Accessibility-driven habitat vulnerability in the tropical mountain landscape of Idukki district, India

Mountain districts within biodiversity hotspots often experience increasing ecological pressure despite retaining extensive forest cover. In the Western Ghats of India, Idukki district has undergone rapid tourism expansion, infrastructure development, and land-use reconfiguration over the past decade. This study assesses how changes in urban nature accessibility and population demand influence ecosystem service distribution and habitat vulnerability using the InVEST modelling framework. Urban Nature Access and balance indicators accessibility, per-capita balance, and total population balance were evaluated alongside a Habitat Risk Assessment for 2011 and 2025. The results indicate a growing spatial mismatch between population demand and accessible natural spaces, with strongly negative urban nature balance values expanding across central and southern Idukki by 2025. Accessibility and population pressure have become increasingly concentrated along valley floors, plantation belts, and transport corridors, while large forested areas remain functionally inaccessible. Habitat Risk Assessment results show that human-modified land-cover classes experience disproportionately higher risk, with built-up areas exhibiting the highest mean risk (R̄ = 0.42), followed by plantations (R̄ = 0.38) and croplands (R̄ = 0.34). Deciduous forests display lower vulnerability (R̄ = 0.22), and water bodies remain largely unaffected (R̄ = 0.05). More than one-third of built-up and plantation landscapes fall within medium to high habitat risk categories. High-risk zones identified by the model spatially coincide with landslide-prone regions that experienced repeated slope failures during extreme monsoon years (2018–2020), particularly in tourism-intensive areas such as Munnar, Adimali, and Peermade. These patterns indicate that ecological vulnerability in Idukki is driven less by absolute forest loss than by accessibility-induced concentration of human activities within steep, geophysically fragile landscapes. The findings emphasize the importance of integrating accessibility-aware ecosystem service assessments with hazard-sensitive nature-based land-use planning to reduce ecological degradation and disaster risk while supporting sustainable tourism and development in the Western Ghats.