In South Siberian mountains floodplain steppe meadows can be found only within steppe and forest-steppe belts. In the eastern part of the Altai-Sayan mountain region (ASMR) these belts occupy large intermontane depressions, making up the submeridional range at 56–50° N (Fig. 1). The northern part of this range consists of four large depressions (the Nazarovo, North Minusinsk, Middle Minusinsk and South Minusinsk). To the north, the Nazarovo depression merges into the West Siberian plain. The southern border of the South Minusinsk depression is the West Sayan. The southern part of range includes the Turan-Uyuk and Central Tuvinian depressions.
This study is based on the analysis of 260 geobotanical relevés made in the valleys of 47 rivers (21 — in Minusinsk depressions, 26 — in Tuvinian depressions). The set includes the relevés of steppe meadow of different river types (large, medium, small), located in different parts of the studied region. The typical feature of these communities is the permanent coexistence of steppe and meadow species with negligible part of meadow-steppe herbs. All steppe meadows under discussion are similar in appearance. Tall grasses, various in different associations, form a sparse upper sublayer. Depending on the intensity of use, the main part of the herbage can be located in the middle sublayer or in the bottom one. In the middle sublayer, grasses predominate (Bromopsis inermis, Poa angustifolia, Elytrigia repens). Herbs tolerant to grazing (Potentilla bifurca, Amoria repens) make up the bottom sublayer.
We have revealed 6 associations of steppe meadows. Ass. Potentillo bifurcae–Poetum angustifoliae, Potentillo bifurcae–Leymetum dasystachyos, Potentillo bifurcae–Hordeetum brevisubulati are typical for Tuvinian depressions, ass. Artemisio laciniatae–Koelerietum delavignei, Trifolio pratensis–Koelerietum delavignei и Trifolio pratensis–Festucetum valesiacae — for Minusinsk ones (Table 1). The basic bioclimatic barrier of ASMR — the West Sayan divides their areas.
The ordination of new associations along the gradients of moisture supply (horizontal axis) and richness-salinity of soils (vertical axis) demonstrates that areas of associations form two ranges — the Minusinsk and Tuvinian. Every association of the Minusinsk range has corresponding association of the Tuvinian range (Fig. 2). DCA-ordination (Fig. 3) and cluster analysis (Fig. 4) of syntaxa from the South Urals, West Siberia, Yakutia and new associations have detected the specificity of the last ones, so a new alliance Potentillo bifurcae–Poion angustifoliae (order Galietalia veri, class Molinio-Arrhenatheretea) has been described. It comprises steppe meadows of the Eastern part of ASMR.
Floodplain steppe meadows of the Eastern part of the Altai-Sayan mountain region
