Introduction: Floristic analysis of a region can serve as a valuable tool for a deeper understanding of its ecological conditions and as a foundation for further research. Given that elevation above sea level is one of the physiographic factors influencing the flora of a region, the aim of this study was to investigate the flora, life forms, and chorology of vascular plant species along an elevational gradient in the northern Zagros oak forests (Baneh forests).

Materials and Methods: A systematic-random sampling method was employed. Considering the elevational distribution range of the forests (1100 to 2300 m a.s.l.), sampling was conducted on northern and southern aspects within four 300-m elevational classes. Sampling was performed using 24 transects along the elevational gradient at approximately 300-m intervals. The first plot in each transect was established randomly, and the remaining plots were established systematically with a 50-m elevation difference. Plot areas for tree-shrub and herbaceous-dwarf woody vegetation were 400 and 64 m², respectively.

Results: In this study, 293 plant taxa belonging to 37 families and 145 genera, including 26 tree-shrub and 267 herbaceous-dwarf woody species, were identified. The families Asteraceae and Fabaceae, with 51 and 43 species respectively, had the highest number of taxa. The highest numbers of herbaceous-dwarf woody (121 species) and tree-shrub (20 species) species were recorded on the northern aspect within the 1700–2000 m elevational class, while the lowest numbers were observed on the southern aspect within the 1100–1400 m class, with 47 herbaceous and 3 tree species. Regarding life forms, hemicryptophytes with 112 species on the northern aspect and therophytes with 107 species on the southern aspect were dominant; both groups reached their maximum abundance in the 1700–2000 m class (56 and 54 species, respectively). In terms of chorology, Irano-Turanian elements with 132 species (45.1%) were the most dominant chorotype, with their highest frequency (53 herbaceous and 10 tree species) observed on the northern aspect within the 1700–2000 m class. The ratio of Irano-Turanian to Euro-Siberian elements increased from approximately 3:1 at lower elevations to over 5:1 at higher elevations, indicating a gradual replacement of chorotypes along the elevational gradient.

Conclusion: The families Asteraceae and Fabaceae had the highest number of species in the study area. The increased presence of species from these families can be attributed to their wide tolerance range to adverse ecological conditions, the influence of environmental factors (temperature, humidity, and light), insect pollination, and the presence of stress and disturbances in the region. The highest number of species was observed on the northern aspect within the 1700–2000 m elevational class. This pattern is mainly due to more favorable microclimatic conditions (more moderate temperature and humidity) and denser oak canopy cover. In contrast, the decrease in species richness at lower elevations (below 1400 m) can be interpreted within the framework of the interaction between elevational gradient and aspect on microclimatic conditions. At higher elevations, a higher number of shrub and dwarf-woody species was observed. Important reasons for these changes include lower temperatures, reduced soil depth and quality, a shorter growing season, strong winds, and transition to the ecotone zone. The high abundance of hemicryptophytes across all elevational classes indicates the general adaptation of this life form to the cold climate of mountainous regions and the soil moisture resulting from snowmelt. Overall, elevation and geographical aspect have a significant influence on the floristic composition, life form spectrum, and chorology of plant species in the northern Zagros oak forests. These results can serve as a basis for conservation prioritization and management focused on biodiversity conservation across different elevational classes and geographical aspects.