Tree growth is related to light interception and wood density in two mixed dipterocarp forests of Malaysia

1. The development of simple predictors of tree growth is important in understanding forest dynamics. For this purpose, tree height, crown width in two perpendicular directions, trunk diameter at 1.3 m height (d.b.h.) and crown illumination index (CI) were determined for 727 pole-sized trees (8-20 cm d.b.h.) of 21 species, on forest dynamics plots at Pasoh Forest Reserve, Peninsular Malaysia and Lambir Hills National Park, Sarawak, Malaysia. A light-interception index (LI = A(cr)CI(2), where A(cr) is crown area) was calculated for each tree, and wood density (stem wood dry mass/fresh volume) was estimated for each species from reported values. 2. Diameter growth rates were linearly correlated with LI (mean per species r(2) = 0.45, excluding substantially damaged and vine-covered trees). 3. Among trees of all species, diameter growth rate was highly correlated with LI/wood density. 4. Mean growth rate per species varied 10-fold among the study species, but increased linearly with mean LI/wood density ratio (r(2) = 0.78), consistent with the previous pattern. 5. Thus much of the variability in tree growth rates, both within and among species, can be accounted for by the simple mechanistic assumption that, within a given size class, growth is proportional to light interception/wood density.