Asymptotic height as a predictor of growth and allometric characteristics Malaysian rain forest trees

The growth and physiological characteristics of canopy trees are expected to differ systematically from those of understory trees on the basis of size-dependent aspects of biomechanics, resource availability, and life history. Although such differences have previously been noted, there has been relatively little effort to quantify these in terms of interspecific allometric relationships. Asymptotic maximal height (H-max) is advocated as a measure of the size of dicotyledonous woody plants for this purpose. Height diameter (H-D) relationships in 38 species within six genera of Malaysian rain forest trees are well described by an asymptotic model, and thus provide a basis for estimating H-max using static observational data. Three important aspects of tree growth strategies are shown to be predictable on the basis of these values: average tree growth rates are positively related to H-max, while wood density and the initial allometric slope of (species-specific) H-D relationships are negatively related to H-max. These patterns may be explained by an association of low light levels with slow growth and high density wood in understory species; the latter property may in turn allow for relatively high allometric slopes of H-D relationships in saplings of small-statured species. Analyses that control for phylogenetic differences provide evidence that such interspecific allometric patterns are the product of convergent evolution. These results are consistent with the idea thee much ecological variation within species-rich taxa of southeast Asian rain forest trees is related to differentiation along a vertical axis of tree size.