USING PLANT FUNCTIONAL ATTRIBUTES TO QUANTIFY SITE PRODUCTIVITY AND GROWTH-PATTERNS IN MIXED FORESTS

Forest growth models form one of several important prerequisites for s ustainable management. The complexity of tropical moist forest means t hat there is often little objective information to classify sites and species for growth modelling and yield prediction. Classification base d on observable morphological characteristics may be a useful surrogat e for, or supplement to, other alternatives. This study investigated t he utility of plant functional attributes (PFAs) for site and species classification. PFAs describe a plant in terms of its photosynthetic a nd vascular support system, and the sum of individual PFAs for all spe cies on a plot provides an efficient summary of vegetation features at the site. Preliminary observations suggested that the PFA summary may also indicate site productivity, and that specific PFAs may be used t o group species for modelling growth and yield, Data from 17 permanent plots in the tropical rainforests of North Queensland were used to te st these preliminary observations. Standard PFA proformas were complet ed for each plot in January 1995, and the relationships between the PF As, site productivity and specific growth patterns were examined using discriminant analysis, linear regression and standard statistical tes ts. Results indicate that mean leaf size, and the incidence of species with vertical leaf inclination (more than 30 degrees above horizontal ) are significantly correlated with site productivity. Of the PFAs ass essed, five elements appear to offer a useful basis for grouping speci es for modelling: leaf size and inclination, a furcation index (i.e. r elative height to first fork or break in the main stem), and the prese nce of lenticels and chlorophyllous tissue on the main stem. The restr icted nature of our database limits comment on the general utility of the method, but results suggest that further work on PFAs is warranted . (C) 1997 Elsevier Science B.V.