Resilience of cushion Astragalus to climate change in the Zagros Biodiversity hotspot: a species distribution modeling approach

The Zagros Mountains in Iran, part of the Irano-Anatolian biodiversity hotspot, are renowned for their Astragalus diversity. This study employed stratified random sampling to record vegetation attributes in southwestern Isfahan province within the Zagros region. Cluster analysis identified three distinct groups of cushion Astragalus species, each named after its dominant species: Astragalus verus Olivier, Astragalus compactus Lam, and Astragalus gossypinus Fischer. The current and future habitats of these three dominant Astragalus species were predicted using the Generalized Boosted Model (GBM) and Maximum Entropy (Maxent) modeling approaches. The GBM model outperformed Maxent, as indicated by higher True Skill Statistic (TSS) and Area Under the Curve (AUC) values. Key environmental factors influencing the distribution of Astragalus species were identified as the mean temperature of the coldest quarter (Bio11) and annual precipitation (Bio12). Optimal conditions for these cushion Astragalus species were found to be an annual precipitation range of 200 to 220 mm and elevations between 2200 and 2400 m above sea level (asl). Under the CANESM2-RCP2.6 and CANESM2-RCP6.0 climate change scenarios, these species are projected to shift towards higher elevations, resulting in habitat reductions of 75.9% and 85.6%, respectively, by 2050. This study underscores the significance of species distribution models in mountainous regions, highlighting their critical role in understanding and conserving cushion species within complex ecosystems. These models provide essential insights for effective conservation planning in mountainous landscapes.