Geoecological conditions of habitats of floodplain oak forests in river valleys of the Upper Dnieper basin

This article presents the results of research on the geoecological conditions of floodplain oak forest habitats on the basis of the inventory of their phytocoenotic diversity in the large nature region of Southwestern Nechernozemye of Russia. The authors created a database on flood-plain oak forest distribution in the Upper Dnieper basin (Bryansk, Kaluga, Smolensk regions of Russia), comprising the author's unpublished geobotanical releves made in 2005-2018, as well as available materials on the regional floodplain forest syntaxonomy. Location information and taxonomic affiliation are organized in a spatial database created with use of MapInfo Professional and reflected on an electronic map, which became the basis for the identification and justification of distribution factors of floodplain oak forests. Communities of hygro-and mesohygrophyte oak forests with a wide enough variety of dominants amid similar overall floristic composition and structure combines ass. Filipendulo ulmariae-Quercetum roboris Polozov et Solomeshch in Semenishchenkov 2015, established by the method of J. Braun-Blanquet. Ten variants formed in different geoecological conditions were identified and described. DCA-ordination of syntaxonomical units demonstrates some ecological patterns of distribution of floodplain oak forests. Despite exponential differences in the composition of coenoflors, syntaxa don not take compact space in the diagram. This is due to the fact that the floristic composition of communities of floodplain forests largely depends on the mode flood length and the height of the flood, which vary from season to season. Coenoflors of floodplain forests consist of ecologically dissimilar species, which enter the communities during periods of environmental fluctuation and then are differentially maintained in communities or eliminated. Often, these communities have high rates of species richness. Variability of edafical conditions and regime of flood, geochemical characteristics of soil, and features of microrelief in floodplain generates high variety of floristic composition of communities and phytocoenotic diversity of floodplain oak forests, which is reflected in their syntaxonomy. Syntaxa of floristic classification, characteristic species of which have expressed environmental preferences, may be use as indicators of geoecological conditions in floodplains. Some types of communities are formed as a result of anthropogenic impact (grazing, trampling, recreational use, fire), which is reflected in their poor floristic composition.