Aim We assessed the rates of turnover of tree species with distance (beta diversity) in wet forests of the Western Ghats (WG) complex of India to see whether climate, topographic variation or species traits influence beta diversity.Location The Western Ghats is a chain of mountains about 1600 km in length, running parallel to the western coast of the Indian Peninsula from above 8° N to almost 21° N latitude.Methods We used data from 60 small plot inventories concentrated in three regions: the southernmost part of the Western Ghats (SWG) (8°24' to 9°37' N), the Nilgiri Hills (11°12' to 11°14' N), and the central Western Ghats (CWG) (12°32' to 14°51' N). We used Sorensen's index (SI) to estimate the similarity in species composition between two plots and regressed SI against the logarithm of the distance between plots to assess beta diversity. A bootstrapping procedure provided confidence intervals for regression coefficients. To test for the effects of climate, we regressed seasonal!ty differences between plots against SI for low-elevation (< 800 m) plots along the north-south axis, and all plots in the SWG. We assessed the impact of the rainfall gradient in the Kogar region.Results Among all three regions, beta diversity was highest along the latitudinal axis, and along the rainfall gradient in the Kogar region. Differences in seasonal!ty between sites were strongly related to beta diversity along the north-south seasonally gradient and within the SWG. Within the three regions, beta diversity was highest in the region with the strongest rainfall gradient and lowest for the topographically heterogeneous SWG. Beta diversity did not differ between forest strata and dispersal modes.Main conclusions We conclude that climate, particularly seasonality, is probably the primary driver of beta diversity among rain forest trees of the Western Ghats complex.

We tested whether local abundance of rain forest trees in the medium elevation wet forests of the southern Western Ghats (WG) was related to environmental tolerance, life form, and geographical range. We selected trees in medium elevation wet forests (750-1700 m asl) of the southern WG, using two data bases: a small plot (30 × 30 m) data base of 288 species of trees (≥ 3 cm dbh) in 33 plots totaling 2.97 ha, and a data base of 135 species of tree (≥ 10 cm dbh) in larger plots of 1 ha each, totaling 4.84 ha. The species density per hectare and number of records in the plot network was used in a factor analysis to give a measure of the local abundance of each species. The altitude and seasonality ranges of these species in the WG was assessed from independent data bases and used to generate an environmental tolerance score. Results indicated that as a species became locally more abundant, it occurred across a wider range of environmental gradients, but regional distribution was not related to geographical distribution. Understory species tended to be rarer with smaller range sizes and lower environmental tolerances than overstory species. Climate change is predicted to have drastic effects on restricted range species with limited environmental tolerances.

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