Thinning-response modifier term in growth models: An application on clonal Tectona grandis Linn F. stands at the amazonian region

Abstract

Thinning is a widely used silvicultural method in the Tectona grandis Linn. F. (teak) stands, however, limited work has been done on modeling for predicting both short- and long-term responses to this treatment. Dynamic growth models for teak stands in Easter Amazon were developed and evaluated from data of 67 plots measured between two and ten years old. We tested the models of Chapman-Richards, Hossfeld, and Lundqvist-Korf using the generalized algebraic difference approach (GADA) to describe the basal area of the stand, including the effect of thinning, which was quantified from a silvicultural treatment response function. Dominant height was described using a dynamic equation derived onwards by Lundqvist-Korf model, considering one parameter to be site specific, while the stand volume was described as of Chapman-Richards model using the theory of covariates. We used 80% of the data for fitting and 20% for validating the developed models. The following fitting statistics were used: Akaike's information criterion, square root of the mean percent error and estimation efficiency. For the validation, was used the equivalence test (regression based TOST using bootstrap). The equation derived from the Chapman-Richards function from GADA integrated with a thinning modifier provided the best performance in describing stand dynamics. The developed thinning modifier were shown to significantly improve predictions of stand-level basal area growth, and the results showed that models that disregard silvicultural treatment cannot be used to obtain reliable projections of the stands under analysis. The growth models provided detailed and accurate description of the dynamics of teak stands in the Amazon region, allowing for a well-defined maximum volume rotation. Overall, the study highlights the importance of including thinning modifiers in growth and yield models, especially for shade intolerant species, such as teak.