The spatial distribution of forest biomass in the Brazilian Amazon: a comparison of estimates

The amount of carbon released to the atmosphere as a result of deforestatio n is determined, in part, by the amount of carbon held in the biomass of th e forests converted to other uses. Uncertainty in forest biomass is respons ible for much of the uncertainty in current estimates of the flux of carbon from land-use change. In the present contribution several estimates of for est biomass are compared for the Brazilian Amazon, based on spatial interpo lations of direct measurements, relationships to climatic variables, and re mote sensing data. Three questions were posed: First, do the methods yield similar estimates? Second, do they yield similar spatial patterns of distri bution of biomass? And, third, what factors need most attention if we are t o predict more accurately the distribution of forest biomass over large are as? The answer to the first two questions is that estimates of biomass for Braz il's Amazonian forests (including dead and belowground biomass) vary by mor e than a factor of two, from a low of 39 PgC to a high of 93 PgC. Furthermo re, the estimates disagree as to the regions of high and low biomass. The l ack of agreement among estimates confirms the need for reliable determinati on of aboveground biomass over large areas. Potential methods include direc t measurement of biomass through forest inventories with improved allometri c regression equations, dynamic modelling of forest recovery following obse rved stand-replacing disturbances, and estimation of aboveground biomass fr om airborne or satellite-based instruments sensitive to the vertical struct ure plant canopies.