TREE SPECIES DIVERSITY, COMMUNITY COMPOSITION, AND FOREST STRUCTURE ACROSS THE ECOLOGICAL TRANSITION ZONE LINKING THE EASTERN AND WESTERN GHATS, SOUTH INDIA
Abstract
Transitional forest zones that link major biogeographic regions often harbor high ecological complexity and species turnover, yet remain poorly studied. This research assesses tree species diversity, community composition, and forest structure along a 68 km east-to-west ecological gradient spanning four protected areas in Karnataka, South India—Bannerghatta National Park, Cauvery Wildlife Sanctuary, MM Hills Wildlife Sanctuary, and Biligiri Rangaswamy Temple (BRT) Tiger Reserve. A total of 42 plots (20 m × 20 m) were established at 5 km intervals to record all trees with girth at breast height (GBH) >15 cm. Across the transect, 123 tree species representing 42 families were documented. Species richness and diversity indices (Shannon-Wiener H′ and Simpson’s Index) increased progressively from east to west, reflecting a transition from dry deciduous forests in Bannerghatta (25 species, H′ = 2.1) to semi-evergreen and moist deciduous forests in BRT (61 species, H′ = 3.8).
Basal area and stem density showed similar trends, increasing from 12.5 m²/ha and 350 trees/ha in the drier forests to 28.7 m²/ha and 550 trees/ha in the wetter forests, suggesting older, more mature stands in the western Ghats. Dominant species varied regionally: Anogeissus latifolia and Albizia amara in dry zones; Tectona grandis in mid-zones; and Syzygium cumini, Terminalia paniculata, and Machilus macrantha in wetter zones. Importance Value Index (IVI) and family-level richness analyses highlighted Fabaceae, Combretaceae, and Rubiaceae as ecologically prominent. Statistical analyses, including ANOVA, correlation matrices, and species accumulation curves, confirmed that elevation, moisture, and forest type significantly influenced diversity and structure. These findings underscore the conservation significance of ecotonal corridors in promoting biodiversity, enhancing ecological connectivity, and supporting forest resilience across climate and disturbance gradients.
