Successive anthropogenic changes of the vegetation in the Kilyan arm of the Danube Delta (Ukraine)

Background. In the past, floodplain vegetation, typical of estuarine ecosystems affected by a moderate surge wind phenomenon, prevailed in the Kilyan arm of the Danube Delta (Ukraine). The vegetation of this territory was represented mainly by meadows, swamps, and wetlands. Forest vegetation occupied only small areas. At the beginning of the previous century, natural complexes of the Kilyan arm of the Danube Delta underwent significant anthropogenic transformations. We distinguish two types of anthropogenic factors – large-scale and local – the latter referred to as successive. While anthropogenic, especially large-scale, pressure on natural ecosystems of the delta leads to a catastrophic alteration of the ecological regime and degradation of native flora complexes and plant communities, successive changes lead mostly to a decreased species diversity, biological productivity, and degradation of biocenoses. The main factors of local anthropogenic transformation of ecosystems are grazing-induced vegetation changes, mowing-induced vegetation changes (harvesting of reed and hay cutting), pyrogenic, biochemical changes, and afforestation. With their long-term influence and heavy load on biotopes, successive changes turn into catastrophic. On the contrary, when their influence is insignificant, or removed, the original native vegetation is restored. Materials and Methods. Long-term comparative phytocoenotic surveys and semi-stationary studies were used in this research. The studies of the anthropogenic dyna­mics of vegetation were carried out by direct methods – on semi-stationary sites, as well as by indirect methods. The direct methods included comparing the current data with historical maps and geobotanical descriptions presented in the monograph «Reserve “Wetlands of the Danube”». Indirect methods included the reconstruction of successive trends based on the analysis of ecological and coenotic profiles. Results and Discussion. The syntaxonomic structure of vegetation in the delta is analyzed. The paper highlights the main local successive anthropogenic changes of vegetation identified based on long-term comparative phytocoenotic surveys and semistationary studies. The anthropic changes in vegetation occur under the influence of powerful external factors associated with human activity. In the delta area, the anthropic changes exceed natural in terms of their scale and degree of influence. The main factors of such changes are grazing-induced and mowing-induced vegetation changes, pyrogenic, biochemical changes, afforestation etc. The halophytic and halophytic meadow vegetation of the coastal areas is most affected by the pasture. The sandy steppe and shrub vegetation are influenced by pyrogenic factor and forest logging. The influence of the mowing-induced factor is manifested on a narrower scale. The pressure of local anthropic factors are enhanced by the influence of global or local natural factors. The complex effect of local anthropogenic and global climatic factors on communities leads to their unification, loss of the autochthonous elements, and formation of unproductive associations. The most endangered are steppe and psammophyte vegetation with representatives of the psammophilous-littoral neoendemic pontic floristic complex. Conclusion. The strategy for optimizing the vegetation cover of the Kilyan arm of the Danube delta is offered. Preservation, restoration, and maintenance of the delta vege­tation in the conditions of regulated river flow and climate change can be achieved through the extraction of a certain volume of plant material by mowing, grazing, and winter burning of grass. These measures should be preceded by an assessment of negative changes and their trends, as well as careful control over their implementation. A moderate pasture and mowing loading contributes to the increase of the species composition and communities’ productivity and the preservation of rare species.