Comparison of formulae for biomass content determination in a tropical rain forest site in the state of Para, Brazil

Abstract

The aboveground biomass content of a region can be estimated by either direct or indirect methods. The direct method corresponds to sampling the biomass content by weighing and extrapolating results to larger areas. It is a destructive and very laborious procedure. The indirect method utilizes formulas whose predictor parameters are obtained from forest inventories. Forest inventories are conducted with the purpose of planning exploitation and land use, and the data derived from inventory are frequently not suitable for biomass estimation. Problems with both these methods increase in the Amazon region, where little information is available on forest biomass. The objective of this paper is to compare a number of biomass equations taken from previous studies and establish an appropriate mathematical formula to estimate the vegetation weight of a particular region in the Amazon forest. A 0.2 ha area of 'terra firme' forest was chosen for the comparison. This effort was part of a major forest clearing experiment conducted in Tome Acu, a town located 250 km south of Belem, the capital of the Brazilian state of Para. The entire biomass in the 0.2 ha area was weighed A detailed inventory was carried out in the area prior to the cut and then the biomass was estimated with the inventory data inserted in the selected equations. Fourteen different biomass equations taken from previous studies were used. A comparison of the data of real mass and the mass obtained through the application of the fourteen formulas indicated that the two formulas more suitable for the region are given by (a) FW=αD(β)H(γ), where FW is total fresh weight (kg), D the diameter at breast height (cm), H the total height of the tree (m) and α, β, and γ the regression coefficients, equal to 0.026, 1.529, and 1.747, respectively, and (b) FW=αD(β)/(1-M), where α and β are 0.465 and 2.202, respectively, and M the moisture content, defined in terms of mass of moisture per unit mass of fresh biomass. The aboveground fresh biomass weight predicted by the above equations were within ±0.6% of the weight determined in the field.