The first dataset of vascular plant species occurrences on kurgans in Southern Ukraine

Abstract Background The dataset contains the records of vascular plant species occurrences and distribution on Ukrainian kurgans (burial mounds, barrows), located in various zones of steppe vegetation: desert steppe, grass steppe, herb-rich grass steppe and forest steppe. Much of the studied kurgans belongs to the territory historically known as the “Wild Fields”. Besides the occurrence data, the publication presents a comparison of the floristic richness amongst five microhabitats distinguished on kurgans (top, northern slope, northern bottom, southern slope, and southern bottom) and amongst kurgans located in different steppe zones. The Original publication includes 721 species of vascular plants) within four vegetation zone (desert steppe, grass steppe, herb-rich grass steppe and forest steppe). The report shows also sozological value of kurgans in southern Ukraine, as they play a role of steppe habitat islands in a landscape almost completely transformed to arable land. The obtained flora inventory was analyzed in various aspects. This occurrence dataset is the first public record of species from kurgans in Ukraine. New information This is the first occurrence dataset from kurgans in Ukraine. The dataset includes 28,456 occurrences of vascular plants recorded in the years 2004-2009 on Ukrainian kurgans. The dataset includes information about 1446 occurrences of rare species on kurgans (69 species). It contains information on the kurgan flora within four vegetation zone (desert steppe, grass steppe, herb-rich grass steppe and forest steppe) on the area ca. 32000 km2. Of the approximately 450 mounds visited, the ones with the best preserved vegetation cover were selected. For each of 106 investigated mounds, floristic lists from five microhabitats were compiled - 530 lists in total.


Introduction
A "kurgan" is a word derived from the old Turkish language meaning: refuge, fortress, but also high grave. A kurgan is defined as a mound of earth (and/or pile of stones), often conical or hemispherical in shape, constructed over a burial chamber, containing a single or multiple graves. The following terms are used as synonyms: barrow, burial mound, tumulus or tomb.
Kurgans are not associated with specific climatic-vegetation zones, but most of them are located in the steppes. Barrows were built by nomadic peoples from the Eurasian steppes, but also by Indian tribes from the prairies of North America. Kurgans in Eurasia were built from the Eneolithic through the Bronze and Iron Ages, up to the early Middle Ages and provide evidence of migrations and wars conducted by nomadic or semi-sedentary peoples. Most of the barrows were attributed to: Cimmerians, Scythians, Sarmatians (Iron Age) and later: Huns, Bulgarians, Magyars, Polovtsians, Nogays and others. The earliest information about the barrows on the north shore of the Black Sea was provided by Herodotus in "The Histories". Some sporadic information also comes from the late Middle Ages (Sudnik-Wójcikowska et al. 2012).
The steppe biome is considered to be the most transformed of all biomes in the world. It is estimated that 82-90% of steppe vegetation in Ukraine has been destroyed due to agricultural practices and the development of human settlements. In consequence, its area has been reduced 50-fold during the past 2000 years. Kurgans constituted an impediment to large-scale agriculture. Before the "taming of the steppe", which occurred about 200 years ago (e.g. Sunderland (2004), Khodarkovsky (2009)), the barrows in southern Ukraine were surrounded by virgin steppe vegetation, which promoted formation of the plant cover similar to the natural steppe vegetation. Kurgans are some of the most characteristic features of the Ukrainian landscape. Ukraine is referred to as "the land of kurgans" and it is hard to imagine the history and landscape of Ukraine without the barrows. The original number of kurgans in Ukraine is estimated at half a million, of which probably about 100,000 (according to other authors, 50,000 or 150,000) survive to this day. A high number of barrows were destroyed because they hindered farming activities. Those that survived (usually larger ones) became isolated because they were surrounded by extensive arable fields. The larger barrows that remained, vary in terms of the state of preservation of their plant cover. Nevertheless, they resemble the "native flora islands" in ''the ocean'' of arable fields. The best preserved kurgans are of high conservation value and can play a significant role as refugia of the steppe flora (Sudnik-Wójcikowska et al. 2011, Sudnik-Wójcikowska et al. 2012).
Our field investigation (2004)(2005)(2006)(2007)(2008)(2009) has shown the great importance of kurgans in preserving biodiversity. The examined barrows were spread over an area of about 32,000 km in Kherson, Mykolaiv, Poltava, Cherkasy and Kirovograd regions. Of the approximately 450 visited kurgans, we chose 106 with the most interesting flora. The kurgan flora database includes 719 taxa of vascular plants. The total number of occurrences is 28,456. Amongst the recorded taxa, the notable number is protected and listed in the Red Data Book of Plants of Ukraine (Ed. Didukh 2009) and other levels of protection. The burial mounds should, therefore, be particularly protected, not only as the monuments of archaeology, but also because of their natural value. growing interest in kurgans. Natural scientists are looking for evidence to protect them. Our long-term floristic survey serves this purpose.
The floristic data, collected on the kurgans, were compiled into a database. We used the database to achieve the following goals: 1.
to characterise the total flora of the barrows; 2.
to compare the flora of microhabitats within the kurgans; 3.
to present the similarity of flora of the kurgans and the flora of the climaticvegetation zones in which the barrows are located; 4.
to indicate the most valuable species (legally protected or listed in the Red Data Book of Plants of Ukraine (Ed. Didukh (2009)); 5.
to emphasise the role of kurgans in the process of restitution of the steppes -the most damaged biome in the world.

Project description
Personnel: Ivan Moysiyenko, Barbara Sudnik-Wójcikowska Funding: The collecting of floristic data, field investigations and further data analysis were supported by the projects of the Polish Ministry of Science and Higher Education: "Kurgans as a refuge of the steppe flora in the agricultural landscape of southern Ukraine" 2 PO4G 046 27 (2004)(2005)(2006)(2007) and "Kurgans as centers of floristic diversity requiring special protection in the anthropogenic landscape in the zone of steppes and forest steppe of southern Ukraine" NN 304 081835 (2008)(2009)(2010)(2011). The data publishing was supported by the project: "Impact of war on cultural heritage sites as refugia of biological diversity in Ukraine" D596 (2022).
The dataset was prepared in collaboration with the University of Warsaw (Contract of employment BSP-NN-10757/22).
We are also grateful to "Finnish Biodiversity Information Facility (FinBIF)" for their call for authors in the project "Northern Eurasia 2022".

Description:
The study area is located within four climatic-vegetation zones (three zones of the steppe and the forest steppe zone). Administratively, the area is located in the following regions of Ukraine: Kherson, Mykolaiv, Poltava, Cherkasy and Kirovograd (Fig. 1).
The examined barrows were spread over an area of approximately 32000 km . Historically, most of the studied area is referred to as a "Wild Field". The first dataset of vascular plant species occurrences on kurgans in Southern ... Characteristics of the kurgans investigated in the steppe zones and forest steppe zone. A complete inventory of the flora of vascular plants was carried out on the selected mounds. Every kurgan was examined at least 2-3 times during the growing season (spring, summer and autumn). Each of the 106 examined kurgans was divided into five microhabitats (T -the top of the barrow, Ss -the southern slope, Sn -the northern slope, Bs -the southern foot, Bn -the northern foot, see Floristic richness of microhabitats on kurgans). We determined the abundance of individual species in each of the microhabitats according to a simple 3-point scale (rare, fairly frequent, common species).

Characteristics of the investigated kurgans
A separate floristic list was prepared for each microhabitat. We filled out special forms for the flora inventory. The identification of vascular plant species was held in the field. Specimens that could not be identified in the field were collected to the Kherson State University Laboratory of Plant Ecology and Environmental Protection. Coordinates of records were checked using Google Earth service (Google Earth 2022).
Step description: The following steps were taken: 1. The study of vascular plant flora on kurgans in southern Ukraine was carried out for 6 years (2004)(2005)(2006)(2007)(2008)(2009) 2. Each of the 106 examined kurgans was divided into five microhabitats (the top of the barrow, northern and southern slopes, the southern and northern foots). For each microhabitat and barrow, we prepared a floristic list (530 in total). We determined the abundance of individual species in each of the microhabitats according to a simple 3-point scale.
3. To make the lists of flora comparable, we strived to visit each kurgan at different times of the growing season (spring, summer, autumn). Thus, the floristic lists were successively supplemented.
4. We collected herbarium documentation (a total of about 600 sheets deposited in two university herbaria (KHER -Kherson State University and WA -University of Warsaw) and photographic documentation.
5. The obtained census of the kurgan flora includes 719 species and 28,456 occurrences compiled in an .CSV file.

Geographic coverage
Description: The study area is located in the Black Sea Lowland and Dnieper Upland, within the Kherson, Mykolaiv, Kirovograd, Cherkasy and Poltava regions, in four climaticvegetation zones (Fig. 1). It covers a large area of southern and central Ukraine (about 32,000 km ). The concentration of kurgans in this area is greater than anywhere else in Europe, although they vary in their origin, history, degree of isolation and the intensity of anthropogenic factors. The area is diverse in terms of climate, soil and history of use. The amount of rainfall gradually increases from south to north and the annual temperatures decrease. Hence, the characteristics of the steppes change in the following zones (Bohn et al . 2000): - Due to its salinity, the area is partly closed for use or used mainly as pastures.
-The grass steppe -located to the north of the desert steppe. Together with the next zone, it covers a strip 50 to 300 km wide. The soils are fertile. Dark chestnut soils predominate, passing northwards in southern chernozems with a thick layer of humus. Average annual rainfall ranges from 300 mm in the south to 400 mm in the north. Clump grasses of the genera Stipa, Festuca and Koeleria dominate, yet the area is heavily transformed by agricultural use.
-The herb-rich grass steppe -with increasing rainfall (up to 450 mm per year) and soil fertility, the share of dicotyledonous perennials and creeping grasses is growing. The area is intensively used for agriculture (ploughed even to 95%) and the steppe has survived only in marginal areas, the least useful for agriculture, for example, the balkas, the river valleys, of the outcrops of granite or limestone.
-The forest steppe -reaches the furthest north, where the mean annual rainfall is 450-750 mm. The humidity is only slightly lower than in the forest zone. On fertile soils (black earths, rendzinas, grey forest soils), a macromosaic of forests (mainly thermophilic deciduous) and very rich in species flowering (meadow) steppe developed. The forest steppe is very intensively transformed by agriculture.

Additional information Floristical richness and taxonomical value of kurgans in the "Wild Field"
We identified 719 taxa of vascular plants on 106 kurgans, which make up 14.1% of the total flora of Ukraine (Mosyakin and Fedoronchuk 1999). Such a high number of species is not surprising, due to the large study area that has variable climatic conditions and different historical backgrounds. Most of the species belong to the class Magnoliopsida (Fig. 3). The most represented families in the kurgan flora are: Asteraceae, Poaceae and Fabaceae. These families are also well represented in the flora of Ukraine. The genera with the highest number of species identified on the kurgans were Veronica (18 species), Trifolium (12), Astragalus (10), Euphorbia (10), Potentilla (10) and Centaurea (9). The genera Achillea, Artemisia, Carex, Galium, Vicia and Viola were represented by eight species and Allium and Salvia by seven species.

Floristic richness of microhabitats on kurgans
The microhabitats within the kurgans vary with regard to different environmental conditions (Fig. 4, Table 2). Not only the southern slopes receive more solar radiation than the north facing ones, but also a vertical moisture gradient is observed. The rate of soil erosion varies depending on the site conditions (the top and base of the kurgan). All these factors imply differences in the composition of plant communities. For all 530 microhabitats at 106 kurgans, the lists of vascular plants were elaborated. On average, 54 species per microhabitat (min. -13, max. -117) were recorded. The floristic richness of microhabitats is growing from the top of kurgans to the bottom and from the southern exposition to the northern. As the average number of species of microhabitats increases, the following gradient occurs: T -Ss -Sn -Bs -Bn.

Floristic richness of kurgans between zones
The long-term botanical studies conducted in the steppe and forest steppe zones of Ukraine (e.g. Lavrenko et al. (1991)) confirmed the high floristic diversity of these areas and showed that the species richness increase from south to north in the subsequent climatic-vegetation zones. This is associated with the gradually changing climatic The taxonomic distribution of occurrences.
The first dataset of vascular plant species occurrences on kurgans in Southern ...
conditions. In turn, the climate becomes milder towards the north (higher precipitation rates, lower summer temperatures). Out of the total of 719 species recorded on the kurgans, 42% were represented in the desert steppe zone (located southwards) and 64% in the forest steppe zone (located Table 2. Floristic richness in microhabitats. northwards). The difference in the number of species between the kurgans in the four zones studied amounted to approximately 160 species. Our study confirmed (Table 3) that the total species richness on the kurgans was the lowest in the desert steppe zone (305 species), increased gradually in the grass steppe zone and the herb-rich grass steppe and was the highest in the forest steppe zone (460 species). In each zone, we examined almost the same number of barrows (25-29), which showed differences in the floristic richness, in accordance to the zone. The higher kurgan total flora diversity in the forest steppe could be also explained by a greater variety of biotopes on kurgans: from "dry steppe" on the tops and southern slopes, to more moist forest-like communities on the northern slopes and the bottom of the barrows. The anthropogenic influences and the occurrence of synanthropic species were probably also important.  (Table 3). We used the mean number of species per kurgan in particular climate-vegetation zone as an indicator of floristic diversity. The mean number of species in the desert steppe was 82.3, in the grass steppe -110 and in the herb-rich grass steppe -125.5, respectively. The kurgans of the herb-rich grass steppe appeared to be the richest amongst kurgans examined in all other zones. Surprisingly, the mean number of species per kurgan in the forest steppe zone was 107.5. Despite the northernmost geographic location of the forest steppe zone, the particular barrows appeared to be less species-rich. This may be due to the fact that, in the forest steppe zone (at least in the area under investigation), it was much more difficult to find kurgans which would meet the set-up criteria. The kurgans were usually smaller (i.e. the mean height and diameter of the investigated forest steppe kurgans were 4.98 m and 54.1 m, respectively and, in the case of the herb-rich grass steppe zone, it was 5.7 m and 67.1 m, respectively) ( Table 2). In addition, many of the kurgans were in poor condition. Table 3.
The basic parameters characterising the flora of kurgans in three types of steppe and forest steppe zones in Ukraine.
The worse condition of the barrows, at least locally, could be ascribed to the very early and still intensive agricultural practices in the forest steppe zone.

Sozological value of the flora of Ukrainian kurgans
The kurgans are protected as archaeological monuments, but this is often not sufficient. The mounds are subjected to significant anthropogenic impacts. The main threats to the steppe flora on kurgans are: ploughing, archaeological excavations, illegal digging and looting, mechanical or agrichemical damages, afforestations, overgrazing, too frequent burning or mowing, littering, plant invasions from nearby agricultural landscapes etc. The kurgans have been influenced by some invasive alien species. This is evidenced by the presence of such species as: Ailanthus ltissima, Asclepias syriaca, Eleagnus angustifolia and Grindelia squarrosa. Species have a tendency to inhabit the kurgans. Amongst these threats, it is especially unfortunate that the vegetation on the mounds is damaged by modern excavation technologies, during which the mounds are completely excavated and the vegetation is completely destroyed by archaeologists. A preventative action, from the point of view of habitat restoration, is the creation of protection zones around the mounds and creating of educational networks for understanding of value of kurgans. Moderate grazing, or haying, is also important to prevent "reserve succession". Reintroduction of vulnerable steppe species will also accelerate the natural process of restoration of typical vegetation. These preventative actions aiming at habitat restoration on kurgans, should concentrate on the creation of protection zones (buffer zones) around the mounds. The presence of buffer zones would prevent damaging the mounds by ploughing, as well as significantly reduce the ingress of pesticides. Kurgans, persisting within the intensively cultivated arable land of Ukraine, constitute the enclaves of natural steppe flora and an exceptional gene bank, which are representative for the particular climate-vegetation zones. Together with other fragments of natural or semi-natural steppe vegetation, they could play a significant role in the restoration of the European steppes, acting as "micro hotspots" and as donors of diaspores for the areas set free from intensive agricultural practices (Sudnik-Wójcikowska et al. 2012).
Amongst all recorded species, 69 (about 10%) were species of special concern, included in international and regional Red Lists (Sudnik-Wójcikowska et al. 2011). The sozophytes identified on the kurgans represented 26 families and 50 genera. The species represented the class Magnoliophyta (only one species belonged the class Pinophyta). Amongst the 69 taxa, 58 species occurred with frequency below 20% and four species with frequency between 20 and 40%. Two species were quite common: Stipa capillata (93%) and Linaria biebersteinii (74%). Rare species were present at all 106 kurgans. About 90% of the sozophytes recorded within kurgans had optimal conditions for growth on the slopes of the barrows. Only eight species (12%) were most frequently recorded at the base of kurgans (mesophilic or woody species). None of the species of special concern was associated with the top of a barrow -anthropophytes and hemi-apophytes clearly dominated in this type of microhabitat (Sudnik-Wójcikowska et al. 2011).
The dataset includes information about 1446 occurrences of rare species on kurgans. The occurrence of rare species on kurgans is growing from south to north and as follows: the desert steppe -195 species, the grass steppe -335 species, the herb-rich grass steppe -418 species, the forest steppe -498 species. The populations of these species are particularly vulnerable, because enclaves, such as kurgans, are usually small in size and isolated due to the huge fields around them. Anthropogenic factors (destruction of the base of the barrows by agricultural practices, the use of herbicides, mowing, grazing, trampling, illegal archaeological works etc.) also play a negative role. Populations of rare species on barrows are extremely sensitive and, therefore, require special measures to preserve them (Fig. 5).