National level carbon budgets are needed to meet the requirement of the Framework Convention on Climate Change that nations prepare inventories of net greenhouse gas emissions. In the conterminous U.S., the rate of land conversions is relatively low and most agricultural lands are considered to be in carbon equilibrium since they have been in cultivation over many decades. Thus, the forest sector dominates the biologically-driven net carbon flux.
Forest growth, estimated from detailed forest age class distributions, exceeds mortality associated with logging and other factors. The resulting accumulation of tree carbon and wood debris is particularly strong in the northeastern region. Nationally, the forest land base is currently a carbon sink of about 90 Tg yr1 with an additional 35 Tg yr1 accumulating in forest products still in use or in landfills.
Results from coupling of a forest economic model, a forest inventory model, and a forest carbon model suggest that the current forest sector sink will decrease in coming decades, and thus offset a decreasing proportion of U.S. fossil fuel emissions. Alternative policy scenarios, such as afforestation of marginal pasturelands (4 Mha), increased paper recycling, and reduced logging on public lands, have been examined and may produce additional forest sector carbon sinks. The U.S. carbon budget is being compared with those of Brazil and the former Soviet Union in order to develop a common budgeting framework which is applicable in boreal, temperate and tropical countries.
Key words: carbon, pools, flux, budget, United States.
Correspondence: David P. Turner, ManTech Environmental Research Services Corp., USEPA Environmental Research Laboratory, 200 S.W. 35th Street, Corvallis, OR 97333 U.S.A.
Telefax: 503-754-4818
E-mail: dave@mail.cor.epa.gov