Tree Diametric Relationships and Their Implications for Estimation of Above-ground Biomass in a Tropical Rainforest

The use of diameter at breast height (DBH) measurement in allometric equations for estimation of biomass (AGB) requires that measurements be taken precisely at 130cm from the ground level. However, obtaining this measurement is not always possible. This study aimed to i) investigate the relationship between the DBH and diameters measured at different heights below 130 cm on tree stems, ii) develop an equation for converting diameters measured below 130cm to DBH, and iii) evaluate the accuracy of using converted DBH values to estimate the AGB. We measured the diameters of 376 trees at various stem heights at intervals of 25 cm up to the DBH, in a protected area of the Atlantic Forest, Brazil. Three theoretical models were applied and tested, and the best equation was selected. The relationships between DBH and diameters at 50, 75, and 100 cm did not differ, which allowed the use of one general equation for converting these diameters to DBH. Measurements taken below 50 cm may lead to biased estimations; thus, we propose two additional equations for estimating DBH from these heights. The DBH converted from diameters measured at other heights can be accurately used to estimate the tree AGB and carbon stocks.