Impact of patch size on woody tree species richness and abundance in a tropical montane evergreen forest patches of south India

Abstract

We examined the effects of forest patch size on woody tree species richness and abundance in tropical montane evergreen forest patches of the Nilgiri region, south India. We sampled woody trees (≥ 1 cm dbh) from 21 forest patches in the upper Nilgiri hills (> 2000 m elevation) and recorded a total of 35,146 individuals of 61 species, 45 genera and 30 families. Species richness and abundance of sapling/shrubs (≥ 1 to < 10 cm dbh) increased significantly with increasing patch size, but the species richness and abundance of small, medium and larger trees (≥ 10 to < 30, ≥ 30 to < 60 and ≥ 60 cm dbh, respectively) did not. Overall, forest interior species richness and abundance increased significantly with increasing patch size but edge species richness did not. Species richness and abundance of shade-tolerant and shade-demanding tree species also increased with increasing patch size. The abundance of zoochory dispersed tree species was significantly related to increasing patch size, but those dispersed by autochory did not display any clear relationship between patch size and species richness or abundance. Our findings suggest that with increasing forest patch area, tree compositional patterns may be driven by species specific shade-tolerance adaptations and dispersal patterns. Differential responses in these traits by the plant community within the individual habitat zones of forest edge and interiors likely plays a major role in determining the inherent plant community and thus the subsequent ecological processes of forest patches, including their responses to increasing patch area.