Paper birch Betula papyrifera The volume of paper birch has decreased significantly since 1983. This is a result of both natural succession and increased mortality. The numbers of saplings and poles have also decreased suggesting that paper birch will play a less prominent role in the future. Models suggest that volume of this species will decrease by over 70% by midcentury. In the last three decades, growth rates have decreased and are currently negative (mortality exceeds growth). Paper birch has the lowest ratio of growth to volume of all species in the state. Whereas paper birch makes up about 2.2% of all volume of trees in Wisconsin, it accounts for 8.4% of total mortality. Paper birch roundwood production made up 6% of the statewide product in 2009. Because biomass of birch is decreasing so rapidly, it is not likely to be a major source of biofuel.  How has the paper birch resource changed?  Where is paper birch found in Wisconsin? Volume and diameter class distribution: Growing stock volume by region with map  What kind of sites does paper birch grow on?  How fast is paper birch growing? Habitat type and site index distribution Average annual net growth: trends and ratio of growth to volume  How healthy is paper birch in Wisconsin? Average annual mortality: trends and ratio of mortality to volume  How much paper birch do we harvest? Roundwood production by product and ratio of growth to removals  How much paper birch biomass do we have?  Can we predict the future of paper birch? Tons of aboveground biomass by region of the state Modelling future volumes Division of Forestry WI Dept of Natural Resources 2016 “How has the paper birch resource changed?” Growing stock volume and diameter class distribution million cubic feet or about 2.2% of total statewide volume. Volume of paper birch has decreased 54% since 1983 and 43% since 1996. The volume and number of trees is decreasing in all size classes (charts below). Pole-sized trees have decreased in number by 45% since 1996. Saplings and sawtimber trees have decreased as well, suggesting that paper birch will play a less prominent role in the future. Growing stock volume of paper birch 1200 1000 Mllion cft The growing stock volume of paper birch (chart on right) was about 481 800 600 481 400 200 0 1938 1943 1948 1953 1958 1963 1968 1973 1978 1983 1988 1993 1996 2004 2009 2015 Growing stock volume (million cubic feet) by inventory year. Source: USDA Forest Inventory and Analysis data Percentage change in tree numbers: Paper birch Volume of paper birch by diameter class Million cft 700 0% 600 5-8.9 500 9-12.9 400 13-16.9 300 200 100 0 1983 1996 2015 Growing stock volume (trees over 5 inches dbh) by diameter class (inches). Source: USDA Forest Inventory and Analysis data -10% -12% -20% 17-20.9 -30% 21-24.9 -40% 25+ -50% -30% -45% Sapling Pole Sawtimber Percentage change in the number of live trees by size class between 1996 and 2015. Source: USDA Forest Inventory and Analysis data: 1996 and 2015. “Where does paper birch grow in Wisconsin?” Growing stock volume by region with map The largest volume of paper birch, 68%, is located in northern Wisconsin with lesser amounts in the southwest and central parts of the state. Most paper birch is part of the aspen / birch forest type and, to a lesser extent, the maple / basswood type. In southern and central Wisconsin, it’s also a part of the oak / hickory forest type. Table 1. Growing stock volume (million cft) by species and region of the state. Species Paper Birch Percent of total Central North east North west South east South west Total 54 151 176 29 70 481 11% 31% 37% 6% 15% 100% Source: USDA Forest Service, Forest Inventory and Analysis For a table of Volume by County go to: http://dnr.wi.gov/topic/ForestBusinesses/documents/tables/VolumeCountySpecies.pdf “What kind of sites does paper birch grow on?” Habitat type1 and site index distribution Paper birch occurs on a wide variety of habitat types (chart below). About ¼ of volume is located on dry habitat types, another ¼ on mesic types and another 30% on mesic to wet and wet habitat types. Habitat type group1 Paper Birch 3% 21% Very Dry to Dry 7% Dry to Dry-mesic Dry-mesic, 16% Dry-mesic Wet, 8% 4% Mesic to Wet-mesic, 21% Dry-mesic to Mesic Mesic Mesic, 20% Mesic to Wet-mesic Wet Undefined Percent distribution of growing stock volume by habitat type group (USDA Forest Inventory & Analysis data). Percent of volume by site index The 30% 25% majority of paper birch growing stock volume (62%) is found in stands with site indices over 60 (chart on left). 20% 15% Paper Birch 10% All Species The average site index by volume for paper birch is 65.7 slightly lower than the average for all species. 5% 0% <41 41 - 50 51 - 60 61 - 70 71 - 80 81 - 90 91+ Site index class Percent distribution of growing stock volume by site index class (USDA Forest Inventory & Analysis data). 1 For more information on habitat types see Schmidt, Thomas L. 1997. Wisconsin forest statistics, 1996. Resource Bulletin NC-183. St. Paul, MN: U.S. Dept. of Agriculture, Forest Service, North Central “How fast is paper birch growing?” Average annual net growth: trends and ratio of growth to volume Average annual net growth of paper birch The average annual net growth of paper birch (chart on 60 right) has been negative since 2009, indicating that mortality exceeded growth during this period. Growth decreased by 78% between 1983 and 1996. 50 Million cft 40 30 20 10 49.3 34.6 -4.3 7.5 0 Table 2. Average annual net growth (million cft/year) of growing stock and the ratio of growth to volume by region of the state Net growth Ratio of growth to volume Northeast 0.2 0.2% Northwest -3.6 -2.1% Central 0.5 0.9% Southwest -0.7 -0.9% Southeast -0.8 -2.6% Statewide -4.3 -0.9% Region -1.0 -10 1968 1983 1996 2009 2015 Average annual net growth (million cubic feet). Source: USDA Forest Inventory & Analysis data Growth rates for paper birch are negative throughout the state except in central and northeast Wisconsin meaning that mortality exceeded growth in these regions (Table 2). The statewide ratio of growth to volume for all species is 2.7%, much higher than the negative growth rate of paper birch. Source: USDA Forest Inventory and Analysis For a table of Average annual growth, mortality and removals by region go to: http://dnr.wi.gov/topic/ForestBusinesses/documents/tables/GrowthMortalityRemovals.pdf “How healthy is paper birch in Wisconsin?” Average annual mortality and the ratio of mortality to volume Average annual mortality of paper birch 25 cubic feet per year, has increased over fivefold since 1983 (chart on right) but has changed little since 1996. 20 Million cubic feet Average annual mortality of paper birch, about 19.7 million The ratio of mortality to volume is 4.1% for paper birch, much higher than the statewide average of 1.1%, is among the highest of all species (Table 3). Whereas paper birch accounts for 2.2% of total growing stock volume in the state, this species makes up over 8.4% of total mortality. 15 10 5 1.2 4.1 20.3 19.3 19.7 1968 1983 1996 2009 2015 0 Average annual mortality (million cubic feet) by inventory year. Source: USDA Forest Inventory & Analysis data Table 3. Mortality, volume and the ratio of mortality to volume. Species Paper Birch Average annual mortality (cft) Growing stock volume (cft) Mortality / volume 19,700,397 480,657,983 4.1% Source: USDA Forest Inventory & Analysis data For a table of Average annual growth, mortality and removals by region go to: http://dnr.wi.gov/topic/ForestBusinesses/documents/tables/GrowthMortalityRemovals.pdf “How much paper birch do we harvest?” Roundwood production by product and the ratio of growth to removals Volume of roundwood by product: Paper birch 1999 In 2009, paper birch accounted for 18.6 million cubic 2009 25 20 Million cft feet or 4.9% of Wisconsin’s total roundwood production (chart on right). Over 60% of this was used for pulpwood. Birch pulpwood accounts for almost 7% of total production. 2004 15 10 Between 2004 and 2009-2012, paper birch roundwood 5 production fell 32% and pulpwood alone fell 45%. 0 Pulpwood Composite products Saw / veneer logs Fuelwood Misc products* Volume of roundwood. Most recent figures for pulpwood and composite products are from 2012 while other product volumes are from 2009. * Miscellaneous products include poles, posts and pilings. Source: Ronald Piva, USDA Forest Service, Northern Research Station, St. Paul MN Ratio of growth to removals: Paper birch 10 Removals of paper birch totaled 13.1 million cubic feet per year from 2010 to 8 6 2015. This is equal to 4.3% of total removals in the state. 7.6 The ratio of average annual growth to removals (chart of left) has been negative 4 since 2009 as mortality increased and volume and growth decreased. 2 0.5 0 -0.3 -0.3 -2 1983 1996 2009 2015 For a table of Average annual growth, mortality and removals by region go to: Source: USDA Forest Inventory & Analysis data http://dnr.wi.gov/topic/ForestBusinesses/documents/tables/GrowthMortalityRemovals.pdf “How much paper birch biomass do we have?” Aboveground biomass by region of the state There are currently 16.1 million tons of aboveground biomass in live paper birch trees, a decrease of 53% from 1983. This is equivalent to approximately 8 million tons of carbon and represents 2.5% of all biomass statewide. As with volume, most paper birch is located in northern Wisconsin (chart below). Paper Biomass of all live trees: Paper birch 1983 1996 2015 Million oven dry tons 16 14 12 10 8 birch wood is of about average density for hardwoods, with a ratio of biomass to volume of 34 oven-dry lbs. per cubic foot (ODP/cft). The average for all trees is about 33 ODP/cubic feet and for hardwoods, 36 ODP/cubic feet. Approximately, 72% of all biomass is located in the main stem and 19.5% in the branches. 6 4 2 - Northeast Northwest Central Southwest Southeast Biomass (above ground dry weight of live trees >1 in dbh, short tons) by year and region of the state. Source: USDA Forest Inventory & Analysis data For a table of Biomass by County go to: http://dnr.wi.gov/topic/ForestBusinesses/documents/tables/BiomassByCounty.pdf “Can we predict the future of paper birch?” Predicted volumes based on current rates of mortality and harvest The 5-year ratios of mortality to volume and removals to volume are significantly higher for paper birch and growth to volume is significantly lower for compared to all species in the state (chart on right). All of these trends would tend to decrease future volumes. The Forest Vegetation Simulator (FVS ) was used to predict future volumes of 1 basswood through 2054. Three scenarios are forecast. One with current rates of mortality and removals (i.e. average annual mortality and removals for 2009 to 2014). Another with current mortality rates and the lower 67% confidence interval for current removals and another with the upper 67% confidence interval for removals. Paper Birch All species 25% 20% 15% 10% 5% 0% -5% Growth/volume Mortality/volume Removals/volume Five year ratios of mortality, removals and growth to volume. Source: USDA Forest Inventory & Analysis data Modelled future volume of paper birch under three harvest levels 600 500 By 495 Million cubic feet 400 300 200 128 111 96 100 2054, volume of paper birch decreases substantially in all three scenarios, 78% for current average removal levels, 74% for low removals and 81% for high removals. Without more regeneration, paper birch may be a scarce species in 50 years. 2014 2019 2024 Average removals 2029 2034 Low removals 2039 2044 2049 2054 High removals The Forest Vegetation Simulator is a forest growth and yield simulation model created by the USDA Forest Service, see http://www.fs.fed.us/fmsc/fvs/.