SITE INDEX AND TIMBER PRODUCTION IN FOREST PLANTATIONS OF Gmelina arborea IN TABASCO, MÉXICO

Abstract

Site index is a graphical representation of the productivity of a forest area and describes the relationship between dominant height and age of a tree stand or individual of a particular species. In this study, the growth models of Von Bertalanffy, Chapman, Monomolecular, Logistic, Gompertz, Weibull, Hossfeld IV, Levakovic III, Korf and Sloboda were fitted to generate anamorphic curves of site index for Gmelina arborea Roxb., using age-dominant height data obtained from the measurements and re-measurements from sampling plots within commercial forest plantations in the state of Tabasco, México. The guide curve method was used; the growth parameters of the fitted models were obtained by non-lineal regression using SAS. In accordance with the goodness of fit, residual analysis, efficient validation, mean error and mean absolute difference of the model, six models were satisfactory. Five site index curves were determined, using 10 years as the base age, and were classified as poor (14.5 m), fair (19.5 m), good (24.5 m), very good (29.5 m) and excellent (34.5 m). Equations for quantifying the site index on the basis of the basal area and plantation age were fitted. The evolution of the quadratic mean diameter, the timber volume of the plantations in relation to age and the generated value for the site index were modelled; these were useful until the plantation reached an age of 5 years or 19 m² ha^-1 basal area. These equations will be beneficial in defining the quality of forest plantations, predicting timber production (m³ ha^-1/año) and the turn wherein a determined cut diameter is attained.