Persian oak (Quercus brantii) is a critical, economic, and environmental species of Zagros forests in Iran. The effects of climate change and drought have caused a decline in Persian oak populations, leading to a severe reduction in genetic resources for future conservation programs. This study aims to evaluate the diversity and population structure of Persian oak in the western forests of Iran using morphological features. A total of 187 samples were collected from 15 locations in the Ilam province. Twenty phenotypic traits related to leaf, seed, and trunk characteristics were evaluated. Several multivariate statistical analyses were performed. The results revealed significant morphological diversity among the Persian oak ecotypes. Correlation analyses revealed a significant positive correlation between leaf length attribute and distance from leaf base to maximum leaf width (0.55) and maximum width of the leaflet (0.64) traits. The leaf width at 50% attribute with the maximum width of the leaflet and distance from leaf base to maximum leaf width have a positive (0.8 and 0.51 respectively) and significant correlation (p≤0.05). According to principal component analysis, the components of leaf and seed traits have the most impact on morphological variance. Hierarchical cluster analysis divided the locations into two groups, with some oak locations distributed in two clusters, indicating higher diversity of this species in different locations. Further research is needed to determine the optimal ecotype; however, the oaks in Ghallaje region have characteristics that can increase their ability to resist water scarcity, making them potentially appropriate for reforestation in Ilam province. Manuscript profile

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. Manuscript profile