Invasion-fragmentation feedbacks reshaping Indian tropical deciduous forests

Introduction Tropical dry forests play a critical role in regulating ecological processes and sustaining rich floral and faunal diversity. However, these ecosystems are increasingly threatened by forest fragmentation and the proliferation of invasive plant species (IPS), necessitating urgent conservation measures to maintain ecological balance and support local communities. In this context, the present study evaluates long-term forest fragmentation dynamics in the Palamau Tiger Reserve (PTR), Eastern India, using multi-temporal satellite observations (Landsat TM and Landsat OLI/TIRS) spanning three decades (1993-2023). Methods Fragmentation was assessed using core, interior, edge, and patch metrics and quantified through the Combined Fragmentation Index (CFI). Field-based surveys of IPS across 90 forest grids and spatial analyses were conducted to evaluate IPS dynamics in relation to fragmentation and climatic variables. The analysis provides an empirical basis for identifying threshold levels of forest cover and optimal spatial configurations required to enhance landscape resilience and mitigate fragmentation impacts. Results It reveal a significant decline in forest cover from 1993 to 956.60 km 2 in 2013, followed by a partial recovery to 1002.22 km² in 2023. Despite the recent gain in forest area, spatial analyses indicate that forest structural integrity remains compromised. The CFI increased substantially from 3.00 in 1993 to 18.92 in 2013, reflecting heightened fragmentation across the landscape. Discussion The observed degradation is associated with the widespread expansion of IPS, particularly Lantana camara L., Chromolaena odorata (L.) R.M. King & H. Rob., and Mesosphaerum suaveolens (L.), which are concentrated in the central, northern, and northeastern regions of PTR. Importantly, the relationship between fragmentation and biological invasion appears reciprocal: forest fragmentation facilitates IPS establishment and spread, while invasive species further exacerbate fragmentation by homogenizing plant communities, suppressing native tree regeneration, and altering fire regimes. These findings demonstrate that increases in forest cover alone do not necessarily signify ecological recovery. Therefore, integrating forest cover assessments with fragmentation metrics is essential for developing effective conservation and restoration strategies aimed at improving ecosystem resilience and long-term forest sustainability.