Introduction

Dry grasslands of the Eurasian steppes represented one of the largest continuous temperate grassland ecosystems (> 10 million km2) in prehistoric times. They still support high biodiversity and provide habitat for numerous endemic plant and animal species (Kirschner et al., 2020). These landscapes co-evolved with local human societies, affecting their history, culture, and overall way of living (Forero et al., 2023; Wilkin et al., 2021). In the western regions of the steppes, these ancient societies were predominantly nomadic herders such as the Yamnaya Culture (Late Copper and Early Bronze Age; 3300–2500 BC), Scythians (Early Iron Age; 900–200 BC), Sarmatians (300 BC – 350 AD), and Turkish ethnic groups (Middle Ages), who adapted to the environmental conditions and resources provided by steppe ecosystems and sustainably used the landscape (Wilkin et al., 2021).

Since Medieval times, increasing human pressure led to huge losses of steppe habitats (Wesche et al., 2016). Grasslands were increasingly impacted by transformation into agricultural, rural, and urban areas. With a shift from a nomadic to a settled lifestyle, several areas of grassland close to settlements became overgrazed, while those located further out were abandoned, which also had a negative effect on grassland-related biodiversity (Deák et al., 2017). These processes led to severe losses in grasslands, degradation of natural values, and drastic socio-economic changes (Biró et al., 2018). In Europe, this process started in the Neolithic era but has intensified since the Industrial Revolution (eighteenth − nineteenth century). Despite increasing nature conservation awareness, even present-day grasslands are significantly threatened by land use intensification (Biró et al., 2018). Due to these processes, the steppes are among the most endangered ecosystems in the world, having lost approximately 57% of their total area in Eurasia. Habitat loss is most apparent in the western regions such as Hungary and Ukraine, where more than 90% of steppes have been converted to agriculture (Wesche et al., 2016).

Habitat loss is most obvious in densely populated areas, primarily where steppes were formed on fertile soils such as chernozem (Deák et al., 2016). In these areas, remaining stands are generally restricted to the few nature reserves or small fragments (e.g., in road verges, field margins, and steep slopes of river valleys) unsuitable for arable farming (Dembicz et al., 2020). Besides these ‘conventional’ safe havens, steppe species also remain in certain sites holding a high cultural and spiritual importance (Deák et al., 2023a; Wild & McLeod, 2008). Sacred sites such as groves, mountains, shrines, churchyards, old cemeteries, and ancient burial mounds are found globally, and their cultural and spiritual significance varies with their geographical location and the cultural context (Bhagwat & Rutte, 2006; Deák et al., 2023a; Dudley et al., 2009; Jackson & Ormsby, 2017; Löki et al., 2019; Zannini et al., 2021). Local populations respect these sites because of their cultural, religious, or historical significance (Valkó et al., 2023). Sacred sites often include burial sites, are locations of important historical events or a living expression of ancestors, have sacred features and buildings, sometimes associated with a specific deity, and have their mythologies and legends (Dudley et al., 2009; Deák et al., 2023a; Jackson & Ormsby, 2017). Sacred sites are often maintained by the local populations using traditional methods and extensive management that provide the potential for conserving grassland habitats and grassland-related species even in densely populated landscapes (Deák et al., 2023a; Ormsby & Bhagwat, 2010; Zannini et al., 2021).

In the Eurasian steppes, ancient burial mounds (called ‘kurgans’) are the most widespread manmade sacred sites to protect grassland flora (Deák et al., 2023a). Most kurgans were built during the Copper, Bronze, and Iron Ages, but many date to the Migration Period and Middle Ages (Deák et al., 2016; Gimbutas, 2000). Although, during the past millennia, a considerable number have been destroyed, presently, there are approximately 600,000 kurgans documented in the Eurasian steppes (Deák et al., 2016). Typically, a mound was built on a central pit grave and was 0.5–15 m in height and 5–50 m in radius (Deák et al., 2016; Dembicz et al., 2020). Most were built by the Yamnaya Culture (also known as the Pit Grave Culture) between 3300 and 2500 BC (Gimbutas, 2000). Later, other nomadic Indo-European tribes (such as the Scythians and Sarmatians), ancient Turkish cultures (e.g., Cumanians, Kipchak, and Khazar groups), and the Thracians also built mounds (Apostolova et al., 2022; Deák et al., 2016; Gołębiowska-Tobiasz, 2013). The main function of the burial mounds was to provide an iconic monument for the deceased, and they were generally large and conspicuous in the otherwise flat and open landscapes (Bede et al., 2015). Eurasian steppe mounds have many analogues in the world, such as mounds in West and North Europe (Andersen, 2012) and pre-Columbian mounds in North (Steponaitis, 1986) and South America (del Puerto et al., 2023), which are of a similar size and also served sites for religious rituals, ceremonies, and funerals.

Recent recognition of the importance of kurgans as sacred sites in biodiversity conservation has generated several studies focusing on grassland kurgans situated in transformed landscapes of Hungary, Ukraine, and Bulgaria, where steppe habitats have become especially endangered. These studies revealed that kurgans could act as biodiversity hotspots and safe havens for grassland plant and animal species even with the large-scale transformation of the neighboring landscape (Apostolova et al., 2022; Deák et al., 2020; Dembicz et al., 2020; Lisetskii et al., 2014; Sudnik-Wójcikowská et al., 2011). However, only a few of these have evaluated the direct linkage between the cultural and conservation values of the mounds.

A recent continental-scale study revealed that Eurasian kurgans still serve as important cultural and religious sites for local communities and hold several cultural and religious buildings and objects from successive cultures (e.g., stone pillars and statues, churches, cemeteries, and memorial statues) (Deák et al., 2023a). Also, in many cases, intangible folkloristic values (such as old tales or legends) are connected to the mounds, which can considerably increase the chance of preserving dry grassland habitats on the mounds. Valkó et al., (2023) found a positive correlation between the number of toponyms (place names) and the naturalness of the vegetation on the kurgans, emphasizing close connections between cultural and natural values. However, the sample size of both studies (n = 1079 and n = 1521, respectively) precluded a fine-scale picture of the multi-layered cultural aspects of kurgans and their temporal dimensions that might support various components of the biodiversity on the mounds.

Thus, our goal here is to establish links between kurgans' cultural and natural values through a comprehensive multi-layered evaluation of cultural attributes, botanical composition, and landscape history on representative mounds in three countries. We used historical maps, published literature, and field surveys to (i) explore the cultural values associated with the mounds, (ii) provide an overview of the landscape changes during the past 280 years, and (iii) explore the plant biodiversity of the kurgans. Based on our results, we evaluate factors that can support or endanger the grasslands on kurgans and assess whether there are synergies or trade-offs between cultural and natural values.

Methods

Study Areas

We focused on the Carpathian Basin's lowlands, where kurgans and steppe habitats have their westernmost distribution. We selected six kurgans situated in the Maros–Körös Interfluve (Hungary and Romania), Crişana (Romania), and Vojvodina (Serbia) (Fig. 1). During the Late Copper–Early Bronze (3350–2450 BC) and Roman Ages (50–400 AD) these regions were inhabited by steppe nomadic cultures and ethnic groups such as the Yamnayas and the Sarmatians who built many kurgans (Dani, 2020; Masek et al., 2019). Based on the investigations of Bede (2019), about 2,300 mounds existed in the central part of Tiszántúl region (8,000 km2) in the eighteenth century. However, due to human activities such as soil levelling in agricultural fields, the establishment of rice fields or fishponds, and expansion of urban infrastructure, approximately 30% of the mounds have been destroyed, and only 1,400 mounds remain (Bede, 2019). Despite the large number of kurgans in both the regions of Crişana and Vojvodina (Jarosz et al., 2021), we have a very incomplete knowledge of their number and location because of the scarcity of available publications (Diaconescu et al., 2017; Fazecaş & Marta, 2015; Jarosz et al., 2021) and lack of comprehensive systematic kurgan surveys.

Fig. 1
figure 1

Map and photos of the studied kurgans. A − Kálvária-domb (‘Calvary Mound’; Szentes, Hungary); B − Akasztó-halom (‘Hanger Mound’; Békés, Hungary); C – Temető-halom (‘Cemetry Mound’, Iratoșu, Romania), D − Cinci Movile (‘Five Mounds’; Vladimirescu, Romania); E – Humka Kalvarija (‘Calvary Mound’; Kanjiža; Serbia); F – Kamenita umka (‘Stony Mound’; Žabalj, Serbia). Photos were taken by Kristóf Süveges

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Before land use intensification, the study area was characterized by extensive stands of continental forest-steppe vegetation composed of a complex mosaic of dry and mesic grasslands and compact forest patches (Biró et al., 2018; Molnár et al., 2023). Due to the large-scale transformation of natural habitats to arable lands and urban infrastructure, grasslands suffered a severe decline in the study areas (Biró et al., 2018). This significantly affected dry grasslands and the species confined to them, posing a considerable challenge to present-day nature conservation (Deák et al., 2021). For example, loess steppe grasslands, the most species-rich dry grassland habitat of forest steppes, have lost 98% of their original extent since the eighteenth century (Biró et al., 2018). In transformed landscapes of the Carpathian Basin (similarly to many regions in Bulgaria, Ukraine, and Russia), the last remnants of dry grasslands are often restricted to very few nature conservation areas and small, non-protected habitat fragments persisting on road verges, field margins, midfield islands, rocky outcrops, and kurgans (Apostolova et al., 2022; Deák et al., 2016).

Selection of Mounds

To assess the past and present cultural and natural values of kurgans, we selected mounds that (i) were covered by dry grassland vegetation (represented by the most endangered loess grasslands), (ii) had available historical maps and publications, and (iii) held various cultural values (religious objects, documented historical events, or folkloristic material). All mounds were situated in landscapes heavily affected by human activities, especially intensive agriculture.

Data Collection

Kurgans, highly visible orientation points in flat homogenous landscapes, have historically often been marked on military maps (Valkó et al., 2023). For our survey, we used a time series of maps from the 1st (1782–1785), 2nd (1858–1864), and 3rd (1881–1884) military surveys of the Habsburg Empire from the Institute and Museum of Military History, Budapest (Timár et al., 2010), and other handmade and printed maps from the eighteenth-twentieth centuries (mapire.hu, hungaricana.hu). From these maps, we can evaluate landscape changes in the kurgans and the neighbouring landscape. We calculated the area proportion of grasslands within a 300-m buffer around the kurgans using Quantum GIS (QGIS Development Team 2023).Footnote 1 We chose 300 m for the buffer, as dry grassland species have a limited dispersal radius of generally less than 100 m (Deák et al., 2020).

We collected all available publications (dating back to 1750) on the historical data and cultural values related to the studied kurgans. As papers about individual kurgans are scarce in modern international scientific publications, we focused on local peer-reviewed and grey literature (including book chapters, site descriptions, and dissertations). During the literature search, we focused on mentions of intangible cultural values (such as mentions of critical historical events or folkloristic values) connected to the kurgans and reports about objects with cultural importance, which we considered indicators of the mounds' importance for the local communities.

We visited each kurgan in June 2023. During the field survey, we recorded the presence of all culture-related buildings and objects and also recorded whether or not they were used by local communities in the present. We considered each item a positive indicator of cultural awareness.

We also inventoried and calculated the list and percentage cover of all vascular plant species. Percentage cover was calculated as a relative ratio considering only that area of the kurgan that potentially could hold any kind of vegetation (we excluded areas occupied by built environment). We distinguished between naturally occurring and planted species. For evaluating the conservation status of the kurgans, we assigned herbaceous plant species to three functional groups (grassland species, generalists, and weeds) based on their habitat preference using the descriptions of regional plant identification books (Boșcaiu et al., 1994; Ciocârlan, 2009; Josifović, 1970–1977; Király, 2009). We considered a species as a grassland species if it occurs only in grassland habitats in the studied region. We categorised a species as a generalist if, besides grasslands, its populations also occur in any other kinds of natural habitats (such as forests or wetlands) and occasionally in disturbed early successional sites. From a nature conservation viewpoint, specialist and generalist species can be considered favourable species indicating a good conservation status (Gaston & Fuller, 2008), as these species occur typically in the remaining few intact grasslands of the studied regions. We assigned those species to the weed group that predominantly occurs in degraded and anthropogenically transformed habitats, such as arable lands, young fallows, or disturbed soil surfaces. In interpreting the results, we also focused on the presence of woody and adventive species, which can indicate habitat degradation and inadequate management. We calculated the total species richness and cover of the selected functional groups. Using the collected data, we qualitatively assessed the cultural and natural values of the studied kurgans. As a part of the field survey, we also recorded the applied management activities on the kurgans (e.g., mowing, shrub cutting, and abandonment), as these measures reflect the presence or absence of traditional land use and the potential for the maintenance of the original grassland vegetation.

Results

Cultural Values of Kurgans

Based on the collected historical data, most of the studied mounds have been actively used as religious places for millennia up to the present (Table 1; for a detailed description of the cultural values of each mound, see Supplementary Material 1). The sites have been used as cemeteries or held objects related to the Catholic Church, such as calvaries, crucifixes, chapels, and crypts. In the past, they also had other special functions; for instance, they were used as sentinel mounds or execution sites. The studied mounds still have an active role in everyday life of the local population for ceremonial or folkloristic events (such as the Humka Kalvarija, a place of pilgrimage during Easter, or the Kálvária-domb that is used for the celebrations during Lent), recreation, and are also mentioned in many legends still known by the local population. The kurgans had a minimum of one and a maximum of eight toponyms. Alternative names involve the same name in different languages, such as ‘öt’ (Hungarian) and ‘cinci’ (Romanian), meaning five. They can also reflect different origin stories, such as the Kamenita umka, which has six names. Kamenita umka (Serbian) and Kő-halom (Hungarian) refer to the ruins of the medieval church (‘Stony Mound’). The names Žabalj (Frog mound; Serbian), Jurišina kosa (Yuri’s hair; Serbian), Jurišina humka (‘Yuri’s Mound’; Serbian) reflect different sagas bound to the mound. The name Žabalj (Serbian) and Zsablya (Hungarian) (Zsablya Mound; Hungarian) indicates that the kurgan was situated in the land of a particular settlement. Cultural objects covered a large area (< 30%) on three mounds and a negligible area (< 3%) on the others.

Table 1 Characteristics of the studied mounds
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Historical Landscape Changes

We found that after the eighteenth century, in the case of five of the studied kurgans, there was a considerable decline in the proportion of grassland areas in the landscape (Supplementary Material 1; Fig. 2). Large-scale loss of grassland habitats was primarily due to the expansion of arable lands and urban areas. We detected a slight increase in grassland area during the nineteenth century in the case of one kurgan (Humka Kalvarija) due to the expansion of secondary grasslands following the abandonment of arable fields. However, the grassland area decreased again at the end of the century (Fig. 3.)

Fig. 2
figure 2

Changes in the percentage proportion of grasslands in the 300 m vicinity of the kurgans

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Fig. 3
figure 3

Changes in the area of grassland habitats (marked with hatched patterned polygons) in the landscape around the Temető-halom (RO). Studied periods are marked under each map. Dashed lines denote 300 and 1000 m buffers around the mounds

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Vegetation

The surveyed kurgans were typically covered by dry grasslands with small patches of woody species (see Supplementary Materials 1 and 2). We found a total of 215 vascular plant species (99 in Hungary, 136 in Romania, and 95 in Serbia). Species richness ranged from 56 to 89 species per mound (Table 2). Each surveyed kurgan held populations of grassland specialist plant species. We found the most grassland species on the Romanian mounds (26 and 21) and the fewest on the Hungarian mounds (10 and 5). In general, grassland species had a high cover on the kurgans, but on the Kálvária-domb they were underrepresented (3.4%). In many cases kurgans held red-listed grassland species such as Amygdalus nana, Adonis vernalis, Allium sphaerocephalon, Linaria biebersteinii and Ornithogalum brevistylum.

Table 2 The applied management, species richness (SR) and percentage cover (%) of plant functional groups on the studied kurgans
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Each kurgan was characterised by a high species richness and cover of generalist species typical of natural mesic habitats (e.g., Alopecurus pratensis, Arrhenatherum elatius), forest edges (e.g., Astragalus glycyphyllos, Viola odorata), and species typical of grassland vegetation formed on slightly disturbed open soil surfaces or characteristis of old fields with regenerating grassland vegetation (pioneer grassland species such as Falcaria vulgaris, Hieracium bauhinii, Hypericum perforatum, Knautia arvensis, Medicago minima, Melica transsilvanica, and Verbascum austriacum).

We found that weed species were abundant in many kurgans. Besides weeds that are typical of intensively used ploughlands and pastures, we also found several rare weed species confined to extensively used ploughlands (Ajuga chamaepitys, Anagallis foemina, Calepina irregularis, Camelina microcarpa, Erodium ciconium, Glaucium corniculatum, Nigella arvensis, Rumex pulcher, and Valerianella dentata). Encroachment of woody species was especially typical in Hungary and Romania, where woody cover ranged between 17.9% and 54.1%. Many of the woody species were adventive and planted for practical purposes (Juglans regia, Persica vulgaris, and Prunus domestica) or ornamental (Picea pungens, Robinia pseudoacacia, Syringa vulgaris, and Thuja orientalis). We also found many adventive woody species (Ailanthus altissima, Celtis occidentalis, and Lycium barbarum) spontaneously established on the kurgans.

Most kurgans were managed by mowing. In the case of the Temető-halom, a part of the woody vegetation has been removed, while the Humka Kalvarija was unmanaged.

Discussion

Cultural Values of Kurgans

Our study revealed that the recognition of the spirituality of the mounds has persisted over millennia through transmission among subsequent cultures, as evidenced by the archaeological findings; in the Carpathian Basin, the same kurgan was often used for burial by different steppe cultures (i.e., the Yamnaya Culture, Sarmatians, Avars, and Hungarians) that otherwise did not overlap in time (Dani, 2020). The probable reason for this phenomenon is the common origin of the nature-centric beliefs of nomadic steppe cultures and also the fact that kurgans are the most visible places in flat landscapes, functioning as ‘elevated ground’ to which people are drawn (Kassabaum et al., 2021). Our results support this thesis, as we found many still existing and functioning cultural and sacred functions (independent from nomadic religions) associated with the kurgans during the past centuries.

The studied kurgans held many objects related to sacred functions, such as an old cemetery, gravestone, crucifix, calvary, crypt, and chapel. These objects were all related to the Christian (Catholic) religion that replaced ancient faiths in the Carpathian Basin during the eleventh century (Berend et al., 2007). At that time, small churches were built on the top of the kurgans in many locations as a kind of sacred extension and probably also as a sign of dominance over the past religion (Deák et al., 2023a). Even now, many old churches and religious objects can be found on the kurgans that are actively used by local communities (Deák et al., 2023a; see also Dudley et al., 2009).Footnote 2

Besides built sacred and cultural values, we found that many tales and legends are connected to certain kurgans (such as Cinci Movile in Romania), some of which can be linked to historical events. However, in many cases, they are folklore. In either case, they can increase the likelihood of preserving the kurgan, as they are part of the living history bound to the kurgan, maintaining awareness of local communities (Deák et al., 2023a). Also, toponym diversity (the number of different name varieties used by the local population) indicates the cultural awareness and diversity related to the kurgan. Alternative names involved the same name in different languages, reflected different origin stories, and referred to the ruins, persons’ names, or sagas. An earlier study reported that kurgans with more names have a higher chance of preserving intact grassland vegetation as they are less affected by human disturbances compared to kurgans with only one name or without a name (Valkó et al., 2023).

The kurgans of Kálvária-domb and Akasztó-halom in Hungary, and Temető-halom in Romania have visible graves from previous centuries. In the case of Kamenita umka, the graves are not visible, but human remains are found on the surface. During our survey, we observed the graves being maintained by the local communities, leading us to conclude that cultural traditions that are mitigating disturbing burial places (Barrett & Barrett, 2001) can also support the conservation of kurgans. Because of the presence of graves and other spiritual and cultural values, people avoid unfavourable land use changes to protect the original state of the site (Löki et al., 2019). This is also a key element in the long-term existence of grassland cover on kurgans.

We also found that in some cases, practical functions were added to sacred ones (e.g., sentinel function – Kálvária-domb in Hungary, Cinci Movile in Romania; using mound as a scaffold – Akasztó-halom in Hungary; using mound as a border mark – Temető-halom in Romania; geodetic point – Kálvária-domb in Hungary, Cinci Movile in Romania and Kamenita umka in Serbia). These practical functions often appeared in the various toponyms of the kurgans (see Supplementary Material 1). Because these practical functions were essential for the operation of the whole society, maintenance of kurgans’ integrity was an important common interest that indirectly could also support the conservation of grassland habitats on the mounds. Another practical use of the kurgans lies in their position in the landscape. Just like the ‘cerritos’ (South American earthen mounds) that were built approximately five millennia ago (del Puerto et al., 2023), kurgans were also frequently constructed near rivers and were used as safe places for people and livestock during floods (Bede & Czukor, 2019).

Historical Landscape Changes

Our analyses of historical landscape changes revealed considerable alterations over the past three centuries to lands adjacent to the kurgans. Most grassland habitats were lost to arable lands and urban areas. The most drastic changes occurred between the end of the eighteenth and the middle of the nineteenth century, driven by rapid socio-economic changes with agricultural intensification, significant industrial developments, and a growing population (Biró et al., 2018). Despite these adverse landscape-scale changes, the studied kurgans preserved grassland habitats on them. We argue that under these land use patterns, the cultural importance of the kurgans was a crucial factor that mitigated their destruction by ploughing or construction. A similar pattern was reported in Central Italy, where despite the marked changes in the land use systems at the regional scale, land in the vicinity of monasteries and shrines retained its natural vegetation (Frascaroli et al., 2016). In India, Bhagwat and Rutte (2006) reported that sacred groves remained intact despite a high level of deforestation since people keep sacred groves as set aside areas because of their spiritual values. This suggests that synergy between cultural and natural values is especially important in intensively used landscapes.

We assume that not demolishing certain kurgans was most probably a conscious decision of the land users to protect these cultural keystone places. A recent questionnaire survey from the Maros–Körös Interfluve (Rákóczi & Barczi, 2017) indicated that farmers who were aware of the cultural importance of the kurgans were more willing to tolerate a specific reduction in their income if they could protect a piece of their cultural heritage. This result reveals that by engaging with landowners about the cultural values associated with the kurgans and treating land users as partners in kurgan protection, the preservation of these critical biocultural heritage sites can be considerably enhanced.

Synergies and Trade-offs Between Cultural and Natural Values

The relatively undisturbed status and continuous extensive management supported the maintenance of several grassland specialist plants on the studied mounds. We found many species on the kurgans that have become very rare in the landscape (such as Agropyron pectinatum and Stipa capillata) or even registered on the regional red lists (such as Amygdalus nana, Adonis vernalis, Linaria biebersteinii, and Ornithogalum brevistylum). The kurgans also had a high species number and cover of generalist species that, together with specialists, are essential elements of dry grasslands in the studied regions. Thus, in this case, high proportions of generalists also highlight the favourable conservation status of grassland fragments. The group of generalists consisted of species typical of mesic grasslands, forest edges, and pioneer species of slightly disturbed grasslands and/or old fields. These species are essential elements of grassland communities and increase overall biodiversity. The high species richness of specialists and generalists is the high level of habitat diversity within the kurgans. Kurgan slopes with different aspects and the top of the kurgan are characterised by contrasting microclimates, soil moisture, and soil properties that allow for the co-existence of plant species with different environmental needs (Deák et al., 2021). High biodiversity and their relatively undisturbed state allowed kurgans to function as grassland islands embedded in human-transformed landscapes.

As noted earlier, Eurasian kurgans function similarly to ‘cerritos’ (ancient mounds in Uruguay). As del Puerto et al. (2023) observed, cerritos situated in temperate pampa grasslands acted as manmade habitats for unique vegetation with a high conservation value. One difference between Eurasian and South American mounds is that in South America, they provide habitat islands for unique woody vegetation in the sea of vast grasslands. At the same time, in Eurasia, they preserve grassland habitats in agricultural landscapes. Although cerritos provide a haven for many rare woody species due to the unique environmental conditions they provide, their species composition differs from woody vegetation occurring in plain landscapes. Deák et al. (2021) reported a similar pattern in the case of Central European kurgans. They argued that the heterogeneity of abiotic conditions provided by these anthropogenic structures allowed for the co-existence of high biodiversity and endangered species that otherwise would not occur in the landscape (see also Frascaroli et al., 2016). As with the cerritos, we found that through biocultural processes of niche construction, ancient cultures built permanent landmarks that continue to influence biodiversity patterns. Despite their different origin and location, kurgans have many similar societal functions and consequently similar conservation potential as other sacred sites such as sacred groves (Asia; Bhagwat & Rutte, 2006; Lee et al., 2023), ancient cemeteries (Europe, Asia; Löki et al., 2019), churchyards (Europe; Frascaroli et al., 2016; Zannini et al., 2021), and tombs of local saints (Africa; Deil et al., 2005; Frosch et al., 2016).

We found significant variations in the species richness and cover of specialist and generalist species in the three countries. The variations were most probably related to the intensity of human presence in and near the mounds. However, even in the Hungarian kurgans where the area of the built cultural objects was the highest, they reached considerable proportions. In general, our results suggested that kurgans, which are culturally important for the local communities, have the potential to act as safe havens for grassland-related species in transformed, densely populated landscapes. This is an essential function, as natural habitats are especially rare in these landscapes. Thus, grassland habitat islands preserved by the kurgans have a high importance in maintaining landscape-scale biodiversity (Deák et al., 2020).

Mowing is an effective way to maintain dry grassland habitats (Tälle et al., 2016) since it hinders the encroachment of woody and weedy species by reducing the amount of litter and thus provides open micro-habitats for the establishment of grassland-related species. Furthermore, the mowing also reduces inter- and intraspecific competition within the habitat, which supports the maintenance of grassland species with low competitive ability (Tälle et al., 2016). We found that extensive mowing is a practice that maintains a synergy between cultural and natural values. The importance of management related to cultural values was most evident in those kurgans, where mowing only occurred near objects (such as a crucifix or religious building). In these scenarios, grassland species were often restricted to the managed areas, whilst other parts of the kurgans were affected by the encroachment of woody species. Grassland management for aesthetic reasons is often beneficial also for the biodiversity of other types of sacred sites, such as old cemeteries (Löki et al., 2019; Skobel et al., 2023) and churchyards (Frascaroli et al., 2016; Zannini et al., 2021). At a larger scale, similar patterns were observed in sacred forests and sacred mountains in Asia and Africa (Bhagwat & Rutte, 2006; Lee et al., 2023; Dudley et al., 2009), where due to religious regulations and taboos, local populations use the sites sustainably and extensively aiming to maintain their religious functions and ecosystem services.

Interestingly, only Kamenita umka lacked any kind of maintenance management despite being a locally protected landmark, although it has no functioning cultural objects. Consequently, the kurgan was prone to litter accumulation, increasing the risk of unprescribed fire events that could spread from the neighbouring fallows. Both increasing litter and fire had negative effects on the natural values of the kurgan, leading to the disappearance of several important grassland species, such as the protected Bassia laniflora, Centaurea scabiosa subsp. sadleriana, Hypericum elegans, Ranunculus illyricus, Salvia austriaca, and Taraxacum serotinum, and other rare species such as Allium flavum, Astragalus onobrychis, Plantago media, and Viola suavis (Vida & Kovačev, 2011) that were not detected during our field survey. This suggests that formal protection of a particular site cannot necessarily substitute the protection by cultural recognition. In the case of kurgans and other biocultural hotspots, besides providing protected status, it is also essential to maintain the cultural connection of the site with local communities.

Although human activities related to maintaining the cultural functions of the mounds can have a marked positive effect on the vegetation, we also found necessary trade-offs. Built objects decreased the grassland cover area, and several weedy and invasive species could establish and spread near them. Visitors also probably contribute to weed encroachment on some of the studied mounds by trampling and unintended seed dispersal on clothing and shoes (Lukács et al., 2024), which all support the establishment of unwanted species, as was formerly described on Ukrainian mounds (Sudnik-Wójcikowska et al., 2011).

As reported for old cemeteries in Hungary and Transylvania (Molnár & Löki, 2018), and Albania (Molnár et al., 2017), the use of modern materials such as concrete and the expansion of built areas of sites related to cultural functions can considerably decrease the area that can potentially be occupied by grassland species (see also the review of Löki et al., 2019). Although ‘renovation’ of old graves by the complete elimination of the original vegetation around the graves, establishment of concrete sidewalks around the graves, and staircases on the slope of the mound might produce a tidier appearance (in a modern sense), it interrupts the millennia-old human-nature relationship. It leads to the erosion of the natural values of the kurgans (see Molnár & Löki, 2018). Traditionally, in many old cemeteries, graves were marked by wooden grave markers and they are covered by semi-natural vegetation, still holding many rare and protected species. However, wooden grave markers were replaced by concrete, and graves were covered by concrete, leading to the disappearance of traditional cultural values and biodiversity. Decreasing the area of natural surfaces can be problematic because grasslands on the kurgans are highly isolated. Areas that can be occupied by grassland species are crucial for the long-term maintenance of small populations, which will collapse under a certain threshold (Jacquemyn et al., 2010).

Ornamental landscaping using herbaceous and woody species has a long history and is widely used in European sacred sites (Löki et al., 2019; Skobel et al., 2023). As our results show, planted ornamental plants on kurgans were mostly woody species not native to that particular region (Syringa vulgaris, Sophora japonica, Thuja orientalis, Ulmus pumila), and some of them were invasives, such as the black locust (Robinia pseudoacacia). Over time, these species can spread on the kurgans, suppressing the remnant grassland vegetation (Deák et al., 2020). However, in some instances, planting can support conservation issues. For example, on the Kálvária-domb (Hungary), we found a red-listed forest steppe dwarf shrub species (Amygdalus nana; see also Deák et al., 2023b) planted on the graves.

Conclusions and Prospects

Our case studies revealed that kurgans act as cultural hotspots in transformed landscapes and hold many cultural layers and time dimensions. The extensive land use and management connected to the cultural functions of the kurgans could contribute to the preservation of grassland habitat on the mounds. Thus, cultural and natural values are in synergy. We argue that preserving the material and intangible cultural values connected to the mounds can also support the conservation of natural values. Being iconic landscape elements with long histories, kurgans play an essential role in the life of local societies, as evidenced by legends and literature. As was proven in the case of other sacred sites, sacredness seems to have an essential protective function in the case of kurgans. However, further studies are needed to explore this phenomenon mainly because related research has focused chiefly on India, Africa, and circum-Mediterranean parts of Europe (see Dudley et al., 2009; Zannini et al., 2021) at the expense of temperate Eurasian regions.

Since, in many cases, local populations respect the historical heritage and cultural values confined to mounds, the remnants of natural habitats have a higher chance for preservation in these sites due to the governing power of taboos and community norms. Such a ‘bottom-up’ approach can be even more effective than legislative restrictions. As human-driven mechanisms sustaining natural values on kurgans can be generalised in many societies, our results from Central European mounds can be upscaled to more significant geographic regions that have mounds (such as Eurasia and North and South America), and can contribute to understanding the mechanisms present in other biocultural hotspots.

Although there is wide awareness related to cultural and natural values of kurgans, in many landscapes they are still at a high risk due to land use intensification, infrastructure developments, and inadequate or no management. Another potential risk is the ‘modernisation’ of existing or establishment of new cultural objects on the mounds as they can lead to the loss of areas that are key for grassland species and/or change traditional land use systems. For preserving the valuable biocultural systems of the kurgans, it is essential to focus efforts on the maintenance and documentation of the already existing, traditional cultural functions of these sacred sites. Furthermore, exploring the biocultural values associated with the kurgans is essential to support the traditional, nature-friendly cultural functions and the awareness of local societies of the values of these sites. Our results suggest that synergistic preservation of sacred sites' cultural and natural values can contribute to the maintenance of small self-sustaining natural islands even in intensively used landscapes. These habitat islands can sustain high biodiversity and complement protected areas' networks as stepping stones or green corridors.