Volume and biomass of trees in central Amazonia: influence of irregularly shaped and hollow trunks

Abstract

Conventional measurements of diameter, basal area and volume of the bole assume that any cross section of the bole is circular and that the bole is a solid of revolution. These assumptions lead to error when the bole is irregularly shaped and/or hollow. These errors were quantified for trees in central Amazonia after adjusting the number of trees sampled in each class based on the diameter distribution of a large inventory. For large trees (DBH ≥50 cm) total basal area was overestimated by 30%, while the overestimate was 11% for all trees with DBH ≥5 cm. The total bole volume per hectare was overestimated by 11.2% (∼40 m 3/ha). Most of this volume correction is attributed to the non-circular form of the cross section; the effect of hollow areas on the volume of the bole was only 0.7%. For trees above 31.8 cm DBH, which is the minimum diameter in the Projeto RADAMBRASIL inventories, the volume per hectare was overestimated by 4.4% using conventional measurements. Because of compensating errors in commonly used formulas, however, the volume overestimate associated with conventional methods does not imply biomass overestimation in studies that have used the RADAMBRASIL dataset.