Plant diversity in the understory of plant communities along the elevational gradient in western Aladagh Mountains, northeastern Iran

Understanding the different patterns of plant diversity and distribution along the environmental gradients is essential for managing ecosystems, especially in fragmented habitats due to intensive human pressure. The Darkash area is located in the western Aladagh Mountains in Khorassan-Kopet Dagh Floristic Province. The easternmost patches of the Hyrcanian montane forests grow in this area. The three main vegetation types in the area are shrublands/scrub forests, oak forests (Quercus castaneifolia), and subalpine vegetation. In this study, we aimed to evaluate the plant diversity in the understory of plant communities along the elevational gradient. We sampled 187 vegetation plots (2m x  2m) along a 1300m elevational gradient (in 100-m classes) using the stratified-random method and estimated the abundance and canopy cover of the species. Floristic characteristics and different diversity indices were measured. In total, 252 plant species belonging to 161 genera and 44 families were identified. Of these, 41 species were found to be endemic or semi-endemic. Hemicryptophytes and therophytes are the dominant life-forms in the study area. The Irano-Turanian elements (46.8%) make the major chorotype in the flora of the area, followed by Bi-regional (17.5%), Tri-regional (17.5%), Pluri-regional (11.5%), and Euro-Siberian (6.7%) elements. The shrubland understory has the highest Hill's and beta diversity indices, followed by the oak forest and the subalpine understory. The biodiversity changes sinusoidally along the elevation. In order to protect plant species, especially young oak seedlings, it is recommended to create a protective corridor along the elevational gradient in this area. This strategy is essential to protect plant diversity in these habitats.