AMAZONIAN DEFORESTATION AND GLOBAL WARMING - CARBON STOCKS IN VEGETATION REPLACING BRAZIL AMAZON FOREST

Carbon stocks in vegetation replacing forest in Brazilian Amazonia aff ect net emissions of greenhouse gases from land-use change. A Markov m atrix of annual transition probabilities was constructed to estimate l andscape composition in 1990 and to project future changes, assuming b ehavior of farmers and ranchers remains unchanged. The estimated 1990 landscape was 5.4% farmland, 44.8% productive pasture, 2.2% degraded p asture, 2.1% 'young' (1970 or later) secondary forest derived from agr iculture, 28.1% 'young' secondary forest derived from pasture, and 17. 4% 'old' (pre-1970) secondary forest. The landscape would eventually a pproach an equilibrium of 4.0% farmland, 43.8% productive pasture, 5.2 % degraded pasture, 2.0% secondary forest derived from agriculture, an d 44.9% secondary forest derived from pasture. An insignificant amount is regenerated 'forest' (defined as secondary forest over 100 years o ld). Average total biomass (dry matter, including below-ground and dea d components) was 43.5 t ha(-1) in 1990 in the 410 X 10(3) km(2) defor ested by that year for uses other than hydroelectric dams. At equilibr ium, average biomass would be 28.5 t ha(-1) over all deforested areas (excluding dams). These biomass values are more than double those form ing the basis of deforestation emission estimates currently used by th e Intergovernmental Panel on Climate Change (IPCC). Although higher re placement landscape biomass decreases net emissions from deforestation , these estimates still imply large net releases.