Growth and mortality are related to adult tree size in a Malaysian mixed dipterocarp forest

Tree stature is an important ecological and silvicultural characteristic and the high diversity of many tropical forests is associated with a broad range in species stature. A measure of adult size, the 95th percentile of trunk diameter of all diameters >= 0.1 x maximum observed diameter (D95(0.1)) was found to be independent of species abundance and highly correlated with maximum height. D95(0.1) was determined for 573 species with at least 20 trees with diameters >= 0.1 x maximum observed diameter in old-growth, lowland evergreen forest on the 50-ha forest dynamics plot at Pasoh Forest Reserve, Malaysia. These species, comprising 98.3% of all trees >= 1 cm diameter in the plot, were then divided into five life forms of differing stature; shrubs (D95(0.1) < 5 cm), treelets (5 cm <= D95(0.1) < 12 cm), understory trees (12 cm < D95(0.1) < 25 cm), canopy trees (25 cm <= D95(0.1) < 60 cm) and emergents (D95(0.1) >= 60 cm). Each life form showed a distinctive pattern of mortality versus trunk diameter, but all showed higher mortality in the largest diameter class per life form. Mean growth rates increased with trunk diameter within each life form, consistent with reported increases in irradiance with height at Pasoh. Among trees of similar diameter, growth rates increased across life forms from the smallest to largest. These differences in growth rate among life forms may be due to associated differences in allometry, photosynthetic capacity and reproductive allocation. (c) 2005 Elsevier B.V. All rights reserved.