Nature Conservation 39: | 13—132 (2020) AN Nanir “ei re doi: 10.3897/natureconservation.39.52798 RESEARCH ARTICLE SO) "apa Seca http:/ /natureconservation. pen soft.net Launched to accelerate biodiversity conservation Legacies of past land use challenge grassland recovery — An example from dry grasslands on ancient burial mounds Balazs Dedk"’, Orsolya Valké'", Csaba Albert Téth?, Agnes Botos?, Tibor Jézsef Novak* | MTA-OK Lendiilet Seed Ecology Research Group, Institute of Ecology and Botany, Centre for Ecological Research, Alkotmany str. 2-4, H-2163 Vacratét, Hungary 2 University of Debrecen, Faculty of Science and Technology, Institute of Earth Sciences, Department of Physical Geography and Geoinformatics, Egyetem sqr. 1, H-4032 Debrecen, Hungary 3 University of Debrecen, Faculty of Science and Technology, Doctoral School of Earth Sciences, Egyetem sqr. 1, H-4032 Debrecen, Hungary 4 University of Debrecen, Faculty of Science and Technology, Institute of Earth Sciences, Department of Landscape Protection and Environmental Geography, Egyetem sqr. 1, H-4032 Debrecen, Hungary Corresponding author: Orsolya Valk6 (valkoorsi@gmail.com) Academic editor: Stefano Chelli | Received 1 April 2020 | Accepted 12 May 2020 | Published 4 June 2020 http://zoobank.org/AFB2F158-ECC5-41B9-AE73-6091 106D 1 B82 Citation: Deak B, Valké O, Téth CA, Botos A, Novak TJ (2020) Legacies of past land use challenge grassland recovery — An example from dry grasslands on ancient burial mounds Nature Conservation 39: 113-132. https://doi.org/10.3897/ natureconservation.39.52798 Abstract Due to large-scale agricultural intensification, grasslands are often restricted to habitat islands in human- transformed landscapes. There are approximately half a million ancient burial mounds built by nomadic steppic tribes in the Eurasian steppe and forest steppe zones, which act as habitat islands for dry grassland vegetation. Land use intensification, such as arable farming and afforestation by non-native woody spe- cies are amongst the major threats for Eurasian dry grasslands, including grasslands on mounds. After the launch of the Good Agricultural and Environmental Condition framework of the European Union, in Hungary there is a tendency for ceasing crop production and cutting non-native woody plantations, in order to conserve these unique landmarks and restore the historical grassland vegetation on the mounds. In this study, restoration prospects of dry grassland habitats were studied on kurgans formerly covered by croplands and Robinia pseudoacacia plantations. Soil and vegetation characteristics were studied in the * The first two authors contributed equally to the manuscript. Copyright Baldzs Dedk et al. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. 114 Balizs Deak et al. / Nature Conservation 39: 113—132 (2020) spontaneously recovering grasslands. The following questions were addressed: 1; How does site history affect the spontaneous grassland recovery? 2; Do residual soil nutrients play a role in grassland recovery? In former croplands, excess phosphorus, while in former Rodinia plantations, excess nitrogen was present in the soil even four years after the land use change and grassland vegetation was in an early or mid- successional stage both on the mounds. ‘The results showed that, without proper management measures, recovery of grassland vegetation is slow on mounds formerly used as cropland or black locust plantation. However, restoration efforts, focused on the restoration of mounds formerly covered by croplands, can be more effective compared to the restoration of mounds formerly covered by forest plantations. Keywords cropland, grassland restoration, kurgan, nitrogen, phosphorus, Robinia pseudoacacia, soil, steppe Introduction In intensively used agricultural landscapes, the remaining natural and semi-natural habitats often occur on small natural features (SNFs). Many of SNFs, such as verges, field margins and midfield islets are physically inappropriate for agricultural utilisation (Lindborg et al. 2014; Jakobsson et al. 2018; Fekete et al. 2019). Other types of SNFs have religious or cultural importance, which prevented their agricultural utilisation (Dudley et al. 2009; Molnar V. et al. 2017; Loki et al. 2019). Amongst them, ancient burial mounds (also called kurgans) of the Eurasian steppe and forest steppe regions are of particular importance (Sudnik-W6jcikowska et al. 2011; Bede et al. 2015; Bede and Csathé 2019; Deak et al. 2016a, 2019; Dembicz et al. 2018). They are earthen mounds of a few metres height, which were constructed from the topsoil layers of the surround- ing areas by nomadic steppic tribes several millennia ago, mainly for burial purposes (Dembicz et al. 2016; Lisetskii et al. 2016). The estimated number of these mounds is more than 600,000 in Eurasia and they are typical landscape elements from Hungary to Mongolia (Deak et al. 2016a, 2019). A considerable proportion of these mounds still hold grassland vegetation; hence, mounds are valued as being stepping stones or bio- diversity hotspots for grassland specialist plant and animal species even in transformed agricultural landscapes (Bede and Csathé 2019; Toth et al. 2019; Deak et al. 2020). Despite their cultural importance and steep slopes, many of the mounds have been exposed to ploughing and afforestation works in the past centuries (Deak et al. 2016a, b). Restoration of their former vegetation is an important task for nature conservation (Valko et al. 2018). Such restoration projects can increase the habitat area of dry grass- lands, create stepping stones for grassland specialist species and the restored mounds can be used as demonstration sites for environmental education (Valk6 et al. 2018). The Cross-Compliance system of the European Union Common Agricultural Policy is a progressive initiative that contributes to a more environmental-friendly ag- riculture. One of its pillars is the Good Agricultural and Environmental Condition framework, which contributes to the development of a long-term and ecologically sustainable agricultural environment (Brady et al. 2009). As there are more than 1600 Grassland recovery on former croplands and plantations 115 ancient steppic burial mounds in Hungary (Téth 2006), that is why they were se- lected as the landscape elements typical to the country according to the GAEC regu- lations. Due to this, now there is a tendency for the cessation of crop production on the mounds and sometimes also in a surrounding buffer zone (Rakéczi and Barczi 2014; Toth et al. 2018). For reconstructing the original vegetation of these important landscape elements, national park directorates and NGOs are increasingly involved in the restoration of grasslands on mounds (Valk6 et al. 2018). As part of this initiative, black locust plantations have been cut on many mounds in order to reconstruct the historical landscape and increase the landscape value of the mounds. However, due to limited capacity and financial resources, in most of the cases the abovementioned fa- vourable land use changes on mounds (i.e. cessation of crop production and cutting of non-native plantations) were not followed by any other restoration measures; thus the grasslands are recovering spontaneously. Another challenge is the isolated situation of the mounds: most of them are surrounded by arable fields, therefore, post-restoration management by grazing or mowing is particularly challenging (Deak et al. 2020). In grassland restoration, spontaneous recovery became increasingly acknowledged (Prach and Rehounkov4 2008; Tork et al. 201 1a). In many cases, it is the best op- tion, because it is a natural method, it has low costs and if proper propagule sources of target species are present, successful grassland recovery can be expected (Hedberg and Kotowski 2010; Kiehl et al. 2010). Promising examples of spontaneous grassland recovery were reported from many parts of Central and Eastern Europe, such as the Czech Republic (e.g. Prach and Rehounkova 2008; Lencova and Prach 2011, Jirova et al. 2012), Hungary (e.g. Csecserits and Rédei 2001; Csecserits et al. 2011; Torok et al. 2011b; Albert et al. 2014) and Romania (e.g. Ruprecht 2005, 2006). However, on isolated sites where propagule sources are limited, vegetation development may stall at a stage dominated by weeds (Prach and Pysek 2001; Matus et al. 2003). Here we study two scenarios of grassland recovery: recovery on former croplands and former plantations on mounds. Ploughing and afforestation are responsible for the reduction of grassland area and decline of grassland species richness in many parts of Eurasia (Deak et al. 2016a, b; Bird et al. 2018). Loess grasslands on fertile chernozem soils were the most severely affected by conversion to croplands or plantations (Bird et al. 2018). Amongst plantations, the North-American invasive black locust (Robinia pseudo- acacia L., Fabaceae) represents a large conservation problem due to its high persistence, excellent vegetative and generative spread, intense evaporation and competition for re- sources, shading and nutrient accumulation effects, which all lead to the degradation and disappearance of the formerly typical grassland vegetation (Vitkova et al. 2017). The objective was to evaluate the prospects for restoring grasslands in degraded (ploughed and planted with black locust) ancient burial mounds, in order to provide information that will support the development of management plans, restoration and conservation of the local biota. We asked the following questions: 1; How does site his- tory affect the spontaneous grassland recovery? 2; Do residual soil nutrients play a role in grassland recovery? Our final goal was to give recommendations for the restoration of grasslands on variously degraded burial mounds. 116 Balazs Dedk et al. / Nature Conservation 39: I 13—132 (2020) Material and methods Study sites We studied soil and vegetation of six mounds situated in the Hortobadgy National Park, EastHungary (Figure 1). Climate conditions are warm temperate, fully hu- mid, with hot summers (Kottek et al. 2006), the calculated annual mean temperature for the area between 1961 and 2010 is 10.7 °C, the average annual precipitation is 544 mm (Lakatos et al. 2013). The area is in the Great Hungarian Plain, dominantly consisting of Pleistocene-Holocene alluvial silt and clay, mixed with aeolian dust. The surface is plain (86-89 m a.s.I.), with nearly negligible elevation differences, be- ing < 1-2 m km” on average, from which the studied mounds rise 3-6 metres above the surrounding landscape. The mounds were built using soil material collected from the topsoil layer of the neighbouring areas around several thousands of years ago. The mounds are always located on the highest position of the landscape, their surround- ing being typically covered by chernozemic soils. The classification status of the soils of these landscapes according to the World Reference Base range from Chernozems over Kastanozems to Phaeozems, depending on the topsoil aggregate quality and the subsoil’s carbonate status. The typical natural habitat types in the region are alkaline wetlands in the lowest elevation, alkaline dry grasslands at medium and dry loess Studied mounds land use o Grassland eo Former cropland e Former plantation Figure I. Study area: location of the studied mounds. Grassland recovery on former croplands and plantations 117 N fixation N consumption by vegetation new balance of nutrients topsoil deposition | in the topsoil of mounds rtilization® fe aie Nn ie Hy Figure 2. The soil and vegetation development of the studied mounds. grasslands at the highest-elevated areas (Deak et al. 2014). Besides natural habitats, there are several croplands in the national park, where cereals, alfalfa and maize are the most typical crops. The majority of croplands are managed in an extensive way as farmers manage their lands according to the regulations of agri-environmental schemes, which limit the use of chemicals. The vegetation of four surveyed mounds was formerly seriously degraded: two mounds (Porosdllas- and Vajda-mounds) were formerly covered by black locust (2. pseudoacacia) plantations and two mounds were used as arable fields (Boda- and T6k- mounds). According to the oldest available orthophotos, all the two mounds with former croplands were already ploughed and the two mounds with Robinia plantations were already afforested in 1961. Based on archive descriptions, we can estimate that af- forestation lasted for at least 80 years and crop production for at least 200 years on the studied mounds. Spontaneous grassland recovery started in 2012 in all sites: planta- tions have been cut and ploughing was stopped. As reference, we selected two mounds (Kettés- and Lapos-mounds) with well-preserved pristine grassland vegetation. Figure 2 shows the land use changes and the related processes of soil and vegetation develop- ment in the study sites in the past 6000 years. Field sampling Soil conditions were sampled in ten randomly distributed 1 m x 1 m permanent plots on each mound. From each plot, three subsamples were collected with 100 cm* stain- less steel sampling cylinders, representing the uppermost 5 cm of the soil. First soil sampling was carried out in late June 2014 and it was repeated in late June 2016. On each mound, we designated ten 1 m x 1 m plots (altogether 60 plots), in which we recorded the percentage cover of vascular plant species in June 2016. 118 Balizs Deak et al. / Nature Conservation 39: 113—132 (2020) Laboratory analyses Soil subsamples from the same plots and same year were then mixed and, after homogeni- sation, dried at 40 °C until weight constancy (approximately three days). In the laboratory, pH (H,O; KCl), plant available nitrogen content and plant available phosphorus content were measured. Soil pH was measured with standard glass electrode in 1:2.5 suspensions prepared with water (pH,,,,,), and KCI solution (pH,,.,), respectively (MSZ-08-0206:1978 2.1). Plant available P was determined after extraction with 0.1 M ammonium-lactate so- lution buffered with 0.4 M acetic acid at pH 3.7. Plant available NO,-N was extracted with 1 M KCl solution. Both N and P content of extracts were determined by spectropho- tometric measurements, according the Hungarian standards (MSZ 20135 1999). Data processing We calculated cover-weighted scores of Ellenberg ecological indicator values for water (WB), nutrient (NB) and light (LB) adapted to the Hungarian conditions (Borhidi 1995). Based on the social behaviour type (SBT) system of (Borhidi 1995), we categorised the species into two ecological groups, grassland species and weeds. We considered specialists (S), generalists (G) and competitors (C) as grassland species and adventive competitors (AC), ruderal competitors (RC) and weeds (W) as weeds. The SBT system assigns a natu- ralness value to each category, ranging from -3 (AC) to +6 (S). We calculated the cover- weighted mean naturalness index for each plot, to characterise the overall naturalness. For visualising the vegetation patterns on the mounds with different site history, we used Detrended Correspondence Analysis (DCA), based on specific cover scores. Soil nitrate and phosphorus content were included as overlay (CANOCO 5; ter Braak and Smilauer 2012). We performed indicator species analysis to identify species confined to mounds with a certain site history (Dufréne and Legendre 1997). For the analyses, we used the ‘labdsv’ package (Roberts 2019) in an R environment (R Core Team 2020). To explore the effects of ‘site history’, time since grassland recovery started (‘year’) and their interaction (explanatory variables) on soil pH (pH),,,)3 PH xcy)> soil nitrate and phosphorus content (dependent variables), we used Repeated Measures General Linear Models (RM GLMs) accounting for the normal distribution of the dependent variables (Zuur et al. 2009). Scores of soil variables were log-transformed to approximate them to normal distribution. We used the Greenhouse-Geisser correction for calculat- ing degrees of freedoms and Tukey’s test for calculating post-hoc pair-wise comparisons. We used Generalised Linear Mixed Models (GLMMs) to explore the effects of ‘site history’ and two soil parameters (‘soil nitrate content’ and ‘soil phosphorus content’) (explanatory variables) on the naturalness index, ecological indicator values and the species richness and cover of grassland species and weeds in 2016 (dependent vari- ables). The ID of the ‘study sites’ was included in the models as a random factor. Scores of naturalness index, ecological indicator values and cover of grassland and weed spe- cies were log-transformed to approximate them to normal distribution. Species num- ber of grassland specialists and weeds were fitted using Poisson distribution with a log Grassland recovery on former croplands and plantations 119 link. We used Tukey’s test for calculating post-hoc pair-wise comparisons. The RM GLMs and GLMMs were calculated using IBM SPSS Statistics v. 22 programme (Ar- monk, NY: IBM Corp). Significance level was set at p < 0.05. Results Soil characteristics and pH_,... of the studied mounds We did not detect any difference in the soil pH j,,.) ness and pH_,.. were recorded in the former (Table 1). The highest values for both pHs es croplands in 2014, but the difference between mounds with different history was not significant (Figure 3). Site history had a significant effect on plant available soil N content (NO,,). N content was the highest in former black locust plantations and the lowest in former croplands. Plant available soil P content was affected by time since grassland regeneration started (‘year’) and ‘site history (Table 1, Figure 3). P content was the highest in former croplands and the lowest in former black locust plantations. pH(KCl) i —f] he —i: ORE pee © 4 Former Former Former Former : Grassland ; Grassland cropland plantation cropland plantation C 300 D c 60 b be 2 = D 2 40 £ [©] € Ww es abc 8 w ac 2 5 20 = a 8 a Am o 0) Former Former Grassland Former Former cropland plantation cropland plantation Figure 3. Soil characteristics (A — PH asa Be Pilea C—NO,-N content and D — P content (P,O,)) measured in the studied mounds (grasslands, former croplands and former plantations). White boxes Grassland represent data from 2014, grey boxes represent data from 2016. Different letters indicate significant dif- ferences between groups (Tukey test, p < 0.05). 120 Balizs Deak et al. / Nature Conservation 39: 113—132 (2020) Table I. Effects of site history, year and their interaction on soil attributes (RM GLM). Notations: *** p < 0.001; ** p< 0.01; * p < 0.05; n.s.: non-significant. Parameter Site history Year Site history x Year df, df... F p df df... F p df df... F Pp pHing) 2 L067 2,636" — s,s. 1 1 0.425 ns eZ 1.247 1.426 ns. Pcs 2 1.088 2.822 nos. 1 1 1.080 ns 2 Le2de E972 “ais. NO,-N content 2 VAG: 37,289" 1 1 2 AIOO™ nis; 2 1.331 0,138: - nis. P content (P,O,) 2 1.730 10.592 ** 1 1 17.590 ** 2 1.363 3.120 ns. Table 2. Results of indicator species analyses of the vegetation of mounds with different site history. Notations: G — mounds covered by grassland; A — mounds formerly covered by arable land; P — mounds formerly covered by Robinia plantation; *** p < 0.001; ** p < 0.01; * p < 0.05. Species Site history Indicator p Frequency value Carex praecox Schreb. G 0.55 a 11 Koeleria cristata (L.) Pers. em. Borbds ex Domin G 0.49 i 14 Salvia nemorosa L. G 0.40 ny 8 Festuca pseudovina Hack. ex Wiesb. G 0.40 a 13 Elymus hispidus (Opiz) Melderis G 0.35 aie is Arenaria serpyllifolia L. G 0.33 + 18 Plantago lanceolata L. G 0.32 mt 8 Bromus hordeaceus L. G O32 2 14 Trifolium retusum L. G 0.30 ae 6 Euphorbia virgata Waldst. et Kit. G 0.30 een 6 Erodium cicutarium (L.) LHer. G 0.26 * 8 Eryngium campestre L. G 0.25 . 5 Trifolium striatum L. G 0.25 a 5 Stipa capillata L. G 0.20 * 4 Cerastium semidecandrum L. G 0.20 if 4 Bromus tectorum L. A 0.84 a 18 Torilis arvensis (Huds.) Link A 0.49 ts 12 Convolvulus arvensis L. A 0.44 34 Alopecurus pratensis L. A 0.43 om 12 Achillea collina Becker ex Rchb. A 0.42 * 18 Veronica arvensis Murray A 0.34 = 8 Geranium molle L. A 0.26 7 9 Xanthium strumarium L. A 0.25 a 5 Vicia grandiflora Scop. A 0.20 & 4 Lolium perenne L. A 0.20 . 4 Elymus repens (L.) Gould ly 0.65 Ss 30 Ballota nigra L. iP 0.51 ia 14 Bromus sterilis L. P 0.35 oa 7 Silene alba (Mill.) E.H.L. Krause P 0.28 ss 11 Galium aparine L. P 0.26 x 13 Conium maculatum L. P 0.20 ‘| 4 Grassland recovery on former croplands and plantations 12a Vegetation We found altogether 92 vascular plant species on the studied mounds. Total species numbers were 64 in the grasslands, 50 in the former croplands and 24 in the former plantations. The vegetation composition of mounds with a different site history was well separated on the DCA ordination (Figure 4). We detected a considerable differ- ence between the vegetation of the two mounds covered by grasslands. Indicator species of grasslands were Carex praecox Schreb., Koeleria cristata (L.) Pers., Salvia nemorosa L. and Festuca pseudovina Hack. ex Wiesb. (Table 2). Typical species of former croplands included Bromus tectorum L., Torilis arvensis (Huds.) Link, Convolvulus arvensis L., Alopecurus pratensis L. and Achillea collina Becker ex Rchb. Former black locust plantations were characterised by Elymus repens (L.) Gould and Ballota nigra L. (Table 2). LO - Oo O Oo ™ a Oo 2 < Oo < Po q) O Ch ‘oa Bo xe) = N J nitrate “t 1st DCA axis 6 Figure 4. DCA plot of the vegetation of study sites, based on the species composition. Soil nitrate and phosphorus content were included as an overlay. Notations: squares — grasslands; diamonds — former crop- lands, circles — former plantations. Eigenvalues were 0.753 and 0.548 for the first and second axis, respec- tively. Cumulative explained variance of the first and the second axis were 12.72% and 21.98%, respectively. 122 co (o>) is i) Species richness of grassland species oO = = = o>) ceo) Oo ho So oO oO Oo oO Cover of grassland species i) oO LB Balizs Dedk et al. / Nature Conservation 39: 113—132 (2020) A 8) B a a n o g 6 a ue 5 a wn o 24 <= 2 b 8 iB 2 Q ip) b Former Former G land Former Former Grassland rasslan ' cropland plantation cropland plantation C 120) D : a 100 wm 80 b <2) oO o = 60 ie) 2 40 [e) O a b 20 ch : ) Grassland Former Former Grassland Former Former cropland plantation cropland plantation E b b a Grassland Former Former Grasceand Former Former cropland plantation cropland plantation G 51H a a b 4 b : b w ® 2 Cc g Bp c = 0 A -2 Grassland Former Former Grassland Former Former cropland plantation cropland plantation Figure 5. Vegetation characteristics in the studied mounds (grasslands, former croplands and former plantations): A species richness of grassland species B species richness of weeds C cover of grassland spe- cies D cover of weeds E cover-weighted ecological indicator scores for nutrients (NB) F cover-weighted ecological indicator scores for water (WB) G cover-weighted ecological indicator scores for light (LB) H naturalness score. Different letters indicate significant differences between groups (Tukey test, p < 0.05). Grassland recovery on former croplands and plantations 123) Table 3. Effects of site history, soil nitrate and phosphorus content on the vegetation characteristics of the studied mounds (Generalised Linear Mixed Models). *** p < 0.001; ** p < 0.01; * p < 0.05; n.s., non- significant. Notations: NB, WB, LB: cover-weighted means of ecological indicator values for nutrients, water and light, respectively. Site history Nitrate Phosphorus F Pp F Pp F Pp Naturalness 46.35 is 5.15 i 5.40 Bi Species richness Grassland 17.59 ae" 0.19 n.s. 1.80 n.s. species Weeds 1.95 n.s. 0.61 n.s. 0.61 n.s. Cover Grassland 17.74 wae 0.20 n.s. 3.09 n.s. species Weeds 70.27 ‘dog 0.03 n.s. 0.01 n.s. Ecological indicator values NB 9.02 Fs 0.93 n.s. 1.19 n.s. WB 7.97 Se 2.51 n.s. 0.44 n.s. LB 21.38 Dor 13.09 vu 3.25 n.s. The re-sprouting ramets of the black locust were only present in the plots of the Vajda- mound and the average cover of black locust was 0.9% in the plots. Site history significantly affected the naturalness of the vegetation, it was the low- est in former plantations and the highest in grasslands (Table 3, Figure 5). Soil nitrate content decreased the naturalness of the vegetation (coefficient = -0.068; t = -2.324; GLMM), whilst soil phosphorus content increased it (coefficient = 0.010; t = 2.269; GLMM). Both cover and species richness of grassland species were affected by site his- tory; their scores were significantly lower in former plantations and croplands. Cover of weeds was affected by site history; it was the highest in former plantations. Cover- weighted NB, WB and LB scores were affected by site history. Cover-weighted NB scores were higher in former plantations and croplands compared to grasslands. Cover- weighted WB scores were the highest in former plantations. Cover-weighted LB scores were the highest in grasslands. Discussion Soil characteristics We found that pH was highest, close to 7 or even greater, in former cropland in 2014. The likely reason for this is that, in croplands, there was no organic matter accumula- tion on the surface and the surficial soil layer was constantly mixed with subsoil and the subsoils’ carbonate saturation status was always higher in these soils than at the sur- face. During the study period, pH was not changed significantly in any of the mounds, but a slight increase in former plantation and slight decrease on former cropland could 124 Balizs Deak et al. / Nature Conservation 39: 113—132 (2020) be detected. Soil pH was much more heterogeneous in the grasslands compared to the former croplands and plantations. This supports the findings of the Penksza et al. (2011), Deak et al. (2016a,b) and Lisetskii et al. (2016) who emphasised the role of environmental heterogeneity in driving the plant diversity on steppic burial mounds. Heterogeneity of pH can be an important driver of small-scale plant diversity (Moes- lund et al. 2013). Plant available N content was the lowest in the former cropland and its amount did not change by time since abandonment. This is due to the additive effect of the depletion of soil N stocks by decades-long cultivation and the slow soil N-recovery during secondary succession (Matamala et al. 2008; An et al. 2019). Besides being a limiting factor for the establishment of grassland plant species, limited availability of soil N stocks may also limit the development of the vegetation by suppressing micro- bial decomposition and soil carbon sequestration (Knops and Tilman 2000). The high- est N content was measured in former plantations as a legacy of the former presence of the black locust. By the enhanced nitrogen-fixing of the black locust and the decom- position of its nitrogen-rich leaves, the soil of these former plantations had a high N content (Bolat et al. 2015). Although we detected a slight decrease in soil N content after the plantation had been cut, this difference was not significant. These findings underline the long-term impact of this invasive alien plant on natural ecosystems by increasing the soil N content over a long term. Plant available P content was the highest in the former croplands in 2014 as result of former P-fertilisation, but after the abandonment, it started to decrease significantly. As P has a low mobility in soils, this decrease can be a result of the P consumption by the vegetation and soil microbes. In the grasslands and former plantations, P content was similarly low, in both cases low pH likely facilitated the mobilisation (Alt et al. 2011), i.e. leaching from topsoil. In former plantations and grassland, there were no temporal changes between the two sampling dates. The high N in the soils of former plantations and the high P availability in the soil of former croplands, should be con- sidered as a relevant regulating factor in subsequent grassland recovery (Alt et al. 2011) and might hinder vegetation recovery for almost a decade (An et al. 2019). Vegetation changes We found that, four years after land use change, grassland vegetation was in an early or mid-successional stage, both on the mounds formerly used as cropland and forest plantation. The three vegetation types were clearly separated by their species composi- tion (Figure 4). The recovering grasslands had a few common species with the reference grasslands and were mostly characterised by weed species. The indicator species of the recovering grasslands reflected the different site histories. On mounds, formerly coy- ered by croplands, mostly weeds typical of former arable lands and fallows were present, such as C. arvensis, L. perenne, T. arvensis and X. strumarium (Table 3). Mounds, for- merly covered by plantations, were characterised by weed species typical of the under- Grassland recovery on former croplands and plantations 125 storey of black locust plantations, such as B. nigra, B. sterilis and G. aparine. However, some weed and disturbance-tolerant species occurring also in dry grasslands were also present, such as A. collina, V. arvensis and V. grandiflora. ‘The only indicator species on former croplands which is typical of undisturbed grasslands was A. pratensis. The latter is a typical competitor species of alkali meadows, but it can also cope with dry habitat conditions, thus, it often can be found in the loess grasslands of the region (Borhidi et al. 2012, Deak et al. 2014). Indicator species of mounds covered by grasslands were mostly species typical to alkali (F pseudovina, P lanceolata and T: retusum) and loess grasslands (C. praecox, E. hispidus, E. virgata, K. cristata and S. nemorosa) (Borhidi et al. 2012, Deak et al. 2014) (Table 3). Only a few weed species such as B. hordeaceus and E. cicutarium were present, likely due to moderate grazing (God6 et al. 2017). Species composition of weeds reflected well the site history. Weeds are generally R-strategists and have a dense and persistent seed bank (Torok et al. 2012; Melnik et al. 2017). Thus, even several years after the cessation of crop production and cutting of plantations, weed species were able to germinate from the seed bank. Contrarily, the usually K-strategist grassland species generally have a sparse and transient seed bank (Bossuyt and Honnay 2008), thus their seed bank is generally depleted even after a few years of improper management (Valk et al. 2011). As the studied mounds were used as arable land or black locust plantation for decades, there was no possibility for the grassland species to recover from the seed bank. Another reason for the low proportion of grassland species on the recovering mound vegetation is the lack of dispersal vec- tors (Deak et al. 2016b). Even though semi-natural grasslands were present near the recovering mounds, the dispersal vectors (the grazing livestock) were missing. As many grassland plant species have a limited dispersal ability and thus a limited dispersal radi- us, lack of active dispersal vectors can considerably hinder their establishment, even in semi-natural landscapes (Jacquemyn et al. 2010; Auffret 2011). The results regarding the naturalness of the vegetation also suggested that vegetation recovery is at an initial stage even four years after land use change. The naturalness of the recovering vegeta- tion was low in case of both former croplands and plantations (Figure 5). However, it is shown by the results of the GLMM that the vegetation recovery was more successful on former croplands compared to former plantations (Table 2). The proportion of spe- cies typical of natural habitats was significantly higher on mounds formerly covered by cropland than on mounds formerly covered by black locust plantation. The reason for the low success of vegetation recovery on former plantations is the legacy of the former woody vegetation and forestry practices. For establishing a forest plantation, more drastic soil works are needed compared to arable use. Even though the soil works are not so frequent, such as in the case of arable use, they can affect the soil structure in deeper layers. Thus, it affects the chemical properties of the soil in a more intense way; furthermore, deep ploughing transports the seed bank of grassland species to such deep layers (even 1 m deep) from where they are not able to germinate and re-establish. Due to the shading effect of woody vegetation, a milder micro-climate is present in the understorey of the woody habitats (Télgyesi et al. 2020), which affects their species composition. It could still be observed by the low cover-weighted cover of 126 Balizs Dedk et al. / Nature Conservation 39: 113—132 (2020) LB and high WB scores of the vegetation. Another detrimental effect of black locust on dry grassland species is that, due to its nitrogen fixation, it considerably increases the nitrate content of the soil (Figure 3; and see also Cierjacks et al. 2013; Vitkova et al. 2017). The increased residual nitrate content could even be observed four years after eliminating black locust trees (Table 1) and it had a considerable effect on the vegeta- tion by decreasing the naturalness index (Table 3). The high nitrate content gener- ally favours species adapted to ruderal habitats (low naturalness index) and suppresses stress-tolerant species adapted to dystrophic soil (Jentsch and Beyschlag 2003; Albert et al. 2014). Black locust is a species that can re-sprout very effectively after disturbance (Vitkova et al. 2017). Under the studied climatic and edaphic conditions, only very few re-sprouting ramets were observed three years after the removal of Robinia. How- ever, regular monitoring is needed to detect the abundance of black locust ramets and apply follow-up management, if necessary. Conclusions Our results suggest that the legacy of a former intensive land use (i.e. cropland and plantation) is more complex than the effect of excess soil nutrients. Even though for- mer croplands were characterised by excess P and former plantations by excess N (Fig- ure 3), the reasons for differences in vegetation characteristics are likely more complex. The long-lasting various disturbance regimes (fertilisation, herbicide application, till- age) typical for croplands, shading and altered microclimate typical for plantations and the deep cultivation typical for both, are the most likely legacies that hamper or slow down the grassland recovery in the studied habitats. We found that, without proper management measures, recovery of grassland veg- etation is slow on mounds formerly used as cropland or black locust plantation. This is in line with the findings of Torok et al. (2011b), who found that a significant decrease in the proportion of the weeds can be expected approximately 10 years after cessation of croplands in the studied region. Our results suggest that arable use transformed the habitat conditions in a more moderate way than the establishment of plantations. Thus, restoration efforts, focused on the restoration of mounds formerly covered by arable lands, can be more effective compared to the restoration of mounds formerly covered by forest plantations. From a practitioner point, it should also be noted that costs associated with the elimination of woody vegetation is high. Especially if we take into account that, in many countries (like in Hungary), a high penalty (ca. 11000 euros per hectare) should be paid in case of elimination of a forest parcel (regardless of whether it is a native forest or an invasive plantation) or, alternatively, another forest of the same area has to be established elsewhere. Even though spontaneous regeneration of grassland habitats can be a good solu- tion in nature conservation practice, it might be risky as the vegetation development is often unpredictable. The outcome of spontaneous succession is highly dependent on initial site conditions, including land use intensity, landscape context, climatic Grassland recovery on former croplands and plantations 127 and edaphic factors. Spontaneous recovery is often unpredictable also due to the founder effect, i.e. that the vegetation composition of late successional phases strong- ly depends on the initial plant assemblages (Grime 1998). As in case of spontaneous succession, where the initial plant establishment processes have a random pattern, the outcome of the succession can be unfavourable from a nature conservation view or even can stack in a weed dominated phase (Deak et al. 2015; Albert et al. 2014). In case of spontaneously recovering former arable lands and forest plantations, the dense seed bank of the weed species might shift the vegetation development to un- desirable pathways. In case of former plantations, resprouting of woody vegetation might also occur (Cierjacks et al. 2013). Thus, continuous monitoring of the spon- taneously recovering vegetation is recommended. In case of unfavourable vegetation changes, further measures might be necessary, such as seed sowing of good competi- tor grassland species (Valk6 et al. 2018). Acknowledgements The study was supported by the NKFI KH 130338, NKFI KH 126476, NKFI FK 124404 and NKFIH-1150-6/2019 grants. BD, OV and TJN were supported by the Bolyai Janos Scholarship of the Hungarian Academy of Sciences. TJN was supported by the UNKP-19-4-DE-129 New National Excellence Program (Bolyai+) of the Min- istry for Innovation and Technology. The authors are grateful to Iva Apostolova and Igor Soares dos Santos for their useful suggestions on the manuscript. References Albert A-J, Kelemen A, Valké O, Miglécz T, Csecserits A, Rédei T, Dedk B, Tothmérész B, Torok P (2014) Secondary succession in sandy old-fields: A promising example of spontaneous grassland recovery. Applied Vegetation Science 17(2): 214-224. https://doi.org/10.1111/ avsc.12068 Alt F Oelmann Y, Herold N, Schrumpf M, Wilcke W (2011) Phosphorus partitioning in grassland and forest soils of Germany as related to land-use type, management intensity, and land use-related pH. Journal of Plant Nutrition and Soil Science 174(2): 195-209. https://doi.org/10.1002/jpln.20 1000142 An H, Zhang B, Thomas BW, Beck R, Willms WD, Li Y, Hao X (2019) Short term recovery of vegetation and soil after abandoning cultivated mixed-grass prairies in Alberta, Canada. Catena 173: 321-329. https://doi.org/10.1016/j.catena.2018.10.017 Auffret AG (2011) Can seed dispersal by human activity play a useful role for the conser- vation of European grasslands? Applied Vegetation Science 14(3): 291-303. https://doi. org/10.1111/j.1654-109X.2011.01124.x Bede A, Csathé AI (2019) Complex characterization of kurgans in the Csandadi-hat region, Hungary. Tajokolégiai Lapok 17(2): 131-145. 128 Balizs Deak et al. / Nature Conservation 39: 113—132 (2020) Bede A, Salisbury RB, Csathé AI, Czukor P, Pall DG, Szilagyi G, Stimegi P (2015) Report of the complex geoarcheological survey at the Ecse-halom kurgan in Hortobagy, Hungary. Central European Geology 58(3): 268-289. https://doi.org/10.1556/24.58.2015.3.5 Bird M, Boléni J, Molnar Z (2018) Use of long-term data to evaluate loss and endangerment status of Natura 2000 habitats and effects of protected areas. Conservation Biology 3(3): 660-671. https://doi.org/10.1111/cobi.13038 Bolat I, Kara O, Sensoy H, Yiiksel K (2015) Influences of Black Locust (Robinia pseudoacacia L.) afforestation on soil microbial biomass and activity. iForest — Biogeosciences and For- estry 9: 171-177. https://doi.org/10.3832/ifor1410-007 Borhidi A (1995) Social behaviour types, the naturalness and relative ecological indicator values of the higher plants in the Hungarian Flora. Acta Botanica Hungarica 39: 97-181. Borhidi A, Kevey B, Lendvai G (2012) Plant communities of Hungary. Akadémiai Kiad6, Budapest. Bossuyt B, Honnay O (2008) Can the seed bank be used for ecological restoration? An over- view of seed bank characteristics in European communities. Journal of Vegetation Science 19(6): 875-884. https://doi.org/10.3170/2008-8-18462 Brady M, Kellermann K, Sahrbacher C, Jelinek L (2009) Impacts of decoupled agricultural sup- port on farm structure, biodiversity and landscape mosaic: Some EU results. Journal of Agri- cultural Economics 60(3): 563-585. https://doi.org/10.1111/j.1477-9552.2009.00216.x Cierjacks A, Kowarik I, Joshi J, Hemplel S, Ristow M, von der Lippe M, Weber E (2013) Biological flora of the British Isles: Robinia pseudoacacia. Journal of Ecology 101(6): 1623— 1640. https://doi.org/10.1111/1365-2745.12162 Csecserits A, Rédei T (2001) Secondary succession on sandy old-fields in Hungary. Applied Vegetation Science 4(1): 63-74. https://doi.org/10.1111/j.1654-109X.2001.tb00235.x Csecserits A, Halassy M, Kréel-Dulay G, Rédei T, Szitar K, Szabé R (2011) Different regenera- tion success of sandy old-fields in the forest-steppe region of Hungary. Plant Biosystems 145: 715-729. https://doi.org/10.1080/11263504.2011.601340 Deak B, Valké O, Alexander C, Miicke W, Kania A, Tamas J, Heilmeier H (2014) Fine-scale vertical position as an indicator of vegetation in alkali grasslands — case study based on re- motely sensed data. Flora 209(12): 693-697. https://doi.org/10.1016/j.flora.2014.09.005 Deak B, Valké O, Tordk P, Kelemen A, Miglécz T, Szabo S, Szabé G, Téthmérész B (2015) Mi- cro-topographic heterogeneity increases plant diversity in old stages of restored grasslands. Basic and Applied Ecology 16(4): 291-299. https://doi.org/10.1016/j.baae.2015.02.008 Deak B, Tothmérész B, Valko O, Sudnik-W6jcikowska B, Bragina TM, Moysiyenko II, Bragina TM, Apostolova I, Dembicz I, Bykov NI, Torok P (2016a) Cultural monuments and na- ture conservation: The role of kurgans in maintaining steppe vegetation. Biodiversity and Conservation 25: 2473-2490. https://doi.org/10.1007/s10531-016-1081-2 Deak B, Valko O, Torék P, Tothmérész B (2016b) Factors threatening grassland specialist plants — A multi-proxy study on the vegetation of isolated grasslands. Biological Conservation 204: 255-262. https://doi.org/10.1016/j.biocon.2016.10.023 Dedk B, Téth CA, Bede A, Apostolova I, Bragina TM, Bathori F Ban M (2019) Eurasian Kur- gan Database — a citizen science tool for conserving grasslands on historical sites. Hacquetia 18(2): 185-193. https://doi.org/10.2478/hacq-2019-0007 Grassland recovery on former croplands and plantations 129 Deak B, Valko O, Nagy DD, Torok P, Torma A, Lérinczi G, Kelemen A, Nagy A, Bede A, Mizser S, Csathé AI, Téthmérész B (2020) Habitat islands outside nature reserves — threat- ened biodiversity hotspots of grassland specialist plant and arthropod species. Biological Conservation 241: 108254. https://doi.org/10.1016/j.biocon.2019.108254 Dembicz I, Moysiyenko II, Shaposhnikova A, Vynokurov D, Kozub L, Sudnik-Wojcikowska B (2016) Isolation and patch size drive specialist plant species density within steppe is- lands: A case study of kurgans in southern Ukraine. Biodiversity and Conservation 25(12): 2289-2307. https://doi.org/10.1007/s10531-016-1077-y Dembicz I, Szczeparska L, Moysiyenko H, Wodkiewicz M (2018) High genetic diversity in fragmented Iris pumila L. populations in Ukrainian steppe enclaves. Basic and Applied Ecology 28: 37-47. https://doi.org/10.1016/j.baae.2018.02.009 Dudley N, Higgins-Zogib L, Mansourian S (2009) The links between protected areas, faiths, and sacred natural sites. Conservation Biology 23(3): 568-577. https://doi.org/10.1111/ j.1523-1739.2009.01201.x Dufréne M, Legendre P (1997) Species assemblages and indicator species: The need for a flexible asymmetrical approach. Ecological Monographs 67: 345-366. https://doi. org/10.2307/2963459 Fekete R, Loki V, Urgyan R, Siiveges K, Lovas-Kiss A, Vincze O, Molnar VA (2019) Roadside verges and cemeteries: Comparative analysis of anthropogenic orchid habitats in the East- ern Mediterranean. Ecology and Evolution 9(11): 6655-6664. https://doi.org/10.1002/ ece3.5245 God6 L, Valké O, Tothmérész B, Tordk P, Kelemen A, Deak B (2017) Scale-dependent effects of grazing on the species richness of alkaline and sand grasslands. Tuexenia 37: 229-246. Grime JP (1998) Benefits of plant diversity to ecosystems: Immediate, filter and founder effects. Journal of Ecology 86(6): 902-910. https://doi.org/10.1046/j.1365-2745.1998.00306.x Hedberg P, Kotowski W (2010) New nature by sowing? The current state of species introduc- tion in grassland restoration, and the road ahead. Journal for Nature Conservation 18(4): 304-308. https://doi.org/10.1016/j.jnc.2010.01.003 Jacquemyn H, Roldan-Ruiz I, Honnay O (2010) Evidence for demographic bottlenecks and limited gene flow leading to low genetic diversity in a rare thistle. Conservation Genetics 11(5): 1979-1987. https://doi.org/10.1007/s10592-010-0089-5 Jakobsson S, Bernes C, Bullock JM, Verheyen K, Lindborg R (2018) How does roadside veg- etation management affect the diversity of vascular plants and invertebrates? A systematic review. Environmental Evidence 7(1): 17. https://doi.org/10.1186/s13750-018-0129-z Jentsch A, Beyschlag W (2003) Vegetation ecology of dry acidic grasslands in the lowland area of Central Europe. Flora 198(1): 3-25. https://doi.org/10.1078/0367-2530-0007 1 Jirova A, Klaudisova A, Prach K (2012) Spontaneous restoration of target vegetation in old- fields in a central European landscape: A repeated analysis after three decades. Applied Vegetation Science 15(2): 245-252. https://doi.org/10.1111/j.1654-109X.2011.01165.x Kiehl K, Kirmer A, Donath T, Rasran L, Hélzel N (2010) Species introduction in restoration projects. Evaluation of different techniques for the establishment of semi natural grasslands in Central and Northwestern Europe. Basic and Applied Ecology 11(4): 285-299. https:// doi.org/10.1016/j.baae.2009.12.004 130 Baldzs Deak et al. / Nature Conservation 39: 113—132 (2020) Knops JM, Tilman D (2000) Dynamics of soil nitrogen and carbon accumulation for 61 years after agricultural abandonment. Ecology 81(1): 88-98. https://doi.org/10.1890/0012- 9658(2000)081[0088: DOSNAC]2.0.CO;2 Kottek M, Grieser J, Beck C, Rudolf B, Rubel F (2006) World Map of Koppen-Geiger Cli- mate Classification updated. Meteorologische Zeitschrift 15(3): 259-263. https://doi. org/10.1127/0941-2948/2006/0130 Lakatos M, Szentimrey T, Bihari Z, Szalai S (2013) Creation of a homogenized climate da- tabase for the Carpathian region by applying the MASH procedure and the preliminary analysis of the data. Id6jards 117: 143-158. Lencova K, Prach K (2011) Restoration of hay meadows on ex-arable land: Commercial seed mixtures vs. spontaneous succession. Grass and Forage Science 66(2): 265-271. https:// doi.org/10.1111/j.1365-2494.2011.00786.x Lindborg R, Plue J, Andersson K, Cousins SAO (2014) Function of small habitat elements for enhancing plant diversity in different agricultural landscapes. Biological Conservation 169: 206-213. https://doi.org/10.1016/j.biocon.2013.11.015 Lisetskii FN, Sudnik-W6jcikowska B, Moysiyenko H (2016) Flora differentiation among local ecotypes in the transzonal study of forest-steppe and steppe mounds. ‘The Biological Bul- letin 43(2): 169-176. https://doi.org/10.1134/S1062359016010106 Loki V, Molnar VA, Siiveges K, Heimeier H, Takacs A, Nagy T, Fekete R, Lovas-Kiss A, Kreutz CAJK, Sramk6é G, Tokélyi J (2019) Predictors of conservation value of Turkish cemeter- ies: A case study using orchids. Landscape and Urban Planning 186: 36-44. https://doi. org/10.1016/j.landurbplan.2019.02.016 Matamala R, Jastrow JD, Miller RM, Garten CT (2008) Temporal changes in C and N stocks of restored prairie: Implications for C sequestration strategies. Ecological Applications 18(6): 1470-1488. https://doi.org/10.1890/07-1609.1 Matus G, Téthmérész B, Papp M (2003) Restoration prospects of abandoned species-rich sandy grassland in Hungary. Applied Vegetation Science 6(2): 169-178. https://doi.org/10.1111/ j.1654-109X.2003.tb00577.x Melnik K, Landhausser SM, Devito K (2017) Role of microtopography in the expression of soil propagule banks on reclamation sites. Restoration Ecology 26(S2): S200—S210. https:// doi.org/10.1111/rec.12587 Moeslund JE, Arge L, Bacher PK, Dalgaard T, Odgaard MV, Nygaard B, Svenning JC (2013) Topographically controlled soil moisture is the primary driver of local vegetation patterns across a lowland region. Ecosphere 4(7): 1-26. https://doi.org/10.1890/ES13-00134.1 Molnar VA, Nagy T, Loki V, Siiveges K, Takacs A, Bodis J, Tokolyi J (2017) Turkish graveyards as refuges for orchids against tuber harvest. Ecology and Evolution 7(24): 11257-11264. https://doi.org/10.1002/ece3.3562 Penksza K, Loksa G, Barczi A, Joé K, Malatinszky A (2011) Effects of extrazonal and climatic conditions on the vegetation of kurgans. A pilot study from the Hortobagy (Csipé-halom). In: Peté A, Barczi A (Eds) Kurgan studies: An environmental and archaeological mul- tiproxy study of burial mounds in the Eurasian steppe zone. BAR International Series, Oxford, 347-350. Grassland recovery on former croplands and plantations 13} Prach K, Pysek P (2001) Using spontaneous succession for restoration of human-disturbed habitats: Experience from Central Europe. Ecological Engineering 17(1): 55-62. https:// doi.org/10.1016/S0925-8574(00)00132-4 Prach K, Rehounkov4 K (2008) Spontaneous vegetation succession in gravel—sand pits: A potential for restoration. Restoration Ecology 16(2): 305-312. https://doi.org/10.1111/ j-1526-100X.2007.00316.x R Core Team (2020) R: A Language and Environment for Statistical Computing. R Founda- tion for Statistical Computing, Vienna. Rakoczi A, Barczi A (2014) Protected landscape elements in the European Union, the influence of EC decree 73/2009 on the condition of Hungarian mounds. Tajokolégiai Lapok 12(1): 95-105. [Védett tajelemek az Eurdpai Unidban, a 73/2009 EK rendelet hatdsai a magyar kunhalmok allapotaral] Roberts DW (2019) Ordination and Multivariate Analysis for Ecology. Version 2.0-1 URL http://ecology.msu.montana.edu/labdsv/R Ruprecht E (2005) Secondary succession in old-fields in the Transylvanian Lowland (Roma- nia). Preslia 77: 145-157. Ruprecht E (2006) Successfully recovered grassland: A promising example from Roma- nian old-fields. Restoration Ecology 14(3): 473-480. https://doi.org/10.1111/j.1526- 100X.2006.00155.x Sudnik-W6jcikowska B, Moysiyenko II, Zachwatowicz M, Jabtonska E (2011) The value and need for protection of kurgan flora in the anthropogenic landscape of steppe zone in Ukraine. Plant Biosystems 145(3): 638-653. https://doi.org/10.1080/11263504.2011.6 01335 Ter Braak C, Smilauer P (2012) Canoco Reference Manual and User’s Guide: Software for Ca- nonical Community Ordination (version 5.0). Microcomputer Power, Ithaca, NY, USA, 496 pp. Tolgyesi C, Torok P, Habenczyus AA, Batori Z, Valké6 O, Deak B, Tothmérész B, Erdés L, Kelemen A (2020) Underground deserts below fertility islands? — Woody species desiccate lower soil layers in sandy drylands. Ecography. https://doi.org/10.1111/ecog.04906 Torok P, Vida E, Deak B, Lengyel S, Téthmérész B (2011a) Grassland restoration on former croplands in Europe: An assessment of applicability of techniques and costs. Biodiversity and Conservation 20(11): 2311-2332. https://doi.org/10.1007/s10531-011-9992-4 Torok P, Kelemen A, Valk6 O, Deak B, Lukacs BA, Téthmérész B (2011b) Lucerne dominated fields recover native grass diversity without intensive management actions. Journal of Ap- plied Ecology 48(1): 257-264. https://doi.org/10.1111/j.1365-2664.2010.01903.x Torok PB, Miglécz T, Valké O, Kelemen A, Deak B, Lengyel S, Tothmérész B (2012) Recovery of native grass biodiversity by sowing on former croplands: Is weed suppression a feasible goal for grassland restoration? Journal for Nature Conservation 20(1): 41-48. https://doi. org/10.1016/;.jnc.2011.07.006 Toth CA (2006) Results of the national mound cadastering from the aspect of geological con- servation. Acta GGM Debrecina Geology, Geomorphology, Physical Geography Series 1: 129-135. 132 Balizs Dedk et al. / Nature Conservation 39: 113—132 (2020) Téth CA, Rakéczi A, Toth S (2018) Protection of the state of prehistoric mounds in Hungary: Law as a conservation measure. Conservation and Management of Archaeological Sites 20(3): 113-142. https://doi.org/10.1080/13505033.2018.1486125 Téth CA, Deak B, Nyilas I, Bertalan L, Valk6 O, Novak T (2019) Iron age burial mounds as refugia for steppe specialist plants and invertebrates — case study from the Zsolca mounds (NE Hungary). Hacquetia 18(2): 195-206. https://doi.org/10.2478/hacq-2019-0009 Valké O, Térdk P, Téthmérész B, Matus G (2011) Restoration potential in seed banks of acidic fen and dry-mesophilous meadows: Can restoration be based on local seed banks? Restora- tion Ecology 19(101): 9-15. https://doi.org/10.1111/j.1526-100X.2010.00679.x Valké O, Téth K, Kelemen A, Miglécz T, Sonkoly J, Téthmérész B, Toérdk P, Deak B (2018) Cultural heritage and biodiversity conservation — Plant introduction and practical restora- tion on ancient burial mounds. Nature Conservation 24: 65-80. https://doi.org/10.3897/ natureconservation.24.20019 Vitkova M, Miillerova J, Sddlo J, Pergl J, PySek P (2017) Black locust (Robinia pseudoacacia) beloved and despised: A story of an invasive tree in Central Europe. Forest Ecology and Management 384: 287-302. https://doi.org/10.1016/j.foreco.2016.10.057 Zuur AF, Ieno EN, Walker N, Saveliev AA, Smith GM (2009) Mixed Effects Models and Extensions in Ecology. Springer, New York, 574 pp. https://doi.org/10.1007/978-0-387- 87458-6