WOOD DENSITY FOR ESTIMATING FOREST BIOMASS IN BRAZILIAN AMAZONIA

Reliable estimates of the biomass of Amazonian forests are needed for calculations of greenhouse gas emissions from deforestation. Interpret ation of forest volume data for the region is the most practical means of obtaining representative biomass estimates, The density of the woo d used in converting volume data to biomass is a key factor affecting estimates of biomass and of emissions. Interpreting density data for b iomass purposes, which is different from the normal use of these data for commercial timber uses, is complicated by a variety of factors. Th ere is variability among individuals of a given species, among geograp hic locations, and within the vertical and radial dimensions of indivi dual trees. Considerable confusion has resulted from the variety of wa ys that densities are reported with respect to humidity at time of the weight and volume measurements used in calculating the density value. The most appropriate measure for biomass is basic density, or oven-dr y weight divided by wet volume. Corrections for hollow trees and the p osition of samples within trunks are also needed. Here, available data are brought together for 268 species of trees, with an unweighted mea n basic density of 0.65 (range 0.14-1.21). Weighting the mean by the v olume of wood of each species in a sample of vegetation types, and wei ghting the means of the vegetation types by the extent of each in the region, yields a mean density of 0.69. Although the weighted mean dens ity calculated here has a much firmer empirical basis than previously available estimates for this parameter, uncertainty is still considera ble, particularly as a result of doubt concerning taxonomic identifica tions in the forestry surveys. Were the wood density of a small but bo tanically well-studied plot near Manaus to apply to the region as a wh ole, Brazil's 1990 emissions of greenhouse gases would be higher by an amount equivalent to two-thirds of the country's annual emission from fossil fuels.