Attenuated tree species diversity in human-impacted tropical evergreen forest sites at Kolli hills, Eastern Ghats, India.

Abstract

Tree diversity (≥30 cm gbh) in undisturbed and human-impacted tropical evergreen forest sites was investigated in the Kolli hills, Eastern Ghats, India. Four 2-ha contiguous permanent plots were erected, one each in Perumakkai shola (site PS), Vengodai shola (VS), Kuzhivalavu shola (KS) and Mottukkadu shola (MS) at 1000, 1050, 1200 and 1250 m elevation, with increasing human disturbance, to evaluate the difference in tree species composition, stand structure and dynamics. This paper discusses the results of the first survey. A total of 3825 individuals and 78 species from 61 genera and 36 families were enumerated in the 8 ha area. Among the four 2-ha sites, species richness was greatest (58) in the undisturbed site PS and lowest (39) in the highly disturbed site MS. Shannon, Simpson, Hill diversity and evenness indexes revealed a progressive reduction in diversity with increasing disturbance. The asymptote species-area curves imply adequate site sampling. Tree density (1151 to 651 trees ha−2) and basal area (106 to 46.6 m2 ha−2) decreased from undisturbed to disturbed site, due to selective felling. Single species, Memecylon umbellatum dominated sites MS (39%) and VS (26%), while Nothopegia heyneana, Memecylon umbellatum and Diospyros ovalifolia were dominant in PS, and Meliosma simplicifolia, Myristica dactyloides and Phoebe wightii in KS. Based on species abundance, we classify the study area as Memecylon–Phoebe–Beilschmiedia association with Neolitsea and Myristica as codominants. Tree population structure revealed a step-wise decline in girth frequencies with increasing size class in undisturbed site PS, whereas tree density fell sharp (>50%) in medium girth class in the disturbed site MS. Population of the dominant species varied widely. The diversity values of this inventory are compared with similar studies in India and other tropical forests. Evidently, the reduction in species richness (by 52%), basal area (56%) and tree density (58%) in disturbed sites, with 57.6% of species rarity of this tropical evergreen forest, in secluded patches (‘sholas’) of Kolli hills, underlines conservation need to prevent species loss.