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USDA Forest
Service Northern Global Change Research Program Research Projects U.S. Forest Carbon Budget |
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CARBON BUDGET OF UNITED STATES FORESTS Questions & Answers What is a carbon budget? SOURCE: This text is more fully developed in Heath, L.S., and L.A. Joyce. 1997. Carbon sequestration in forests as a national policy issue. In: Communicating the role of silviculture in managing the national forests: Proceedings of the National Silviculture Workshop; 1997 May 19-21; Warren, PA. General Technical Report NE-238. U. S. Department of Agriculture, Forest Service, Northeastern Forest Experiment Station: 29-36. A: A carbon budget (sometimes called carbon balance) shows the inventory of C in C pools and the balance of exchange between the pools. The rate of exchange between the pools is called C flux. The most direct method of tracking the amount of C in ecosystems for policy analysis is the calculation of C budgets based on biomass inventories. For forests, this generally involves multiplying inventory data collected at different times for trees, woody detritus, leaf litter, understory, and soil by conversion factors to express all units in terms of weight of C. Common units are million metric tons (MMT=Teragrams=1012 grams), megagrams (Mg=106 grams), and billion metric tons (petagrams=1015 grams) Therefore, we can represent the pool of C in forests as: Vt = Tt+WDt+Lt+Ut+St, where Vt=total C in the forest, Tt=the amount of C in trees, aboveground and belowground, WDt=C in woody detritus, Lt= the amount of C in the leaf litter layer, Ut= the amount of C in the understory, and St=the amount of soil C in the forest, all at time t. Carbon flux would be calculated as Fp=Vt-Vt-1, with Fp=C flux for period p, expressed on an annual basis by dividing Fp by length of period. Carbon budgets or balances are often also calculated for individual plants in physiological terms, including photosynthesis, respiration, and allocation (which refers to the relative amount of C stored in specific organs) using time steps on the order of hours or daily. Generally, the models producing these budgets are called process models, as they describe the process underlying the system under study. The models are quite useful for investigating certain aspects of C budgets, but they are generally less accurate within observed limits and more expensive for policy analysis than empirical models based on biomass. Q: How much carbon is stored in U.S. forests? A: Our most recent (1992) carbon estimates by region and forest ecosystem component are: SOURCE: Birdsey, R. A., and L. S. Heath. 1995. Carbon changes in U.S. forests. IN: Joyce, L. A., ed. Productivity of America's forests and climate change. U.S. Department of Agriculture, Forest Service, General Technical Report RM-271, Rocky Mountain Forest and Range Experiment Station, Ft. Collins, CO. 70 p. Area of forest land and carbon storage by region, forest class, and forest ecosystem component, 1992.
1 For definitions of Regions, click here. 2 Forest land is defined as land at least 10% stocked by forest trees of any size, including land that formally had such tree cover and will be naturally or artificially regenerated. Timberland is defined as forest land that is capable of producing more than 20 cubic feet per acre per year of industrial wood in natural stands. Currently inaccessible and inoperable stands are included, but land reserved from harvesting is excluded. Reserved forestlands are withdrawn from timber utilization by statute or administrative regulation. Wilderness is an example of reserved lands. Other forest land is forest land that is not capable of producing 20 cubic feet per acre per year of industrial wood. For further information, see the glossary in reference listed in footnote 3. 3 From Powell , D. S., and others. 1993. Forest resources of the United States, 1992. U.S. Department of Agriculture, Forest Service, General Technical Report RM-234, Rocky Mountain Forest and Range Experiment Station. 132 p. + map. Q: What is the current carbon flux of forests in the U.S.? A: Our carbon flux estimates for coterminous U.S. forests are: SOURCE: Birdsey, R. A., and L. S. Heath. 1995. Carbon changes in U.S. forests. IN: Joyce, L. A., ed. Productivity of America's forests and climate change. U.S. Department of Agriculture, Forest Service, General Technical Report RM-271, Rocky Mountain Forest and Range Experiment Station. Ft. Collins, CO. 70 p. Average annual carbon flux (million metric tons/year) for the period 1987-2000. Live flux includes understory and trees. Dead flux includes forest floor and soil. A positive number indicates that the forest is sequestering more carbon than it is emitting to the atmosphere.
Q: How much carbon is in forest products? A: Carbon in wood harvested from forests ends up in a variety of uses, from bring sequestered in lumber in buildings or furniture for a century or more, to quickly being released into the atmosphere as logging debris is burned in preparation for planting. We consider four general categories for the fate of wood: products, landfills, energy production, and decomposition without energy production. Carbon in historical removals was estimated beginning in 1900. In 1995, a net annual average of about 37 million metric tons (MMT) C/yr was being stored in products and landfills (Heath and others 1995) , which is approximately two-fifths of the carbon being sequestered in forest trees of the U.S. (Birdsey and Heath 1995). An additional 50 MMT C/year is emitted when wood is burned for energy. Because of the large magnitude in the wood burned for energy category, how one accounts for emissions from wood used as a substitute for fossil fuels can have a great influence on how forests are managed for carbon sequestration. See Figure 1 for carbon flux in disposition categories over time. Harvests are projected to continue to increase under "business-as-usual" assumptions about population and society over the next 50 years. Approximately 20 MMT C/yr will be stored in forest products, and about the same amount will be stored in landfills. If all harvesting in the United States ceased in 1990, the annual average flux of carbon emissions from existing products would be about 53 MMT/yr, and about 12 MMT/yr from landfills. The U.S produced about 20% of the sawnwood, 25% of wood-based panels, 30% of paper and paperboards, and about 5% of the fuelwood as compared to the rest of the world in 1990 (Brooks 1993). This roughly means that C in wood products in the world is currently increasing about 100 MMT C/yr. (insert Figure 4 from the BANFF.wdp file). [NOTE: Rosemary, I am uncertain of the copyright laws in using this figure. I have checked with Mary Buchanan about this and the best thing to do is to contact Springer-Verlag and ask for permission to post this Figure on the Internet. Since govt. work is not copyrightable, this may not be a problem but it is best to ask. While you are waiting for the permission, you could just leave off this figure-- ] SOURCE: Heath, L.S., R.A. Birdsey, C. Row, and A.J. Plantinga. 1996. Carbon pools and flux in U.S. forest products. In: Forest Ecosystems, Forest Management, and the Global Carbon Cycle, (M.J. Apps and D.T. Price, eds). NATO ASI Series I: Global Environmental Changes, Volume 40, Springer-Verlag, p. 271-278. Q: What is the outlook for carbon sequestration in U.S. forests in the future? A: The trend in carbon flux by region and the U.S. over time is illustrated in the figures. The numbers from 1960-1990 are estimates based on forest inventory data; the numbers from 2000-2030 are projections from a business-as-usual scenario. (insert figures here from Figure 4.4--Birdsey and Heath) Q: How much carbon could be sequestered if more trees were planted? A: The amount of carbon sequestered is a function of the area on which forest landowners could be convinced to plant trees. Incentives include Federal cost-shares, forest management assistance programs, and tax credits, and generally are targeted at land which is marginal for agriculture. We projected carbon sequestered under a scenarios which require a $110 million/year investment for ten years. We adopted area estimates from a study by Moulton and Richards (1990). They estimated how much area would be planted in forests if $110 million/year were invested for ten years to provide incentives for private landowners to plant trees. Funding was assumed to be distributed across regions in a way to maximize carbon sequestration. About an additional 2 MMT/yr of C (Birdsey and Heath, 1995) could be sequestered above the base scenarios over a fifty year period. For more information about the scenario, see Haynes and others (1995). SOURCE: Birdsey, R. A., and L. S. Heath. 1995. Carbon changes in U.S. forests. IN: Joyce, L. A., ed. Productivity of America's forests and climate change. U.S. Department of Agriculture, Forest Service, General Technical Report RM-271, Rocky Mountain Forest and Range Experiment Station. Ft. Collins, CO. 70 p.
References: Haynes, R. W., D. M. Adams, and J. R. Mills. 1995. The 1993 RPA timber assessment update. U.S. Department of Agriculture, Forest Service, General Technical Report RM-259, Rocky Mountain Forest and Range Experiment Station. Ft. Collins, CO. 66 p. Q: How much carbon could be sequestered if higher rates of recycling was encouraged? A: This scenario increases recycling by increasing the percentage of wastepaper used as raw material for paper production. Approximately 9 MMT/yr of carbon could be sequestered above the base projection (Birdsey and Heath, 1995). For more information about the scenario, see Haynes and others (1995). For additional information about recycling, see Heath and Birdsey (1993), Ince and others (1995), and Skog and others (1996). SOURCE: Birdsey, R. A., and L. S. Heath. 1995. Carbon changes in U.S. forests. IN: Joyce, L. A., ed. Productivity of America's forests and climate change. U.S. Department of Agriculture, Forest Service, General Technical Report RM-271, Rocky Mountain Forest and Range Experiment Station. Ft. Collins, CO. 70 p.
References: Ince, P. J., K. E. Skog, and L. S. Heath. 1995. Recycling in the big picture--the really big picture. Resource Recycling 14: 41-45. Skog, K.E., T. Marcin, and L.S. Heath. 1996. Opportunities to reduce carbon emissions and increase storage by wood substitution, recycling, and improved utilization. In: Forests and Global Change, Volume 2: Forest management opportunities for mitigating carbon emissions,p. 209-215. Heath, L.S. and R.A. Birdsey. 1993. Impacts of alternative forest management policies on carbon sequestration on U.S. timberlands. World Resource Review 5: 171-179. Q: Are publicly owned forests in the U.S. sequestering carbon? A: Yes. Publicly owned forests are currently storing more carbon than they are emitting, and projections indicate they will continue to sequester carbon. Table 1 contains estimates of public lands divided into two categories, National Forest (NF) forest land and Other Government (OG) forest lands. In this table, Other Government lands include lands owned by Native Americans.
SOURCE: Details of the methods for calculating these estimates are found in: Heath, L.S. (In press.) Assessing carbon sequestration on public timberland in the coterminous United States. In: The 7th Symposium on System Analysis in Forest Resources, May 28-31, 1997, Bellaire, MI. U. S. Department of Agriculture, Forest Service, North Central Forest Experiment Station, General Technical Report. |
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