Atmospheric Carbon Dioxide from Deforestation in Southeast Asia

Abstract

The reduction of carbon in the vegetation and soils of Southeast Asia as a result of changes in land use since 1860 has been analyzed. Several independent estimates of deforestation and of forest biomass were used to construct a range of estimates for the loss of carbon from the land. A net release of carbon to the atmosphere of between 8 and 19 x 1015 g was calculated for the period from 1860 to 1980. In 1980 the net release was 0.15-0.43 x 1015 g C. The largest contributors to this release were the conversion of forests to shifting cultivation and the expansion of permanently cleared land. The greatest uncertainties in the analysis induded estimates of biomass, estimates of the area deared annually by shifting cultivators and the fate of those lands, and the lack of historical or current data on the extent of grasslands in Southeast Asia. FOLLOWING A DECADE OF CONTROVERSY, general agreement now exists that the conversion of terrestrial ecosystems has contributed and is still contributing to the increase in atmospheric carbon dioxide (Clark 1982). Although the losses and accumulations of carbon in the temperate and boreal zones of the earth may approximately balance now, deforestation in the tropics is causing a net flux of carbon to the atmosphere. The estimates of the flux from the tropics range from 0.4 to 4.2 x 1015 g C/yr (Table 1) and are dependent on the carbon held in these ecosystems and the rates at which they are being converted to other land uses. Tropical ecosystems are important not only because they contain large stocks of carbon that result in large releases of CO2 to the atmosphere when disturbed, but also because most of the differences in current estimates of the worldwide biotic release of carbon are caused by uncertainty in the rates of land-use change in the tropics (Houghton et al. 1983). The objective of our research was to examine, in greater detail, land use in the tropics in an attempt to refine and narrow the range in estimates of CO2 flux. This report presents a detailed analysis of the annual net flux of carbon from Southeast Asia between 1860 and 1980. Southeast Asia was chosen because the range of fluxes was greater in this region than any other (0.221.47 x 1015 g C in 1980) (Houghton et al. 1983). The analysis described here included a more detailed division of ecosystems than the earlier study, a greater specificity of ecological parameters to describe carbon stocks and changes in carbon following changes in land use, a more thorough examination of historical data on land use, and the results of a recent FAO/UNEP study (1981) of current rates of deforestation in the tropics. The new range for the estimated flux of carbon was 0.15-0.43 x 1015 g C/yr in 1980, a reduction of the earlier range by 75 percent. The reliability of data and possibility for further refinement of the estimates of net flux of carbon are dis-