Climate-Driven Habitat Redistribution and Conservation Gaps of the Medicinal Fern Sceptridium ternatum in China

Climate change may redistribute understory medicinal plants, but national predictions are useful when model uncertainty and field constraints are explicit. We aimed to identify the current and future suitable habitat of Sceptridium ternatum and translate predictions into survey and conservation priorities. We compiled 187 occurrences, screened 104 candidate predictors to 9, calibrated MaxEnt with kuenm, and evaluated it using partial ROC, omission rate, AICc, random and spatial-block cross-validation, and the Boyce index. Future suitability was projected with two GCMs under SSP1-2.6 and SSP5-8.5. October precipitation had the highest permutation importance, and growing-season thermal accumulation was another major contribution. NDVI had high percent contribution but no unique permutation importance. The selected model achieved mean random-fold and spatial-block test AUCs of 0.9217 and 0.8575, respectively, and a Boyce index of 0.8211. Late-century SSP5-8.5 reduced total and highly suitable habitat by 45.06% and 89.96%, respectively. Protected areas covered only 14.77% of highly suitable habitat. The resulting framework separates regional climatic suitability from habitat compatibility and management feasibility, a distinction relevant to other data-limited understory medicinal plants. It distinguishes sites for population verification, germplasm collection, and long-term monitoring, and plot-scale decisions require measurements of canopy, moisture, substrate, population state, and mycorrhizal context.