Changes in Terrestrial Carbon Over the Last 135 Years

About 2100 Pg of organic C are held in the earth’s terrestrial ecosystems: 550 Pg in living plants and 1500 Pg in the organic matter of soils (Houghton et al. 1985b). Because this terrestrial reservoir of carbon is about 3 times greater than the atmospheric reservoir of carbon, and because the annual exchanges of carbon between terrestrial ecosystems and the atmosphere are large (100–120 PgC), changes in terrestrial ecosystems are important in affecting the atmospheric concentration of CO2. Attempts to estimate such changes have been underway for more than a decade (Woodwell and Pecan 1973, Bolin 1977, Woodwell and Houghton 1977, Woodwell et al. 1978).