In order to determine optimal environmental conditions for the development of shrub vegetation, 12 diagnostic species of Rhamno-Prunetea class were studied. These represent plant species of forest edges, forest glades, shrub thickets in steppes which also occur in undergrowth and shrub layer of mixed, deciduous, and ravine forests: Acer campestre, Acer tataricum, Amygdalus nana, Berberis vulgaris, Caragana frutex, Cerasus fruticosa, Euonymus europaeus, Ligustrum vulgare, Prunus spinosa, Prunus stepposa, Rhamnus cathartica, Swida sanguinea. Synphytoindication analysis of more than 9000 phytosociological relevés featuring the studied species was carried out. For comparison of ecological amplitudes and their ranges for the species as well as determination of tolerance indices, we applied methods for determining the ecological valence. Synphytoindication optimum of the studied diagnostic species in respect of their ecological valence is quite variable and represented by mesophytic conditions – fresh forest and meadow habitats with unevenly moistened root layer, with slightly acidic clay or sandy salt-deficient soils, poor in carbonates and mineral nitrogen. Climatic factors have narrower amplitude; for thermoclimate the optimum lies in submesothermic conditions – from subboreal to nemoral thermal zone. Climate humidity mainly varies within subaridophytic conditions, while only S. sanguinea belongs to ombrophytes. As for the climate continentality, optimum conditions correspond to hemicontinental climate. Optimum values of cryoregime are mainly within hemicryophytic conditions. As for lighting conditions, the indicators range from shadowed to semi-lightened conditions. The original results of quantitative assessment of synphytoindication amplitude for Rhamno-Prunetea diagnostic species are a basis for predicting changes in shrub vegetation under the influence of various environmental factors, which is very important for understanding and modeling changes and relations between forest and steppe.
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