Height–diameter relationship of trees in Omo strict nature forest reserve, Nigeria

Abstract

The height and diameter of trees are important variables in estimating the aboveground biomass of trees. Tree height measurements are often difficult in tropical forests hence tree height–diameter models are often used as an alternative for predicting tree heights. This study was carried out to develop height–diameter models for tree species in Omo strict nature forest reserve in Nigeria. Height and diameter data used for the study comprised of 100 tree species, which were classified into three groups using cluster analysis. Eight commonly used non-linear height–diameter functions were tested for predicting heights of the species groups using nonlinear least squares (Nls) method. The power function was selected based on its performance, and fitted using mixed-effects modeling approach to account for between-plot height variability. The Mixed-effects models were evaluated using the Akaike information criteria and Residual standard error. The models were calibrated using three subsample selection approaches. The best calibration results were obtained using subsamples of four trees from four diameter classes per plot. The best calibrated mixed-effect models outperformed the Nls models for all the tree species groups; increasing the accuracy of tree height prediction.