New associations of the class Molinio-Arrhenatheretea in the in Southern Nechernozemie region of Russia
3 new associations, distributed in the Southern Nechernozemie of Russia, are described for the first time with use of the Braun-Blanquet approach: Poo angustifoliae-Arrhenatheretum elatioris, Festuco pratensis-Leucanthemetum vulgaris, Trifolio arven-si-Rumicetum thyrsiflori. The synecological amplitudes of humidity, acidity and soil richness by mineral nitrogen of the associations are defined. Communities of ass. Poo angustifoliae-Arrhenatheretum elatioris are distributed on the flat slopes of ravines on the dry, subacidic, grey wood loamy soils moderately rich by mineral nitrogen. Communities of ass. Festuco pratensis-Leucan-themetum vulgaris are distributed on fresh, subacidic, rather poor in mineral nitrogen grey and dark grey wood loamy soils on the fallow lands of various age within landscapes of loess plateau; on sod-podzolic loamy, sandy and subsandy soils within landscapes of fluvioglacial loamy and moraine-outwash plains. They can meet occasionally on grey wood loamy soils. Communities of the Potentilla argentea var. are distributed on grey and dark grey wood loamy soils on the fallow lands within landscapes of loess plateau. Communities of the Medicago lupulina var. are distributed on sod-podzolic loamy, sandy and subsandy subacidic, rather poor in mineral nitrogen soils on the fallow lands of various age. They may occur in the small sites on the continental meadows or along highways. Occasionally these plant communities can be found on grey wood loamy soils. Communities of ass. Trifolio arvensi-Rumicetum thyrsiflori are distributed on raised sites on gentle-wavy outwash or moraine-outwash plains on dry and moderately sour, poor by mineral nitrogen easily sandy and sandy podzol soils. For the estimation of a homotoneity of established syntaxa the index of homotoneity of H. Passarge (1979) is used. The ass. Poo angustifoliae-Arrhenatheretum elatioris is characteristic by the high homogenetic variability. Totally, association’s index of homotoneity is high - 0.52. The low index of a homotoneity is characteristic for аss. Festuco pratensis-Leucanthemetum vulgaris - 0.35, for the Potentilla argentea var. - 0.33 and Medicago lupulina var. - 0.44. Following associations have a low index of the homotoneity: аss. Trifolio arvensi-Rumicetum thyrsiflori - 0.33, as in subass. T. a.-R. th. typicum - 0.33, and in subass. T. a.-R. th. helichrysetosum arenarii - 0.44. Such low indexes of a homotoneity are characteristic for semiruderal and serial communities.