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The genus Cotoneaster is considered an important taxon in the woodlands of the Mediterranean and Irano-Turanian regions. Some species of this genus were reported from the Irano-Turanian alpine woodlands. Irano-Turanian mountainous wood and shrublands have a great importance in terms of water and soil conservation, biodiversity and plant richness. There is a lack of quantitative and qualitative statistics available for many of these ecosystems. This research focused on the ecology and phytosociology of Cotoneaster shrublands in central Alborz (Iran), with emphasis on C. kotschyi, an endemic drought-tolerant species. Data was collected based on the Braun-Blanquet method. TWINSPAN was used to analyse the vegetation data. Species-environment analysis was performed by CCA (Canonical Correspondence Analysis) and oneway ANOVA.

Releves were classified into three distinct groups regarding their floristic composition. By organizing the phytosociological table, a new subassociation was defined and named as Rhamno pallasii-Juniperetum excelsae cotoneastretosum kotschyi subass. nova. This syntaxon is distributed in the range of 2,200-2,430 m a.s.l. between two other groups, i.e. Cotoneastro nummulariis-Juniperetum excelsae and Rhamno pallasii-Juniperetum excelsae. Cotoneaster kotschyi ecologically is near to Rhamnus pallasii which is characteristic for Juniper communities on shallow soils and stony lands. Among the environmental variables, slope, soil texture, pH, lime and saturation percent are the most important distinguishing factors of this subassociation. So, the new syntaxon is found in the habitat with an average slope of 60%, sandy-loam soils and pH and lime percent less than other studied communities. The subassociation cotoneastretosum kotschyi has a higher amount of sand content compared to the other vegetation groups.

Cotoneaster nummularius is an indicator of vegetation communities with relatively evolved soils. However, C. kotschyi grows in poor and shallow soils. C. kotschyi is a differential species which indicates the variability between the two main Alpine associations of the Irano-Turanian region. It is an appropriate species for plantation in the semi-arid mountainous areas. The ecological demands and the floristic composition of these plantations are determined in this article.