| Zusammenfassung: | Questions: The vegetation of high-alpine and subnival scree habitats in Iranian mountains has been poorly investigated so far despite the large variety of narrowly distributed vascular plant species and the expected vulnerability of these ecosystems to global warming. Which plant communities occupy these ecosystems and what is their syntaxonomic position? Which environmental factors determine the species composition of these habitats? Location: Alborz and Azerbaijan Mountains in N and NW Iran. Methods: A total of 141 phytosociological relevés were collected from 3200 to 4800 m a.s.l. This data set was classified using TWINSPAN, and the numerical classification was translated into a syntaxonomic system. Floristic differences between vegetation types were evaluated with detrended correspondence analysis (DCA). We determined the means and SD of measured environmental and vegetation parameters for all associations. Differences in the major environmental parameters among associations and alliances were analysed using ANOVA and post-hoc tests. Moreover, we determined the mean cover percentage of life forms in all associations. Results: All high-alpine and subnival scree communities are arranged in one class (Didymophyso aucheri-Dracocephaletea aucheri), two orders (Physoptychio gnaphalodis-Brometalia tomentosi, Didymophysetalia aucheri), three alliances (Elymo longearistati-Astragalion macrosemii, Erigerontion venusti, Didymophysion aucheri) and ten associations, which are new to science, except for one association. The territory of the class extends from Alborz to NW Iran and probably to E Anatolia, Transcaucasia and the Zagros Mountains. Altitude, aspect and edaphic qualities are the major ecological factors influencing the species composition and vegetation mosaic. Conclusions: Our study introduces a formal syntaxonomic classification of the scree vegetation at high altitudes in Iran, thus providing a scheme for ongoing ecological surveys and monitoring programmes to assess the impacts of climate warming and of human land use on these unique ecosystems.
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