Systematic ecological investigations of the steppe rivers’ marsh vegetation existing in the current ecological and hydrological conditions of the Buh left bank area environment within the borders of Mykolaiv region are conducted. The spatial and species structure of the small rivers’ marsh vegetation is generally typical for short-flow watercourses. The factor of the hydrological regime of the marsh ecotope promotes differentiation of biotopes and their vegetation cover. According to the latter, we distinguish: biotopes of constant water flowage; biotopes of partial watering and excess humidification; biotopes of sufficient and insufficient humidification. Due to the instability of the trophic modes and the flowability of the hydrotope, the biotopes of constant flow rate are found to have low levels of phytodiversity (Simpson index – 1.6 (average index)) and are typical for the valley bottoms of the South Buh, the Inhul, and only the estuarine sections of medium and small steppe streams. Ecotonic, bank areas of typical marsh vegetation including highly productive, multi-species wetland Cyperaceae and Gramineae coenoses have the highest level of phytodiversity (Simpson index – 3.2). Wetland and meadow biotopes of sufficient humidification are characterized by a high level of floristic richness (Simpson index – 2.68) and populated by polydominant hygromesophytes, mesophytes, meadowhalophytic and halophytic coenoses. At the same time, the salinity of the edaphotope causes a significant decrease in species richness (Simpson index – 1.8) and simplification of the phytogroups’ species structure. Up to 25% of the floodplain area of steppe rivers is represented by zones of insufficient moisture covered by stepped-meadow phytocoenoses, which is not peculiar to the marsh landscape. Accordingly, our research indicates the conversion of natural marsh vegetation into saline and steppe meadows formed by low-yielding, mesoxerophyte dwarf grasses with a significant proportion of ruderals (up to 50% of projective coverage) and low levels of floristic variety (Simpson index – 1.8-2.23)
marshes; marsh vegetation; Mykolaiv region; floodplain of the Southern Buh; the Buh left bank area; ecological and hydrological changes