Optimizing stand density in Teak plantations using growth models based on intrinsic biological units

Abstract

Attempts were made to develop a growth simulation model for even-aged teak stands using intrinsic biological units and to utilize the model to derive optimal density management plans. Additionally, optimal rotation age, effect of understorey species on the growth of teak and certain eco-physiological parameters of the species were examined. The growth model consisted of five modules such as effects of site index, unrestrained growth, aging, density of teak and density of miscellaneous species. Age and size at inflection point of diameter at breast-height were taken as intrinsic units. Since the study was aimed at developing growth models based on intrinsic biological units, the values of these units were utilized for estimating the parameters of the growth model. The intrinsic units viz., age and size (diameter) at inflection point were estimated from an external data set as 8 years and 10.6 cm including the bark at breast-height level, respectively. The growth model was calibrated based on the data gathered from sixty-nine permanent sample plots established in teak plantations in the State of Kerala, India. One parameter of the growth model of special importance was the index of self-tolerance, which was estimated as 1.28. By the value that is obtained for the said parameter, high mortality should not be caused by slight increases in mean diameter of the stand. The value of fractal dimension (2.13) obtained was biologically justifiable considering the light demanding nature of the species. Based on the estimated equations, a growth simulator was developed in SAS language and several alternative runs were made in order to identify the optimum density trajectory that maximized the net present value (NPV) of cash flows. Optimum density regimes were worked out for different interest rates in all the site quality classes, with and without miscellaneous species (understorey) in the stands. The relative initial density that maximized the NPV varied from 0.41 for site quality I to 0.21 for site quality IV regardless.