Roshchyna N. Anthropogenic-climatic transformation of the flora and vegetation of lakes in the northern steppe within the Dnieper region

The thesis paper presented the results of studies on flora and vegetation current state of lakes in the northern steppe of the Dnieper region, identification of main patterns of transformation in flora and vegetation growing in lakes of different types, as well as determining the main directions of vegetation dynamics under the influence of anthropogenic-climatic factors. In the lake flora, 200 species of aquatic and riparian plants were counted with dominance of hemicryptophytes, perennial grasses, hygrophytes, scioheliophytes, mesotrophs, aquants, and paludants. Adventive fraction of flora comprised 10 species, fraction of rare plant species amounted 49 species of higher plants. Creation of reservoir was determined as the main anthropogenic factor caused changes in hydrological regime of lakes in the Dnieper region and estuary area of the Samara River, resulting in reduction of flora composition in floodplain lakes by 15 and 30 species, respectively. An increase in average annual temperatures caused a decrease in the number of boreal species (by 8) and an increase in the number of Mediterranean species (by 12). Synergistic effect of climatic and anthropogenic factors resulted in irreversible changes (exogenous successions) by the following succession series: cenoses of hydathophytes (submerged plants) → cenoses of pleistophytes (floating-leaved vegetation) → cenoses of helophytes (aero-aquatic plants). A comparative analysis on hemerobia degree showed that lakes of the Diyovsky subdistrict have the highest transformation (30% euhemerobes, 15% polyhemerobes); the lakes within the Samara Forest subdistrict were less transformed (15% euhemerobes, 4% polyhemerobes). Characteristics of species hemerobity allowed defining indicator species for the subsequent assessment of such biotopes.