Appropriate Volume Functions for Leguminosae Family in Two Tropical Rainforests in Cross River State, Nigeria

Abstract

Volume equations were developed for tree species of leguminosae family in two tropical rainforest, Nigeria. The data used consist of merchantable volume, stump diameter, diameter at breast height and merchantable height for 22 tree species. The number of observations per species ranged from 1 to 30 while the diameter at breast height ranged from 10.00 cm to 132.20 cm. The result in this study shows that generalised logarithmic volume function (also termed Schumacher’s volume function) performed better than other forms of volume functions. For example, the best adjudged volume for all species combined were  and . The merchantable volume developed from double-variable function indicates negative intercept while the single-variable volume function represents the logarithmic nonlinear function and performed best within the limit of data used for each species group. The method of species grouping in this study was morphological and was based on sub-families of tree species. The results indicate that D²H as weighting factor was found to be appropriate in reducing heteroscedasticity. The model being significant indicates a good fits and confirmed the effectiveness of weighted predictor in stabilising error variance. The resulting volume functions possessed desirable statistical properties and model behaviours, and can be used to estimate timber volume in the tropical rain forest areas of Nigeria. The volume equations based on stump diameter alone are adequate to provide estimates of tree volume illegally removed.