Simultaneous growth and yield models for Eucalyptus grandis (Hill) Maiden plantations in Zimbabwe

Abstract

Simultaneous stand-level growth and yield models for Eucalyptus grandis in Zimbabwe were developed from Correlated Curve Trend (CCT) and Nelder wheel experiments replicated on five different sites. Nonlinear three-stage least squares method was used to simultaneously fit prediction and projection equations for stand basal area, volume and stand density (S/ha). The age-dominant height model was fitted separately to the data to enable the estimation of site indices for the plots. The data consisted of a total of 313 growth periods of stands ranging in age from 1.3 years to 19.5 years, and site indices from 14 m to 37 m (at an index age of 7 years). The models were validated both quantitatively and qualitatively. Correlation between error components for basal area and volume was strong and significant while the correlation of stand density with basal area and volume was either weak or non-significant. Degree of determination was relatively high for all the models. The mean biases for basal area, volume and stand density predictions were negative. The use of these models in stands managed for pole or saw log production was recommended.


Southern African Forestry Journal No.191 2001: 1-8