Syntaxonomy and ecological differentiation of the pioneer vegetation of Ukraine Classes: Isoëto-Nanojuncetea, Bidentetea

The studies of the pioneer vegetation of freshwater shorelines of water bodies are of particular interest owing to the specific ecology of these habitats and the short cycle for their development in which periods of flooding and subsequent drainage alternate. Using the methods of phytosociological classification and cluster analysis based on the interpretation of 414 phytosociological relevés, the syntaxonomic structure of the pioneer vegetation of freshwater shorelines of the water bodies of Ukraine has been established that are represented by the phytosociological classes Isoëto-Nanojuncetea and Bidentetea. The class Isoëto-Nanojuncetea includes 8 associations that belong to 2 alliances and 1 order and the class Bidentetea includes 10 associations belonging to 2 alliances and 1 order. Phytocoenoses of both classes are more typical for the Polissia region and the forest-steppe zone of Ukraine, where there are favourable habitats with a flat relief, low degree of dissection and a high level of soil humidity. Using a DCA ordination analysis of associations their position in ecological space was determined. It was established that the main factors of ecological differentiation for Isoëto-Nanojuncetea habitats are soil humidity, soil aeration, nitrogen content, as well as temperature regime. Differentiation in the hyperspace of abiotic factors of the class Bidentetea occurs mainly along the gradients of soil humidity, salt regime and acidity. The ecological distribution of syntaxa of this class is also significantly influenced by the concentration of mineral nitrogen compounds in the soil.