TREE SPECIES DIVERSITY, VEGETATION STRUCTURE, AND IMPORTANCE VALUE INDICES OF SHOLA FORESTS IN THE CENTRAL WESTERN GHATS, CHIKKAMAGALURU, KARNATAKA, INDIA

Abstract

Shola forests, relict montane rainforests endemic to the Western Ghats–Nilgiris Hills complex, represent one of South Asia's most threatened yet species-rich ecosystems. Quantitative assessments of tree diversity, vegetation structure, and Importance Value Index (IVI) along elevational gradients in the Central Western Ghats remain underrepresented in the literature. This study addresses this gap through systematic vegetation sampling across 23 belt transect plots (20 × 20 m; total 0.92 ha) in Shola forests of the Bhadra Tiger Reserve (BTR; 17 plots, 0.68 ha) and the Chikkamagaluru Territorial Forest Division (CTF; 6 plots, 0.24 ha), spanning an elevational range of 1,300–1,930 m. All trees with a diameter at breast height (DBH) ≥ 10 cm were enumerated, and vegetation structure was analysed using basal area, relative density (RD), relative frequency (RF), relative dominance, IVI, Shannon-Wiener Diversity Index (H′), Simpson's Diversity Index (D), and Pielou's Evenness Index (J′). Floristic data were cross-referenced with IUCN Red List of Threatened Species (Version 2023-1).

A total of 727 trees were documented across 68 species, 33 genera, and 29 families. BTR Sholas exhibited higher species richness (59 species, 25 families; H′ = 3.3, D = 0.1, J′ = 0.80), indicative of a mature climax community, while CTF Sholas recorded 31 species and 21 families (H′ = 2.9, D= 0.07, J′ = 0.85). Lauraceae dominated both zones; in BTR, Litsea floribunda (IVI = 30.26) and Cryptocarya stocksii (IVI = 26.48) were the most prominent species, with Syzygium cumini contributing the highest basal area per species (5.78 m²). Twelve IUCN-threatened taxa were identified, underscoring the conservation urgency. Girth class distributions peaked at mid-elevations (1,500–1,700 m) and declined above 1,700 m.

The Chikkamagaluru Shola forests harbour exceptional diversity, including a high proportion of endemic and threatened taxa, and provide critical ecosystem services including carbon storage, watershed regulation, and climate buffering. Lauraceae dominance and elevated late-successional IVI values confirm the climax status of these communities. Urgent conservation interventions, including invasive species removal, habitat restoration, and adaptive management, are needed. The findings provide a robust baseline dataset for SDG Target 15.4, the Kunming-Montreal Global Biodiversity Framework, and state-level conservation policy.