Spatial distributions of tree species in a subtropical forest of China

The spatial dispersion of individuals in a species is an important pattern that is controlled by many mechanisms. In this study we analyzed spatial distributions of tree species in a large-scale (20 ha) stem-mapping plot in a species-rich subtropical forest of China. O-ring statistic was used to measure spatial patterns of species with abundance 10. V010, the mean conspecific density within 10 m of a tree, was used as a measure of the intensity of aggregation of a species. Our results showed: (1) aggregated distribution was the dominant pattern in the plot. The percentage of aggregated species decreased with increased spatial scale. (2) The percentages of significantly aggregated species decreased from abundant to intermediate and to rare species. Rare species was more strongly aggregated than common species. Aggregation was weaker in larger diameter classes. (3) Seed traits determined the spatial patterns of trees. Seed dispersal mode can influence spatial patterns of species, with species dispersed by both modes being less clumped than species dispersed by animal or wind, respectively. Considering these results, we concluded that seed dispersal limitation, self-thinning and habitat heterogeneity primarily contributed to spatial patterns and species coexistence in the forest. Aggregated distribution in species is a widespread pattern in nature. Of the numerous mechanisms that contribute to aggregation, the major mechanisms include niche segrega-tion (Pielou 1961), habitat heterogeneity (Harms et al. 2001), reproductive or foraging behavior, differential predation (Janzen 1970, Connell 1971), neighborhood competition (Firbank and Watkinson 1987, Kenkel 1988, He and Duncan 2000) and dispersal limitation (Thioulous