Impact of Bioclimatic Factors on Diversity Patterns in Quercus brantii (Persian Oak) Populations within the Western Iranian Forest Ecosystem

The woodlands in western Iran, especially the Zagros forests, are ecologically crucial for their ability to withstand environmental stresses and conserve water and soil. These ecosystems have suffered significant degradation, particularly in Ilam province, where Persian oak trees (Quercus brantii) have experienced widespread mortality. Understanding the impact of climatic factors on tree species dominance and forest composition is vital for ecosystem conservation. Despite some knowledge about oak species diversity, research on the influence of bioclimatic parameters on Q. brantii, a native Iranian species, is limited. This study aimed to explore how topographical and climatic factors have shaped the population structure and diversity of Q. brantii in western Iran. The study collected data from five habitats within three forested regions in the Ilam province, including 183 samples. A total of 20 phenotypic traits, three geographic, and 19 bioclimatic parameters were measured, and statistical analyses revealed distinct oak ecotypes based on leaf and seed characteristics. Based on the morphological characteristics, a clustering analysis identified two distinct groups among all ecotypes. Redundancy analysis (RDA) revealed that three bioclimatic factors namely annual mean temperature, annual precipitation, and altitude significantly influenced population diversity. Specifically, they had a significant impact on fruit formation and seed morphology and together accounted for 86.9% of the observed variability. The spatial distribution analysis based on PCNM indices revealed that the Sarmast, Kochali, and Sirvan locations had the highest morphotypic diversity. This study emphasizes how bioclimatic and geographic factors shape Iranian oak diversity, informing conservation and sustainable management in western Iran.