MODELLING THE TREE GROWTH IN MIXED TROPICAL FORESTS I. USE OF DIAMETER AND BASAL AREA INCREMENTS

Abstract

Tree growth can be expressed by either diameter increment (dD) or basal area increment (dBA). Little work has been done to determine which of these two parameters is the appropriate dependent variable for use in growth models. This paper examines the growth of regenerated mixed tropical forests in Peninsular Malaysia which were measured over a period of 13-20 y. Least squares regression equations were developed to relate dD and dBA to initial tree diameter at breast height (DBHOB) in 36 permanent growth plots of 0.4 ha each. The residual plots relating dD and dBA to DBHOB show the existence of non-homogeneity of variance. The transformations of dD and dBA to remove non-homogeneity of variance were carried out and used to relate to DBHOB. Furnival Index was then constructed and adjusted to compare likelihoods of different statistical models for dependent variables that have been expressed in the same sample space. The result indicates that diameter increment is a more appropriate dependent variable to be used in growth models in mixed tropical forests.