New dynamic equation of dominant height and site index for Pinus chiapensis (Martínez) Andresen in Puebla and Veracruz, Mexico

Introduction: Pinus chiapensis (Martínez) Andresen lacks in many areas of site index (SI) models to classify timber productivity. Objective: To develop a dynamic SI equation, using the generalized algebraic difference approach (GADA) to describe the dominant height growth pattern and classify the productivity of natural stands of P. chiapensis in Puebla and Veracruz, Mexico. Materials and methods: Four theoretical growth models were used to derive six equations in GADA, fitted to dominant height-age observations from stem analyses of 31 trees. Fitting was performed using the Dummy variable method, which is invariant to the base age; autocorrelation and heteroscedasticity were corrected. Results and discussion: Quantitative evaluation, graphical analysis of residuals and growth trends of equations allowed the selection of an equation derived from the Levakovic II model with higher predictive capacity. With this equation and a base age of 50 years, polymorphic SI curves with variable asymptotes were constructed to classify productivity into low, medium and high, corresponding to SI of 25, 32 and 39 m, respectively. The maximum mean annual increase for the SI of 32 m was 1.07 m∙yr-1 and occurred at 11.08 years. The equation exhibited better performance relative to a previously reported polymorphic equation. Conclusions: It is recommended to use the developed equation to predict dominant height growth and SI of P. chiapensis stands in Puebla and Veracruz, Mexico.