Ancient settlements in Southern Ukraine : how do local and landscape factors shape vascular plant diversity patterns in the last remnants of grass steppe vegetation?

Agricultural intensification in the last century resulted in a significant loss and fragmentation of steppe habitats. As a result, steppes are scattered and rarely preserved in highly transformed landscapes. Steppe patches have often remained on sites with cultural importance, such as ancient burial mounds (kurgans), old cemeteries or ancient settlements (earthworks). Thus, not only natural but also cultural objects could show a high conservation value. We hypothesised that ancient settlements (3rd – 2nd century BC) may act as steppe habitat islands, equally important as e.g. burial mounds for steppe plant protection. The aim of this study was to examine the local and landscape factors affecting vascular plants’ richness patterns in ancient settlements and to check the importance of such ancient settlements for nature conservation. We asked the following questions: 1) How high is the species richness of vascular plants on ancient settlements? 2) Do ancient settlements have a nature conservation value comparable to other steppe enclaves of the studied zone? 3) Which factors are the most important for the species richness and species composition in ancient settlements? We analysed total richness and its separate categories as dependent variables in simple regressions against seven environmental variables such as ancient settlement’s area, microhabitat variety index, afforestation degree, steppe cover in 1 km buffer around an ancient settlement, distance to the closest settlements, area of settlements in 1 km buffer around an ancient settlement and mean annual precipitation. In 18 studied ancient settlements located in the Lower Dnipro basin (Southern Ukraine), we recorded a considerable number of native (396 species, 75.6%), steppe (239 species, 45.6%) and non-synanthropic plants (225 species, 42.9%), which indicated a good state of preservation of the steppe on these objects. The microhabitat variety index, as a measure of habitat heterogeneity, appeared to be the most significant positive predictor of total species richness, followed by ancient settlement’s area, afforestation degree and steppe cover around the ancient settlements. The same factors were significant for the richness of non-synanthropic plants. Distance to settlements was a significant negative predictor for established alien species richness. Our study confirmed that ancient settlements are valuable enclaves of steppe flora, surprisingly species-rich and of relatively Manuscript received 15 March 2020, accepted 29 May 2020 Co-ordinating Editor: Balázs Deák 460 high ratio of steppe and non-synanthropic plants compared to the flora of nature reserves and kurgans. Our results could help to better plan active protection of plant diversity on ancient settlements, e.g. through steppe restoration around the ancient settlements, maintenance of small-scale disturbance and microhabitat diversity (pastures, mown areas, burnt areas, loess or limestone extraction sites etc.) and limiting afforestation to a certain degree.