Predicting Current and Future Habitat Suitability for Barringtonia fusicarpa in China Using an Optimized MaxEnt Model

Barringtonia fusicarpa Hu, an endemic tree species of southern China that is listed as Vulnerable, is increasingly threatened by anthropogenic disturbance and illegal logging, yet its potential distribution remains poorly quantified. Based on 31 occurrence records and 37 environmental variables, we developed an optimized Maximum Entropy (MaxEnt) model to predict the current potential suitable habitat of the species, to identify the dominant environmental drivers, and to project spatiotemporal shifts under three Shared Socioeconomic Pathway scenarios (SSP1-2.6, SSP2-4.5 and SSP5-8.5) across four future periods (2021–2040, 2041–2060, 2061–2080 and 2081–2100). The optimized model exhibited excellent predictive performance, with a mean area under the receiver operating characteristic curve (AUC) of 0.947. The mean temperature of the coldest quarter (Bio11), temperature seasonality (Bio4), precipitation of the driest quarter (Bio17) and isothermality (Bio3) were the dominant drivers, together accounting for 99.2% of the total percent contribution; their optimal ranges were 11.6–26 °C, 134–540, 45–230 mm and 42%–57%, respectively. Under the current climate, the total suitable habitat covered approximately 87.29 × 104 km2 (9.10% of China’s terrestrial area), of which 8.03 × 104 km2 was highly suitable, 29.84 × 104 km2 moderately suitable and 49.42 × 104 km2 marginally suitable, mainly in Guangxi, Guangdong, Yunnan, Hainan and Taiwan, China. Under future scenarios, the total suitable area is projected to expand overall, mainly driven by gains in low- and moderately suitable habitat; the highly suitable zone remains close to its current extent. The distribution centroid shifts northeastwards under SSP1-2.6 and SSP2-4.5, whereas under SSP5-8.5 it shifts southwest of its baseline position by the 2081–2100. These results indicate that temperature-related variables primarily constrain the distribution of B. fusicarpa and that proactive, climate-informed conservation planning—including in situ protection and germplasm collection in southern Yunnan and Hainan—is needed to secure the species’ long-term persistence.