The study is devoted to the investigation of the current state of the nature reserve "Yelanetskyi Step" vegetation,analysis of plant cover dynamic changes over the 20 years of the object, the development of recommendations for the conservation of phytodiversity. Based on the ecological and floristic approach, the syntaxonomic structure of the reserve's vegetation has been established. The classification scheme includes 8 classes, 12 orders, 14 alliances, 20 associations, 1 sub-association, and 2 derivative communities. Based on the method of synphytoindication, the ecological analysis of the leading edaphic and climatic factors was performed. It is established that between the most common classes of herbaceous vegetation there is a clear differentiation by factors of soil moisture, substrate aeration, carbonate, and nitrogen content in the soil. The distribution of plant communities depending on the terrain and the values of environmental factors has certain patterns that are reflected in the ecological profiles. Potentillo arenariae–Stipetum capillatae (Hueck 1931) Krausch 1961 and Stipo lessingianae–Salvietum nutantis Vynokurov 2014 communities are located on the plateaus and slopes of the ravines. In areas of slopes where there is a sharp bend, the content of calcium, acidity, and salts is higher, develops shrub communities Vinco herbaceae-Caraganetum fruticis Korotchenko et Didukh 1997. Communities of association Lino tenuifolii-Jurineetum brachycephalae Krasova et Smetana 1999 develop at limestone outcrops where there is thin soil layer on the surface, lower salt content, higher nitrogen content and humidification is less stable. Agropyretum repentis Felföldy 1942 communities are confined to the wettest bottoms of ravines. It is established that the main trends of the vegetation dynamics on the reserve territory are demutation changes that occur after the cessation of grazing, burning, plowing, and forest reclamation measures. However, since the restoration of vegetation in the study area takes place in absolutely protected conditions, demutation processes due to the lack of factors that alienate excess biomass, acquire common features of postreserving successions. In the last decade of the reserve's existence, the problem of vegetation degradation in the fence with bison has arized, as the number of animals exceeded the allowable level, so this area is overgrazed. To establish the ecological changes of vegetation during the last 20 years, a comparison of the conditions of the reserve in the initial state of 1996 and 2017 was made. For this purpose, a synphytoindication analysis of six representative syntaxons was performed. It was found that among the ecological parameters a significant difference in values is observed for climatic factors, in particular for the thermal regime, climate humidity, and continentality. We proposed the classification of habitats of the studied area, which includes 5 types: С, D, E, F, I. The highest degree of differentiation is observed by types E and I. Based on dominant classification the characteristics of 15 associations of 6 steppe vegetation formations included in the Green Data Book of Ukraine are given. The adaptive capacity of adventive species Ulmus pumila L., Gleditsia triacanthos L., Elaeagnus angustifolia L., Robinia pseudoacacia L. was studied. Based on the data of synphytoindication analysis, it could be concluded that two species out of four, namely Ulmus pumila and Elaeagnus angustifolia, are able to adapt to the ecological conditions of the study area. They have broad ecological amplitude and have the capacity to penetrate steppe communities. Their distribution is not limited by ecological conditions but is complicated by the integrity of the structure of steppe coenoses. The distribution of Robinia pseudoacacia and Gleditsia triacanthos species, in addition to the intact steppe areas, is constrained by lack of humidity. The scientific novelty of the work is that for the first time based on the Brown-Blanke ecological-floristic method, a classification scheme of the «Yelanetskyi step» nature reserve was established. For the first time, a list of biotopes on the territory of the nature reserve has been determined, some of them are detailed to 6-7th levels. Features of vegetation restoration on the territory of the reserve after the influence of plowing, grazing, roasting, forest reclamationfor 20 years of its existence are described. For the first time, the possibilities of adaptation of adventitious tree species to the ecological conditions of the studied territory were investigated. The dissertation materials were provided for the«Yelanetskyi Step» Nature Reserve Chronicles of the nature. Geobotanical relevés and ecological profiles will be used for vegetation changes monitoring. The necessity of measures for the restoration of steppe communities is substantiated.
