Phytosociological and ecological description of the high alpine vegetation of NW Iran.

Aims: This is the first attempt to describe the diversity of the thorn-cushion and snowbed vegetation of the high mountains of NW Iran. Our main aim was to identify plant communities occurring in these habitats, and to clarify their syntaxonomic position. We also explored the key environmental factors influencing the species composition of these communities. Study area: Sahand Mts. (3707 m a.s.l.), Sabalan Mts. (4810 m a.s.l.) and Bozqush Mts. (3302 m a.s.l.) in NW Iran. Methods: A total of 166 phytosociological relevés were sampled at elevations ranging from 2800 to 3700 m a.s.l. The data set was classified using the TWINSPAN algorithm, and the result of the numerical classification was interpreted through a syntaxonomic system. Floristic differences were evaluated using a Detrended Correspondence Analysis. Results: We distinguished two alliances of thorncushion grasslands: Astragalion polyanthi all. nov. on windswept sites (including three associations) and Astragalion sahendi all. nov. on sites with longer snow cover duration (including two associations). Snowbed communities were classified into seven associations and assigned to the previously described alliance Taraxaco brevirostris-Polygonion serpyllacei. Conclusions: The duration of snow cover (i.e. the time of snowmelt) strongly determines the distribution of the studied communities. Among other ecological factors affecting the species composition are elevation, aspect, slope inclination and soil structure. [ABSTRACT FROM AUTHOR]