Biodiversity assessment of trees in five inland tropical dry evergreen forests of peninsular India

Abstract

A biodiversity inventory of trees was carried out in five hitherto understudied inland tropical dry evergreen forests of peninsular India, by establishing a 1‐ha permanent plot in each (Araiyapatti‐AP, Karisakkadu‐KK, Maramadakki‐MM, Shanmuganathapuram‐SP and Rayapatti‐RP). These sites are also sacred groves and forest fragments experiencing various levels of human disturbance and can be classified as relatively undisturbed (AP), moderately disturbed (KR, SP and RP) or highly disturbed (MM). Site disturbances were categorized based on forest encroachment, temple visitors’ impact, resource extraction and the degree of cattle and goat browsing. All trees ≥ 10 cm girth at breast height in the five plots were enumerated, their girth measured and tagged. A total of 60 tree species belonging to 49 genera and 26 families were recorded. Tree species richness was as low as 19 species per hectare in the moderately disturbed site RP to as high as 35 species in the relatively undisturbed site AP. Tree density ranged from 596 stems per hectare in site KR to 1663 trees in site SP and that of basal area from 12.4 m2 (in RP) to 22.1 m2 per hectare (in SP). Three species Memecylon umbellatum, Chloroxylon swietenia and Pterospermum canescens scored high importance value index. The Rubiaceae, Mimosaceae, Euphorbiaceae, Rutaceae and Sapindaceae constituted the most‐speciose families. Among the five sites, SP exemplified a mono‐specific dominant tropical forest, with Memecylon umbellatum occupying 69% of the total forest stand density. In all five sites tree species richness and density decreased with increasing girth class. The stand structure of forest sites displayed a reverse J‐shaped curve with the exception of site KR. Spatial patterns of trees in the five sites revealed that the individuals of most species are clumped at the 1‐ha scale. The non‐metric multidimensional scaling ordination, based on species richness, diversity indices, stand density, basal area, species population density and disturbance scores, organized the sites into three clusters, chiefly influenced by three variables - species richness, density of predominant species and site disturbance score. In the light of the extant biodiversity, forest fragmentation coupled with human disturbance, and also the cultural tradition associated with the local people, the need for conservation of the sites is emphasized.