ABOVEGROUND BIOMASS ESTIMATES FOR TROPICAL MOIST FORESTS OF THE BRAZILIAN AMAZON

One of the major uncertainties in estimating the effect of forest clearing in Brazil's Legal Amazon on atmospheric carbon dioxide is the biomass or carbon content of the forests. Using data from large-scale forest inventories done in the 1950s-60s, we obtained aboveground biomass estimates that ranged from 90 to 397 Mg/ha, with an area weighted mean of 268 Mg/ha. Based on data from a Legal Amazon-wide inventory done about two decades later, forest biomass estimates ranged from 85 to 330 Mg/ha with a weighted mean of 162 Mg/ha. Biomass estimates based on small-scale studies (direct or indirect methods of estimation) ranged between 330 to 550 Mg/ha, well outside of the range of those from large-scale inventories. We suggest that small-scale studies are inappropriate for biomass estimation because of the problem of sampling large trees. The estimates based on large-scale inventories present a more realistic picture of the biomass of Amazonian forests and we suggest that the differences in biomass between the two inventory periods are due to degradation of forests by humans in the intervening period.