Tree species composition, dispersion and diversity along a disturbance gradient in a dry tropical forest region of India

Abstract

Forest inventory data were collected in 1998-2000 from fifteen 1 ha permanent plots along a disturbance gradient in a dry tropical forest region of India. A total of 4033 stems, 49 species, 44 genera and 24 families of adult trees (≧ 30 cm CBH), occurred in the 15 ha of forest area. The study indicated that the dry tropical forest is characterised by a patchy distribution of species and individuals with mixed species composition, and the sites are represented by different combinations of the dominants and co-dominant species. A PCA ordination indicated that the variation in species composition of the sites is explained by the variation in soil nitrogen as well as the degree of disturbance. About half the analysed species showed changing nature in dispersion along the disturbance gradient. The distribution of Boswellia serrata, Holarrhena antidysenterica and Lannea coromandelica changed from clumped to uniform and the distribution of Butea monosperma, Cassia fistula and Elaeodendron glaucum changed from uniform to clumped as the degree of disturbance increased. The mean stem density was highest (419 stems ha⁻¹) at the least disturbed site and lowest (35 stems ha⁻¹) at the highly disturbed site, and for basal area, the highest value (13.78 m² ha⁻¹) was for the second least disturbed forest site and the lowest value (1.30 m² ha⁻¹) was for the most disturbed site. The total number of stems, indices of species richness, evenness and α -diversity decreased with disturbance. A strong influence of number of species per individual on β-diversity suggests that for resisting change in floristics due to disturbance, a site must have low species-individual ratio.