Habitat specialisation of tree species in a Malaysian tropical rain forest
This thesis investigates the relationship between spatial distribution of tropical trees and variation in edaphic factors, particularly soil nutrient supply, and tests the importance of interspecific differences in growth rates and foliar nutrient concentrations as determinants of habitat specialisation. The distribution of some tree species at Pasoh Forest Reserve, Peninsular Malaysia, was correlated with variation in soil properties, especially available P concentrations, on a 50 ha plot. Seeding relative growth rates were highest on the alluvial soils, which had higher available P than the shale-derived soils in the absence of nutrient addition. The effect of habitat variation (characterised in terms of their nutrient and water availability) on tree growth of 115 species was examined within and between species. Overall, differences in tree growth rates between habitats correspond to variation in the pattern of nutrient supply and not water availability. Despite significant differences in growth rates between habitat types for some of the species, the differences in tree growth were a poor indicator of habitat preferences of tree species as defined by bias in their spatial distribution. Foliar nutrient concentrations of habitat generalists and two kinds of habitat specialists (alluvial and non-alluvial specialists) were compared using phylogenetically controlled comparisons. Sign tests showed only one significant difference in mean foliar nutrient (N, P, K, Ca and Mg) concentrations between distribution categories. The distribution of the differences in foliar mg concentrations between habitat generalists and alluvial specialists was significant at P < 0.05 and suggested that Mg concentrations were significantly greater in the habitat generalists. These results suggest that foliar nutrient concentrations are unlikely to explain differences between species in their habitat associations with respect to soil types at Pasoh.