MODELLING OF TREE DIAMETER GROWTH USING BETA FUNCTION

Abstract

Diameter growth data over time of two common tree species of Delhi urban forest viz. Polyalthia longifolia L. (PL) and Pongamia pinnata L. (PP) were evaluated. Mean diameter growth was measured over a time period of 11 consecutive years and was eventually modelled applying a three parametric beta function. Results, suggested that PL performed slightly better than PP on the 2 basis of model performance. RMSE (0.551) and AIC (-10.601) values for PL were found to be low than that of PP. However, adjusted R for both data sets were same (0.998). Moreover, maximum growth rate at ti was higher for PP (4.49) as compared to PL (3.22). Diameter growth of PP was quick and inection time i.e., time at which maximum growth rate is achieved hits early than that of PL. All model parameters were stable and showed statistical signicance over time. The objective of this study was to use beta function to predict diameter growth and derive growth parameters of two tree species in question. The function was found to be suitable to indicate for the sigmoidal pattern of determinate growth.