Climate-Driven Range Shift of the Medicinal Herb Epimedium sagittatum: An Optimized MaxEnt Projection for China

Epimedium sagittatum is an important understory shade-tolerant medicinal plant native to China. However, assessments of its responses to climate change under multiple scenarios and time periods remain insufficient, particularly regarding the mitigation of model overfitting and the quantitative disentanglement of hydrothermal constraints. In this study, based on 269 valid occurrence records and 24 initial environmental variables (reduced to 13 after collinearity screening), we employed a parameter-optimized MaxEnt 3.4.4 model (RM = 3.5, FC = QHP) coupled with the BCC-CSM2-MR climate model to project the dynamics of potential suitable habitats under current (1970–2000) and future (2050s, 2070s, 2090s) scenarios (SSP126, SSP370, SSP585). The results showed that the optimized model substantially reduced the risk of overfitting compared with the default parameters (ΔAICc dropped from 82.16 to 0) and achieved an AUC of 0.934. Precipitation of the Driest Quarter (Bio14, 53.4% contribution) and Minimum Temperature of the Coldest Month (Bio6, 20.5% contribution) were identified as the dominant factors governing the species’ distribution, with optimum conditions of ≥1.58 mm and −8.34 °C to 13.61 °C, respectively. Under future climate scenarios, the centroid of suitable habitats shifted progressively southwestward, with a cumulative displacement of approximately 127.47 km under SSP585, and water availability, rather than temperature, dominated the direction of this shift. Under the high-emission scenario, suitable areas exhibited a spatial reorganization characterized by westward expansion and eastward contraction. Based on these findings, this study proposes a three-tier planning framework comprising in situ conservation, climate-smart introduction, and assisted migration, providing a scientific basis for the conservation of germplasm resources and the spatial planning of artificial cultivation of E. sagittatum.