Introduction

Dry and semi-dry perennial grasslands on calcareous bedrock are habitats with unique flora and fauna listed in Annex I of the EU Habitats Directive (92/43/EEC). Rupicolous Pannonic grasslands (Stipo-Festucetalia pallentis, habitat 6190), semi-natural dry grasslands and scrub on calcareous substrates (Festuco-Brometalia, habitat 6210), and sub-Pannonic steppic grasslands (habitat 6240) are classified as vulnerable in the European Red List of Habitats (Janssen et al. 2016).

These habitats are characterized by xerothermophilous species adapted to drought, such as deep root system, reduced surface-to-volume ratio, tough leaves, wax layer, and rosette or shrubby growth forms (Pott 1996; Bylebyl 2007). Dry calcareous grasslands in Central Europe host a remarkable number of Mediterranean (xerothermophilous) and Sarmat-Pontic (xerophytic) species, adapted to summer heat and drought or year-round drought in the continental climate of the Eastern European steppes (Bylebyl 2007). These species, partly remnants of the late Pleistocen steppes (Chytrý et al. 2022) are vulnerable to environmental changes and can be outcompeted by taller, fast-growing species in richer, moister conditions. It is considered that even the driest grasslands in Central Europe are part of forest-steppe habitats under recent climatic conditions (Erdős et al. 2018; Chytrý et al. 2022) and the recent distribution of xerothermophilous species in Europe is largely due to historical and climatic changes, especially during the Quaternary period. Since the Neolithic era, the original small-scale habitats of xerothermophilous species on rocks, shallow soils and edges have expanded mainly due to human activity – grazing, deforestation, burning and felling (Pott 1996; Poschlod and Bonn 1998; Dúbravková and Hajnalová 2012). Intensive and diverse human activity has in the past increased not only the size but also the species richness of dry grassland habitats (Poschlod and Bonn 1998; Poschlod and WallisDeVries 2002), so we currently rank them among the habitats with the highest species diversity (Peet et al. 1983; Willems et al. 1993; Korneck et al. 1998; Dengler 2005; Barańska et al. 2010; Hájková et al. 2011). The high species richness in these habitats reflects a species pool from Pleistocene herbivore-structured environments, which was preserved by the introduction of prehistoric agriculture after the extinction of Pleistocene megafauna (Eriksson 2021).

The largest expansion of dry grassland habitats in Central Europe occurred between the fifteenth and twentieth centuries, especially after the end of three-field farming and the introduction of transhumant shepherding, in which large herds of animals were moved over a radius of more than 100 km for grazing in different regions throughout the year (Hornberger 1959; Ellenberg 1996; Poschlod and WallisDeVries 2002). Recent substantial and widespread reductions in the extent and quality of dry grassland habitats have been caused primarily by agricultural intensification, abandonment of traditional pastoralism, and the subsequent spread of scrub and woodland (Poschlod and Schumacher 1998; Poschlod and WallisDeVries 2002; Wallis de Vries et al. 2002; Janssen et al. 2016; Eriksson 2021). The remaining habitats are heavily fragmented and individual species populations are at risk of extinction, genetic drift, or hybrid depression due to disrupted ecological links between isolated populations (Fischer and Stöcklin 1997).

At present, much attention is paid to the protection and restoration of dry grassland communities. Maintaining traditionally managed agricultural landscapes is of paramount importance to prevent species loss (Eriksson 2021). The traditional management of dry grassland sites used at the area for centuries until the late 1950′s is not applicable in the conditions and human lifestyle of the twenty-first century. Therefore, alternative management methods are being sought to ensure dry grassland conservation and restoration that would mimic traditional practices but be less costly and time-consuming and easily organizable in recent conditions (Bylebyl 2007; Schröder et al. 2008). In the best case it should be integrated into a farming system. A promising approach to dry grassland restoration and maintenance has been implemented in the Hainburger Berge Mountains within the NATURA 2000 Hundsheimer Berge reserve since the 1980′s and is still in operation till the present days.

Historically, the local grasslands were primarily used for sheep grazing in the 18th and early 19th century, with pastures located on mountains, as well as in wet areas near rivers and villages. The sheep were traditionally grazed in large flocks continually moving around the pastures in whole area and guided by a skilled shepheard. Cattle gradually replaced sheep until grazing ended in the 1960′s when local farmers switched to pig breeding. All flat-area pastures were then converted to arable land. In the 1970′s and 1980′s, the Hainburger Berge were studied intensively by botanists and zoologists, and the results confirmed a unique biodiversity in the area and its high importance for nature conservation purposes. A study by Waitzbauer (1990) proposed a new grazing schedule according to a complex set of rules and a conservation grazing scheme. This grazing scheme has been initiated and realized by Elisabeth and Erich Zillner since 1983 after a lengthy period of grassland abandonment. It has been thoroughly applied long-term until the present. In general, the dry grasslands are now used as summer pastures. A small sheep flock grazes the parcels devided into smaller fenced sections for one or two days per a period from May to October, with rotation of grazing time.

In 2018, we investigated the grasslands in the Hainburger Berge Mountains as part of a supra-national Carpathian study (Janišová et al. 2021a) with the aim of evaluating the plant diversity at selected sites. We resampled phytosociological relevés that were originally recorded in 2007 (Dúbravková et al. 2010b), to compare the recent vegetation relevés (2018) with original relevés (2007) from the same sites. We also used older (historical) relevés recorded between 1930 and 2001 to indicate if changes between only two consecutive samplings could already be interpreted as trends. The results of our analyses, along with a discussion of the effectiveness of recent dry grassland management, are presented in this study. The aims of this study are to i) evaluate the plant diversity and conservation status at various spatial scales and its relation with grassland management, particularly grazing intensity; ii) detect temporal trends in vegetation composition and identify the driving factors using resampled (2018), original (2007) and historical phytosociological relevés (1930–2001); iii) summarise the land-use history of the recently sampled sites; iv) outline the limits and constraints of farming and present-future perspectives for maintaining dry grassland biodiversity in protected areas.

Methods

Study area

The Hainburger Berge Mountains are the southernmost part of the Devín Carpathians and the only Austrian part of the Carpathian Mountains. The mountain range covering only 36 km2 comprises three hills – the Hundsheimer Berg (480 m a.s.l.), Braunsberg (346 m a.s.l.), and Spitzerberg (302 m a.s.l.). The location on a crossroads of migration routes on the border of the Alps, the Carpathians and the Pannonian Basin, a stable, dry and mild climate (Hainburg: 10.2 °C mean annual temperature, 616 mm annual precipitation, retrieved in July 2023; https://chelsa-climate.org/climate-diagrams/; Karger et al. 2017 and 2018), and thousands of years of human activity have led to an enormous diversity of flora and fauna, including rare plant species and over 1315 butterfly and moth species (Pokorny and Strudl 1986; Waitzbauer 1990; Niklfeld and Schratt-Ehrendorfer 1999; Englisch and Jakubowsky 2001; Rötzer 2009; Schratt-Ehrendorfer et al. 2022). In 1965 Braunsberg and Hundsheimer Berg were declared nature reserves with Spitzerberg following in 1981. In 1989 the European Council listed the three sites as biogenetic reserves. The whole area became a NATURA 2000 reserve named Hundsheimer Berge, which contains ten habitats and six species of European importance occurring on the territory of 2140 ha (Rötzer 2009).

Sampling of plant diversity and site factors

Plant diversity was sampled by selecting six grassland plots using a stratified random plot selection (Janišová et al. 2021a). The stratification was based on terrain configuration and topography as land-use type is often determined by these factors. To maximize investigated variability in vegetation composition, six nested plot series were studied, two in a flat area, one on a moderate slope with aspect of the nothern hemicycle (W-N-E), one on a steep W-N-E slope, one on a moderate slope with aspect of the southern hemicycle (E-S-W), and one on a steep E-S-W slope (Table 2, Fig. 3). The six nested plots are designated by discontinuous field numbering (H2, H5, H6, H8, H11 and H13). During fieldwork, the location of predetermined coordinates was identified, and the vegetation was checked for homogeneity before establishing nested plot series. The nested plots covered seven spatial scales (0.0001 m2, 0.001 m2, 0.01 m2, 0.1 m2, 1 m2, 10 m2, 100 m2). In the 10-m2 plots, the shoot presence and visually estimated percentage cover of all species of vascular plants, bryophytes, and lichens were recorded. Simultaneously, environmental data were obtained on topography and soil: altitude (m a.s.l.), inclination (°), soil depth (measured on each plot at five random points with a steel rod of 1 cm diameter); cover of stones and rocks (particle size diameter > 63 mm), cover of gravel (particle size diameter 2–63 mm; Janišová et al. 2021a). A mixed soil sample of the uppermost 10 cm of the mineral soil was taken from five random locations. Air-dried soil samples were analysed in the lab for the following soil parameters: pH (measured in KCl), accessible phosphorus (P), potassium (K) and magnesium (Mg) content in mg/kg, and calcium (Ca), organic carbon (C), and total nitrogen (N) content in g/kg (Appendix 2). Soil humus content was calculated from the organic carbon content. The C/N ratio was calculated as a surrogate of soil accessible nutrients. Height of the herb layer was measured at five points – in the middle of the edges and in the plot centre (Appendix 2). Percentage covers of herb, cryptogam, and litter layers were estimated (Table 3; Appendix 2).

Vegetation resampling and historical relevés

To assess changes in vegetation composition and environmental conditions over the 11-year period, we resampled three vegetation plots of rupicouls pannonic grasslands (habitat 6190) and sub-Pannonic steppic grasslands (habitat 6240) representing three different communities (Poo badensis-Festucetum pallentis, Festuco pallentis-Caricetum humilis and Festuco valesiacae-Stipetum capillatae). The size of the resampled plots was 25 m2, which was the same as the size used during the original sampling in 2007 (Dúbravková et al. 2010b).

We also used historical relevés from the Hainburger Berge (Hundsheimer Berg, Braunsberg, Hainburg and its close suroundings) sampled between 1930 and 2001 obtained from the Austrian Vegetation Database (https://www.givd.info/ID/EU-AT-001) to indicate if changes between only two consecutive samplings could already be interpreted as trends. Only relevés recorded at plot sizes between 5 and 100 m2 were included in the analyses (36 relevés in total, including the original relevés from the resampled plots). The used historical relevés came from these sources: Klika (1931), Wagner (1941), Knapp (1944), Niklfeld (1964), Tracey (1980, unpublished), Waitzbauer (1990), Chytrý et al. (1997) and Willner et al. (2004). After the addition of resampled relevés and nested plot series recorded in 2018, the dataset contained 45 samples.

Land use history

To obtain a comprehensive understanding of vegetation development, we made efforts to gather all available information on the land use history of the plots. We compiled data from literature sources and personally interviewed farmers who are currently operating at the study sites. To facilitate comprehension and enable easy comparisons, we categorized the land use information for the plots into three time periods: before 1950, 1950–1990, and 2018.

Data analysis

The detrended correspondence analysis (DCA) was used to project the sampling plots on a background of available historical vegetation relevés from the study region. Bryophyte and lichen species were omitted in the DCA as not all historical relevés contained information on the cryptogam layer composition. Non-weighted averages of Borhidi indicator values (BIV) for light, temperature, continentality, soil reaction, moisture, and nutrients (Borhidi 1995) were calculated for each relevé. Together with altitude, slope inclination, and sampling year, the BIV were post-hoc correlated with the first two DCA ordination axes to refine their interpretation.

Nomenclature, syntaxonomy and red list categorisation

Vascular plant nomenclature was unified according to Euro + Med Plantbase (Euro+Med 2006) and the bryophyte nomenclature according to Hill et al. (2006). Syntaxonomical classification concept and nomenclature of grassland syntaxa follow Dúbravková et al. (2010a). We used an expert system for classification of relevés to higher vegetation units (Hegedüšová Vantarová and Škodová, 2014). Red list categories of endangered species follow Schratt-Ehrendorfer et al. (2022) for vascular plants and Grims and Köckinger (1999) for bryophytes.

Results

Grassland variability and species richness

The random nested plots selected, stratified by slope, aspect and inclination, covered a range of grassland types with varying levels of moisture and nutrient availability (as shown in Fig. 1a, Fig. 2; Table 1; Appendix 1). The first DCA axis primarily explained the variability of studied vegetation due to the increase of moisture and nutrient levels, combined with decreasing soil reaction. The second DCA axis was most closely correlated with increasing light availability (Fig. 1a).

Fig. 1
figure 1

a) DCA ordination graph of historical and recent relevés from Hainburg and surroundings (total inertia 5.9, eigenvalues: 1st axis 0.59, 2nd axis 0.27). The red arrows above the graphs represent passively correlated environmental variables and Borhidi indicator values calculated as non-weighted averages for individual relevés. b) Phytosociological affiliation of the sampled vegetation. Species richness of vascular plants is indicated by symbol size, recent relevés sampled in 2018 are shown by coloured symbols with black outline

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Fig. 2
figure 2

DCA ordination graph of historical and recent relevés of a narrow selection from the Hundsheimer Berg (total inertia 3.5, eigenvalues: 1st axis 0.49, 2nd axis 0.26). The red arrows above the graphs represent passively correlated environmental variables and Borhidi indicator values calculated as non-weighted averages for individual relevés. The green italic numbers show the sampling year

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Table 1 Floristic composition of the recently studied sampling plots (H2-H13), original plots (Dúbravková et al. 2010b) and resampled plots. Full compositional data for the nested plot series are presented in Appendix 1
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The six randomly located nested plot series included rocky, xeric and mesic grasslands, which are the primary types found in the region. Phytosociologically, the grasslands were classified into two classes: Festuco-Brometea (including rocky grasslands in plots H5 and H6; and xeric grasslands in plots H8 and H11) and Molinio-Arrhenatheretea (including mesic grasslands in plots H2 and H13). The vegetation classification of the individual plots to associations and higher vegetation units is given in Table 2 and Fig. 1b.

Table 2 Header data to the relevés included in Table 1. The authors′ initials: DD – D. Dúbravková, KD – K. Devánová, KH – K. Hegedüšová, MJ – M. Janišová, MM – M. Magnes
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The average species richness in the 10 m2 plots (H2–H13) was 41 vascular plants (ranging from 16 to 60) and 6 cryptogam species (ranging from 4 to 13; Table 3; Fig. 1b). The richest in species were the xeric steppe grasslands on deeper soils belonging to the Festuco valesiacae-Stipetum capillatae association (Festucion valesiacae alliance): plot H11 hosted the highest number of vascular plant species (60), and plot H8 had the highest number of bryophyte species (12). The primary open rocky steppe (plot H5) of the Poo badensis-Festucetum pallentis association (Bromo pannonici-Festucion pallentis alliance) was the poorest in species, with only 16 vascular plants, three bryophytes, and one lichen species (Fig. 3).

Table 3 Plant diversity parameters and representation of endangered species. Species richness of vascular plants, bryophytes, and lichens are compared with the mean values of the respective grassland categories (European grasslands of the temperate mid-latitudes; xeric and rocky grasslands of Festuco-Brometea, and mesic grasslands of Molinio-Arrhenatheretea) in the GrassPlot database (Biurrun et al. 2021). The bold font depicts values above the average of the respective category. Red list categories of vascular plants are according to Schratt-Ehrendorfer et al. (2022), those of bryophytes follow Grims and Köckinger (1999). Numbers of endangered species in nested plot series are shown for two plot sizes, 10 and 100 m2 (in parentheses)
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Fig. 3
figure 3

Nested plot series in the Hainburger Berge Mountains, May 2018 (plot numbers in the left lower corner). Photos: M. Janišová

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Total species richness at seven different spatial scales of the nested plot series is presented in Fig. 4. Grazed plots (H2, H6, H8) were the richest at the smallest scales, while at the largest scales the plots belonging to the Festucion valesiacae alliance (H8, H11) were richest in species. Plots recorded in the rocky steppes of the Bromo-Festucion pallentis were the poorest at all spatial scales.

Fig. 4
figure 4

Increase in total species number (incl. vascular plants, bryophytes and lichens) in six nested-plot series across seven spatial scales (from 0.0001 m2 to 100 m2) and its relation to the applied management practices. The series are ordered by decreasing species richness

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To compare the plant diversity of the sampled plots with similar grasslands in temperate Europe, we used the GrassPlot Diversity Explorer (Biurrun et al. 2021, https://edgg.org/databases/GrasslandDiversityExplorer). At a 10 m2 scale, all plots except plot H5 had a higher number of vascular plants than the average for their respective grassland category (Table 3). Plots H2, H8, H11, and H13 also had more bryophyte species than the category average, while plot H8 had more lichen species as well. Notably, the highest richness values were recorded in plot H11 for vascular plants (60 species) and in plot H8 for bryophytes (12 species), which come close to the maximum values reported for xeric grasslands and steppes of the Festuco-Brometea class in temperate Europe (63 species of vascular plants and 16 species of bryophytes). Xeric steppes of the Festucion valesiacae alliance (H8, H11) displayed the highest species richness among the surveyed grasslands at both 10 m2 and 100 m2 scales.

Representation of endangered species

Out of 148 vascular plants recorded in the 10 m2 plots, one species (Astragalus vesicarius subsp. vesicarius) was critically endangered, six species (Bromus squarrosus, Leopoldia tenuiflora, Ranunculus illyricus, Papaver dubium subsp. confine, Saxifraga bulbifera, and Tephroseris integrifolia) were endangered, 32 were vulnerable, and 30 were near threatened species (see Table 1 for details). In 100 m2 plots, one endangered species (Echinops ritro subsp. ruthenicus), and two vulnerable species (Ornithogalum orthophyllum subsp. kochii and Rosa spinosissima) were recorded additionally (Appendix 1).

Out of 25 bryophyte species (Table 1), one species (Rhynchostegium megapolitanum) was classified as eradicated, extinct, or lost, one was endangered (Pleurochaete squarrosa), and one was potentially endangered (Pseudocrossidium hornschuchianum).

Xeric grasslands of Festucion valesiacae (H8, H11) were richest in endangered species, containing 18 and 19 species from some of the three higher red list categories (CR, EN, VU), respectively (Table 3). The proportion of endangered species in the total number of occurring vascular plants in the 10 m2 plots was higher than 30% in both plots (33.3% in H8 and 31.7% in H11). When the plot size was increased to 100 m2, these plots contained 20 and 25 species of endangered vascular plant species, respectively (Table 3).

Rocky grasslands (H5, H6) contained four and fourteen endangered species, forming 25% and 33% of the total number of vascular plants, respectively. Mesic grasslands (H2, H13) contained the least number of endangered species (two and five), and their proportion did not exceed 13% (see Table 3 for details). The representation of endangered bryophytes did not differ between xeric, rocky, and mesic grasslands; in each of the plots, one endangered species was present. There were no endangered lichen species recorded in the nested plots.

Temporal changes in dry grassland communites

The drivers of changes in the grassland vegetation over time were estimated by analyzing the correlation between the sampling year and Borhidi indicator values derived from species composition. The results for the entire area of the Hainburger Berge Mountains (Fig. 1a) showed that the sampling year was positively correlated with nutrients BIV (0.562) and moisture BIV (0.425), and negatively correlated with soil reaction BIV (-0.440), temperature BIV (-0.428), light BIV (-0.321), and continentality BIV (-0.299).

Examining the relevé selection from the Hundsheimer Berg only (Fig. 2), similar results were found. The sampling year showed a positive correlation with nutrients BIV (0.568) and moisture BIV (0.423), and a negative correlation with temperature BIV (-0.468), soil reaction BIV (-0.375), light BIV (-0.322), and continentality BIV (-0.304).

The temporal changes in xeric (plot 15) and rocky grassland (plots14 and 16) communites observed on the resampled plots are summarized below.

Hundsheimer Berg, 15/07 vs. 15/18 (Festuco valesiacae-Stipetum capillatae, Appendix 4)

As indicated by the DCA (Fig. 1a and Fig. 2) and Borhidi indicator values (Table 2) there was slight temporal shift of the community floristic composition in the environmental space (slight shift along the 2nd ordination axis, slight increase of all BIVs except continentality BIV, which remained similar). The herb layer cover increased from 70 to 90% probably due to increase in Festuca stricta subsp. sulcata cover from + to 2a (Braun-Blanquet scale), F. valesiaca from 2a to 3, Bromopsis erecta from + to 3, and Potentilla incana from + to 2a. The increase in grass cover might have resulted from the decrease in grazing intensity. The number of vascular plants increased from 35 to 48 and the number of endangered species increased by one endangered, two vulnerable and five near threatened species (Table 3).

In 2018 the following additional species we found in comparison with 2007 (endangered species indicated in bold, cover values in the Braun-Blanquet scale in the parentheses):

E1: Bromus hordeaceus ( +), Carduus nutans ( +), Camelina microcarpa ( +), Medicago falcata (1), EN Ranunculus illyricus (r), Taraxacum sect. Erythrosoperma ( +), Thymus pannonicus ( +), T. praecox ( +), VU Trinia glauca (1), and many therophytes and early spring species, which could have been invisible in the end of June 2007 and thus were not reported: Arabis auriculata ( +), Cerastium glutinosum ( +), VU Cruciata pedemontana ( +), Holosteum umbellatum (r), Muscari neglectum ( +), Myosotis stricta ( +), EN Saxifraga bulbifera (r), S. tridactylites (r), Thlaspi perfoliatum ( +).

E0: Barbula convoluta (R), Bryum argenteum (R), Bryum caespiticium (R), Syntrichia ruralis (R).

The following species were missing in 2018 (in comparison with 2007):

E1: Bothriochloa ischaemum ( +), Cuscuta epithymum ( +), Echium vulgare ( +), Sedum sexangulare ( +), VU Veronica praecox (r).

E0: Ceratodon purpureus ( +).

Hundsheimer Berg, 14/07 vs. 14/18 (Festuco pallentis-Caricetum humilis, Fig. 5)

Fig. 5
figure 5

Plot 14 on the Hundsheimer Berg (above) and plot 16 on the Braunsberg (below) in 2007 and 2018. Photos: D. Dúbravková and M. Janišová

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As indicated by the DCA (Fig. 1a and Fig. 2) and Borhidi indicator values (Table 2) there was slight temporal shift of the community floristic composition in the environmental space (slight shift mainly along the 1st ordination axis, increase of all BIVs except light BIV, which decreased, indicating successional development). Cover of cryptogams decreased from 20 to 5% (maybe due to a longer dry period in spring 2018). The number of vascular plants increased from 39 to 45 and the number of endangered species increased by one vulnerable and three near threatened species (Table 3).

In 2018 the following additional species we found (in comparison with 2007):

E1: Achillea collina (2 m), Alyssum alyssoides ( +), Anthriscus cerefolium (r), Eryngium campestre ( +), VU Erysimum odoratum ( +), Fumana procumbens ( +), VU Helictochloa pratensis (1), VU Hesperis tristis (r), VU Inula ensifolia ( +), VU Minuartia rubra ( +), Orobanche teucrii ( +), Poa angustifolia ( +), Scabiosa ochroleuca ( +), VU Seseli osseum ( +), Teucrium chamaedrys (1).

The following species were missing in 2018 (in comparison with 2007):

E1: Carduus nutans ( +), Echium vulgare ( +), VU Erysimum diffusum (R), Festuca stricta subsp. sulcate ( +), Genista pilosa ( +), VU Orlaya grandiflora ( +), VU Ornithogalum pannonicum ( +), VU Seseli hippomarathrum ( +), VU Veronica spicata ( +).

E0: Bryum caespiticium (2a), Syntrichia ruralis (2a), Cladonia symphycarpa ( +).

Braunsberg, 16/07 vs. 16/18 (Poo badensis-Festucetum pallentis, Fig. 5)

In this resampled plot the temporal changes in floristic composition were more pronounced although only slight shift was indicated in the environmental space (along the 2nd DCA ordination axis; Fig. 1a). However, changes of the Borhidi indicator values (Table 2) were more significant and had different direction as in the two former plots (increase of light, temperature, continentality and soil reaction BIVs and simultaneous decrease in nutrient and moisture BIVs). The number of vascular plants decreased from 44 to 33 (23 species were confirmed, 21 species were missing and 10 species new-appered in 2018 compared to 2007). Many habitat specialists disappeared including not only the ephemeral taxa. The number of endangered species decreased by one vulnerable and five near threatened species (Table 3). The cover of herb layer decreased from 55 to 40% and cover of cryptogam layer decreased from 20 to 10%. The changes indicate possible shift to species poorer grassland of draught-resistant species and slight ruderalisation (Table 1). A possible explanation is the increased whole year grazing preasure by the local wild sheep flock (Appendix 6b).

In 2018 the following additional species we found:

E1: EN Campanula sibirica (r), Carduus nutans (r), Descurainia sophia (r), Draba verna agg. ( +), VU Euphorbia segueriana ( +), Festuca pallens (1), Hornungia petraea ( +), VU Inula ensifolia ( +), Medicago minima (r), Thymus praecox ( +).

E0: (3) Pleurochaete squarrosa (2a).

The following species were missing (in comparison with 2007):

E1: Allium flavum ( +), Anthyllis vulneraria (r), Arabis hirsuta ( +), Asperula cynanchica ( +), VU Dianthus praecox subsp. lumnitzeri ( +), VU Dictamnus albus ( +), Echium vulgare ( +), Fumana procumbens ( +), Linum tenuifolium ( +), VU Minuartia rubra (r), Odontites vulgaris ( +), Peucedanum oreoselinum ( +), Rhamnus cathartica ( +), Rhodax canus ( +), Salvia nemorosa ( +), Scabiosa ochroleuca (r), VU Scorzonera austriaca ( +), Sedum acre ( +), S. album ( +), Stachys recta ( +), Stipa capillata ( +).

E0: Aspicilia sp. ( +), Tortella inclinata (1), (3) Weissia condensa ( +).

Recent vs. historical management

According to historical sources, literature, and interviews with farmers (see Appendix 3 for details), the management of grasslands in the Hainburger Berge Mountains has undergone significant changes in last 100 years. In the past, all non-ploughed parcels that were historically used as pastures were abandoned for a period of at least 30 years between 1950 and 1990 (Fig. 4). While grazing was later reintroduced to most sampled parcels, it is no longer carried out in the traditional manner. Instead of grazing cow herds and sheep flocks guided by shepherds, grazing in enclosures was introduced for sheep on Hundsheimer Berg (plots H5, H6, H8, 14/18, 15/18), and for horses on Braunsberg (H2). Additionally, wild sheep graze freely now on Braunsberg (H11, 16/18). Details on the historical and recent management for all sampled plots are provided in Appendix 3.

Discussion

Grassland variability and species richness

Our results confirmed that the grassland vegetation in the Hainburger Berge Mountains has a high conservation status, relating to both species diversity and the presence of endangered species. The study used six randomly located nested plot series to gain insights into the variability and plant diversity of local grasslands. These plots included xeric, rocky, and mesic grasslands, which are the primary types found in the region. Comparing the sampled plots with similar grasslands in temperate Europe, all investigated plots except H5 displayed higher than average species richness at 10 m2. The maximum recorded richness values were recorded in xeric steppes of the Festucion valesiacae alliance: 60 species of vascular plants in plot H11 and 12 species of bryophytes in plot H8. These values come close to the maximum values reported for xeric grasslands and steppes of the Festuco-Brometea class in temperate Europe (63 species of vascular plants and 16 species of bryophytes; Biurrun et al. 2021, https://edgg.org/databases/GrasslandDiversityExplorer).

The abundant species diversity in these steppe grasslands, situated on calcareous bedrock, is primarily attributed to a large “species pool”, which is significantly greater for alkaline substrates compared to acidic ones in glaciated regions of Europe (Pärtel 2002; Ewald 2003). Although actual calcicolous species are in the minority (Pfadenhauer and Klötzli 2014), other factors like stressors (such as nutrient scarcity, drought, grazing, and various disturbances) also contribute positively to maintaining a diverse community of stress-tolerant species and preventing the dominance of highly competitive species (Grime 1979; Kiehl 2008).

Species composition at different spatial scales, as deduced from the nested plot series, demonstrated a positive effect of summer grazing on species richness. Grazing management led to increased species diversity at the smallest spatial scales across various vegetation types. The highest number of species was observed in plots with intensive grazing within three different vegetation alliances: Cynosurion cristati (plot H2), Festucion valesiacae (H8), and Bromo-Festucion (H6). This finding suggests the high importance of animals for species distribution.

Primary open rocky steppe of the Bromo-Festucion pallentis alliance (plot H5), had the lowest species richness at all spatial scales. Currently, the plot is either unused or used as a low-intensity goat pasture (see Appendix 6a), where even grazing-induced disturbances do not significantly contribute to an increase in species richness at smaller scales. This is likely due to the sparse vegetation density caused by the harsh conditions of rocky habitat. The similarity of the compositional data with historical plots from the time of traditional pasturing suggests the presence of primary steppe cores. Despite the relatively extensive recent management, there is little evidence of succession towards higher-growing vegetation.

Representation of endangered species

Endangered species with varying levels of endangerment are abundantly represented in the grasslands of the Hainburger Berge Mountains. Many of these species are bound to warm and dry climate regions of Lower Austria, which hosts some of the most xerothermophilous plant communities in Austria. Out of the Natura 2000 habiats, the 6240 Sub-Pannonic steppic grasslands (Festucion valesiacae) were confirmed to be richest in endangered species, which is valid both for their counts and proportions in total species numbers. The richest plots of Hundsheimer Berg (H8) and Braunsberg (H11) contained more than 30% of endangered species, in both plots. These numbers are surprisingly high, considering that the Hainburger Berge Mountains are categorized as areas with only intermediate numbers of endangered species in Austria (Schratt-Ehrendorfer et al. 2022). Rocky steppes of 6190 Rupicolous Pannonic grasslands (Stipo-Festucetalia pallentis) had moderate numbers and proportions of endangered species. While mesic grasslands habitats (Lowland hay meadows of Arrhenatherion elatioris and Mesophile pastures of Cynosurion cristati) had the lowest representation of endangered species, they still can contain species of significant conservation interest and contribute thus to local plant diversity.

Temporal changes in dry grassland communities

In a context of shifting land-use patterns characterized by periods of strong overgrazing and subsequent abandonment, coupled with the influences of airborne pollution and climate change, it is likely that vegetation changes have occurred. Our analysis revealed that the overall change observed was indicative of continuous successional development spanning several decades, leading to a denser vegetation canopy and reduced light availability, accompanied by increased moisture and nutrient availability. However, changes since 2007, as evidenced by plot resampling, have not been significant and can mostly be attributed to interannual dynamics rather than substantial shifts in species composition or a clear directional trend. We assume that the continuation of grazing since the late 1980′s, may have contributed positively to the maintenance of the target dry grassland habitats in favorable conditions and is a principal reason for the successional hold during the recent decade (2007–2018).

The most significant changes occurred in the rocky grassland of plot 16, where the number of vascular plant and bryophyte species, as well as the number of endangered vascular plants, decreased. This decline can be attributed to the presence of a flock of wild sheep that has been residing in the area for some time. These sheep use the steep and rocky terrain as a retreat and possibly stay there overnight, which exerts a greater influence on the relatively small area than expected due to the small number of animals.

When comparing recent grassland communities to historical relevés, we observed that the present communities have fewer species typically associated with base-rich substrates and warm, well-lit conditions (e.g. Allium flavum, Teucrium montanum) while they contain a greater number of species that thrive also in moister and nutrient-richer environments (e.g. Achillea collina, Bromopsis erecta). Interestingly, we did not observe any spread of Arrhenatherum elatius, a competitively strong grass commonly found in mesic meadows, as has been reported from both calcareous and acidic dry grasslands in Central Europe (Dostálek and Frantík 2008, 2012; Harásek et al. 2022).

The decline of weakly competitive dry grassland specialists, and increase of competitive generalists has been documented in numerous studies for over two decades (e.g., Fischer and Stöcklin 1997; Newton et al. 2012; Hülber et al. 2017; Harásek et al. 2022; Staude et al. 2022). This suggests a process of homogenization is taking place, with potential long-term implications for the survival of target dry grassland species. The succession and subsequent spread of scrub and woodland, as reported on nearby National Nature Reserve Devínska Kobyla in Slovakia (Hegedüšová and Senko 2011) are not occurring at the study plots due to active grazing management applied at the sites since the late 1980′s. The vegetation homogenization may result from both the accumulation of aerial nitrogen (Bieringer and Sauberer 2001; Maskell et al. 2010) and the insufficient modern way of grazing management, which cannot fully replicate the benefits of traditional pastoralism under which dry grasslands have developed and persisted for ages (Molnár et al. 2016, 2017).

Historical vs. recent grassland management in the studied land parcels

The dry grasslands of the Hainburger Berge Mountains have undergone significant changes in the last 100–200 years in terms of land use and vegetation patterns. The local land use changes were closely related to the supra regional socio-economic changes as a result of the step-by-step processes of intensification of agriculture and later industrialisation of western European countries since the beginning of the twentieth century (Jepsen et al. 2015). Over the past two centuries, the pasture area, number of animals kept and number of people working in agriculture have radicaly declined (Schweickhardt 1832; Waitzbauer 1990; Statistik Austria; Janišová et al. 2021b), which resulted in gradual or abrupt decrease in grazing intensity and large areas of former pastures overgrown by shrubs and trees (Waitzbauer 1990; Bernhardt et al. 2016). The continuity of traditional grassland management was irretrievably stopped. The cessation of any grazing activities in most areas lasted over 30 years. The consequences of radical land-use changes in the study area are described in Bernhardt et al. (2016), and Janišová et al. (2021b). The land use history of the studied land parcels (Appendix 3) revieled many common features. Large areas of sheep and later cattle pastures have shrunk to small patches and lost connectivity. The sheep were traditionally grazed in large flocks, counting hundreds to thousands of animals, continually moving around the pastures in the whole area and guided by skilled shepheards. The historical grazing intensity is documented in old scientific reports (Ptačovský 1959) and historical photos (Steiner 2013; Appendix 5). Overgrazing by sheep flocks in the mid-twentieth century was probably widespread on both sides of the Danube river. It was explicitly described by botanist Klement Ptačovský, as resulting in "bare sites without any vegetation, or only few dry nibbled stalks in some places" (Ptačovský 1959).

Although sheep grazing was reestablished in some areas in the 1980′s, the historical grazing intensity has not been achieved again. The traditional way of grazing at dry grassland sites used at the region for centuries (cow herds and large sheep flocks guided by shepherds) is not applicable in the conditions, property rights and human lifestyle including working thought and the consumer world of the twenty-first century. Therefore, alternative management methods are being sought to ensure dry grassland conservation and restoration that would mimic traditional practices but be less costly and time-consuming and easily organizable in recent conditions (Bylebyl 2007; Schröder et al. 2008). Generally, the dry grasslands in the Hainburger Berge Mountains are now used as summer pastures. Small flock of sheep and some goats graze smaller fenced sections of the parcels in enclosures for one or two days per a period from May to October, with rotation of grazing time (Appendix 7b). As the animals stay in an isolated area for the whole growing season, the grazing does not immitate the ancient practice of transhumant shepherding, in which large herds of animals were moved over a radius of more than 100 km for grazing in different regions throughout the year, that resulted in spreading of grassland species via seeds that were carried in the fur and hoofs of the animals (Hornberger 1959; Ellenberg 1996; Poschlod and WallisDeVries 2002; Janišová et al. 2023). This process played a significant role in the dispersal of typical grassland species for centuries (Diacon-Bolli et al. 2012) however the modern way of grazing cannot serve this function anymore and cannot fully prevent the vegetation homogenisation.

In light of our results, we propose that grazing should be considered as an optimal and crucial management treatment for both xeric and mesic grasslands in the Hainburger Berge Mountains. While rocky grasslands are primarily constrained by their habitat conditions and have lower productivity, controlled disturbances, such as grazing, carried out in a manageable manner, can still have a positive impact on maintaining a diverse community of stress-tolerant species and help prevent the dominance of competitive species (Grime 1979; Kiehl 2008).

Future visions for grassland conservation in protected areas

To preserve the plant and animal diversity in calcareous grasslands, many experts advocate for maintaining a diverse range of land use types and their configurations within the landscape (Maurer et al. 2006; Diacon-Bolli et al. 2012). This can be achieved by either i) involving a greater number of farmers or managers in the management of the grasslands or ii) providing more flexibility to the farmers/managers in terms of when and how they can graze and mow the grasslands depending on weather conditions. Currently, mowing dates are set by public authorities, but allowing for more flexibility could be beneficial. Ideally, subsidy systems should also be based on results achieved, not just methods used, to increase the motivation of farmers and allow for faster adaptation to land use intensity, which is needed in times of climate change and increasing aerial nitrogen intake (Bieringer and Sauberer 2001). However, this strategy requires a deep understanding of the environmental processes that contribute to increased biodiversity (Schüle et al. 2023). Therefore, especially the farmers operating in the protected areas should be greatly supported and educated by nature conservationists and vegetation scientists so that mutual goals can be achieved through cooperation. The most sustainable and practical approach, considering both the national economy and ecology, would be to integrate management practices into the farming system with animals. Recent agropolitical decisions to reduce subsidies for rocky grasslands, as they do not meet pasture requirements, not only hinder the necessary development of sustainable agriculture but also create an unfair competition between agro-industry and traditional farming.