Northward shifts and emerging refugia: Future habitat dynamics of Zygophyllum xanthoxylum

Dryland restoration is increasingly constrained by climate change-driven shifts in the ecological niches of foundation shrubs, yet forecasts often underrepresent geomorphic heterogeneity and model complexity. We assessed future habitat dynamics for Zygophyllum xanthoxylum (Bunge) Maxim., a xerophytic shrub central to desert-steppe restoration in northwestern China, by integrating 114 spatially thinned occurrence records with climate, soil, topographic and geomorphological predictors in an ENMeval-optimized MaxEnt framework. Projections for 2041-2100 under SSP2-4.5, SSP3-7.0 and SSP5-8.5 were evaluated across suitability classes, provinces, landforms and centroid trajectories. The selected model (RM = 1.2; FC = LQH) showed high discrimination, with a mean AUC of 0.943 and a TSS of 0.7582. Suitability was governed chiefly by winter cold, dry-month precipitation, diurnal thermal range, elevation, slope and precipitation seasonality, indicating that both climatic stress and terrain-mediated water balance constrain the species niche. Current suitable habitat occupied 54.10 × 10⁴ km², representing 5.6% of China, and was concentrated in Xinjiang, Gansu, Qinghai, Ningxia and Inner Mongolia. Future projections revealed redistribution rather than monotonic expansion: total suitability increased under SSP2-4.5 and SSP3-7.0, whereas SSP5-8.5 showed a sharp mid-century decline followed by partial recovery. Future changes in suitable geomorphic areas exhibit a pattern characterized by the continued expansion of low-to mid-elevation gentle geomorphic units, sustained high suitability in mid-elevation hills and plateaus, slight increases in high-elevation geomorphic units, and declining suitability in very high-elevation and strongly rugged mountainous geomorphic units. Habitat centroids moved northeastward by 308-437 km. This study provides scientific support and a methodological framework for formulating ecological restoration strategies under the Three-North Shelterbelt Program, optimizing species deployment, and assessing climate-change responses of similar xerophytic plants.