Predicting the Habitat Suitability for Endangered Tree Species Pterocarpus marsupium in Nepal, Using Ensemble Species Distribution Models.

Pterocarpus marsupium Roxb., locally known as Bijaysal, is a high-value tropical deciduous tree with a restricted and fragmented distribution in Nepal. We integrated 129 spatially occurring records with climatic, anthropogenic, edaphic, and topographic variables in an ensemble species distribution modeling framework (biomod2) to project current and future (2050s and 2090s) habitat suitability under four shared socioeconomic pathways (SSP) scenarios. Minimum temperature of the coldest month and precipitation seasonality were the dominant climatic drivers, followed by soil organic carbon, bulk density, and human footprint. The current suitable habitat is limited (11,154 km2; 7.6% of Nepal) and confined to the western and central lowlands. Future projections conditional on the BCC-CSM2-MR GCM climatic model indicate potential habitat expansion ranging from ~40% (SSP1-2.62090s) to 313% (SSP2-4.52050s) with consistent southeastward centroid shifts, reflecting a leading-edge expansion into the northern mid-hills alongside a major redistribution of suitable core habitats toward eastern and southeastern lowlands. However, these projections should be interpreted with caution, as actual migration may be limited by seed dispersal mechanisms, biotic interaction, future land use change, and soil suitability in high-elevation zones. The human footprint response suggests that conservation strategies outside strictly protected areas may also play an important role. These findings may help identify potential areas for further field assessment, but assisted colonization would require site-specific soil, dispersal, and genetic feasibility studies before implementation.