[The analysis of the factors determining species richness of Southern Ural forest communities]

There was analyzed the influence of warmth, moisture, and soil fertility on species richness and phytosociological spectrum of phytocenoses of three classes of Southern Ural autochthonous forests: Querco-Fagetea (nemoraloher-bosa), Vaccinio-Peceetea (boreal forests), and Brachypodio-Betuletea (hemiboreal forests). Environmental factors were estimated by Landolt's scales. We studied the changes of syntaxa of association rank by means of gradient phy-tosociological analysis. In phytosociological specter, in addition to the cenoflora of the three investigated classes, we estimated the representation of species from steppes (class Festuco-Brometea), xerothermal forest edges (class Tri-folio-Geranietea), and meadows (class Molinio-Arrhenatheretea). For boreal and hemiboreal forests, the dependence of cenoses species richness on environmental factors is parabolic, with its maximum in the middle of the gradient. With respect to nemoral forests, species richness declines with increase of environmental factors values. Maximum species richness is registered when the proportion of species of the own cenosis class in the community is maximal. The contribution of the ecotone effect (inclusion of other classes' species in the community composition) enhances as species richness reduces.