Estimating the terrestrial carbon pools of the former Soviet Union, conterminous U.S., and Brazil

Terrestrial-carbon (C) pool sizes are of interest in relation to quantifying current sources and sinks of C, and evaluating the possibilities for future C sequestration or release by the biosphere. In this study, the C pools in the terrestrial ecosystems of the former Soviet Union (SUf), conterminous United States (USc), and Brazil were estimated for a nominal 1990 base year. Data sources included recent vegetation maps, resource inventories (particularly for forests), and published values for C densities (mass per unit area). Methodology varied by nation depending upon data availability but generally consisted of identifying a suitable land cover classification system, quantifying the area of each land cover type using traditional mapping approaches or satellite remote sensing, and assigning a mean C density to each cover type with separation by phytomass, litter plus coarse woody debris, and soil. Total organic C for the 3 geographic areas was estimated at 839 Pg (Pg = g × 10¹⁵) C in 1990, 38% of a literature-based estimate of the global terrestrial-C pool on an area representing 28% of the world's lands (excluding Antarctica). The soil C pool was the largest component in the SUf (84 % of the total) and USc (76%) but not in Brazil (47%). Correspondingly, the proportion as phytomass was greatest in Brazil (48%) compared to the SUf (10%) and USc (17%). The forest land cover class contained by far the largest proportion of C among the land cover classes except in the SUf where peatlands were dominant with 37 % of the total. The 2 largest C pools isolated in this study are potentially long-term sources of C to the atmosphere: soil C in peatlands of SUf (212 Pg) which may be lost via climate change, and phytomass C in the tropical-moist forests of Brazil (105 Pg) which may be lost via deforestation.