Modeling the height–diameter relationship and volume of young African mahoganies established in successional agroforestry systems in northeastern Brazil

Abstract

The aim of this study was to fit and select height–diameter and stem volume equations for two African mahogany species (Khaya ivorensis and Khaya anthotheca) in the initial development phase (between 2 and 5 years old), established in agroforestry systems in northeastern Brazil. We used linear and nonlinear models to predict the total height (h) and stem volume (v), based on data from forest inventories and stem measurements of standing trees. We tested the following hypotheses: (1) the simple linear model is the most accurate to estimate the total height of young African mahogany trees in relation to different types of height–diameter models (linearized, nonlinear and those with transformed variables); (2) simple and double-entry stem volume models have the same precision in estimating the individual volume of young African mahogany trees. The results showed that the simple linear height–diameter model was most accurate to estimate the height of both African mahogany species. The age’s effect (young trees) and probably the predominantly monopodial development of the Khaya spp. trees sampled were discussed as the causes of the linear nature of the models that best described the height–diameter relationship. The stem volume equations for Khaya ivorensis and Khaya anthotheca were well adjusted. However, the double-entry Spurr’s model was more accurate than the other models for both species. Furthermore, for the Khaya ivorensis, the one-entry (diameter) Husch’s model generated similar stem volume estimates to Spurr’s model.