T R Shankar Raman
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Impact of fragmentation and plantations on rainforest birds in the Anamalai hills, southern Western Ghats, India.

The conversion of large tracts of tropical rainforest to smaller patches embedded in a landscape matrix of human-altered habitats such as plantations is one of the serious and reigning concerns in the field of conservation biology. Here, I describe the effects of rainforest fragmentation and conversion to tea, coffee, and Eucalyptus plantations on bird communities in the highly man-modified landscape of the Anamalai hills in the southern Western Ghats hill ranges, India. Systematic point-count sampling for birds and habitat sampling for vegetation description were carried out in the three plantations types and in 13 rainforest fragments ranging in area from 0.3 ha to 2,600 ha. A total of 106 bird species were recorded, including 75 typical rainforest species and 31 species of open-country and drier forests that had colonised disturbed fragments and plantations. Total bird species richness was higher in medium-sized fragments (10 − 100 ha), due to the entry of these widespread open-country species, along with the persistence of many rainforest species. Null models of passive sampling in relation to area or abundance did not predict bird species richness. Rainforest bird species richness instead increased virtually log-linearly with fragment area, with substantial decrease in species richness below a fragment area threshold of 10 ha. In addition, the structural development of rainforest canopy and vertical foliage distribution had positive effects on rainforest bird species. Medium-sized fragments, particularly with relatively undisturbed vegetation, held significant populations of rainforest bird species, including endemic species, and are important repositories and refuges in the landscape for birds. The similarity in bird community composition between sites was positively related to their similarity in tree species composition, and negatively with their difference in area or physical distance separating them. The compositional changes showed a nested-subset structure, indicating possible differential extinction of species in relation to changing area and habitat. Plantations, particularly of tea and Eucalyptus, detrimentally affected rainforest birds, although a number of rainforest birds thrived in shade-coffee plantations. Although 17 rainforest bird species did not occur in any plantations, those species that did occur also persisted or occurred at higher densities in small and medium-sized fragments in the landscape. The conversion of shade-coffee to tea plantations is a matter of concern for bird conservation in the region and needs to be offset through commercially viable incentives. The study also highlights the value of rainforest fragments and the need to reverse degradation through active efforts at restoring tree species composition and rainforest structure for rainforest bird conservation.

NCF Technical Report No. 5. Nature Conservation Foundation, Mysore.