Escarpment refugia under threat: climate-driven redistribution modeling of four endemic succulent species in Saudi Arabia

This study models the current and future habitat suitability of four narrow-range endemic succulents of Saudi Arabia Aloe armatissima Lavranos & Collen., Aloe shadensis Lavranos & Collen., Euphorbia saudiarabica Fayed & Al-Zahrani, and Euphorbia taifensis Fayed & Al-Zahrani. Endemic plant species confined to mountain refugia are especially vulnerable to the warming and increased aridity projected across the Arabian Peninsula, yet quantitative, spatially explicit assessments of their habitat suitability under future climate scenarios remain scarce for Saudi Arabia. There is currently limited information on the suitability of endemic plant habitats in the Kingdom of Saudi Arabia. Occurrence records derived from field surveys and literature were combined with WorldClim climate variables and elevation-based terrain layers, and maximum entropy (MaxEnt) species distribution models were projected under CMIP6 (Coupled Model Intercomparison Project Phase 6) SSP245 and SSP585 scenarios for mid- and late-century periods. Habitat suitability patterns revealed strong spatial restriction of all species to the southwestern escarpment, particularly across Jizan, Asir, Al Baha, and southern Makkah. Models achieved high discriminatory performance for all four species (mean training AUC 0.998–1.000; testing AUC 0.914–0.999, lowest for E. saudiarabica ) and identified current suitable habitat covering between 0.58% and 2.90% of Saudi Arabia’s land area. Future climate projections indicated pronounced species-specific responses to climate change: as each species is represented by few verified occurrences (6–9 records; 31 in total), these projections are interpreted as testable hypotheses rather than precise range maps. A.armatissima and E. taifensis experienced substantial habitat contractions under SSP245 (Shared Socioeconomic Pathway 245, an intermediate-emissions scenario). At the same time, A.shadensis and E.saudiarabica showed notable gains by the 2061–2080 period. Range-change analysis showed high spatial turnover, with expanding gain areas for A. shadensis and E. saudiarabica , and dominant loss areas for A. armatissima . In all cases, suitable habitats were largely confined to mountainous regions. Precipitation seasonality and elevation were the most important environmental drivers shaping present and future distributions. The results illuminate the vulnerability of escarpment refugia and underscore the urgent need for targeted conservation measures to protect the distinctive endemic plant diversity of Saudi Arabia.