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 land-use change and associated per hectare changes in vegetation and soil to calculate changes in the amount of carbon held in terrestrial ecosystems and wood products. The total release of carbon to the atmosphere over the period 1850–1995 was 43.5 PgC. The clearing of forests for permanent croplands released 33.5 PgC, about 75% of the total. The reduction of biomass in the remaining forests, as a result of shifting cultivation, logging, fuelwood extraction, and associated regrowth, was responsible for a net loss of 11.5 PgC, and the establishment of plantations withdrew from the atmosphere 1.5 PgC, most of it since 1980. Based on comparisons with other estimates, 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 significantly with systematic use of satellite data on changes in forest area. In tropical Asia, the emissions of carbon from land-use change in the 1980s accounted for approximately 75% of the region’s total carbon emissions. Since 1990 rates of deforestation and their associated emissions have declined, while 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.