural land cover up to 50% as long be met and supported, they should be. as riparian areas contained less than 10% agriculture. Conversely, Stanfield et al. Watershed land cover and habitat health Watershed land cover beyond the riparian zone does influence stream ecosystems; however, the relationship is difficult to quantify. Allan (2004) and other authors noted that there is an increasing recognition that human actions at a landscape scale affect stream ecosystems (Allan et al. 1997; Strayer et al. 2003; Townsend et al. 2003). This finding supports the use of detailed subwatershed studies in advising stream management decisions. Large areas of forest or other natural cover, and possibly entire catchments, may be required to maintain stream health (England and Rosemond 2004; Harding et al. 1998). However, there has been only partial success at quantifying associations between land use and effects on stream systems given covariation of human and natural influences, mechanisms operating at different scales, nonlinear stream responses, and underlying historical influences (Allan 2004). Riva-Murray et al. (2010) found that while impervious surface explained 56% of the variation in macroinvertebrate communities in the Delaware River basin, secondary land use measures explained an additional 27%. Beyond impervious cover, other potentially important aspects of watershed land cover can include measures such as urban land with tree cover, forest fragmentation (e.g., aggregation index) or 46 How Much Habitat is Enough? (unpublished) found upland land cover tended not to explain any more variation in fish community composition than could be predicted by riparian buffer composition. Wang et al. (2006) found that fish community composition is more related to watershed land cover above 20% urban and greater than 70% agricultural land cover. In studies in the northeastern Ontario boreal forest and in Wyoming, 25% loss of forest cover led to effects on stream hydraulics and stream substrate composition (Buttle and Metcalfe 2000; Eaglin and Hubert 1993). Allan (2004), in a summary of several studies, noted that there are declines in stream ecosystem health as agricultural land use increases in a watershed. Also, row crops and other more intense uses may have a greater impact on stream health than pasture. Lastly, agricultural landscapes support fewer sensitive fish and insect taxa than forested watersheds. Stream responses in terms of overall ecosystem health vary widely depending upon the study and the nature of the watershed being studied. In the same summary study, urban land use is seen as having a substantial impact on stream ecosystems, more so than agricultural land use. This difference between urban and agricultural land use was similarly observed by Snyder et al. (2003). A number of papers examined links between cover to fair stream health, 44.6% tree cover to aquatic ecosystems and percentage of forest good stream health and 50.6% tree cover to cover in the surrounding landscape, and found excellent stream health at the watershed scale. strong connections between levels of forest Helms et al. (2009) linked deciduous forest cover cover and aquatic ecosystem health. Johnston of at least 50% with higher macroinvertebrate and Schmagin (2008) found annual streamflow species richness. Stephenson and Morin (2009) yields were greatest in Great Lakes basin reported that when forest cover was less than watersheds with the highest forest cover and 50%, algal biomass was relatively high (but topographic relief. Stephenson and Morin (2009) patterns were variable), and that fish biomass found that forest cover at the catchment scale began to decline where forest cover was less explained more variation in algal, invertebrate than 45% at the reach scale. and fish biomass than any other metric. Chang (2006) cited studies that found forested Moreover, higher percentages of porous land watersheds normally yield streamflow of higher cover across the watershed, such as forest, quality than that from other land uses. Other wetland and meadow, will have a positive effect North American studies support the importance on stream ecology on the basis that they are not of forests for stream health. Cappiella et al. impervious surfaces. (2005) found healthy aquatic systems in watersheds with at least 45 to 65% forest cover. Forest cover between 40 to 50% has a positive Goetz et al. (2003) looked at ratings of stream effect on stream ecosystem health, which health based on indices of biotic integrity and supports the percentage forest cover guideline linked 29.6% tree cover (including trees outside in the Forest section of this report (see of natural areas) to poor stream health, 37% tree Section 2.3). Table 8. Summary of Riparian and Watershed Habitat Guidelines Parameter Guideline Width of natural vegetation adjacent to stream Both sides of streams should have a minimum 30-metre-wide naturally vegetated riparian area to provide and protect aquatic habitat. The provision of highly functional wildlife habitat may require total vegetated riparian widths greater than 30 metres. Percent of stream length naturally vegetated 75% of stream length should be naturally vegetated. Percent of an urbanizing watershed that is impervious Urbanizing watersheds should maintain less than 10% impervious land cover in order to preserve the abundance and biodiversity of aquatic species. Significant impairment in stream water quality and quantity is highly likely above 10% impervious land cover and can often begin before this threshold is reached. In urban systems that are already degraded, a second threshold is likely reached at the 25 to 30% level. How Much Habitat is Enough? 47 2.2.1 Width of Natural Vegetation Adjacent to Stream > Guideline Both sides of streams should have a minimum 30-metre-wide naturally vegetated riparian area to provide and protect aquatic habitat. The provision of highly functional wildlife habitat may require total vegetated riparian widths greater than 30 metres. > Rationale Vegetation communities within the riparian zone can directly influence aquatic habitat and affect water quality for aquatic life. These functions include moderation of temperature through the provision of shade, filtration of sediments and nutrients, provision of food inputs through organic debris and leaf litter, and contribution to physical habitat in terms of fallen woody material. Vegetated riparian zones also serve as terrestrial habitat and corridors for wildlife as well as places where terrestrial and aquatic food webs interconnect. These diverse functions can be interactive or independent and will vary with watershed context. For example, the ability of riparian vegetation to moderate water temperature may decline with increasing stream width and volume, but it may still provide terrestrial habitat. The riparian zone width requiring maintenance or protection may vary depending on the size (order) of the stream, the steepness of the banks, and the specific management concerns of the local system (USDA 2007). Kennedy et al. (2003) provide detailed tables of riparian widths associated with specific conservation concerns and broader landscape considerations. The 30-metre width guideline provided here is a minimum general approximation intended to capture processes and functions typical of the active riparian zone of a floodplain and the floodplain-to-upland transition with respect to ecological services provided to aquatic habitat. 48 How Much Habitat is Enough? The riparian width guidelines do not directly include transition buffers beyond the riparian zone, but transition buffers should be considered in managing the riparian zone and from an ecosystem management approach. The type of vegetation and other site-specific conditions beyond the immediate riparian zone may be of particular importance in the management of urban watersheds, as urban development entirely changes the characteristic of surface flow that laterally enters the riparian. The effects of vegetation and land cover beyond the riparian zone on stream aquatic habitat are discussed below and in the following section. Also, while adjacent vegetation should be maintained next to lakes for similar reasons as for streams, this guideline was not developed specifically for lakes. In terms of buffering and habitat functions, there are parallels with PZs as discussed in Section 2.1.3, Amount of Natural Vegetation Adjacent to the Wetland, but with a few key differences. Principally, the 30-metre riparian adjacent vegetation guideline is not based on a species- or function-specific need but reflects a general threshold distance for aquatic health and riparian functions. Also, the 30-metre width is meant to capture a variety of protection and habitat functions. And some of the riparian habitat functions, such as wildlife corridors, do not reflect upland habitat needs of aquatic species but the needs of upland species that more specifically the ratio of natural cover utilize the riparian system or stream. While (especially, but not necessarily forest cover) to the PZ, and to a degree CFZ, concepts can human-dominated impervious land covers, will be applied to riparian systems with careful change the effectiveness of riparian buffers. Roy consideration under certain circumstances, et al. (2007) found that 30-metre forested buffers it is suggested that, at a minimum, 30 metres protected fish stream communities, but with of natural vegetation be maintained next diminishing returns above 15% urban land to streams. cover within the catchment. The effects of catchment land cover are important and are Knutson and Naef (1997) reviewed numerous further discussed in subsequent sections. published sources on varying riparian widths and the effect on stream health. Reported widths In reviews by Castelle et al. (1994) and ranged from 3 to 200 metres but with prevalence O’Laughlin and Belt (1995), riparian zone in the 23 to 60 metre range (all of these are widths of 3 to 200 metres were found to be applied to both sides of the stream from effective for bank stabilization and sediment the edge of the watercourse inland). They erosion control, depending on site-specific concluded by recommending that fish-bearing conditions. The Castelle et al. (1994) review streams have buffers of either 46 metres or specifically looked at different riparian widths’ 61 metres (for streams less than or greater than effects on sediment removal. The relationship 1.5 metres’ width respectively), extending to between width and sediment removal was 76 metres for shorelines or streams of state-wide non-linear, with disproportionately wider significance. In a later review that reported on riparian strips required for relatively small studies from across North America and Europe, improvements in sediment removal. For Broadmeadow and Nisbett (2004) cited ranges example, in one test case, widths of 30.5 metres of 15 to 70 metres for stream temperature removed 90% of sediments on a 2% slope; moderation, 15 to 100 metres for sediment however, a width of 60 metres was necessary to removal and control, and 27 to 100 metres for remove 95% of sediments on the same slope. On woody debris and leaf litter supply. A partial steeper slopes, two other studies found that removal or loss of some riparian trees, however, widths of 60 metres were effective in removing may not necessarily impair some riparian buffer greater than 80% of sediments (Castelle functions. For example, Wilkerson et al. (2006) et al. 1994). The frequency and intensity of found only a 60% canopy cover is required to sediment inputs are important criteria for the maintain effective temperature control. effectiveness of the riparian zone in mitigating the effects of sediment inputs. In terms of landscape context, Wang et al. (2003) found that land cover within 30 metres of Castelle and Johnson (2000) found that most streams in Wisconsin and Minnesota explained contributions to aquatic habitat are realized in more variation in fish assemblages than land the first 5 to 30 metres of the vegetated riparian covers beyond 30 metres. Frimpong et al. (2005) zone (with rooted vegetation contributing to found that buffers that were 30 metres wide and sediment filtering and trees contributing wood 600 metres long were the best predictors of the structure and shading). In heavy rain events, composition of fish communities within Indiana riparian sediment filtering may be augmented streams. However, watershed land cover, and through the use of additional grassy strip areas How Much Habitat is Enough? 49 upland of the riparian zone, which can reduce effective in removing nitrogen and phosphorus, concentrated surface flows (Knight et al. 2010). but most areas require a minimum of 10 to Knight et al. (2010) observed forest buffers 15 metres. A 30-metre-wide adjacent land area of 17 to 18 metres remained unbreached (i.e., along a stream next to logging operations did not develop lateral erosion channels) by greatly reduced nutrient levels to better than concentrated flow events with the addition of drinking water standards. Wooded riparian 18 to 22 metres of grassy buffer beyond a treed lands in Maryland removed 80% of excess riparian area. phosphorus and 89% of excess nitrogen, mostly within the first 19 metres. Lee et al. (2003) found Adjacent lands with established vegetation are that more than 97% of sediment and 80 to 90% fairly efficient at removing excess nutrients from of key nutrients could be removed with surface runoff. In some studies, areas with 16.3 metres of mature grass/woody riparian widths as narrow as 4.6 metres have been 90% adjacent land area. Riparian zones as wildlife habitat Riparian systems can provide important wildlife habitat. Habitat may be valuable for its intrinsic values, for example as forested habitat for breeding birds or as habitat for flora or as linear features providing connectivity for terrestrial wildlife movement (Knutson and Naef 1997), rather than any particular relationship to the riparian zone itself. Corridor and habitat widths for mammals, reptiles and amphibians are often dependent on the requirements of individual species, and these are discussed elsewhere in this document. However, it is worth noting that widths to address ecological concerns are much wider than those recommended for water quality concerns (Fischer 2000; Fischer and Fischenich 2000). As the width increases, factors such as overall habitat heterogeneity become important and the habitat requirements of species exceed the area of the riparian zone. Riparian areas, specifically due to their association with water, provide core habitat areas for many herpetile (reptile and amphibian) species. Semlitsch and Brodie (2003) suggest that the 15 to 30 metres of adjacent land often prescribed as a buffer to protect wetland species is inadequate for amphibians and reptiles, as riparian areas are not buffers per se but rather are core terrestrial habitats used by these species. The minimum suggested riparian zone requirements for some herpetiles ranged from 127 to 205 metres. There is a wide range of suggested appropriate riparian widths based on function, with the published range in the literature varying from a few metres to over 100 metres, depending on the study and level of representation and confidence (e.g., 95% occurrence within 175 metres). The recommended 30-metre width is supported in the literature as a general guideline minimum for many riparian systems. The 30-metre guideline may provide for basic terrestrial habitat; however, a greater width may be required to provide for a highly functional wildlife habitat. 50 How Much Habitat is Enough? 2.2.2 Percent of Stream Length Naturally Vegetated > Guideline Seventy-five percent (75%) of stream length should be naturally vegetated. > Rationale This guideline focuses on the cumulative effect of the riparian zone on stream habitat, and water quality as related to stream habitat. As described, riparian zones contribute to stream habitats in many ways. At the local scale, natural but otherwise open landscapes (i.e., not forested) require a forested riparian zone of at least 150 metres in order to generate substrate habitat capable of supporting benthic communities other than those tolerant to human disturbance (Wooster and DeBano 2006). A Toronto-area study found stream degradation occurred when riparian vegetation amounted to less than 75% cover along the length of firstto third-order streams (Steedman 1987). Alternatively, in a field test of this guideline, the Toronto and Region Conservation Authority commented that there are many cold water streams that have less than 75%, or even less than 50%, vegetated riparian habitats, pointing to an ability for some streams to resist degradation below the 75% threshold. Related comments were provided by Gartner Lee Limited (1997a) in a field test in Hogg Creek located in the Severn Sound Area of Concern, Ontario. In Hogg Creek, only 43% of the firstto third-order streams had vegetated riparian zones. Several tributaries of the main branch of Hogg Creek exhibited cold water characteristics that seemed to relate to a high ratio of baseflow (approximately 47%) as a percentage of average annual discharge per square kilometre. Gartner Lee Limited (1997b) also noted that the presence of cold water streams is heavily dependent on the geological characteristics of the area. Riparian vegetation provides proportionately greater benefits to stream aquatic habitat along the headwaters of streams. There is growing literature on the interaction between stream and adjacent terrestrial communities (Iwata et al. 2010; Nakano and Murakami 2001). From a watershed perspective, planting vegetation along smaller systems (i.e., less than third-order) will produce greater aquatic habitat benefits than planting along higher-order rivers, although both provide benefits. Vegetation along a smaller stream may have a greater potential to provide sufficient cover in order to lower the summer maximum stream temperatures than along the banks of a large river, but more importantly, aquatic/terrestrial biomass exchange may be more balanced in smaller streams with abundant adjacent cover. Given that the form and function of headwater streams are strongly influenced by the character of adjacent lands, a lack of adjacent natural vegetation can result in dramatic alterations in flow and sediment regimes. How Much Habitat is Enough? 51 Riparian vegetation, however, will still be of great value along larger rivers for species such 1st order 1st order 2nd order as waterfowl, reptiles and amphibians, as well as mammals such as North American River 2nd order Otter, American Mink and Beaver. 3rd order In this context, there is a similarity 3rd order to wetland CFZs (see Section 2.1.3): within riparian zones, there 4th order will be species-specific areas of adjacent land required to complete life cycles for species that spend their life cycle in both aquatic and terrestrial habitats. Lower-order streams comprise the Figure 11. Stream order, showing extent of first- to third-order streams majority of stream systems in the lower Great Lakes basin. For example, approximately 75% of the length of the Credit River system is comprised of first- to third-order streams, 83.5% of Duffins Creek is first- to third-order streams, and 75% of Carruthers Creek is first- to thirdorder streams (TRCA 2012; CVC 2012 pers. comm.). 52 How Much Habitat is Enough? The 75% guideline is presented as a minimum, given the literature and the fact that headwaters in southern Ontario tend to comprise approximately 75% of stream lengths. Effective management approaches should consider local watershed conditions (land cover) when applying this guideline, as discussed in the following section. 2.2.3 Percent of an Urbanizing Watershed that Is Impervious > Guideline Urbanizing watersheds should maintain less than 10% impervious land cover in order to preserve the abundance and biodiversity of aquatic species. Significant impairment in stream water quality and quantity is highly likely above 10% impervious land cover and can often begin before this threshold is reached. In urban systems that are already degraded, a second threshold is likely reached at the 25 to 30% level. > Rationale As part of the hydrologic cycle, water falling as precipitation will soak into the ground replenishing ground water and deeper aquifers (infiltration), or will flow above ground as surface water. Both ground and surface water may enter streams, rivers and lakes, eventually flowing into oceans. The base flow of a stream relies on ground water. During a precipitation event, if precipitation exceeds the infiltration capacity, water runs along the surface, either infiltrating elsewhere or entering streams directly. Total surface runoff flowing directly into streams increases with impervious land surfaces, such as pavement and concrete, or even with reduced infiltration, such as on compacted soils (Stanfield and Jackson 2011). The replacement of natural vegetation with impervious surfaces contributes to altered runoff processes within urban watersheds (Booth 1991; Booth 2000; Booth et al. 1997; Knutson and Naef 1997). The loss of fish and wildlife habitat, along with channel erosion and downstream flooding, are primary components of a stream system decline that result from high impervious levels within a watershed (Booth 1997; Booth 2000; Knutson and Naef 1997). While riparian zones can reduce surface runoff through increased infiltration (Bharati et al. 2002), there is a limit to their effectiveness in watershed conservation. In a review of the limits of best management practices, riparian buffers ceased to provide any protection with respect to nutrient loadings and turbidity, regardless of riparian width and percent length stream coverage, when impervious coverage ranged from 12 to 45% (Brabec 2009). More importantly, even with the full retention of complete natural riparian coverage, measurable degradation in stream quality was observed at watershed impervious coverage of just 7 to 10%. The effects of natural vegetation loss to impervious surfaces are often permanent (Booth 1991), and in this regard implementing mitigation efforts after impervious surfaces are established is largely unsuccessful (Booth et al. 1997). Stream biodiversity may continue to be negatively affected by landscape scale disturbances for decades despite improvements to riparian zones and associated buffering functions (Harding et al. 1998). The debate on identifying reasonable thresholds for impervious surfaces within a watershed began in 1979. In his pivotal paper, Klein (1979) reported that impairment in stream quality is first noted at 10 to 12% impervious cover and becomes severely impaired at 30% watershed imperviousness. In a subsequent literature review, the Stormwater Manager’s Resource Center proposed that two thresholds exist How Much Habitat is Enough? 53 within urbanized watersheds: at 10% (Schueler 2003). As impervious cover increased imperviousness, certain stream quality from 8 to 9% within a watershed, there was parameters will be affected, and at 25 to 30% significant decline in wetland aquatic impervious cover, stream quality will macroinvertebrate health (Hicks and Larson consistently shift to a degraded condition 1997). When the percentage of total impervious (Schueler 2003). surfaces surpassed 5 to 10% of a watershed landscape, there was a rapid decline in As watershed imperviousness surpassed 10%, biological stream indicators (May et al. 1997). Booth (1991) and Booth et al. (1994) found that At a study conducted in Washington, D.C., a there was a rapid decline in fish habitat and significant decline in the diversity of aquatic channel stability of riparian zones. In addition, insects was noted at 10% impervious cover Booth (1991) stated that urban development (Anacostia Restoration Team 1992). both magnifies peak discharges and creates new Furthermore, the density and diversity of peak runoff events. wetland plants, amphibians and fish are also impaired as watershed imperviousness exceeds Schueler (1994) reported on a number of 10% (Limburg and Schmidt 1990; Taylor studies that relate imperviousness to runoff et al. 1995). characteristics, stream morphology, water quality, pollutant loading, stream warming, as The most commonly chosen threshold for well as aquatic biodiversity. In his review, he impervious surfaces is 10% of the land cover suggested that impervious land use should within a watershed (Booth 2000). This value is remain below 10% as a guideline to protect proposed as a defensible minimum standard for streams. Snodgrass (1992) reported that water a guideline. Not every watershed, though, will quality became degraded when hard surfaces respond uniformly or as anticipated to proposed from development (e.g., housing, roads) reached impervious surface thresholds. While some 15 to 25% of the watershed. Contemporary watersheds might maintain integrity at 10%, as stormwater management could not prevent imperviousness moves toward 10%, the fish stream-quality impairment in the study community may already have simplified, with provided by Snodgrass (1992). In the past two an increase in generalist fish such as carp and decades, stormwater best management practices perch (Wang et al. 1997; Weaver 1991). Effects have evolved considerably. However, the on aquatic life can be seen between 5 to 8% primary focus of control of peak flow rate and imperviousness (Horner et al. 1997; May et al. the reduction of suspended solids has not 1997; Shaver and Maxted 1995; Yoder and mitigated the widespread and cumulative Rankin 1995), and in some cases even lower hydrologic modification to both streams and the (King et al. 2011; Stranko et al. 2008; Utz et al. broader watershed (CVC and TRCA 2010). 2009; Utz et al. 2010). Wang and Kanehl (2003) found that high-quality macroinvertebrate Various indicators of aquatic macroinvertebrate communities were possible in cold water community health are widely used as streams if impervious land cover constituted relationship indicators between watershed less than 7% of the watershed area, but that low imperviousness and aquatic systems. The quality index scores were inevitable above 10% thresholds presented below are taken from the imperviousness. Imperviousness levels between Stormwater Manager’s Resource Center review 7 and 10% represented a threshold urban 54 How Much Habitat is Enough? development zone where minor changes in imperviousness (Arnold and Gibbons 1996; urbanization could result in major changes Prisloe et al. 2001). Imperviousness also varies in cold-water stream macroinvertebrate with the agricultural type and intensity level. In communities. a New Zealand study addressing land use and overall stream health, Harding et al. (1999) Stranko et al. (2008) observed Brook Trout suggest that measures of agricultural intensity presence in small suburban and urban streams rather than percent cover of agricultural to be strongly positively correlated with land use may provide more useful land watershed forest cover and their absence management thresholds. from cold water streams with as little as 4% watershed impervious cover. Effects on stream In relatively undeveloped rural watersheds, channel geomorphology can be seen at as low stream base flow is dictated by underlying soils as 2% (Morisawa and LaFlure 1979) and 4% and geologic conditions that influence the (Dunne and Leopold 1978). These studies amount of ground water discharge. Within suggest that even a 10% guideline may be too urbanizing watersheds, however, careful high to adequately protect an urbanizing planning may mitigate some of the effects of watershed. Moreover, it is clear that a 10% limit impervious surfaces. Extreme peak flows typical (or any suggested limit) does not necessarily of urban environments can be reduced through represent a tipping point below which streams minimizing hard surfaces. Booth et al. (1997) will not have an impact from impervious cover. suggested that by using construction methods For example, negative linear responses for and products such as permeable pavements that Brook Trout (Stanfield et al. 2006) still occur allow for infiltration of water, surface area below this threshold. Guideline values of 5 covered by otherwise impermeable constructed to 7% impervious cover provide a more surfaces (rooftops, pavement, compacted soils) conservative limit for urbanizing watersheds, can be reduced. though they may be difficult to obtain and maintain. For urban watersheds that have, to Imperviousness provides a surrogate measure date, exceeded the 10% impervious surface of a variety of stream impacts associated guideline, a second threshold of 25 to 30% or with watershed development and land use less impervious surfaces is suggested. conversion. In determining conservation policies, however, it is important to understand In southern Ontario, impervious surfaces are that impervious cover should not only be often associated with particular land uses, and considered as the percent of a watershed or the relationships between land cover and stream subwatershed that is paved or developed. There water quality depends, in large measure, on is emerging literature on the intensity and how land cover is classified (Stantec 2007). nature of land uses and the relationship to While urban lands are generally more aquatic habitat and water quality, such as the impervious than agricultural lands, there can be work by Coles et al. (2010) to develop an urban significant differences in permeability within intensity index related to stream ecological these categories (Stantec 2007). Industrial areas condition. In this study, an urban intensity value with large parking lots can have upwards of was derived using 24 landscape variables and 90% imperviousness while estate lot residential measured at 30 sites representing different areas can have values between 5 and 10% levels of watershed development. From this, a How Much Habitat is Enough? 55 gradient of urban intensity was developed that a watershed. If headwater areas have minimal allowed estimates of expected stream condition impervious cover, and urban areas with high based on level of urbanization. imperviousness are located only in the higherorder sections of the watershed, streams may Stanfield and Kilgour (in review) examine a have a better chance of maintaining integrity. land disturbance index in southern Ontario as a more inclusive measure of disturbance that Future changes can be anticipated both in the measures the cumulative development within way in which imperviousness is calculated and a watershed. Beyond the simple percent the manner in which intensity of land uses is impervious guideline value, effective factored into this assessment. In the interim, the conservation planning and policy should guidelines provided make the best use of the consider where the imperviousness is located in science surrounding this subject. 56 How Much Habitat is Enough? 2.2.4 Additional Riparian and Watershed Considerations Physical and chemical water quality parameters Physical and chemical measures of water quality should be within federal and provincial guidelines. Measures of water quality such as total suspended solids, pH, oxygen, and concentrations of nutrients, metals and other contaminants are important in monitoring the health of streams. Water quality parameters are affected by influences on aquatic habitat such as point source and non-point source upstream tributary inputs, in-stream disturbances (anthropogenic or otherwise), or both, and by the conditions in the broader watershed such as levels of impervious cover (as discussed above). The quantity and quality of riparian habitat can mitigate watershed landscape effects on water quality (Brabec 2009). In Canada, the Canadian Council of Ministers of the Environment (CCME) Water Quality Task Group develops federal guidelines for the protection of aquatic life covering water quality, sediments and tissue. Canadian Environmental Quality Guidelines provide chemical-specific guideline fact sheets indicating environmental limits for over 200 different chemicals and water quality parameters (CCME 1999). Each fact sheet summarizes key scientific information and the rationale for the limit. They also provide detailed implementation advice. The Canadian Summary Tables are available online at http://st-ts.ccme.ca. Beyond individual parameter guidelines, the CCME has also developed a spreadsheet tool that summarizes multiple water, sediment and soil quality variables into a single measure of overall water, sediment or soil quality. The Water Quality Index was developed to provide a standard metric for jurisdictions to track and report water quality information. It is available, along with associated support material, at www.ccme.ca/ourwork/water.html? category_id=102. In southern Ontario, provincial water quality objectives (PWQOs) also provide standard guidelines for physical and chemical water quality parameters for the protection of the health of aquatic life. PWQOs provide guidance in making water quality management decisions and should be considered in the management of riparian zones and broader watersheds, given their influence on streams and other aquatic habitat. The Ontario Ministry of the Environment provides more than 240 provincial water quality objectives in its publication Water Management, Policies, Guidelines: Provincial Water Quality Objectives of the Ministry of the Environment, also known as the “Blue Book.” It is available on the Ministry’s website at www.ene.gov.on.ca/environment/en/ resources/STD01_076352.html. Environmental Quality Guidelines and How Much Habitat is Enough? 57 2.2.5 Fish Community Targets Fish communities are a product of stream and The fundamental characteristics of the stream watershed characteristics, and there are various and watershed dictate the limits and potential guides available to measure the health of aquatic of the stream system. The historic condition habitats and to establish fish community targets. provides a direction for rehabilitation. The existing conditions indicate how far the system In setting fish community targets, there are two is from being healthy or at least resembling basic reference points: historic conditions.  The fundamental or underlying Beyond these fundamental reference points and characteristics of the stream and watershed characteristics, there are a variety of approaches or subwatershed (e.g., drainage area, to restore stream environments and manage geology, stream substrate, gradient, flow fisheries. In order to develop locally relevant regime, etc.), and the makeup of historical fish community targets, it is advisable to contact fish communities; and agencies and organizations working in your  The biota currently present in the stream local watershed, such as the Ontario Ministry of (i.e., fish communities and other aquatic Natural Resources, Conservation Authorities or communities), the existing aquatic habitat non-government groups. conditions, and the factors that presently impact the system and their relative magnitudes. 58 How Much Habitat is Enough? 2.3 Forest Habitat Guidelines In this document, the term “forest” includes all are essential not only for wildlife but for human treed communities (where trees are generally well-being. 6 metres or more in height) with a canopy cover of at least 35%, and more typically 60% or Many flora and fauna species are obligate users greater. This includes both upland forests and of forested habitats—that is, they cannot survive swamps as well as plantations. It generally does without forested habitats. Structurally diverse not include orchards or tree farms. (compared to many other habitats), forests provide a great many habitat niches that are in Prior to European settlement, forest was the turn occupied by a great diversity of species. predominant habitat across the Mixedwood They provide food, water and shelter for these Plains. And today, if human influence and species—whether they are breeding and more or disturbance were to cease, it would be the land less resident, or using forest cover to assist in cover that would be most likely to naturally re- their movements across the landscape. This establish across most of the ecozone. Many of diversity of species includes many that are the types of wildlife that are currently found in considered to be species at risk. the Mixedwood Plains, and the niches they occupy, are a legacy of this past forest matrix. From a wildlife perspective, there is increasing The remnants of this vast forest now exist in a evidence that the total forest cover in a given fragmented state with patches of various sizes area is a major predictor of the persistence and distributed across the settled landscape, with size of bird populations, and it is possible or higher levels of forest cover occurring along the perhaps likely that this pattern extends to northern edges of the ecozone and associated other flora and fauna groups. The pattern of with features such as the Niagara Escarpment distribution of forest cover, the shape, area and and Frontenac Axis. The forest legacy, in terms juxtaposition of remaining forest patches, and of species richness, ecological functions and the quality of forest cover also play major roles ecosystem complexity is still evident in these in determining how valuable forests will be to patches and regional forest matrices. These wildlife and people alike. ecological features are in addition to the previously discussed influence forests have The following series of forest habitat guidelines on water quality and stream hydrology (see relate to the amount of forest cover, the area and Section 2.2, on the riparian zone), and include shape of forest patches, the configuration of reducing soil erosion, producing oxygen, storing forest patches, connectivity between forest carbon and many other ecological services that patches, and forest quality, as summarized in Table 9. How Much Habitat is Enough? 59 Table 9. Summary of Forest Habitat Guidelines Parameter Guideline 30% forest cover at the watershed scale is the minimum forest cover threshold. This equates to a high-risk approach that may only support less than one half of the potential species richness, and marginally healthy aquatic systems; Percent forest cover 40% forest cover at the watershed scale equates to a medium-risk approach that is likely to support more than one half of the potential species richness, and moderately healthy aquatic systems; 50% forest cover or more at the watershed scale equates to a low-risk approach that is likely to support most of the potential species, and healthy aquatic systems. Area of largest forest patch A watershed or other land unit should have at least one, and preferably several, 200-hectare forest patches (measured as forest area that is more than 100 metres from an edge). Forest shape To be of maximum use to species such as forest-breeding birds that are intolerant of edge habitat, forest patches should be circular or square in shape. Percent of watershed that is forest cover 100 m from forest edge The proportion of the watershed that is forest cover and 100 metres or further from the forest edge should be greater than 10%. Proximity to other forested patches Fragmented landscapes and the role of corridors To be of maximum use to species such as forest birds and other wildlife that require large areas of forest habitat, forest patches should be within two kilometres of one another or other supporting habitat features. “Big Woods” areas, representing concentrations of smaller forest patches as well as larger forest patches, should be a cornerstone of protection and enhancement within each watershed or land unit. Connectivity width will vary depending on the objectives of the project and the attributes of the forest nodes that will be connected. Corridors designed to facilitate species movement should be a minimum of 50 to 100 metres in width. Corridors designed to accommodate breeding habitat for specialist species need to meet the habitat requirements of those target species and account for the effects of the intervening lands (the matrix). Forest quality – Watershed forest cover should be representative of the full diversity of naturally species composition occurring forest communities found within the ecoregion. This should include and age structure components of mature and old growth forest. 60 How Much Habitat is Enough? 2.3.1 Percent Forest Cover > Guideline 30% forest cover at the watershed scale is the minimum forest cover threshold. This equates to a high-risk approach that may only support less than one half of the potential species richness, and marginally healthy aquatic systems; 40% forest cover at the watershed scale equates to a medium-risk approach that is likely to support more than one half of the potential species richness, and moderately healthy aquatic systems; 50% forest cover or more at the watershed scale equates to a low-risk approach that is likely to support most of the potential species, and healthy aquatic systems. > Rationale Forest habitat thresholds: proceed with caution… There is tremendous interest in minimum threshold levels for forest cover (and other habitat types) required to support healthy levels of native flora and fauna. Such thresholds can facilitate natural heritage planning and help support initiatives to protect and expand forest cover. However, given the current data gaps in the site-specific and landscape-scale habitat requirements of different species and groups of species, the science that is currently available to support such thresholds is limited. While there are several studies that examine forest cover thresholds, these studies acknowledge that the research has been conducted for relatively few species and taxonomic groups (primarily birds), and is rarely undertaken for long-enough periods of time, at large-enough scales, or with sufficient replicates to make the findings robust (Betts and Villard 2009; Lindemayer et al. 2005; Price et al. 2007; Rompré et al. 2010). Therefore, the values provided here should be viewed as generalized guidance based on the available science. …but consider risk The current science generally supports minimum forest habitat requirements between 30 and 50%, with some limited evidence that the upper limit may be even higher. Price et al. (2007) suggests a risk-based approach to recommendations for minimum habitat requirements that takes the current science, as well as the known uncertainties, into account. Risk-based thresholds provide a more nuanced approach, and the approach has been applied to the forest cover guideline (see Section 2.3.1). This makes intuitive sense, as there is seldom a clear-cut answer to a particular problem in ecology. There is potential to adopt this approach for further habitat guidance within the Mixedwood Plains. How Much Habitat is Enough? 61 Despite new evidence about the influence of the Based on Cadman et al. (1987) and Riley and matrix, current research continues to show that Mohr (1994), it is possible to compare the total overall levels of forest cover are much more number of species present to the number of important determinants of long-term species species that could occur, based on their persistence than the nature of the intervening geographic ranges. At one end of the forest habitats, particularly for forest birds (Price et al. cover scale, 100% of the species that should 2007; Watling and Donnelly 2006). This is occur were present in Ottawa-Carleton, which increasingly evident as levels of forest cover was approximately 30% forested. In contrast, increase in a given landscape. For example, Essex (then at 3% forest cover) had lost almost Donnelly and Marzluff (2004) reported that in 40% of its forest birds. The Ontario Breeding Bird a landscape with about 60% forest cover, bird Atlas (Atlas) results (Cadman et al. 1987) were species richness increased with reserve size used to determine the number of forest- irrespective of the level of urbanization in the dependent bird species in municipalities with surrounding matrix. varying amounts of forest cover (an explanation of how to use the Atlas for local study areas A number of relatively short-term studies (i.e., follows in a subsequent section). Information looking at data for periods of five years or less) related to the current (2005) atlas is available have shown that forest cover requirements online at www.birdsontario.org/atlas/ for forest-dwelling songbirds in fragmented atlasmain.html. These data support the general landscapes varies depending on the species, concept that regions with lower levels of and can range from 10 to 30%, with species forest cover also support lower diversities of persistence requiring at least 20 to 30% cover for forest-dwelling birds. most species (Andrén 1994; Fahrig 1997; both cited in Villard et al. 1999; Betts et al. 2007; Betts The overall effect of a decrease in forest cover on and Villard 2009; Tate 1998). However, current birds in fragmented landscapes is that certain research based on longer-term data suggests species disappear and many of the remaining that landscape forest cover requirements for ones become rare, or fail to reproduce, while forest birds range between 20 and 90%, with species adapted to more open and successional average requirements for long-term persistence habitats, as well as those that are more tolerant being closer to 60% forest cover (Zuckerberg to human-induced disturbances in general are and Porter 2010). Other recent studies have able to persist, and in some cases thrive. Species determined that at least 40% forest cover is with specialized-habitat requirements are most required to protect most sensitive forest bird likely to be affected adversely. In one study area species and sustain even some less sensitive near Ottawa, several species of forest birds species at healthy levels (Brown 2007; Rioux et disappeared as breeders when forest cover al. 2009; Rompré et al. 2010). These data suggest declined to below 30% (Freemark 1988). In Essex that while there is significant species-specific County, where there is about 3% forest cover, variability, to provide habitat for most forest- many wildlife species that are common to dwelling birds in the context of eastern North abundant elsewhere in Ontario are rare (e.g., America generally requires more than 30% Black-capped Chickadee and White-breasted forest cover. Nuthatch [Oldham 1983]), and 80% of the forestinterior species have disappeared. In the Ottawa-Carleton area (with 30% forest cover), 62 How Much Habitat is Enough? Hairy Woodpeckers can be found in woodlands up to one kilometre, as shown in Table 10) 10 hectares or even smaller, whereas in the rather than a landscape or regional scale. As Town of Markham (with about 5% forest with birds, variability among species has been cover), none were found, even though some observed. At scales of up to 1500 metres, woodlands approached 100 hectares in area researchers have found that populations were (Freemark 1988). sustained at basic levels at about 30 to 40% forest cover, and that healthier levels of species Current research has also begun to explore diversity and abundance were correlated with relationships between forest cover and levels of about 50 to 60% (Eigenbrod et al. 2008; amphibians. Studies on both mole salamanders Hermann et al. 2005; Veysey et al. 2009). and frogs have consistently found strong links However, for some amphibians, such as Wood between levels of local forest cover and both Frog, the presence of that forest cover in close species diversity and abundance (e.g., Mazerolle proximity to the breeding ponds appears to be et al. 2005), although these studies have as important as the level of cover (as shown in typically been undertaken at a local scale (e.g., Table 10). Table 10. Summary of Minimum Percent Forest Cover Requirements for Two Amphibian Species (from Homan et al. 2004) Scale of Analysis Spotted Salamander Wood Frog 30 metres 32% 88% 100 metres 28% 78% 500 metres 41% 55% 1000 metres 51% 44% (from breeding pool) The overall amount of forest cover in a importance of overall forest cover versus forest landscape also helps determine its ability to patch size and the ultimate response of support large mammals. Species such as Gray individual wildlife species (e.g., Lee et al. 2002). Wolf, Canada Lynx, and Elk that require However, on balance, the axiom is shifting away extensive forests disappeared from southern from “the bigger, the better” and towards “the Ontario shortly after forest clearing was greater amount of habitat within the landscape initiated, and are now only found in central and mosaic, the better” (see text box below, and northern Ontario where forest cover is more Austen et al. 2001; Fahrig 2002; Golet 2001; extensive. Some smaller mammals, such as Helms et al. 2009; Lindenmayer et al. 2002; Northern Flying squirrels, also require relatively Rosenburg et al. 1999; Vance et al. 2003; Veysey high levels of forest cover in their home ranges et al. 2009). These studies and reviews have all (Ritchie et al. 2009), but landscape-scale data on shown or suggested that forest patch size and many of these species are lacking. shape play a lesser role in maintaining regional or landscape-scale levels of biodiversity than the In general, the literature indicates that a total amount of forest cover, although the three complex relationship exists between the relative metrics are to some extent interrelated. How Much Habitat is Enough? 63 Factors such as overall forest cover, forest patch landscapes with relatively low levels of forest area, shape and degree of fragmentation all cover (e.g., less than 20%), some forest species affect the viability of habitat for wildlife species. will never return regardless of the spatial However, for forest-dependent fauna, overall pattern of the remaining forest (Trzcinski forest cover on the landscape is one of the most et al. 1999). important habitat metrics. This means that in Forest cover loss versus fragmentation Forest habitat loss and habitat fragmentation are widely recognized as two key factors in the decline of wildlife species in the Mixedwood Plains and elsewhere. However, there continues to be uncertainty around the relative importance of habitat fragmentation in influencing thresholds in wildlife populations (Ewers and Didham 2006; McGarigal and Cushman 2002; Zuckerberg and Porter 2010). One of the concepts that helps in understanding the relationship between forest cover, fragmentation and species loss is that of metapopulations. This is a term used to describe semi-isolated populations in a region that are linked by dispersion (Merriam 1988; Opdam 1991). Local extirpations of wildlife populations tend to occur naturally within forests due to failed reproductive efforts linked to (often stochastic) phenomena such as predation, parasitism, adverse weather conditions, natural catastrophes (e.g., fire and floods) and insufficient food. Where forest cover is fairly extensive and well-connected, forest patches naturally become recolonized by individuals from adjacent areas (so-called source-sink dynamics [Howe et al. 1991]). However, as the amount of overall natural area declines, recolonization can be constrained by lack of connectivity as well as reductions in the occurrence of colonizers, and extirpations may become permanent. For breeding birds, it is increasingly evident that the amount of habitat in a given landscape is more important than the spatial configuration (i.e., extent of fragmentation) of that habitat in supporting the long-term persistence of forest birds (Betts et al. 2007; Donnelly and Marzluff 2004; Donnelly and Marzluff 2006; Fahrig 2002; Price et al. 2007; Radford et al. 2005; Zuckerberg and Porter 2010). This is supported by other studies that found forest patch area and edge effects did not significantly affect either nesting success or the productivity of neotropical songbirds (e.g., Friesen et al. 1998). Golet (2001) found that bird relative abundance was not predictable from swamp size, but found that the pattern of distribution was consistent with total forest availability. However, Lee et al. (2002) found that the relative importance of patch characteristics, patch area and landscape forest cover varied for different bird species, and others have found that once the level of overall habitat falls below a certain threshold, the level of fragmentation and spatial configuration of the remaining patches starts to take on more significance in supporting the remaining species in the landscape (Lichstein et al. 2002; Trzcinski et al. 1999). 64 How Much Habitat is Enough? For amphibians, metapopulation dynamics are important in regulating populations (e.g., Knutson et al. 2000), but the actual configuration of habitat in the landscape plays a more decisive role. Gibbs et al. (2005), in one of the few papers to examine long-term population trends at a landscape scale, found that Spring Peeper, Northern Leopard Frog and Wood Frog population persistence across New York State was associated with areas of increased deciduous forest cover. However, habitat configurations at relatively large scales (i.e., 5 to 10 kilometres) were associated with transitions in local populations, supporting the idea that metapopulation processes and fragmentation are also both important for the long-term viability of frog populations. The metapopulations concept can also be used to explain the fact that the breeding bird assemblages in forests change annually (Villard et al. 1999). Common species are always present, but the more specialized species may be sporadic in occurrence. It has been demonstrated that—all else being equal—the number of breeding pairs in a region remains relatively constant, but that the areas used for breeding vary. Thus, a given forest patch may support a given species as infrequently as once every four or five years, yet this woodland is still critical to the overall maintenance of the regional populations. It follows that the disappearance of apparently insignificant forest patches may contribute to regional declines of forest bird populations. How Much Habitat is Enough? 65 2.3.2 Area of Largest Forest Patch > Guideline A watershed or other land unit should have at least one, and preferably several, 200-hectare forest patches (measured as forest area that is more than 100 metres from an edge). > Rationale The concept that large habitat reserves are superior to small reserves for the long-term persistence of area-sensitive forest species and low-mobility habitat specialists (e.g., Cottam et al. 2009; Keller and Yahner 2007; Price et al. 2007) continues to be supported. As well, it is increasingly recognized that high enough numbers of smaller patches in a landscape can also help support overall landscape biodiversity, at least for forest birds and amphibians, if the overall level of cover is above a certain threshold (as discussed in Section 2.3.1). Nonetheless, despite the new emphasis on the importance of overall forest cover, forest patch size remains a vital metric for forest species that are particularly area-sensitive or intolerant of human disturbances, or both. Several studies have suggested that because the relative importance of patch area, patch characteristics and landscape cover varies for different species, these multiple factors should be considered in conservation planning (Andren 1996; Lee et al. 2002; Mörtberg 2001; Villard et al. 1999). For wildlife, small fragment areas (known as patches) impose a maximum limit on population size (and in birds, it would seem to be partially based on species reproductive rates [Vance et al. 2003]), which leaves species vulnerable to local extinction. Therefore, even though small patches can and do provide habitat for some species, preservation of some larger patches in the landscape is required for the long-term survival of forest populations as a 66 How Much Habitat is Enough? whole. For example, some studies have identified only large (i.e., 500 hectares) or continuous forests as sources for Ovenbirds (Burke and Nol 2000; Mancke and Gavin 2000), even though they can breed successfully in smaller or “more fragmented” patches. Cottam et al. (2009) observed that in forest patches of more than 250 hectares, neither nest predation nor landscape matrix were significant factors in decreasing nesting success of Wood Thrush or Acadian Flycatcher, suggesting this area threshold was adequate for sustaining these species, at least in the short term. Larger patches of forest also tend to have a greater diversity of habitat niches and area, and therefore are more likely to support a greater richness or diversity of both plant and wildlife species. For forest plants that do not disperse broadly or quickly, preservation of some relatively undisturbed large forest patches is needed to sustain them because of their restricted dispersal abilities and specialized habitat requirements, and to ensure continued seed or propagation sources for restored or regenerating areas nearby (Honnay et al. 2002; Jacquemyn et al. 2003; Taki et al. 2008). Most studies looking specifically at forest patch area in relation to species diversity and abundance in the context of eastern North America have used birds as their focal species group. Robbins et al. (1989) determined that almost all forest birds in the mid-Atlantic at least 5 species of forest birds were in forest blocks with at least 162 hectares and at least 100 m 120 hectares of “core” habitat. In the Illinois Department of Conservation management guidelines for forest and grassland birds, Herkert et al. (2003) suggest that a 400- 200 ha interior forest hectare forest patch is required to support 75 to 80% of the highly sensitive regional forest bird species, and predict that a 100-hectare forest patch would contain only about 60% of such species. Tate (1998) evaluated these guidelines 200 ha interior Edge forest Figure 12. Two-hundred-hectare interior forest patch by surveying 4 large forest patches ranging in size from 140 to 201 hectares in the Severn Sound Area of Concern. Tate found over 70% of the regional pool of forest bird species in the 4 forest patches collectively, and 79 to 87% of the states occurred at least occasionally in forests expected forest-interior species in individual 100 hectares or smaller in area, but that the patches between 100 and 200 hectares in size. probability of detecting a number of these From this work, it was determined that a single species in this size of patch was as low as 20 to patch of 100 hectares was too small to support 30%. Nol et al. (2005) examined the occurrence the full complement of regional forest bird of 4 forest breeding birds (i.e., Ovenbird, Wood species, but that a forest patch of 200 hectares Thrush, Veery and Rose-breasted Grosbeak) in would be expected to support over 80% of 216 woodlot fragments in southern Ontario. all expected species in this region, and that Neither vegetation features nor area of small maintenance of several tracts of forest of at woodlots adequately explained patterns of least 200 hectares in the Severn Sound Area occupancy for any of the 4 species, and results of Concern would support 90 to 100% of all suggested that maintenance of patches of at least expected species. Table 11 summarizes data 127 to approximately 300 hectares (i.e., with at from Tate (1998) and others relating patch size least 90 to 230 hectares of “core” area—at least to forest bird habitat use. 100 metres from the forest edge) is needed to maintain source populations of forest In a unique study looking at forest patch size breeding birds in the fragmented landscape and bats, Henderson et al. (2008) found a of southern Ontario. positive relationship between total forest area, deciduous forest stands in particular, and the Weber et al. (2008) studied forest bird species presence of Northern Long-eared Bats. They occurrence in forest blocks of 3 size classes found that for every increase in 100 hectares of (i.e., less than 60 hectares, 60 to 100 hectares deciduous forest in a patch, the odds of a pair and more than 200 hectares) in a Maryland of bats occurring increased by 1.6 times, conservation network area. They found the although no specific minimum area thresholds majority (73%) of unlimited-radius plots with were suggested. How Much Habitat is Enough? 67 In general, at least for forest birds, the current or watershed, and at least one that is larger (i.e., science suggests maintenance of 100-hectare closer to 500 hectares). Notably, this assumes patches is inadequate, and that a moderate- to that the patches are not long and thin, but also high-risk approach would be maintenance of at contain a good proportion of “core” habitat that least a few 200-hectare patches in a given region is relatively undisturbed. Table 11. Anticipated Response by Forest Birds to Area of Largest Forest Patch Area of Largest Forest Patch* Response by Forest Associated Breeding Birds 200 hectares Will support approximately 80% of area-sensitive species including most area-sensitive species. 100 hectares Will support approximately 60% of area-sensitive species including most area-sensitive species. 50–75 hectares Will support some area-sensitive species, but several will be absent and species tolerant of edges will dominate. 20–50 hectares May support a few area-sensitive species. < 20 hectares Few to no area-sensitive species. Dominated by species tolerant of edges. * This assumes that these patches are circular or squarish in shape with some “core” habitat, not narrow linear patches. 68 How Much Habitat is Enough? 2.3.3 Percent of Watershed that Is Forest Cover 100 Metres from Edge > Guideline The proportion of the watershed that is forest cover and 100 metres or further from the forest edge should be greater than 10%. > Rationale It continues to be generally agreed that the structure and functions of habitat edges are inherently different from those within habitat cores, and as a result, these areas tend to support a different number and range of species (Ewers and Didham 2006). However, there continues to be lack of certainty about where the “edge habitat” within a forest patch ends, and conflicting evidence about to what extent the presence of edge habitat in and of itself affects the long-term persistence of forest species in a fragmented landscape. The main source of evidence for “edge effects” is from studies of forest-dwelling bird species. In a southern Ontario study, Sandilands and Hounsell (1994) determined that certain bird species avoided forest edges in small forests when they were breeding. In larger forests, one guild (or group) of species typically nested 100 metres or further from the edge, while a second guild consistently nested 200 metres or further from the edge. Subsequent work has supported these findings. For example, Austen et al. (2001) found that edge-intolerant species increased, and edge-tolerant species decreased, with both increasing woodlot size and core area, while Driscoll et al. (2005) found that for Wood Thrush increasing distance from forest-field edge was one of the four key metrics linked to nesting success. “Edge effects” have been documented as extending from as little as a few metres into a forest patch, to more than several hundred metres, depending on the stressor, the effect being measured, the intervening habitat type and the sensitivity of the attribute (e.g., Batáry and Báldi 2004; Murcia 1995; Wood et al. 2006). However, in both scientific and technical studies, 100 metres from the forest edge is typically used as the generic measure of where measurable “edge effects” taper off, and where more undisturbed “core” habitat conditions begin (e.g., Dunford and Freemark 2004; Driscoll et al. 2005; Nol et al. 2005; Weber et al. 2008). While the 100 metres is not necessarily the most accurate measure, and fails to account for the effects of disturbances that may be internal to a given forest patch (e.g., as a result of human use of trails), it does provide a useful metric for generally assessing the overall extent of “core” habitat in a given landscape in relation to the extent of forested edge habitat. Increased avian predation is also welldocumented in forest edges, and is considered to be a reason some species have reduced breeding success in these zones. Studies have shown that brood parasites such as Brownheaded Cowbirds and avian predators such as snakes can be more abundant in forest edges (Batáry and Báldi 2004; Chalfoun et al. 2002a), and that depth or distance to the edge can affect forest breeding bird diversity and abundance (Mancke and Gavin 2000). Some studies report conflicting responses of forest bird species to forest edge habitats. For example, Chapa-Vargas and Robinson (2007) How Much Habitat is Enough? 69 reported that Acadian Flycatchers seem to of the matrix. Ewers and Didham (2006) prefer edge habitats, and show no negative conclude from their review that the more the effects with reduction in presence or extent of matrix differs from the habitat patch, the more cores, while Hoover et al. (2006) observed “edge that edge effects will be evident. Conflicting effects” (i.e., Brown-headed Cowbird nest study results may also be explained by the parasitism extending 600 metres into the forest theory that, at the community level, birds at edge, but most pronounced at 250 metres from more productive sites differentiate across a the edge) for this same species. Similarly, Kaiser gradient in edge, whereas bird communities at and Lindell (2007) and Friesen et al. (1999) less productive sites do not (McWethy et al. found no effect of edge type or distance to edge 2009). They may also be explained by erroneous on nest survival for Wood Thrush. assumptions about expected responses of certain species to different habitat scenarios (e.g., Some studies have found evidence that edge perhaps Wood Thrush and Acadian Flycatcher avoidance is linked to overall density of the are more generalist than previously thought), or species within the patch (Bollinger and Switzer by lack of attention to the matrix (i.e., current 2002). Although the literature is relatively findings suggest that “edge effects” decrease as consistent on the increased negative effects overall forest cover increases, as discussed in of Brown-headed Cowbird nest parasitism Section 2.3.1). and avian predators on edge-nesting birds, Chalfoun et al. (2002b) found that there were Table 12 indicates how forest bird species can be no differences in small- and medium-sized affected by differing percentages of non-forest mammalian predator abundance between edge cover. Notably, when forest cover declines to and core forest habitat. A recent study cautioned around 15% (in combination with fragmentation that the abundance of a potential nest predator into smaller forest patches), 20 to 25% of area- species does not automatically equate to actual sensitive species disappear. An exception is risk of predation for a songbird species, and Haldimand and Norfolk, which continues to that the list of species regularly identified support a high percentage of forest-breeding as common nest predators in urban and birds even with relatively low levels of overall fragmented locales may require revision forest cover. However, this can be partly with respect to their individual importance explained by the fact that these counties contain (L. Friesen, Canadian Wildlife Service, several large (i.e., more than 1000 hectares) Burlington, pers. comm. 2012). forests in relatively close proximity, and several areas within the county contain over 30% forest Perhaps the explanation for the variation in the cover, providing further support for the patch findings of these studies lies more in the nature area guideline (in Section 2.3.2). 70 How Much Habitat is Enough? Table 12. Number of Forest-Associated Bird Species in Five Areas of Southern Ontario with Differing Percentages of Forest Cover (Adjusted for Potential Breeding Ranges Based on Pre-settlement Habitat) Carleton Haldimand and Norfolk Waterloo and Wellington Middlesex Essex Percent forest cover 29.4 16.2 14.8/18.2 13.5 3.0 Total number of species within range 94.0 102.0 100.0 102.0 102.0 Number of species occurring 94.0 98.0 88.0 83.0 63.0 Percent of total number of species within range present 100.0 96.1 88.0 81.5 61.7 Number of FIE and FI species within range 60.0 66.0 64.0 61.0 66.0 Number of FIE and FI species present 60.0 62.0 54.0 50.0 36.0 Percent of FIE and FI species within range present 100.0 93.9 84.4 82.0 54.5 Number of FI species within range 18.0 20.0 20.0 20.0 20.0 Total FI species present 18.0 19.0 15.0 16.0 4.0 Percent of FI species within range present 100.0 95.0 75.0 80.0 20.0 Ottawa- FIE - Forest interior/edge FI - Forest interior Source: Cadman et al. (1987); Riley and Mohr (1994) Irrespective of the gaps in our understanding of that are sensitive to human-induced this issue, the presence of an adequate level of disturbances (Imbeau et al. 2003). Such areas can “core” habitat is still considered a worthwhile accommodate a range of habitats and micro- metric to use in landscape-scale natural heritage habitats created by stochastic events (e.g., tree planning (e.g., Nol et al. 2005; Tate 1998; Weber falls), as well as a range of successional stages et al. 2008). This is largely because forested areas of each habitat type, each with the potential to with large “core” areas (and less “edge”) also, support different species. The presence of these by default, tend to be more diverse habitats elements in a landscape or watershed enhances capable of supporting a broader range of biodiversity, and increases resilience to natural habitats and species, and also tend to be less stressors such as diseases or insect infestations. disturbed and therefore able to support species How Much Habitat is Enough? 71 2.3.4 Forest Shape > Guideline To be of maximum use to species such as forest-breeding birds that are intolerant of edge habitat, forest patches should be circular or square in shape. > Rationale reduced population persistence of indigenous Although forest shape, as a stand-alone metric, has been poorly studied (Ewers and Didham 2006), it is generally accepted that shape is directly related to the concept of “edge effects” species adapted to forest habitats. This is not to say that linear or irregularly shaped forest patches do not provide habitat for a diversity of species. and the extent of In fact, forest patches contiguous core habitat, as dominated by edge and discussed in the previous successional type habitats sections. Figure 13, on have been shown to forest shape determining provide excellent habitat amount of core habitat, for species that are less illustrates how habitat specialized in their shape can influence the requirements, as well amount of core habitat; as those that thrive in square or circular habitats successional areas (Angold provide the greatest et al. 2006; Carafagno and amounts of core habitat Weatherhead 2006; Chapa- compared to the area of habitat that is influenced by edge, while similarly sized linear or irregularly Vargas and Robinson 2007; Figure 13. Forest shape determines the amount of core habitat – avoid narrow linear shapes for maximum core habitat (Kennedy et al. 2003) shaped habitats may contain little or no core habitat. Linear or irregularly shaped forest patches in a fragmented landscape tend to be colonized more frequently and more extensively by predators (particularly in urban environments), more vulnerable to invasive species, and subject to lower rates of reproduction and more wildlife species emigration (Batáry and Báldi 2004; Bowles 1999; Deng and Gao 2005; Hylander et al. 2002; Weldon 2006). This ultimately results in 72 How Much Habitat is Enough? Imbeau et al. 2003; Rioux et al. 2009). However, a predominance of these types of forest patches excludes those species and guilds that require more extensive core forest habitat area for successful foraging and reproduction. From this perspective, it is clear that in terms of restoration opportunities, the “infilling” of irregular forest patches can offer some potential wildlife benefits in terms of increasing the extent of core habitat (and decreasing the extent of edge habitat). 2.3.5 Proximity to Other Forested Patches > Guideline To be of maximum use to species such as forest birds and other wildlife that require large areas of forest habitat, forest patches should be within two kilometres of one another or other supporting habitat features. “Big Woods” areas, representing concentrations of smaller forest patches as well as larger forest patches, should be a cornerstone of protection and enhancement within each watershed or land unit. > Rationale This guideline addresses four metrics: (1) minimum distances between patches, (2) distance to the nearest productive patch, (3) differing mobility of different species or taxonomic groups, and (4) the matrix as a barrier (e.g., busy roads can present a significant barrier between habitats for most forestdwelling herpetofauna, but less so for most forest birds). The underlying hypothesis beneath this guideline is that one of the key effects of habitat fragmentation is that patches of habitat become isolated from one another, particularly as overall levels of cover decrease, disrupting natural species distribution and migration patterns, and requiring dispersing individuals or seeds, spores, bulbs or roots to traverse an intervening matrix. Habitat isolation in both space and time disrupts species distribution patterns, with consequent effects on metapopulation dynamics and the genetic structure of patch-dwelling populations (Ewers and Didham 2006). For forest birds, this distance between patches is related to the theory of source and sink populations. This is a relatively long-standing theory that has recently been re-examined for forest birds in fragmented landscape in southern Ontario (e.g., Nol et al. 2005). The theory is that for some species of forest-breeding birds, productivity is much higher in large forest patches than in small forest patches, and is higher than the level needed to replace individuals within the larger patches. These then serve as “sources” for populating neighbouring, smaller patches (“sinks”) where productivity is lower and not adequate for replacement. Most forest plants have restricted dispersal abilities and require specific conditions for seedling establishment (Honnay et al. 2002; Jacquemyn et al. 2003), which makes them vulnerable to isolation in the context of fragmentation. Endels et al. (2007) looked at understorey species in a Belgian forest with a long history of disturbances and found that spring-flowering herbs (with large seeds and unassisted dispersal) were effectively isolated by their limited ability to colonize young forests. For forest birds, research has found that habitats in close proximity to other natural areas support more species than isolated habitats of the same size, and that some species with large home ranges may use several patches instead of one large area. Recolonization of habitat patches by How Much Habitat is Enough? 73 Scarlet Tanagers (a forest-interior species) was In landscapes with relatively low forest cover found to decrease as the isolation of patches overall, species diversity and survivorship increased (Hames et al. 2001). Austen and increase where the remaining habitat patches Bradstreet (2006) found abundant forest cover are larger and more clumped or aggregated. In within two kilometres of a particular forest the eucalyptus forests of Australia, Radford et patch was a significant predictor for the al. (2005) found that landscapes with fewer presence of bird species that prefer interior larger patches in a more clumped distribution forest habitat in Norfolk County. Nol et al. tended to have a less pronounced extinction (2005) found that for Ovenbird, Wood Thrush, threshold occurring at a higher proportion of Veery and Rose-breasted Grosbeak, with each habitat loss. Donnelly and Marzluff (2006) kilometre increase in distance from a large reported that in the urban setting of Seattle, patch, the probability of occurrence in small Washington, bird species richness was high and patches decreased, and that small occupied many native forest plant species were retained patches were almost all within 14 kilometres, where landscape-level forest cover was at least and on average were within around 48% (including trees outside natural areas) 5 kilometres, of each other. Driscoll et al. (2005) and the remaining forest was at least 64% found that one of the four key variables aggregated across the landscape. In their influencing Wood Thrush nesting success in a examination of breeding bird data across eastern rural area of New York (with just over 50% North America over a 20-year period using forest cover) was total core habitat located 25 kilometres square scale analyses, Zuckerberg within 5 kilometres. and Porter (2010) found that of the 22 forest bird species demonstrating persistence thresholds, Forest amphibians might be expected to be more 16 of them exhibited strong support for the vulnerable to habitat isolation than birds in inclusion of the “clumpiness” variable in the the context of fragmentation because of their threshold model, indicating a preference for relatively more restricted mobility. However, areas where forested habitats were concentrated. the few relevant examples of current research conducted at large scales shows that they have Based on the limited available science, the a surprising capacity to move relatively long isolation between forest patches for forest birds distances, even in fragmented landscapes. generally occurs at about five kilometres, but Eastern Newts were found to require suitable for amphibians at between one and two habitat to complete their life cycle needs within kilometres. For forest plants, some level of 5000 metres of their original breeding pools immediate proximity is required, since effective (Rinehart et al. 2009), while Hermann et al. colonization of many spring ephemerals will (2005) reported that pond breeding amphibians not effectively occur under conditions of require forested habitat within 1000 metres of fragmentation, and so patches must be their breeding pools to ensure healthy local connected by wooded corridors (as described in levels of diversity and abundance. In a unique Section 2.3.6). For landscapes with relatively low study examining frog population trends over a forest cover, species diversity and survivorship vast area and a period of 30 years, Gibbs et al. improves where the remaining habitat patches (2005) found that frog metapopulation processes are both more extensive and more clumped occur at much larger scales than expected (i.e., or aggregated. up to 10 kilometres). 74 How Much Habitat is Enough? Big Woods areas The literature speaks strongly to the importance of concentrations of forest patches and the inclusion of larger habitat patches in landscapes to serve as sources of, as well as reserves for, forest species with specialized or area-sensitive requirements. The concept of “Big Woods” (Mancke and Gavin 2000) recognizes and elevates the importance of aggregations of forest patches, and can provide guidance for future replacement efforts. Two related metrics form the basis of a Big Woods approach: the aggregation of forest patches and the identification of the largest forest patches. Additional metrics for assessing forest function may include the measurement “distance to nearest Big Woods” and level of disturbance within the “Big Woods.” A variation on this method has been used in the Lake Simcoe Basin Natural Heritage System (Beacon Environmental and LSRCA 2007) and the East Gwillimbury Natural Heritage System where a Big Woods Policy Area was established in the Official Plan to help emphasize the importance of smaller forest patches within high forest-cover areas and provide focus areas for restoration activities. How Much Habitat is Enough? 75 2.3.6 Fragmented Landscapes and the Role of Corridors > Guideline Connectivity width will vary depending on the objectives of the project and the attributes of the forest nodes that will be connected. Corridors designed to facilitate species movement should be a minimum of 50 to 100 metres in width. Corridors designed to accommodate breeding habitat for specialist species need to meet the habitat requirements of those target species and account for the effects of the intervening lands (the matrix). > Rationale Dispersal between forest habitat patches is recognized as essential for long-term metapopulation persistence of species in fragmented landscapes (Noss and Harris 1986; Riley and Mohr 1994). The basic premise that an effective conservation strategy connects existing high-quality nodes using actual and potential corridors still persists (Townsend and Levey 2005). Determining the nature of those connections, based on species behaviour and life history, remains a challenge. Current thinking includes the “circuit theory” hypothesis, which suggests that for most species there are a multitude of potential connective pathways (McRae and Beier 2007) and that certain parts of a landscape offer different degrees of resistance and opportunity for species movement. An animal using a corridor likely has no route envisioned as humans would, but moves onward instinctually and is faced with multiple sequential decisions as to the best immediate pathway based on the “least cost” to itself. The utility of corridors to facilitate movement of forest species between forested areas in a fragmented landscape continues to be debated (e.g., Angold et al. 2006; Beier and Brost 2010; Hannon and Schmiegelow 2002; Whitfield 2001). The emerging evidence shows that although corridors may be used by many species to 76 How Much Habitat is Enough? facilitate movement, they are not required by all species or in all landscape contexts (Davies and Pullin 2007; Falcy and Estades 2007). It also shows that the use of designated corridors may depend on the permeability of the matrix (i.e., corridor use in urban landscapes may be more evident and important than in rural landscapes where species may move across open or remnant successional habitats) (Gilbert-Norton et al. 2009; Rizkalla and Swihart 2007). Some species are obligate users of corridors, either being totally dependent upon them to get from one natural patch to another or highly preferring to use them to get across the landscape. Habitat connectivity and corridors in fragmented landscapes have been shown to benefit a number of groups of species (e.g., some plants, amphibians and reptiles) (Damschen et al. 2006; Damschen et al. 2008; Haddad et al. 2003; Milne and Bennett 2007; Veysey et al. 2009). Gilbert-Norton et al. (2009) found, in their meta-analysis of 35 corridor studies, that corridors can increase movement between patches by approximately 50% compared to unconnected patches. They also found corridors were more important for movement of invertebrates, non-avian vertebrates and plants than they were for birds. Corridors can also facilitate movement for some wide, while forest species (e.g., Acadian undesirable species (e.g., invasive plants and Flycatcher, Hairy Woodpecker and Wood pathogens), may increase exposure to predators Thrush) were not recorded in greenways (e.g., Weldon 2006) and may be of limited use to narrower than 50 metres, and were primarily in birds, some forest plants and some mammals. In greenways wider than 100 metres. Other forest a context of regional forest cover of close to 40%, species (e.g., including ground nesters such with wooded patches of 3 to 165 hectares that as Black-and-white Warbler, Louisiana were no more than 325 metres apart, Scarlet Waterthrush and Ovenbird) were only recorded Tanagers in a rural landscape did not utilize in greenways wider than 300 metres. The need corridors to facilitate movement between to look at individual species needs and the patches (Fraser and Stutchbury 2004). Honnay range of factors that need to be considered is et al. (2002) found almost all forest plant species illustrated by Veysey et al. (2009), who found (85%) had extremely low success in colonizing that Spotted Salamanders were able to enter and solitary new suitable forest habitats even after to successfully cross clear cuts between forested 40 years. In a landscape with higher forest patches of up to 100 metres wide, but only connectivity, colonization success was higher under conditions of adequate precipitation. but still insufficient to ensure large-scale colonization. Some species such as Red Fox and Width and length determinations are further Coyote often move through open habitat, while complicated by the difference between the White-tailed Deer tend to travel through open intrinsic habitat values that may be found habitat or along a corridor or corridor edge if it within linear habitat patches (e.g., breeding happens to be leading in a direction that offers habitat for area-sensitive breeding birds), and food, shelter or other benefits. the narrower function of movement (e.g., by plants through pollination and seed dispersal, The determination of optimum corridor widths or animals) along a pathway that facilitates for wildlife movement is challenging, and the movement from one node to another. An area of literature provides limited guidance with only one metre in width may be used as a travel respect to appropriate minimum widths, lengths corridor by some wildlife species, while other or width-to-length ratios. Wooded corridors species that must breed within corridors (e.g., 50 metres in width can facilitate movement for some salamanders, small mammals or insects) common generalist species. In terms of stream may require much wider features that will corridors, widths of 75 to 175 metres have been support productive breeding habitat. suggested for breeding bird species, and 10 to 30 metres were found to be sufficient to include Corridor widths should ultimately be habitat for 90% of streamside plant species determined based on a functional assessment of (Spackman and Hughes 1995). Mason et al. what the corridor is expected to achieve, and (2007) examined species occurrence in long, what species it is expected to accommodate. narrow and largely forested greenway corridors Considering only movement, a minimum in an urban context in North Carolina and found guideline of 50 to 100 metres is supportable. The that urban-adapted species and edge-dwelling provision of breeding habitat for target species birds (i.e., Mourning Dove, House Wren, House would require knowledge of patch size Finch and European Starling) were most requirement and an analysis of the potential for common in greenways less than 100 metres edge effects. In rural landscapes, it has been How Much Habitat is Enough? 77 suggested that corridors should be as wide as natural or existing features versus purpose- 500 metres for specialist species, although this created corridors, which supports the approach begins to overlap corridor function preservation and integration of remaining with other functions such as habitat patch size habitat fragments (wooded riparian areas, use of and shape. Intuitively, in urban environments, “stepping stone” woodlots, hedgerows, etc.) wider corridors would be required to provide over the creation of new corridors, particularly the same level of function in the face of to facilitate movement of forest-dwelling species urban effects. (Gilbert-Norton et al. 2009). Corridors for wildlife must also provide suitable In general, the development of a corridor habitat for the species that are expected to move strategy should consider landscape features along them. Ideally, vegetation composition and attributes (such as natural cover and the in the corridor should be similar to that in composition of surrounding matrix), the the corridor nodes (or reflect soil/historic different dispersal abilities and mobility of the conditions), should be continuous between different species being accommodated, corridor nodes and should be a minimum width along its opportunities and constraints, as well as both entire length. The current literature also points positive and negative potential ecological to the higher effectiveness (i.e., levels of use) of outcomes from corridor creation. 78 How Much Habitat is Enough? 2.3.7 Forest Quality: Species Composition and Age Structure > Guideline Watershed forest cover should be representative of the full diversity of naturally occurring forest communities found within the ecoregion. This should include components of mature and old-growth forest. > Rationale Using remote sensing and GIS, quantitative measures such as percent forest cover or proportion of forest cover within 100 metres from a patch edge can be readily measured. Collecting qualitative information such as species composition, structure and age structure of a forest requires ground-truthing and sitespecific data collection, which is generally more costly and time consuming than remote sensing analyses. However, this information can be just as important, or more so, in terms of fully assessing the ability of a given watershed or region to support various species. For example, forest cover may be plentiful in a particular watershed, but may be dominated by early to mid-successional plant communities, conifer plantations and a variety of non-native species, and will therefore be limited in terms of the range of biodiversity that it can support. Cushman et al. (2008) found that forest cover types in western Oregon determined from satellite imagery were a weak proxy for habitat, explaining only 4% of the variance in bird species abundance. Therefore, it is important to collect and integrate any additional information about the nature of the forest cover into natural heritage planning wherever possible. The literature speaks to the importance of forest composition and the presence of native plants in relation to plant, insect and bird species diversity in both rural and urban landscape contexts. In urban settings, Angold et al. (2006) found that linear greenways with more native species and more structural diversity were used by a greater diversity of insects, while Donnelly and Marzluff (2004; 2006) found positive correlations between proportions of native vegetation species and abundance of native bird species. Austen and Bradstreet (1996) found differences in forest composition, as defined by proportion of deciduous-to-coniferous and swamp-to-upland forest, were important for individual bird species. For example, Veery and American Redstart were found in patches with more deciduous cover, while Blackburnian Warbler, Pine Warbler and Ovenbird were found more often in woodlands with more coniferous forest. The literature also speaks to the importance of mature forests for certain species, and the importance of a diversified forest structure. Betts and Villard (2009) found a strong association between five forest warblers and the presence of mature forest, while Ritchie et al. (2009) observed flying squirrels more frequently in mature than in regenerating forest patches, and Baldwin et al. (2006a) found Spotted Salamander richness was associated with more mature forests having more forest litter and organics. Jaquemyn et al. (2003) reported 50 out of 59 investigated forest plant species had a significantly higher occurrence in older forest patches than regenerating forest patches, indicating that there is a time lag between patch How Much Habitat is Enough? 79 regeneration and effective colonization of patches that are more mature, have more native restored patches for most forest plants. Soil species, and that contain or are close to acidity, nutrient and moisture levels were all permanent or intermittent water features. Milne important factors. The presence of a shrub layer and Bennett (2007) also found that more has also been repeatedly linked to greater levels contiguous, native deciduous forests supported of forest bird diversity and nesting success higher numbers of forest-breeding birds than (Donnelly and Marzluff 2004; Driscoll et al. other wooded areas in a southern Ontario 2005; McWethy et al. 2009). watershed, but noted that coniferous plantations also provided breeding habitat for a number of Weber et al. (2008) conducted a study of forest bird species (e.g., Golden-crowned Kinglet, Pine bird occurrences in variously sized forest blocks Warbler, Yellow-rumped Warbler). in a conservation network in Maryland and found that forest bird richness was higher at Site conditions, such as soil and topography, sites where: disturbance was minimal (i.e., no should also play important roles in determining more than 5% of the area); deciduous trees were which habitat types to restore in a particular dominant; seasonally, semi-permanently or area. In order to guide forest and wetland permanently flooded wetlands were present; restoration in the Niagara River Area of perennial water, including streams, ponds or Concern, Environment Canada used soil permanently flooded wetlands, were present; drainage categories to determine the original and stands were relatively mature (i.e., mean proportion of upland to lowland forest present canopy diameter at breast height was at least (Snell et al. 1998). Due to drastic losses of upland 40.6 centimetres and tree saplings were less forest, they recommended that restoration focus abundant). Forest bird richness was also on drier vegetation communities. Deciding positively correlated with canopy tree richness, which forest types are priorities for restoration and the length of streams and the area of requires a sense of the pre-settlement landscape wetlands within one kilometre. as guidance, in the same manner in which a cumulative impact analysis was recommended These studies show fairly consistent support for for wetlands prior to decisions being made on higher species diversity, and particularly for the wetland restoration projects (Bedford 1999). relatively well-studied bird diversity, in forest 80 How Much Habitat is Enough? 2.4 Grassland Habitat Guidelines Grassland is defined here as areas with less than (Tallgrass Ontario, www.tallgrassontario.org). 35% tree and shrub cover and includes native This likely represents less than 0.15% of prairie, savannah, old fields and meadows, grassland habitat that is present today. For pasture and hay. Alvars are a related habitat example, in 2011, approximately 1.5 million and meadow-type open alvars share many hectares in Ontario were hay, pasture or grassland characteristics, scientific attention and fallow according to the Ontario Ministry of conservation concerns, and for the purposes of Agriculture, Food and Rural Affairs this report are considered grassland habitat. (www.omafra.gov.on.ca/english/stats/ The grassland characteristics of shrub and agriculture_summary.htm). If non-agricultural treed alvars need to be assessed locally at an grasslands are considered, it is likely in 2011 individual site scale. Of all the so-called open that over 2 million hectares of grassland habitats country habitats, only shrublands with more (as defined here) were extant in southern than 35% cover by shrubs, orchards, row crops Ontario alone. Clearly, even compared to and cut-overs are excluded from this discussion. the original extent of tallgrass prairie, the agricultural habitats (often referred to as Southern Ontario has always been a changing “surrogate” habitats) are the most important environment, from glaciation to a forest biome driver for grassland breeding birds today and interspersed with grassland patches and will likely be into the future. landscapes to the matrix of agricultural lands that we see in many areas today. More recently the extent to which First Nations manipulated the forest biome for agricultural purposes has come into question. There is some evidence that large areas of the landscape were cleared to grow corn, among other uses. In one example, the estimated extent of agricultural activity associated with a cluster of First Nations settlement near Stouffville, Ontario, was thought to have extended over 40 square kilometres (R. Williamson, Archaelogical Services Inc., Toronto, pers. comm. 2012). While there is uncertainty as to what extent grasslands formed the dominant local land cover, it is likely that large areas of present-day southern Ontario pre-European contact were suitable habitat for grassland birds. An estimated 100 000 hectares of tallgrass prairie was once found in southern Ontario, while today less than 3 000 hectares remain Grassland as a unique land use and land cover While the exact land cover composition of preEuropean Ontario is unknown, today there is no doubt that open country is the predominant landscape in many areas of the Mixedwood Plains. Much of the present open country is overwhelmingly non-native and largely agriculturally derived (Neave and Baldwin 2011). Many grassland species, notably birds, do use this abundant non-native land cover as habitat while other species, notably plants and insects, prefer, or are restricted to, remnant prairies, savannahs and alvars. For species that thrive in the agricultural landscape, their future presence and populations will be determined by their adaptation to changing land use and land cover. Nearly all grassland patches have simultaneous How Much Habitat is Enough? 81 wildlife and human uses, and land cover is Land use planning can be used to restrict heavily linked to land use. Other habitats in the activities in order to maintain natural land cover Mixedwood Plains do not necessarily have the such as forest and wetland, but it has not same level of concurrent human use. traditionally been used to require activities such as grazing or set-asides, to create or maintain a For the most part, grassland habitat is land cover or wildlife habitat. As agricultural maintained through active disturbance, grassland habitat is a created and managed land including agricultural land use. Unlike forests, cover, there is little regulatory or planning onus grassland can be ephemeral, being created and to continue to maintain or create this cover, lost within the same year or over a period of although there are many examples of programs weeks, and the location of patches may vary aimed at precisely this, either through policy from season to season. Under this disturbance or incentive, both in North America (e.g., the regime, a temporal detachment between land Canadian Permanent Cover Program) and use and land cover can be seen. For example, elsewhere (e.g., Europe). a field may be in hay production all season but the actual land cover of tall grass and its associated habitat value may change suddenly throughout the season depending on hay harvest times and frequency. The relative area devoted to different agricultural crops and farm practices is determined by economic and social forces. These forces act at local, provincial, national and international scales. Both urban and rural Ontario underwent significant change over the last century. Throughout the 20th century, expansion and contraction of agriculture have occurred. Forest and shrubland have reclaimed most abandoned farmland. The relative area devoted to row crops, such as corn, wheat and soybeans, versus forage crops, such as hay and pasture, will change with economic demand. The numbers of farms and the human population that is actively engaged in farming have declined with growing efficiency and specialization, while the non-farm rural population has grown significantly. All of these factors influence the nature and extent of grasslands. 82 How Much Habitat is Enough? Introducing the grassland guidelines Addressing grassland habitat in the How Much Habitat is Enough? series has not been previously contemplated. Notwithstanding the abovenoted realities, in this edition, the subject is being broached by concentrating on native grasslands in the knowledge that, as our understanding of the role of the agricultural landscape evolves, the guidelines will need to be further expanded. The guidance is therefore targeted at public or private lands with conservation potential. While this foundation is meant to target the lost diversity of imperilled native grasslands and the species that are dependent upon them, it is anticipated that they will complement and assist in the larger discussion regarding the overall quantity of non-native grasslands. By necessity, in eastern North America, most of the literature has been drawn from the agricultural landscape and the birds that occupy that landscape. In particular, these guidelines address habitat type, amount and extent, as well as landscape configuration and patch size. Table 13. Summary of Grassland Guidelines Parameter Guideline Where to protect and restore Focus on restoring and creating grassland habitat in existing and potential grassland landscapes. Habitat type and area Maintain, restore and create native grassland patches to their historic extent and type at a county, municipal and/or watershed scale considering past presence and current conditions. Landscape configuration, heterogeneity and connectivity Grassland habitat patches should be clustered or aggregated, and any intervening land cover should be open or semi-open in order to be permeable to species movement. Patch size Maintain and create small and large grassland patches in existing and potential local grassland landscapes, with an average grassland patch area of greater than or equal to 50 hectares and at least one 100hectare patch. Landscape heterogeneity Some grassland habitat should be located adjacent to hedgerows, riparian and wetland habitats for species that require different habitat types in close proximity. Open country How Much Habitat is Enough? addresses grassland habitat that is part of a land cover and land use category known as open country. Open country is the dominant landscape matrix of the Mixedwood Plains and is comprised of any vegetation community where the combined cover of trees and shrubs over 1 m tall is less than 60%. Open country can be expressed as land use, e.g., a hay field, or as a land cover, e.g., grass or hay. Within this category is a variety of land uses and land covers including pastures, hay fields, old fields, prairies and savannas, alvars, rock barrens, burned areas, grains, thickets, and shrublands. Not all open country has equal value as habitat: e.g., some row crops such as corn have very limited habitat value for breeding birds, but migrating or wintering waterfowl will use post-harvest waste grains as food. How Much Habitat is Enough? 83 2.4.1 Where to Protect and Restore > Guideline Focus on restoring and creating grassland habitat in existing and potential grassland landscapes. > Rationale Of all the broad types of native habitats and ecosystems represented in the Mixedwood Plains, there are none that have been so diminished in extent as native grassland communities. Ninety-seven percent (97%) of the original native grassland habitat in southern Ontario has been lost (Bakowsky and Riley 1994). In this guideline, the restoration and creation of grassland patches first focuses on existing and potential local grassland landscapes: those where native grassland communities were historically, or are, the dominant local vegetation feature and/or have a high potential to be re-established. Existing and potential local grassland landscapes:  Have existing or historic native grassland that was a major or dominant local habitat feature;  Are areas with existing populations of grassland species, particularly species at risk; and  Have favourable current conditions and land uses to maintain, manage or restore large areas of grassland. 84 How Much Habitat is Enough? These are the target areas to apply the initial guidance in this report. Historically, landscapes such as the Carden Plain often had large areas of native grassland, and today have large native and agricultural grassland patches. These areas are generally not prime agricultural lands and/or support activities such as grazing or forage crops with current or potential value as suitable agricultural grassland habitat. In these areas, there may be greater opportunities for grassland restoration and maintenance. Likewise, in these grassland landscapes, forest-based restoration targets may be less locally applicable, may already be met, or at least need to be balanced with grassland considerations. 2.4.2 Habitat Type and Area > Guideline Maintain, restore and create native grassland patches to their historic extent and type at a county, municipal and/or watershed scale considering past presence and current conditions. > Rationale Native grassland is regionally rare but a part of the larger ecosystem, responding to a particular expected to have positive effects on populations of species other than birds. scope and diversity of the ecozone, hosting Beyond local landscapes and native grasslands unique species. While some birds will use both In terms of birds, landscapes with a greater area set of environmental conditions. It adds to the native and agricultural habitats, other groups have less flexibility. For example, many invertebrates have particular host plant requirements that are only met in native habitats, such as Karner Blue butterfly with Wild Lupine, and Giant Swallowtail butterfly with Common Hoptree. In addition, other species rely on structural and species diversity only found within native grassland habitat patches. These patches are of value whether they are part of local grassland landscapes, or as naturally occurring meadows or other openings in forested landscapes. Historically, native grasslands were not extensive in the Mixedwood Plains, with only an estimated 100 000 hectares of prairie in southern Ontario (Neave and Baldwin 2011) as well as some meadow- and grass-dominated alvars. Today many grassland species of plants and insects and some birds are rare or endangered. The minimum amount of native grassland required for these species to persist is largely unknown. However, it is likely that many species of conservation concern that rely on native grassland habitat in Ontario are already below any theoretical population and habitat thresholds for long-term persistence. Any gain in the amount of native grassland will be of native or non-native grasslands contain greater avian diversity than landscapes dominated by other agricultural covers such as row crops (Best et al. 2000; Lindsay et al. in review). Studies of the changes in bird populations since the initiation of the Conservation Reserve Program (CRP) in the United States and the Permanent Cover Program (PCP) in Canada show the value of grassland to the landscape. Birds have higher abundances, densities and reproductive success in these restored grasslands than in the croplands they replaced (Best et al. 1997; Johnson and Igl 1995; King and Savidge 1995; Patterson and Best 1996). For example, in Illinois, the creation of undisturbed grassland habitat by the CRP resulted in a 10-fold increase in the Henslow’s Sparrow population and a 5-fold increase in the Grasshopper Sparrow population (Herkert 1997; Herkert 1998; Herkert et al. 2003). In Minnesota, Haroldson et al. (2006) found that for each 10% increase in landscape grass cover, the counts of meadowlarks in the summer increased on average by 11.7 birds per route. For 5 duck species, Reynolds et al. (2001) found higher nesting success and recruitment in CRP lands. In the Canadian prairies, McMaster and Davis (2001) found that 9 of the How Much Habitat is Enough? 85 10 commonly occurring grassland birds were (Table 14). Tews (2008a) found that 6.5% more abundant on PCP sites than cropland sites, suitable habitat within a 100-kilometre-square and PCP also had higher bird species richness landscape was required to maintain a Bobolink than cropland. The CRP- and PCP-related population with less than a 5% probability of studies show the habitat value of grassland. extinction over 50 years, and that this amount increased to 30% suitable habitat within a 100- In general, the probability of species occurrence, kilometre-square landscape to maintain a species abundance or nest productivity functional population. increased with the amount of grassland or less intensive agriculture on the landscape Table 14. Species Presence, Abundance or Population Parameters and the Amount of Habitat in the Landscape Species Relationship with Amount of Habitat in the Landscape Northern Harrier Abundance positively correlated with pasture and hayfield (2); Savannah Sparrow Positive with grassland amount at 800 m scale (1) Abundance positively correlated with amount of natural and seeded pasture and decreased when crop area greater than 60 to 70% in agricultural lands (abundance increased from 0.53/ha in lands with 0.1 to 3% pasture to 0.69/ha in lands with 8 to 28% pasture and from 0.35/ha in lands with 1 to 20% crop to 0.87/ha in lands with 53 to 84% crop (3); Occurrence negatively correlated with percent trees and shrubs in landscape (4); Occurrence positively correlated with grassland cover in 32 km2 landscape (5) Eastern Meadowlark Western Meadowlark Abundance positively correlated with amount of natural and seeded pasture and decreased when crop area greater than 40% in agricultural lands; Relative abundance increased from 0.11/ha in lands with 0.1 to 3% pasture to 0.39/ha in lands with 8 to 28% pasture (3) Occurrence positively correlated with grassland and hay cover within 8 km 2 (5); Abundance positively correlated with grassland cover (6) Abundance positively correlated with amount of natural and seeded pasture and decreased when crop area greater than 40% in agricultural lands; Relative abundance increased from 0.23/ha in lands with 0.1 to 3% pasture to 0.78/ha in lands with 8 to 28% pasture (3); Occurrence positively correlated with grassland and hay (8); Bobolink Abundance positively correlated with grassland in 0.5 km landscape (5); Viable population needs 6.5% habitat within 100 km2 landscape and average patch size greater than 50 ha; Stable population needs 23% habitat within 100 km2 landscape and average patch size greater than 125 ha; Functional population needs 30% habitat within 100 km2 landscape and average patch size greater than 150 ha (7) 86 How Much Habitat is Enough? Species Vesper Sparrow Relationship with Amount of Habitat in the Landscape Abundance positively correlated with crop area in agricultural lands; Relative abundance increased from 0.03/ha in subdivisions with 1 to 20% crop to 0.13/ha in subdivisions with 53 to 84% crop (3) Le Conte’s Sparrow Abundance positively correlated with grassland in 32 km2 landscape (5) American Kestrel Nest box use positively correlated with amount of pasture and hay within 1 km (9) Dabbling Waterfowl Daily nest survival rate greater when 45 to 55% grassland within 41 km 2 landscape compared with 15 to 20% grassland in landscape (11); Nest survival positively correlated with grassland cover within 10.4 and 41.4 km 2 landscapes (12) Clay-colored Sparrow, Bobolink, Savannah Sparrow and Red-winged Blackbird Nest parasitism by Brown-headed Cowbird negatively correlated with tree cover within 2 km (13) Mourning Dove Abundance positively correlated with amount of grassland and cropland in landscape (14) Tree Swallow Number of fledglings and fledging probability decreased with intensification of agricultural land use, but increased with amount of extensive pasture, fallow and hayfield within 5 km (maximum foraging distance) (15) Citations: (1) Niemuth et al. 2005; (2) Kreuzberg and Lindsay 2010; (3) Kreuzberg and Lindsay unpublished data; (4) Winter et al. 2006a; (5) Quamen 2007; (6) Haroldson et al. 2006; (7) Neave et al. 2009; (8) Ribic and Sample 2001; (9) Smallwood et al. 2009; (10) Jobin et al. 2005; (11) Horn et al. 2005; (12) Stephens et al. 2005; (13) Pietz et al. 2009; (14) Elmore et al. 2007; (15) Ghilain and Bélisle 2008. In the upper midwestern United States, Meehan The total area of grassland on a landscape is et al. (2010) showed that there was a threshold the key factor in grassland bird richness and in bird species richness with the amount of abundance. However, while there has been an high-intensity agriculture on the landscape. increase in studies addressing grassland habitat They noted that bird species richness in a thresholds, the number of studies applicable to 25-kilometre square landscape increased linearly the Mixedwood Plains area are limited and with areas of low-input, high-diversity crops based on a small number of species. This (typically pasture); however, when more than currently precludes setting a threshold for 40% of the landscape consisted of high-input, grassland extent based on the current low-diversity crops (typically row crops), bird populations and richness of grassland birds. species richness sharply declined. Species richness also increased linearly with the amount of forest cover on the landscape. How Much Habitat is Enough? 87 2.4.3 Landscape Configuration, Heterogeneity and Connectivity > Guideline Grassland habitat patches should be clustered or aggregated and any intervening land cover should be open or semi-open in order to be permeable to species movement. > Rationale There are varying and interacting responses by species to patch size and patch proximity. In the case of bird species, many are not only sensitive to how much habitat exists in the landscape, but also to how that habitat is arranged spatially and the ease of movement between patches. Other birds are sensitive to area independent of the presence of nearby grassland. Similar to the use of small forest patches by forest fauna, in some cases, smaller grassland patches will be used when they are embedded within a landscape with abundant grassland habitat. Clustering grassland patches will benefit species that are influenced by patch proximity, especially for non-bird species of limited mobility, and will also increase the proportion of grassland in the local land-cover matrix. Also, a permeable intervening land cover on the landscape is preferred. Identifying threshold responses to patch size can be challenging. Ribic et al. (2009) reviewed several studies and identified patch size relationships for 14 grassland bird species that occur within the Mixedwood Plains ecozone (see Table 15); however, many of these studies did not control for local-scale vegetation structure or the amount of suitable habitat available in the landscape, which is likely to confound species-patch size relationships (Bakker et al. 2002; Winter et al. 2006b). Many studies of birds in grassland landscapes have failed to account for the fact that fragmentation (landscape configuration) is confounded with 88 How Much Habitat is Enough? habitat amount (see Fahrig 2003). For example, in mixed-grass and tall grass prairies of southeastern South Dakota, occupancy rates suggest that Sedge Wrens and Clay-colored Sparrows did not discriminate between large and small patches if these were embedded in a grassland-dominated landscape matrix (Bakker et al. 2002). In fact, more individuals were found in small patches within landscapes (400 to 1600 metres surrounding patches) dominated by grassland than in large patches where grassland land cover was low. For shrubland birds in Ohio, densities of most species were greater in patches where greater than 10% of the landscape within a 1-kilometre radius was in early successional stages (Lehnen 2008). In contrast, other species (Grasshopper Sparrow, Dickcissel in mixed-grass prairie and Savannah Sparrow in tall grass prairie) had high occupancy rates in large patches, irrespective of whether or not grassland was dominant in the landscape. This indicates the need to consider the benefit of having habitat patches within a more “open” landscape matrix containing other open patches to accommodate birds that respond positively to being in a grassland matrix. Likewise, in lieu of a grassland matrix, the presence of complementary “open” nearby or adjacent patches will likely have beneficial effects. “Clumping” or aggregating open patches would be a positive action. This could involve seeking opportunities around large “anchor” grassland patches while avoiding fragmentation of forest habitat. Regional population densities, habitat quality to grassland habitat corridors, there is limited and population factors can also influence patch literature and no clear indication of the benefit size relationships, such that area sensitivity may of connecting corridors between grassland vary regionally (Johnson and Igl 2001). For patches. In view of this uncertainty, another example, as the densities of Henslow’s Sparrow approach that would help serve connectivity increased within the landscape, breeding birds needs is to minimize the distances between were found in smaller patches of grassland patches and maintain a matrix that is permeable (Herkert 1994a; Herkert 1994b). to dispersing species. For grassland birds in heterogeneous The value of corridors for plants is also unclear. landscapes, the distance between habitat patches Van Dorp et al. (1997) sees the value of corridors and the quality of the intervening matrix as elusive, while Tikka et al. (2001) concluded determines whether patches will be occupied or that road and railway corridors do serve as not and the viability of individual patches. For dispersal corridors for grassland plants. In terms example, patches of grassland separated by of animals, narrow buffers may increase their more than 15 kilometres of cropland or forest predation while within the corridor (State of were beyond the dispersal distance of most Kentucky 2010). In terms of insects, Öckinger Bobolinks, and would result in isolated and Smith 2007 contend “that corridors do not populations (Tews 2008b). Similarly, patches always have positive effects on insect dispersal,” separated by less than 15 kilometres may be while Haddad (1999) did find that corridors appropriate for many other grassland bird facilitated dispersal in two butterfly species. species, including Upland Sandpiper and In a three-year study of inter-patch insect Henslow’s Sparrow. movement, Collinge (2000) suggests that corridors may have some potential to promote Migratory birds are more mobile than most movement of individuals, but their use needs to species groups, making corridors more be considered along with species characteristics, important for invertebrates, non-avian landscape context, patch size and environmental vertebrates and plants (Gilbert-Norton et al. variation. Having a complementary matrix and 2009). When looking at local ecosystems, the positive role it plays in dispersal and thresholds for grassland patch connectivity and movement is noted as important (Baum et al. configuration will be set by the requirements of 2004). The negative effect of corridors assisting less-mobile species. This is particularly relevant biological invasions is largely unknown, with for native prairie and savannah patches, given Bier and Noss (1998) noting a lack of studies on that these patches are more likely to provide the subject (and there appear to have been few habitat for a greater diversity of species with subsequent studies). Damschen et al. (2006) limited mobility than surrogate habitats. found that corridors do not directly promote invasion by exotic species. However, Hansen The utility of corridors for a variety of habitats and Clevenger (2005) contend that forest has been debated in the literature (Gilbert- corridor edges and grassland habitats act as Norton et al. 2009). Generally, corridors are seen microhabitats for non-native species and are as beneficial if specific species and habitat more prone to invasion by exotic species than attributes are considered, especially in forests, especially if disturbed. addressing forest habitat connectivity. In regard How Much Habitat is Enough? 89 Maintaining a permeable matrix is a more regarding the utility of corridors for grassland attractive strategy given the potential for species and the role of corridors with respect to predation in corridors and uncertainty biological invasions. Table 15. Evidence for Area Sensitivity in Grassland Bird Species that Occur in the Mixedwood Plains Species Occurrencea Referenceb Densityc Referenced American Goldfinch Positive 23 American Kestrel Positive 20 Positive 1,2,7,10 Positive 3,7,11,12,18 Negative 13 Variable 16 Brown Thrasher Negative 2 Brownheaded Cowbird Negative 7,9 Negative 13 Clay-colored Sparrow Positive 7 Positive 7 Positive 22 Bobolink Common Yellowthroat Dickcissel Positive 5,8 Eastern Kingbird Positive 23 Eastern Meadowlark Positive 1,2,10 Grasshopper Sparrow Henslow’s Sparrow Greater than 1000 ha for highest rate of occupancy in nest boxes (20) Greater than 50 ha for occurrence 50% of maximum (1) Capture rate higher in 13 to 16 ha patch compared with 4 to 8 ha patch (22) Patch size did not affect nest success (25) Positive 18 Positive 1,2,9,10,14 Positive 3,8,9,11,13,18 Variable 7 Variable 7 Positive 1,5 Positive 3,6 90 How Much Habitat is Enough? Threshold (Reference)e Greater than 5 ha for occurrence 50% of maximum (1); patch size did not affect nest success (25) Greater than 12 ha for occurrence 50% of maximum (19); greater than 15 ha for presence (14); greater than 30 ha for occurrence 50% of maximum (1); greater than 100 ha for occurrence 50% of maximum (2) Greater than 55 ha for occurrence 50% of maximum (1), mean occupied patch size 421 ha (26) Species Occurrencea Referenceb Densityc Horned Lark Positive 13 Le Conte’s Sparrow Positive 7 Positive Referenced 13 Loggerhead Shrike Greater than 4.6 ha for presence (21) Mallard Positive 23 Mourning Dove Negative 7 Northern Harrier Savannah Sparrow Sedge Wren Positive 1,2 Variable 8 Negative 7 Positive 7,8,23 Nest success higher in larger patch (24) Negative 7 Positive 7,12 Positive 3,7,18 Variable 16 Variable 7 Short-eared Owl Positive 2 Vesper Sparrow Positive 2 White-eyed Vireo Greater than 100 ha for presence (7) Greater than 10 ha for occurrence 50% of maximum (2); greater than 40 ha for occurrence 50% of maximum (1); nest success increased with patch size (15) Greater than 100 ha for presence (7) Upland Sandpiper Western Meadowlark Threshold (Reference)e Positive 3 Greater than 50 ha for presence, greater than 200 ha for occurrence 50% of maximum (2) Greater than 20 ha for occurrence 50% of maximum (2) Positive 4,7,8 Negative 15 Positive 22 Greater than 5 ha for occurrence 50% of maximum (19) Capture rate higher 13 to 16 ha patch compared with 4 to 8 ha patch (22) = occurrence in relation to patch size; b = associated references; c = density in relation to patch size; d = associated references; e = reference for thresholds a Citations from Ribic et al. (2009): (1) Herkert 1994b; (2) Vickery et al. 1994; (3) Bollinger 1995; (4) Bolger et al. 1997; (5) Winter 1998; (6) Winter and Faaborg 1999; (7) Johnson and Igl 2001; (8) Bakker et al. 2002; (9) Horn et al. 2002; (10) Renfrew 2002; (11) Renfrew and Ribic 2002; (12) Skinner 2004; (13) Dejong et al. 2004; (14) Davis 2004; (15) Davis et al. 2006; (16) Winter et al. 2006b; (17) Winter et al. 2006a; (18) Renfrew and Ribic 2008. Additional citations: (19) Helzer and Jelinski 1999; (20) Smallwood et al. 2009; (21) Jobin et al. 2005; (22) Rodewald and Vitz 2005; (23) Riffell et al. 2001; (24) Horn et al. 2005; (25) Walk et al. 2010; (26) Herkert 1994a. How Much Habitat is Enough? 91 2.4.4 Patch Size > Guideline Maintain and create small and large grassland patches in existing and potential local grassland landscapes, with an average grassland patch area of greater than or equal to 50 hectares and at least one 100-hectare patch. > Rationale Patch requirements in terms of quality, size and surrounding land-cover influence vary by bird species and region. If managing for species diversity, then maintaining a diversity of grassland patch sizes and types will suit the needs of many species, and striving for larger average patch size will accommodate areasensitive bird species. Very few studies have examined area sensitivity in grassland birds in Ontario. However, research conducted in other geographical areas suggests that the Upland Sandpiper and Henslow’s Sparrow both require very large patches of grassland to establish territories (greater than 50 hectares and preferably larger—as large as 200 hectares for Upland Sandpiper). Tews (2008b) found that viable Bobolink populations were supported in a landscape with average patch size greater or equal to 50 hectares. American Kestrel prefers nest boxes in larger patches (Smallwood et al. 2009). Other grassland birds are potentially area sensitive but have relatively small patch requirements, such as 4.6 hectares for Loggerhead Shrike (Jobin et al. 2005) and 5.0 hectares for both Eastern Meadowlark (Herkert 1994b) and Western Meadowlark (Helzer and Jelinski 1999). For some species with relatively lower minimum patch-size requirements, there are studies showing positive effects on presence and nesting success when patch sizes are increased, for example nesting success for grassland obligate 92 How Much Habitat is Enough? Savannah Sparrow increased with patch size (Davis et al. 2006). Winter et al. (2006b) suggested that the specific requirements for the size of a grassland habitat patch will vary among regions, depending on: (1) the quality of the habitat in the patch; (2) the amount of trees and shrubs in the surrounding landscape; and (3) the local predator community. In an unpublished account from New York State, 30- to 100-acre (12- to 40-hectare) patches were recommended to “protect a wide assemblage of grassland-dependent species” while acknowledging a larger patch size is required to protect raptors also (Bittner 2011). The challenges associated with identifying consistent patch-size thresholds for grassland species suggest that recommendations for patch size should recognize the value of both smaller (see Quamen 2007; Winter et al. 2006b) and larger patches, with average patch area determined by the species with the largest known area sensitivity. Larger patches also provide habitat for a greater number of individuals from a specific species and may support a less variable and possibly more viable local bird community. Having at least one 100-hectare patch will increase the chances that the most area-sensitive birds will be present in a local landscape, and having a 200-hectare patch will increase the chances of persistence for the most area-sensitive bird species (Table 15). 2.4.5 Landscape Heterogeneity > Guideline Some grassland habitat should be located adjacent to hedgerows, riparian and wetland habitats for species that require different habitat types in close proximity. > Rationale Grassland species often require a variety of other complementary habitats to complete their life cycles (Justus and Sarkar 2002; Pressey et al. 1993), and many grassland birds require these patches in close proximity to support all life stages (see Table 16). Several waterfowl species, for example, nest in upland grasslands adjacent to wetlands, and bird species that forage in croplands typically nest in adjacent linear features such as hedgerows, fencelines or shelterbelts (Best et al. 1990; Best et al. 1995; Rodenhouse and Best 1983). Other species, such as the Northern Bobwhite or the introduced Ring-necked Pheasant, require a mix of cover for nesting and shelter from predation, as well as grassland and cropland for foraging (Burger et al. 2006). There has been much discussion over the benefits of isolated or linear landscape features, such as hedgerows. These features can provide sources of food, shelter, nest sites, roosting, foraging sites and song perches for many grassland birds (Best 1983; Cassell and Wiehe Johnson and Beck 1988; Marcus et al. 2000; Martin and Vohs 1978; Smith et al. 2005; Yahner 1982; Yahner 1983). Structural characteristics (height and width) and floristic richness are known to influence species composition of birds (and other taxa). Generally, wider and more diverse hedgerows and those adjoining forest or shrubland patches support more bird species (Best 1983). Conversely, other studies indicate linear features with woody vegetation may reduce the quality of the adjacent open habitat types (e.g., grassland) for nesting birds, although the impact on density and nesting success may be dependent on the total amount of trees and shrubs on the landscape (Winter et al. 2006b). Nest predation and brood parasitism by Brownheaded Cowbird may be higher in open habitat that is adjacent to areas with woody vegetation. However, the significance of predation can be difficult to predict because the distribution of nest predators in grasslands can be complex (Bergin et al. 2000; Chalfoun et al. 2002b; Winter et al. 2006b). 1980; Conover 2005; Conover et al. 2009; How Much Habitat is Enough? 93 Table 16. Species Requiring a Mix of Grassland and Other Habitat Types Species Open Habitat Type Other Habitat Types Notes American Crow All open habitats Forest Nests in trees, forages in open habitats (1) American Woodcock Old field Shrubland, early successional forest, wetland Various aged early succession forests on 200 to 400 ha tracts within 1 to 3 km of each other preferred (2) (more open habitats are also used in Ontario) Baltimore Oriole Grassland Forest and treed/shrubby edges Primarily uses forest, edge and hedgerow habitats (3) Barn Owl All open habitats Barn, tree hollow or nestbox (4) Barn Swallow Grassland Barn and barnyard preferably with livestock (5) Bank Swallow Grassland Riparian, or lakeshore, requires nesting substrate Probability of extinction declined with proximity to grassland (6) Brewer’s Blackbird Grassland Perch sites such as fencelines, hedgerows, etc., and water (7) Brown Thrasher Old field Shrub and shrubby edge (8) Primarily uses hedgerows and shrubland habitats Windbreaks, trees, water (9), requires structure for nesting Mean colony size positively correlated with amount of flowing/steady water, negatively correlated with amount of cropland within foraging distance; very large colonies associated with high landscape diversity (9) Wetland 90% of grassland nests within 200 m of a wetland, mean 96 m (10) Cliff Swallow Grassland Dabbling Waterfowl (American Wigeon, Grassland Blue-winged Teal, Gadwall, Mallard, Northern Shoveler) Gray Partridge Grassland, cropland Shrubby edge habitats such as fencelines, hedgerows, etc. (11) Northern Bobwhite Grassland, cropland Shrubland/forest (11) 94 How Much Habitat is Enough? Species Open Habitat Type Other Habitat Types Notes Red-tailed Hawk Grassland, cropland Forest, forested edge (11) Ring-necked Pheasant Grassland, cropland Scattered small woodlots (11) Sandhill Crane Grassland Wetland (11) Vesper Sparrow Cropland, grassland Shrubby hedgerows Males arrived earlier and had better pairing success where fencerows were shrubby and croplands contained residue (12) Wild Turkey Grassland, cropland, old field Forest Optimum mix may be 50% forest, 10% row crops, 22% pasture, 13% old field (11) Citations: (1) Whitney and Marzluff 2009; (2) DeGraaf and Yamasaki 2003; (3) Cadman et al. 2007; (4) Sandilands 2010; (5) Ambrosini et al. 2002; (6) Moffatt et al. 2005; (7) Dunn and Gordon 2007; (8) Vickery et al. 1994; (9) Brown et al. 2002; (10) Henshaw and Leadbeater 1998; (11) Sandilands 2005; (12) Best and Rodenhouse 1984. How Much Habitat is Enough? 95 2.4.6 Additional Grassland Considerations Edge density and woody vegetation There has been much discussion in the scientific literature of the positive and negative effects of edges and woody vegetation on grassland species. In terms of edges, some of the observed variation in minimum patch size may be related to the extent of edge effects in different landscapes. In the past, many researchers believed that early successional or shrubland species were not sensitive to patch size and could live in habitat edges. However, a recent meta-analysis for 17 shrubland species occurring in clear-cuts in a forested landscape demonstrated that all of the species were more abundant in the centre, rather than the edge of patches, and that edge effects were significant for 8 species (Schlossberg and King 2008). Although the study took place within a forested landscape context, similar patterns may occur in fragmented or grassland landscapes, suggesting that more extensive habitat patches are required to support breeding territories. In grassland landscapes, edges can be pronounced and are often “harder” and more permanent than in forested landscapes. This is because human land uses create linear features with abrupt changes from one vegetation type to another. The role of multiple edges on ecological processes in fragmented landscapes is largely unknown; however, multiple edges increased the magnitude and extent of the effect of edge on Bobolink in Iowa (Fletcher 2005). Edges also have different microclimates (e.g., light or humidity) than interior habitat, and as a result can affect food supply for various species and can ultimately affect species use, although this has mainly been suggested for forest edges abutting open habitats (Austen et al. 2001; Burke 96 How Much Habitat is Enough? and Nol 2000). Some bird species show a reluctance to cross gaps between a linear noncrop edge and a more hostile open area (such as a crop field) because it exposes them to predation (Bélisle 2005; Bélisle et al. 2001; Bélisle and St. Clair 2001). The quality of edge can also affect bird use of adjacent habitat; for example, some studies have shown that the more complex the edge vegetation, the less likely a bird will venture out into a crop field (Conover et al. 2009). Conversely, other species are attracted to edges such as a fence line because they provide perches from which to forage and vegetation cover for nest sites (Best and Rodenhouse 1984). The National Agri-Environmental Standards Initiative recommends small (1 to 100 hectares) native grassland patches should be surrounded by a greater than or equal to 50-metre buffer comprised of native perennial grasses and forbs, and devoid of woody vegetation and vertical structures (e.g., fences or buildings) (McPherson et al. 2009). Linear features within or separating open habitat patches, such as hedgerows and shelterbelts, have mixed affects, and what constitutes a barrier or a corridor is not always clear. For example, in a study of the effect of adjacent grassland land cover, Bakker et al. (2002) treated tree-belts or windbreaks greater than or equal to 20 metres wide as barriers and excluded minimum-maintenance roads and fencelines. In terms of use of linear or isolated features, grassland species such as Loggerhead Shrike will use hedgerows and isolated trees or shrubs that might otherwise be considered incompatible with grassland habitat patches. However, edges are avoided by many bird species since they attract many predators, including birds, mammals and reptiles that use linear features as corridors in grassland Small changes in the timing of operations could landscapes (Bergin et al. 2000). contribute greatly to maintaining population viability and improving habitat for birds. Land management and restoration decisions in Mowing, for example, can create a habitat sink relation to edges, in particular linear features or ecological trap (an apparently productive such as hedgerows, should consider the needs of area that actually produces a net loss to the grassland and non-grassland species, as well as species). This occurs in hay fields unless the the provision of other ecological functions, such mowing date is adjusted (e.g., after July 7, as soil erosion control. When managing large Nocera et al. 2005; after July 15, Dale et al. 1997; patches, it should be noted that hedgerows, Quamen 2007). Mowing before these dates can shelterbelts and other isolated and linear woody result in as much as 94% mortality in nestling features do not necessarily constitute a break and juvenile birds (Bollinger et al. 1990; Dale et within a patch nor generate a negative edge al. 1997). Herkert’s (1998) recommendations to effect. These features should generally be adopt rotational management combined with retained in the face of other concerns. avoidance of cutting before mid-July may provide one way of reducing the impacts. The Timing Replicating natural seasonal habitat cycles can help address the temporal disconnect between human and wildlife land uses. 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How Much Habitat is Enough? 127 Additional information can be obtained at: Environment Canada Inquiry Centre 10 Wellington Street, 23rd Floor Gatineau QC KIA 0H3 Telephone: 1-800-668-6767 (in Canada only) or 819-997-2800 Fax: 819-994-1412 TTY: 819-994-0736 Email: enviroinfo@ec.gc.ca