Habitat Characteristics and Spatial Heterogeneity of Hoolock Gibbon (Bunopithecus hoolock) in Trishna Wildlife Sanctuary along the Indo-Bangladesh Border

Abstract

The Hoolock gibbon, India’s only ape, is highly dependent on continuous, mature forest canopies for survival, but faces rapid decline due to habitat fragmentation and human disturbance. This study focuses on understanding how habitat structure and spatial heterogeneity in Trishna Wildlife Sanctuary influence gibbon distribution, providing insights for effective conservation. The present study investigated the key habitat characteristics and spatial heterogeneity governing the distribution of western hoolock gibbons (Hoolock hoolock) across Trishna Wildlife Sanctuary and Bison National Park, Tripura, northeastern India, Between February and July 2024. Systematic field surveys were conducted along five belt transects (each 2 km × 10 m), quantifying canopy cover, vertical stratification, gap dynamics, woody plant species composition, and anthropogenic disturbance severity. Visual and spherical densiometer-derived canopy cover exceeded 85% across all study sites, and dense vertical foliage stratification with emergent vegetation reaching 13–19 m above ground typified gibbon-preferred areas. Small canopy gaps (<25 cm) constituted 56.8% of all recorded gaps, supporting understorey regeneration, while large gaps (>200 cm) were rare and locally attributable to Cyclone Remal (2024). Species richness and Simpson diversity index were highest in structurally complex stands. Canopy connectivity showed a strong positive correlation with gibbon detection frequency (Pearson r = 0.78, P < 0.001). Sentinel-2 multitemporal land cover analysis confirmed relative forest stability (>77% forest cover, 2018–2023) with only marginal agricultural encroachment at sanctuary margins. These findings underscore the conservation imperative of maintaining mature, structurally heterogeneous, and well-connected forests for the long-term persistence of this endangered ape.