Trees approach gravitational limits to height in tall lowland forests of Malaysia

1. In the absence of wind, tree height is limited by elastic instability, which occurs when a tree becomes too spindly to erect itself when bent from the vertical. To assess the extent to which trees approach this limit and characterize species stature in diverse tropical forests, we measured tree dimensions in tall, dense forests at Lambir Hills, National Park, Sarawak, Malaysia and Pasoh Forest Reserve, Peninsular Malaysia. From these measurements we determined characteristic adult heights and trunk diameters for 91 species. 2. Across all species, adult height scaled with adult diameter to the 2/3 power, as predicted for a column at its buckling limit. These heights were, on average, 65% of the buckling limit calculated for a cylindrical column with typical wood properties. 3. At a given diameter, the species of Lambir were 9% taller than those of Pasoh, a pattern related to the greater rainfall and density of trees at Lambir. 4. On the topographically rugged Lambir plot, large emergent trees were shorter on ridges than in hollows, whereas small, sheltered trees showed no relation between allometry and elevation. 5. Thus, trees may approach gravitational limits to height in favourable environments for growth where there are large advantages of height for light interception and trees are sheltered from wind.