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

Aims: To provide the first syntaxonomical scheme of the main natural and semi-natural steppic vegetation types along a 3000-m elevational gradient. Location: South-facing slopes Mt. Damavand of the central Alborz Mts., Iran, which is a volcano and the highest peak in SW Asia (5,671 m a.s.l.). Methods: A dataset of 330 phytosociological plots of 25 m2 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 in a hierarchical manner. The differences in abiotic and vegetation parameters among associations/communities was 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. We thus describe two alliances (Artemision aucheri, Cousinion petrocauli) and seven associations formally according to the International Code of Phytosociological Nomenclature. Elevation was the main driver of species composition and formation of the major vegetation groups. Conclusions: This study contributes to advancing the syntaxonomical understanding of the vegetation of Iran and placing it within the international phytosociological classification system. It is particularly valuable as it covers the complete elevational gradient of 3000 m and thus included comprehensively also the vegetation types of the lower elevations that previously had hardly been studied syntaxonomicaly 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, probably belonging to an undescribed order within the Astragalo-Brometea. Since our study was based on a large, but 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.