Simultaneous estimation of above- and below-ground biomass in tropical forests of Viet Nam

Abstract

For carbon accounting or for developing REDD+ (Reducing Emissions from Deforestation and forest Degradation) programs, allometric equations for estimating both above-ground biomass (AGB) and below-ground biomass (BGB) are useful. We developed systems of weighted nonlinear allometric equations to estimate total, above- and below-ground biomass for Dipterocarp forests (DF) and Evergreen broadleaf forests (EBLF) in the Central Highlands of Viet Nam, as well as for a dominant plant family (Dipterocarpaceae; Dip) in the DF. A total of 175 trees were destructively sampled for both AGB and BGB, with whole root extraction as the method of BGB sampling. Different equation forms for AGB and BGB incorporating diameter at breast height (D), tree height (H), wood density (WD) and crown area (CA) were evaluated. The best system of equations for the DF, Dipterocarpaceae in the DF, and EBLF was selected based on validation statistics of percent bias (PBias), mean absolute percentage error (MAPE), and root mean squared percent error (RMSPE). All three systems of equations developed in this study used D2×H×WD as a predictor for AGB and a simpler BGB equation form with either D2×H or D as the sole predictor variable. The addition of WD or CA to BGB equation forms did not substantially improve validation statistics over simpler forms. These allometric equations should contribute to advancing our understanding of carbon distribution of trees in these tropical ecosystems.