Emissions of carbon from forestry and land-use change in tropical Asia

The net emissions of carbon from forestry and changes in land use in south and southeast Asia were calculated here with a book-keeping model that used rates of landuse change and associated per hectare changes in vegetation a nd soil to calculate changes in the amount of carbon held in terrestrial ec osystems and wood products. The total release of carbon to the atmosphere o ver the period 1850-1995 was 43.5 PgC. The clearing of forests for permanen t croplands released 33.5 PgC, about 75% of the total. The reduction of bio mass in the remaining forests, as a result of shifting cultivation, logging , fuelwood extraction, and associated regrowth, was responsible for a net l oss of 11.5 PgC, and the establishment of plantations withdrew from the atm osphere 1.5 PgC, most of it since 1980. Based on comparisons with other est imates, the uncertainty of this long-term flux is estimated to be within +/ -30%. Reducing this uncertainty will be difficult because of the difficulty of documenting the biomass of forests in existence >40 years ago. For the 15-y period 1981-1995, annual emissions averaged 1.07 PgC y(-1), about 50% higher than reported for the 1980s in an earlier study. The uncertainty of recent emissions is probably within +/- 50% but could be reduced significan tly with systematic use of satellite data on changes in forest area. In tro pical Asia, the emissions of carbon from land-use change in the 1980s accou nted for approximately 75% of the region's total carbon emissions. Since 19 90 rates of deforestation and their associated emissions have declined, whi le emissions of carbon from combustion of fossil fuels have increased. The net effect has been a reduction in emissions of CO2 from this region since 1990.