Identification of functional groups in an old-growth tropical montane rain forest on Hainan Island, China

Tropical forests have important roles in conserving global biodiversity and maintaining the functions of the earth's ecosystems. Functional classification of the diverse tropical plant species will lay a good foundation for analysis of tropical forest ecosystems. In this study in an old-growth tropical montane rain forest on Hainan Island, China, we categorized the forest plants (including 252 tree species) into a few functional groups and analyzed their distributions in relation to different environmental factors. Thirteen functional groups were identified using principal components analysis (PCA) and the two-way indicator species analysis (TWINSPAN) program according to seven functional traits: growth form, potential height, buttress size, leaf phenology, seed mass, dispersal agent and wood density. With the exception of shrubs, functional groups (trees, palms, lianas, herbs and epiphytes) were more abundant in the ravine stands than in the mountain slope stands. Buttress size, potential height and seed mass were the key traits for functional group identification, and there were significant positive correlations among them. The ravine stands were composed mainly of functional groups with larger buttress and greater potential height, while the mountain slope stands were composed mainly of functional groups with greater seed mass. The functional groups in the canopy layer (usually composed of species with large buttress, great potential height or large seed mass) could well reflect differences of environmental factors.