Ecological phytocenotic investigations and statistical analysis of the marsh vegetation in the current ecological and hydrological conditions of the marshbiotopes of the rivers of the Tiligul-Southern Bug interfluve were carried out. These conditions for the existence of flooded biotopes are generally typical for the rivers of the steppe zone of Europe and are characterized by the instability of the hydrological regime of floodplains. Accordingly, hydrotope flow and humidification contributes to the differentiation of flooded biotopes and their plant communities.Ecological-phytocenotic statistical analysis of the marsh biotopes of interfluve rivers enabled to determine the tolerance ranges of plant communities. As qualitative indicators, phytocenotic units (point phytosocial communities) and their ratio between the rivers of the studied interfluve were used. It has been established that in the optimum zone there is a swamp-meadow vegetation on biotopes of excessive humidification. Thus, an approximately uniform distribution of plant communities of all rivers of the region was recorded (20-30% of phytocenotic units of hygromesophytes for each river). Aquatic and wetland vegetation on biotopes of partial flooding is in the zones of intolerance and physiological stress, respectively. It was calculated that the largest amplitude of indicators was recorded precisely among hydrophytes. Thus, the proportion of hydrophytes of the drying, flowing biotopes of Tiligul and Chichikliya is only 13% and 8% of plant communities respectively, while about 50% is the share of the Southern Bug. Unstable hydrological regime of marshes and critical drying of their soils form extreme, critical conditions for plant vegetation, which contributes to a decrease in the coenotic diversity of aquatic vegetation in the marsh biotopes of small and medium steppe rivers
marshes; marsh biotopes; marsh vegetation; the Tylihul-Southern Buh interfluve; statistical analysis; ecological tolerance of the species; ecological and hydrological change