Teak growth, yield- and thinnings’ simulation in volume and biomass in Colombia

Abstract

In the Colombian Caribbean, 44 permanent sampling plots (PSPs) on teak (Tectona grandis) plantations in 20 stands ranging in age from 3 to 20 years have been measured annually for 17 years. We have developed a compatible growth and yield model using the state-space approach and Kopf’s growth equation fitted by nonlinear mixed-effects-models (NLMEMs). For each site index class, the transition function of the basal area depends on the initial basal area (G1) and the initial age (t1), projected to a future basal area (G2) and its age (t2). In the transition function, the previous thinnings were added to not underestimate the total yield. We use NLMEMs to prevent autocorrelation by modeling annual measurements in the PSPs. The transition function is inserted in allometric stand models of three key variables: volume over bark, the volume under bark, and above-ground biomass. Tree allometric models for volume over bark, the volume under bark, and biomass were parameterized, self-validated, independently validated, and recalibrated. Stand allometric models for the same three key variables, as a function of the stand basal area, were parameterized by using NLMEMs to evaluate proportional variance to the mean and variance as a potential function of the mean. In both tree and stand allometric models, the assumptions of the regression have been fulfilled. The resulting growth and yield model allows for the estimation of current growth and predicts future yields in volumes and above-ground biomass arising from thinnings treatments. The proposed model is a useful tool for teak efficient plantations management. The proposed growth models for teak in this paper may have a potential utility in newly teak planted areas, where such tools are scarce or non-existent.