TROPICAL DRY EVERGREEN FORESTS ON THE COROMANDEL COAST OF INDIA: STRUCTURE, COMPOSITION AND HUMAN DISTURBANCE

Abstract

The impact of human disturbances on forest stands was investigated in two tropical dry evergreen forests, which are also sacred groves or temple forests at Arasadikuppam (site AK) and Oorani (OR) on the Coromandel (east) coast of India. The two sites differ in their degree of disturbance. Site disturbances were classified into site encroachment, temple visitors' impact, degree of cattle and goat browsing, and resource removal. The total score of disturbance level at AK was more than twice (16) that (7) of the less disturbed site OR. A one-hectare permanent study plot was established at each of these sites. The highly disturbed site AK is characterized by short-statured forest (stand height ~ 5 m) with two strata, whereas the less disturbed site OR is comparatively tall-statured (~ 8 m tall) with three strata. The tree density (stems ≥10 cm girth at breast height - gbh) at site AK was twice that at OR (2815 and 1286 stems ha-1 respectively). Site AK was composed of 75% more multi-stemmed individuals than OR, but the less disturbed site OR was 55% more voluminous (basal area 27.3 m2 ha-1) than the highly disturbed site AK (17.6 m2 ha-1). Site OR comprised 77% evergreen species as against 65% at AK. Site AK contained a greater density (85%) of stems in the lowest girth class of 10-30 cm gbh, indicating a greater state of recovery from past disturbance than the less disturbed site OR (64%), which represents a mature forest stand or climax forest. The forest stand structure exhibited a reversed 'J' curve at AK, which was steeper for both girth frequency as well as basal area, while at OR the girth frequency curve was shallow but the basal area distribution was bell-shaped. The species-abundance-based similarity score between the highly disturbed site AK and the less disturbed site OR was 0.45. Tree diversity data of the two study sites are compared with three other comparable tropical dry evergreen forest sites (Kuzhanthaikuppam-KK, Thirumanikkuzhi-TM and Puthupet-PP) located within ~50 km radius on the Coromandel coast of India. Based on the degree of disturbance, the five sites can be represented as OR<TM<AK<KK<PP. There was not much difference in the forest composition (number of species, genera and families) of the two present study sites, but, when all the five sites are considered, species diversity was 20% less in the highly disturbed site PP. Evidently, human disturbances have an impact on forest stand characteristics such as stand height, number of strata, tree density, and basal area. Accepted 25 January 2003.