Numerical phytosociology of the subalpine belt of the Kazbegi region,Caucasus, USSR

A vegetational transect across a glacial valley was investigated. Structure and species composition, as well as influence of disturbance by biotic factors (grazing of sheep and cattle) and abiotic factors (topography, wind, water) are discussed.According to species composition and community structure, 4 main vegetation types were distinguished by comparing field data from phytosociological relevés with results of numerical treatments (3 methods of numerical classification and DCA ordination): 1) Chamaesciadium acaule-Polygonum viviparum, 2) Festuca cf. woronowii-Carex tristis, 3) Veratrum lobelianum-Taraxacum stevenii and 4) Rhododendron caucasicum-Vaccinium myrtillus communities.Species diversity (evenness, and number of species) was low in the ungrazed dwarf-shrub alpine communities, which were dominated by Rhododendron caucasicum, in comparison with the grazed meadow. The highest values of these characteristics were found in the transitions among the types.