Predicting the upper stem diameters and volume of a tropical dominant tree species

Predicting upper stem diameters and individual tree volumes is important for product quantification and can provide important information for the sustainable management of forests of important commercial tree species (Shorea robusta) in Nepal. The aim of this study was to develop a taper equation for S. robusta. Fifty-four trees were selected and felled in the southern low land of Nepal. A mixed effect modelling approach was used to evaluate 17 different taper functions. ‘Leave-one-out cross-validation’ was used to validate the fitted taper functions. The variable exponent taper function best fitted our data and described more than 99% of the variation in upper stem diameters. Results also showed significant effects of stand density on tree taper. Individual tree volume prediction using the local volume model developed in this study was more accurate compared to the volume predicted through the taper function and existing volume model. The taper function developed in this study provides the benefit of predicting upper stem diameter and can be used for predicting volume to any merchantable height of individual trees. It will have implications in estimates of volume, biomass, and carbon and thus may be a potential supporting tool in carbon trade and revenue generation.