Taxon-specific modeling systems for improving reliability of tree aboveground biomass and its components estimates in tropical dry dipterocarp forests

Abstract The dry dipterocarp forest (DDF) is a major and unique forest type in Asia providing both protection and production functions. DDF's role as a carbon sink is important in Asia, but there is a deficiency in existing biomass models for these forests. This study aimed to develop simultaneous modeling systems to estimate tree above-ground biomass ( AGB ) and its components for mixed species, dominant family, genera, and species. Twenty-eight 0.25 ha plots in the Central highlands and one 1 ha plot in the Southeast ecoregion in Viet Nam were measured. A total of 329 trees were destructively sampled to obtain a dataset of the dry biomass of the stem ( Bst ), branches ( Bbr ), leaves ( Ble ), bark ( Bba ), and AGB . Using K-fold cross validation, we compared AGB predictions from independently developed AGB equation and from a system of biomass equations that estimated component biomass and AGB simultaneously. The estimation methods for independent equation was weighted nonlinear regression fit by maximum likelihood and for simultaneous system it was weighted nonlinear seemingly unrelated regression (SUR) fit by generalized least squares. We also examined different modeling systems for different plant classification at taxonomic levels. The selected form of taxon-specific modeling systems were AGB = a 1  × D b11  × H b12  × WD b13  + a 2  × D b21  + a 3  × D b31  + a 4  × D b41 for mixed species and dominant Dipterocarpaceae family and AGB = a 1  × D b11  + a 2  × D b21  + a 3  × D b31  + a 4  × D b41 for dominant genera of Dipterocarpus and Shorea . The predictors of D, H, and WD are diameter at breast height, tree height and wood density, respectively. Compared to the mixed species modeling system, genus-specific modeling systems improved the reliability of AGB estimation substantially and will reduce the cost of application because the only predictor required for measurement is D . The pantropical genus-specific modeling systems are more reliable than pantropical mixed species models.