Use of GIS for Estimating Potential and Actual Forest Biomass for Continental South and Southeast Asia

Abstract

A geographic information system (GIS) was used to estimate total biomass and biomass density of the tropical forests in South and Southeast Asia because available data from forest inventories were insufficient to extrapolate biomassdensity estimates across the region. Initially, we modeled the biomass density that would be expected if no humans or natural disturbances were present. This value was derived from GIs data layers on elevation, soils, slope, precipitation, and an integrated climate index. Total forest biomass for nine countries was estimated to be 176 Pg (1 Pg = l05 g), or an average potential biomass density (PBD) of 322 Mg/ha. The potential forest biomass map was then masked with a map of forest locations for 1980, resulting in a map of the potential biomass density occurring on locations still in forest in 1980. The total potential biomass estimate for these locations was 63 Pg, representing a loss of 64% of the potential biomass, attributed to land conversion. Average potential biomass density of the forests, on the other hand, increased to 370 Mg/ha, indicating that much of the land converted before 1980 came from lower-biomass-density forests. Finally, the influence of population density was factored into the estimate of PBD. The resulting estimate of total actual forest biomass in 1980 was 33 Pg, which represents a reduction of 52% of the potential biomass of the 1980 forested areas and 19% of the potential biomass across the entire subcontinent. The actual biomass density (ABD) for the South and Southeast Asian tropical forests of 1980 was estimated to be 194 Mg/ha, or 52% of the predicted biomass density of forests in the absence of human activity or other disturbances. The method described appears to be capable of estimating biomass and biomass change across the tropics. The results highlight the importance of considering the degradation of intact forests as well as the outright conversion of forests to other uses when assessing the inputs of carbon to the atmosphere from tropical land-use change.