Vegetation of the southern slopes of Mt. Damavand, Iran: a comprehensive phytosociological classification

Aims : To provide the first syntaxonomic scheme of the main natural and semi-natural steppic vegetation types along a 3000-m elevational gradient. Location : South-facing slopes of Mt. Damavand, Iran. Methods : A dataset of 330 phytosociological plots of 25 m 2 sampled in all main vegetation types of the region was subjected to unsupervised classification with TWINSPAN. After some manual adjustments to maximise the floristic distinctness of clusters, the resulting units were translated into syntaxa at the class, order, alliance and association level. Diagnostic species were determined with phi values as measure of fidelity. The differences in abiotic and vegetation parameters among associations/communities were visualised with boxplots and the environmental gradients associated with the community differentiation via detrended correspondence analysis (DCA). Results : We found four main groups that are ecologically well interpretable and considered at the level of phytosociological classes: rocky habitats ( Tanacetalia kotschyi , class unknown), scree habitats ( Didymophyso aucheri-Dracocephaletea aucheri ), snow-beds ( Salicetea herbaceae ) and grasslands ( Astragalo-Brometea ). We distinguished six orders, nine alliances and 18 association-level communities, which were floristically well separated. Many of these syntaxa were new to science. Elevation was the main driver of species composition and formation of the major vegetation groups. Conclusions : This study contributes to advancing the syntaxonomic understanding of the vegetation of Iran. It is particularly valuable as it covers the complete elevational gradient of 3000 m and thus also comprehensively includes the vegetation types of the lower elevations that previously had been rarely studied syntaxonomically in Iran. Furthermore, this study is the first to examine mown (semi-natural) tall herb rich grasslands in Iran, which were assigned to the new alliance Cousinion petrocauli . Since our study was based on a regionally constrained dataset, we could not solve all syntaxonomic issues conclusively. This underscores the need for more comprehensive studies of the vegetation in the entire Alborz Mts as well as other Iranian mountain ranges in the future. Taxonomic reference : Catalogue of Life (Bánki et al. 2024). Abbreviations : DCA = detrended correspondence analysis, ICPN = International Code of Phytosociological Nomenclature (Theurillat et al. 2021), TWINSPAN = two-way indicator species analysis.