Pattern and process in Alpine communities of the Northwestern Caucasus

Abstract: Patterns in vegetation reflect certain processes affecting plant communities. The present work aims at describing patterns and revealing mechanisms operating in alpine vegetation belonging to four vegetation types: alpine lichen heaths, Festuca varia grasslands, Geranium-Hedysarum meadows and snowbed communities. The main tasks of the present study are: (1) to outline the patterns in species occurrence and vegetation structure, (2) to describe the factors influencing the vegetation types; (3) to find differences between species, in terms of growth form, life-history strategy and other morphological traits. The four vegetation types studied showed different degrees of heterogeneity. The most homogeneous were alpine lichen heaths, the most heterogeneous ones Festuca varia grasslands. There were also considerable differences in species richness and frequency distribution of species.The plant species involved had several features in common: most of them are hemicryptophytes, possess a semi-rosette growth form and a sympodial model of shoot formation. Regarding the types of vegetative mobility, species with low mobility prevail in all four vegetation types. Species without mobility rank second and only a few species are highly mobile. Regarding the Serebryakov life-form system and life-history strategy approach, the vegetation types showed considerable differences in the expression offunctional groups.The most influential factors were largely linked to the snow-melting gradient. Harsh snowfree conditions prevail in alpine lichen heaths; tussock grasses influence the Festuca grasslands; burrowing activity of rodents is important in the Geranium-Hedysarum meadows and variation in topography/time of snowmelting controls the snowbed vegetation. Factors influencing all vegetation types include the "mass effect", i. e. the input of diaspores from adjacent habitats. Finally, the coexistence of species with different traits expressed in their populations contributes to the biodiversity of the communities.