Density-dependence in common tree species in a tropical dry forest in Mudumalai, southern India

摘要

Density-dependence in tree population dynamics has seldom been examined in dry tropical forests. Using long-term data from a large permanent plot, this study examined 16 common species in a dry tropical forest in southern India for density-dependence, Employing quadrat-based analyses, correlations of mortality, recruitment and population change with tree densities were examined. Mortality in 1-10 cm diameter trees was largely negatively correlated with conspecific density, whereas mortality in > 10 cm diameter trees was positively correlated. Mortality was, however, largely unaffected by the basal area and abundance of heterospecific trees. Recruitment was poor in most species, but in Lagerstroemia microcarpa (Lythraceae), Tectona grandis (Verbenaceae) and Cassia fistula (Fabaceae), species that recruited well, strong negative correlations of recruitment with conspecific basal area and abundance were found. In a few other species that could be tested, recruitment was again negatively correlated with conspecific density. In Lagerstroemia, recruitment was positively correlated with the basal area and abundance of heterospecific trees, but these correlations were non-significant in other species. Similarly, although the rates of population change were negatively correlated with conspecific density they were positive when dry-season ground fires occurred in the plot. Thus, the observed positive density-dependence in large-tree mortality and the negative density-dependence in recruitment in many species were such that could potentially regulate tree populations. However, repeated fires influenced density-dependence in the rates of population change in a way that could promote a few common species in the tree community.