Habitat extremity and conservation management stabilise endangered calcareous fens in a changing world

Journal Pre-proofs Habitat extremity and conservation management stabilise endangered calcareous fens in a changing world Michal Hájek, Veronika Horsáková, Petra Hájková, Radovan Coufal, Daniel Dítě, Tomá š Němec, Michal Horsák PII: DOI: Reference:

S0048-9697(19)34684-4 https://doi.org/10.1016/j.scitotenv.2019.134693 STOTEN 134693

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Science of the Total Environment

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22 May 2019 22 September 2019 26 September 2019

Please cite this article as: M. Hájek, V. Horsáková, P. Hájková, R. Coufal, D. Dítě, T. Němec, M. Horsák, Habitat extremity and conservation management stabilise endangered calcareous fens in a changing world, Science of the Total Environment (2019), doi: https://doi.org/10.1016/j.scitotenv.2019.134693

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Habitat extremity and conservation management stabilise endangered calcareous fens in a changing world

Michal Hájek1*, Veronika Horsáková1, Petra Hájková1,2, Radovan Coufal1, Daniel Dítě1,3, Tomáš Němec1 and Michal Horsák1

1 Department

of Botany and Zoology, Masaryk University, Kotlářská 2, CZ-611 37 Brno,

Czech Republic 2 Laboratory

of Paleoecology, Institute of Botany, Academy of Sciences of the Czech

Republic, Lidická 25, CZ-602 00 Brno, Czech Republic 3 Institute

of Botany, Plant Science and Biodiversity Center, Slovak Academy of Sciences,

Dúbravská cesta 9, SK-845 23 Bratislava, Slovakia

*corresponding author

E-mail addresses of authors: MHáj: [email protected] (corresponding author); VH: [email protected]; PH: [email protected]; RC: [email protected]; DD: [email protected]; TN: [email protected]; MHor: [email protected]

Habitat extremity and conservation management stabilise endangered calcareous fens in a changing world

Michal Hájek1*, Veronika Horsáková1, Petra Hájková1,2, Radovan Coufal1, Daniel Dítě1,3, Tomáš Němec1 and Michal Horsák1

1 Department 2 Laboratory

of Botany and Zoology, Masaryk University, Kotlářská 2, CZ-611 37 Brno, Czech Republic

of Paleoecology, Institute of Botany, Academy of Sciences of the Czech Republic, Lidická 25, CZ-

602 00 Brno, Czech Republic 3 Institute

of Botany, Plant Science and Biodiversity Center, Slovak Academy of Sciences, Dúbravská cesta 9,

SK-845 23 Bratislava, Slovakia

*corresponding author

E-mail addresses of authors: MHáj: [email protected] (corresponding author); VH: [email protected]; PH: [email protected]; RC: [email protected]; DD: [email protected]; TN: [email protected]; MHor: [email protected]

Highlights



Ongoing environmental changes threaten island-like unproductive fen ecosystems



Extremity (tufa, water, lack of nutrients) and management stabilise fen communities



Less extreme calcareous fens are more prone to shifts into grasslands and shrublands



Conservation mowing can compensate for low extremity



Management is more important for bryophytes than for vascular plants and snails

Abstract Calcareous fens represent an endangered type of peatlands, acting as refugia for stress-tolerant species in the currently changing landscapes. The resurveys across many regions have reported their recent disappearance or deterioration despite both the extreme habitat conditions (carbonate richness, presence of calcareous tufa, nutrient limitation, high water level) and conservation management. To test the stability of their biotic communities in different environmental and management

configurations, we repeatedly sampled of molluscs (terrestrial and aquatic), vascular plants, and bryophytes at 30 calcareous fens in the Inner Western Carpathians (Slovakia, Poland) after 13-17 years of warm summers and land-use changes. We found a small yet statistically significant effect of sampling period (old versus new survey) on the species composition of all three groups of organisms when the effect of various positions of sites along ecological gradients was controlled for. The compositional changes, interpreted with the help of Ellenberg´s Ecological Indicator Values, suggest an incipient succession towards grasslands and shrublands, driven by decreasing soil moisture and increasing nutrient availability. Although the number of habitat specialists did not change, the number of matrix-derived vascular plant and bryophyte species significantly increased, with six ubiquitous species of productive habitats being significantly more represented currently, while the richness of aquatic molluscs significantly decreased. Fens in which potentially strongly competitive plant species were less stressed because of less intense management and lower habitat extremity were more prone to such succession. There was no single factor that could predict the magnitude of composition changes; instead, tested factors were found to act synergistically. Conservation management was predominantly important for bryophytes, while extreme habitat conditions were predominantly important for terrestrial snails. We suggested a way how nature conservancy authorities can prioritise the management needs by applying an abiotic indicator system, with less environmentally extreme fens requiring more intense conservation management.

Keywords

Calcareous fens; global change; conservation management; environmental stress; molluscs; vegetation

1. Introduction

The Earth system is currently undergoing substantial change in climate and global biogeochemical cycles (Song et al. 2018), which affects the environment at regional and local scales. In many temperate regions, the global environmental change is coupled with land-use changes, and the

resulting synergy accelerates habitat and biodiversity loss (Tilman & Lehman, 2001, Herrera-Pantoja et al. 2012, Harpole et al. 2016). The settings of climate and local conditions in temperate Europe have recently supported the development of highly productive ecosystems dominated by few strongly competitive (C-strategy) species. Stress-tolerant (S-strategy) species have been forced to retreat either to small island-like ecosystems with extreme conditions unsuitable for strong competitors, or to ecosystems experiencing moderate yet frequent disturbances (Closset-Kopp & Decocq 2015, Hájek et al. 2017, Hille et al. 2018, Sand-Jensen et al. 2018). Multiple causes, such as the extinction of large herbivores and modern human interventions (e.g. thorough fire control, and river regulations) underlie the fact that only anthropogenic ecosystems such as mown grasslands, pastures, and military training areas are capable of preserving ancient species pools by maintaining regular disturbance regime (e.g. Pärtel et al. 2005, Warren & Büttner 2008, Cizek et al. 2013, Fajmonová et al. 2013). Calcareous fens are a specific type of peatlands with an active supply by groundwater, acting as a transition between the two types of refugia for stress-tolerant species mentioned above. They are scattered across the globe and occur at different continents from lowlands to mountains (Bedford & Goodwin 2003, Joosten et al. 2017), wherever a carbonate-rich bedrock is present. They have long been valued for their high species biodiversity and capacity to host many rare and endangered species (Bedford & Godwin 2003). Their environmental conditions are stressful for competitive species. Water table is usually high and nutrient availability low (Joosten & Clarke 2002), because of low decomposition rate (Lamers et al. 2015, Emsens et al. 2016, MacDonald et al. 2018), and frequent precipitation of calcium carbonate (tufa), contributing to phosphorus immobilisation (Boyer & Wheeler 1989). A low nutrient availability may stress organisms by resource limitation, while the tufa itself, if present in the form of hard crusts, affects organisms directly due to its specific structure and hardness. The crusts of calcareous tufa may allow, for example, the occurrence of some dryland snail species in spring fens (Horsák & Hájek 2003). Extreme habitat conditions help to maintain the stability of calcareous fens. When environmental conditions become less stressful, calcareous fens undergo natural autogenic or climate-driven succession towards acidic fens and bogs. Therefore, they have declined generally in the course of the Holocene (Walker et al. 1970, Rehell &Virtanen 2016, Hájková et al. 2018). They may further shift towards more productive tall herb, shrubland and

woodland ecosystems if nutrient availability is improved and disturbances are missing (Jensen & Schrautzer 1999, Koch & Jurasinski 2015, Jamrichová et al. 2018). Drainage and eutrophication lower environmental extremity of fens and trigger succession towards the more widespread wetland communities of lower conservation importance (Wołejko et al. 2002, Middleton et al. 2006, van Diggelen et al. 2006, Hájek et al. 2015). This development has been frequently documented by the resurvey studies of fen vegetation after decades (Fojt & Harding 1995, Bergamini et al. 2009, Kapfer et al. 2011, Moradi et al. 2012, Pedrotti et al. 2014, Seer & Schrautzer 2014, Koch & Jurasinski 2015, Pasquet et al. 2015, Navrátilová et al. 2017). Apart from eutrophication and altered hydrology, climate change may trigger or accelerate fen deterioration as well (Herrera-Pantoja et al. 2012, Essl et al. 2012, Jiménez-Alfaro et al. 2016). A dramatic decline in fen area and quality, in terms of the representation of indicator species, has taken place across the entire Europe. The vast majority (85%) of mire habitats are threatened in the European Union, and two habitat types of base-rich (calcareous) fens even belong amongst 10% of the most threatened European habitats (Janssen et al. 2016). In pristine landscapes, the natural disappearance of calcareous fens was slower and balanced by the initiation of new ones. Specialised species could quickly colonise newly appearing calcareous fens due to an undisturbed metapopulation dynamic. Such processes can no longer act in the current agricultural or industrial landscapes where the calcareous fens have a scattered island-like distribution which makes them prone to extinction (Horsák et al. 2018). Preservation of locally stable environmental conditions is therefore crucial to guarantee the future survival of calcareous fens and their biota. Although the stabilising effect of conservation management has been repeatedly documented (e.g. Billeter et al. 2007, Hájková et al. 2009, Galvánek et al. 2015, Ross et al. 2019), the effect of internal environmental filters has been less studied (Boyer & Wheeler 1989, Jabłonska et al. 2014, Grootjans et al. 2015, Horsák et al. 2018a). The lack of knowledge holds not only for plants but also for other organisms (but see Wettstein & Schmid 1999, Hoffmann et al. 2016, Horsák et al. 2018a, Štokmane & Cera 2018) although some of them, especially molluscs, may act as excellent indicators of habitat quality and stability of island-like habitats (Horsák et al. 2012, Horsáková et al. 2018).

The archipelago of calcareous fens in the Western Carpathians represents an excellent model system to test the factors that determine their stability. Calcareous fens locally persisted there even during the last glacial maximum, allowing for survival of calcareous fen specialists such as a land snail Pupilla alpicola (e.g., Ložek 1964) and a vascular plant Primula farinosa, the latter possessing a unique Carpathian haplotype (Theodoridis et al. 2019). During the Late Glacial and Early Holocene, many calcareous fens initiated and the habitat expanded (Hájková et al. 2012, Dítě et al. 2018, Hájková et al. 2018), while during the Middle Holocene most calcareous fens were encroached by woodlands (Hájková et al. 2015, Jamrichová et al. 2018). After this severe bottleneck, the greatest expansion of calcareous fens and fen grasslands has taken place after setting up anthropogenic disturbances such as regular mowing (Hájková et al. 2012, Jamrichová et al. 2014). In recent times, treeless calcareous fens, albeit restored anthropogenically, have become the last refugia for many endangered species. They include land snails Pupilla alpicola, Vertigo angustior and V. geyeri (Horsák et al. 2011), vascular plant specialists such as Primula farinosa, Triglochin maritima and Trichophorum pumilum (Dítě et al. 2013), and endangered bryophytes such as Pseudocalliergon trifarium, Meesia triquetra and Hamatocaulis vernicosus (Hájková et al. 2018). Some of them (V. angustior, V. geyeri and H. vernicosus) are even legally protected by the EC Habitats Directive (Council Directive 92/43/EEC). Most of these rare species are tightly associated with calcareous fens in the study region and do not occur in successionally advanced poor-fen, tall-herb, shrubland or woodland communities that have often replaced calcareous fens during the last decades, usually as a consequence of management cessation (Stanová 2000). To design appropriate conservation measures, it is, therefore, necessary to recognise the factors that determine the stability of calcareous fen islands and help to preserve their unique biodiversity. To obtain such knowledge, we revisited our semipermanent plots located in 30 discrete spring fen grasslands in the Western Carpathians (Slovakia and Poland). We first surveyed these plots for molluscs, vascular plants and bryophytes between 20012005. Since then, the study area has experienced substantial changes in land use, such as decrease or abandonment of mowing. Forest clearcutting and intense agriculture might further affect soil permeability and hydrological conditions in recharge areas. The study area further experiences a high nitrogen deposition (Bytnerowicz 1999, Jiroušek et al. 2011) and climate warming (Birsan et al. 2014),

including the increasing frequency and intensity of summer warm spells (Výberči & Pecho 2018). We aim to test whether the species composition and species richness of the three target and important indicator groups in fens have changed significantly over almost two decades. We hypothesise the compositional change towards the communities poorer in specialists and richer in generalists. We further test the effect of local habitat extremity (calcareous tufa precipitation, nutrient availability, water level, soil water content) and conservation management on the magnitude of compositional change. Understanding these effects can help to design and prioritise active conservation measures in fens.

2. Material and Methods

2.1 Study sites

In late May of 2018, we revisited 30 calcareous fens in the Inner Western Carpathians and closely adjacent regions (Fig. 1). The study area comprises the Inner-Carpathians basins (Liptov, Poprad, Turiec and Orawa-Novy Targ basins) and adjacent highlands and harbours the best-preserved calcareous fens in the Western Carpathians with a high representation of habitat specialists and relicts (Horsák et al. 2012, Dítě et al. 2018). Although most of these fens have initiated thousands of years ago, they mostly show abrupt shifts between woodlands and fens or between fens and other wetland habitats (Hájková et al. 2012, Jamrichová et al. 2018). Since the Middle Ages, and sometimes even since the Iron Age, these fens have served as mown or moderately grazed grasslands. This land use has facilitated the expansion of some calcareous-fen specialists (Hájková et al. 2015). Their pH ranges between 6.5 and 8.2 (mean 7.3) and calcium concentration in water ranges between 7 and 207 (average 78) mg.l-1. See Table 1 for other environmental characteristics.

2.2 Field sampling and explanatory variables

At each site, we found the patch where the first survey (2001-2005) was conducted using the Garmin inReach Explorer+ GPS device (Garmin, USA) with the bias of only a few meters. Four researchers (M.Háj., M.Hor., P.H. and D.D.) participated in both surveys, guaranteeing the same sampling strategy. In the first survey, the plots were preferentially selected to cover homogeneous sedge-moss patches, which are likely to support habitat specialists. Environmental data were not collected. In the second survey, we aimed to find the original plots as accurately as possible, although a small bias in meters cannot be excluded. Relative plant species abundances were estimated using the Braun-Blanquet cover codes at nine-grade scale (r, +, 1, 2m, 2a, 2b, 3, 4, 5) in both surveys. Mollusc individuals were extracted from 12-l samples of topsoil, including litter, bryophytes and herbaceous vegetation (one sample per plot) and processed by the wet sieving technique as described in Horsák (2003). We kept plot sizes the same as in the first sampling period, ranging from 16 to 25 m2. Water pH and water conductivity (μS.cm-1) were measured in shallow boreholes using portable instruments in both surveys. In 2018, we conducted more detailed measurements of local environmental conditions to describe local habitat extremity, including peat chemistry (Ca, Mg, K, Fe, total nitrogen, phosphates and total organic carbon). We collected the bulk peat sample in the central part of each vegetation plot from the depth of 0-10 cm. We estimated the amount of precipitated calcium carbonate in this bulk peat sample in three different ways: as a total inorganic carbon (TIC), loss of ignition at 950 °C (LOI) and by visual estimation in the field on the four-grade scale (0, none; 1, low; 2, intermediate; and 3, high). Because field estimation correlated more strongly with TIC (Pearson’s r = 0.93, p < 0.0001) than with LOI (r = 0.89, p < 0.0001), we used only TIC in subsequent analyses. Water content in the same peat sample was measured volumetrically, as a weight difference between the fresh sample and the sample dried at 105 °C until constant weight. We used the same peat sample also for chemical analyses. Water extraction was used to obtain soil solution. The novAA 350 flame atomic absorption spectrometer from Analytik Jena equipped with an autosampler and dilutor was used to determine the Ca, Mg, K and Fe contents. Phosphate phosphorus, nitrate (NO3-) and ammonium (NH4+) were determined by using the Helios Delta VIS Spectrometer (manufacturer Thermo Electron Corporation) with a sipper unit. Total organic carbon (TOC), total inorganic carbon (TIC) and total nitrogen (TN)

were measured using the Shimadzu TOC-VCPH Analyzer with the TNM-1 module. Total nitrogen correlated strongly with the sum of ammonium and nitrate ions (Pearson’s r = 0.99; p < 0.0001). Depth to water table was measured relative to the apical parts of highest mosses. Management intensity was estimated using observations during the study period and consultations with nature conservancy authorities. We used the four-grade scale: 0, no disturbance reported; 1, occasional mild disturbance (mowing, mulching, grazing or a single tree and shrub cutting event); 2, repeated yet irregular disturbance (typically mowing); and 3, frequent disturbance of mowing by an engine hand brush cutter in most cases. To interpret the compositional shifts between the two sampling periods, we calculated unweighted means of the Ellenberg’s Indicator Values (EIVs; Ellenberg & Leuschner 2010) for moisture and nutrient availability (originally called “nitrogen”). We calculated mean EIVs for each of the old and new vegetation-plot records of vascular plants.

2.3 Species identification and categorization

Molluscs were extracted from the sampled material under a dissecting stereomicroscope and identified based on Horsák et al. (2013); the nomenclature follows Horsák et al. (2018b). Only the individuals alive at the time of sampling were counted, to avoid a potential bias caused by the accumulation and long-term preservation of old mollusc shells at calcium-rich fens (Cernohorsky et al. 2010, Říhová et al. 2018). Bryophytes and rooted or aquatic vascular plants were recorded in the study plots by three experienced botanists (M.Háj., P.H. and D.D.); bryophyte specimens were checked under a microscope to verify the field identifications. The nine-grade Braun-Blanquet scale was transformed to percentages prior to statistical analyses using the protocol of the JUICE software (www.sci.muni.cz/botany/juice/) that slightly overestimates taxa with a lower cover (r = 1%; + = 2%; 1 = 3%; 2m = 4%; 2a = 8%; 2b = 18%; 3 = 38%; 4 = 63%; 5 = 88%). Species of all the three study groups were classified as either habitat specialists or matrixderived species (i.e. those capable of inhabiting surrounding environment), following the extensive

literature review in combination with own field expertise (for details and full lists of species see Horsáková et al. 2018).

2.4 Environmental data and the Extremity Index

To reflect a potentially synergistic or antagonistic effect of multiple stress factors on the species composition, we combined the individual variables into an index reflecting the environmental extremity of a site. Note that in this context, “stress” helps to maintain habitat-specific conditions that are crucial for the survival of fen specialists. With the increasing Extremity Index value, there is an increase in local habitat extremity (environmental stress). It hypothetically blocks the succession from fen communities rich in specialists (mostly S-strategy species) to more productive grassland-like and shrubland communities richer in C-strategy species. The index was compiled by summing the values for individual stress-factors linearly transformed to [0, 1] range. In order to avoid overestimation of some ecological factors, the limited set of mutually uncorrelated environmental factors was included: (1) the amount of calcium carbonate measured as TIC, (2) depth to water table (inverse transformed value; higher value = higher water table), (3) soil water content (not significantly correlated with depth to water table; Pearson’s r = -0.203; p = 0.282), and (4) nutrient availability expressed on the fivegrade scale. The nutrient availability scale was compiled not only to avoid inter-correlated factors in the Extremity Index, but also to cope with the outlying values. We derived the scale from the site clustering in the x-y relationship between total nitrogen (TN) and phosphates (PO43-). The categorical value of 0 (lowest nutrient stress) refers to sites with TN > 4.5 mg.l-1 and PO43- ≥0.02; the value of 0.25 refers to sites with TN = 3-3.5 mg.l-1 and PO43- 0.01-0.022 mg.l-1; the value of 0.5 refers to sites with TN = 1.5-2.5 mg.l-1 and PO43- = 0.001-0.017 mg.l-1; the value of 0.75 refers to sites with TN < 1.8 mg.l1 and

PO43- = 0.003-0.012 mg.l-1 and the value of 1 refers to nutrient-poorest sites with TN < 1.8 mg.l-1

and PO43- < 0.001 mg.l-1. In trial analyses (not shown), we also tested the inclusion of pH, calcium, and their combination (Plesková et al. 2016) to the Extremity Index. The results remained virtually the same, perhaps because of a low variation in alkalinity among study fens. For the sake of simplicity, we, therefore, did not include pH and calcium into the Extremity Index for further analyses.

Separately, we also tested the Extremity Index complemented with management intensity, another factor that may stress competitive species and stabilise sedge-moss fen communities. Hereafter we call it the Extremity & Management Index. We included management intensity using the fourgrade scale as described above, which was linearly transformed to [0, 1] range as well.

2.5 Statistical analyses

Species-by-site matrices of sqrt-transformed abundance data (i.e. numbers of mollusc individuals and percentage plant covers) were created separately for the first (2001-2005) and second (2018) sampling periods. Pairwise distances between the old and new samples were calculated using the Bray-Curtis dissimilarity index. These dissimilarity values were used in further analyses, to express the magnitude of species composition change at each site. To assess the major successional trajectories between the two sampling periods, we conducted an indirect ordination analysis (Metric Multidimensional Scaling, MDS, also known as PCoA). This robust technique to reveal the main compositional changes in ecological data is based on the Bray-Curtis dissimilarities between the samples (Faith et al. 1987). Broken-stick model (Peres-Neto et al. 2003) was used to check the importance and ecological relevance of ordination axes. To interpret the main MDS axes, we projected the selected variables passively into the twodimensional ordination space. These variables include numbers of specialised and matrix-derived species of all studied taxa, number of aquatic molluscs, and EIVs for moisture and nutrient availability. Their fit into the ordination axes was tested using the “envfit” function in the “vegan” package (separately for each MDS analysis). Only significant variables were projected into the ordination diagrams (p < 0.05, 9999 permutations). Species with the highest fit in the two-dimensional ordination space were plotted into the ordination diagrams. Generalized Additive Models (GAMs) on the ln-transformed species abundances of the species occurring in more than ten samples (p < 0.001) were used to identify the influential species. These two procedures allowed for a better understanding of the main compositional shifts between the two sampling periods that are expressed by vectors connecting old and new samples. To test whether there is a significant change in the species

composition between the old and the new samples, we used the partial distance-based redundancy analysis (db-RDA) based on the Bray-Curtis dissimilarities. Variables representing nutrient availability (TN and PO43-), hydrological conditions (depth to water table and soil water content) and calcium richness (adjusted pH and TIC), describing the main ecological gradients operating among the study sites, acted as covariates. Inclusion of covariates allowed us to control for the effect of different positions of sites on the ecological gradients and to test only the effect of sampling period (old versus new samples) on the residual variation (p < 0.05 and 9999 permutations). For this purpose, measurements from the second sampling period were assigned to both the old and new samples, to remove the above described variation in site positions on the ecological gradients. Virtually the same results (although of slightly lower significance) were obtained when either EIVs from the old or new sampling periods were used instead of the exactly measured environmental factors (data not shown). The Indicator Species Analysis (IndVal) was used to find species that are significantly associated with the samples from either the first (2001-2005), or the second (2018) sampling period, based on their relative frequencies and relative average abundances in these periods (Dufrêne & Legendre 1997). The higher the value, the more representative a species is for one of these periods. Pairwise differences in the species counts (total number of species, number of habitat specialists, and number of matrix-derived species) between the old and new samples, and differences in the positions of old and new samples along the principal MDS axis (i.e. site scores), were tested separately for molluscs, vascular plants and bryophytes. We used the nonparametric Wilcoxon signedrank test because the values of some tested variables were not normally distributed. Wilcoxon tests of the species counts were performed separately for land snails and aquatic molluscs because their species richness might be governed by different environmental factors (Schenková et al. 2012). Contrary, multivariate statistics were performed for all molluscs combined. Separate multivariate analyses of land and aquatic molluscs were not possible because of frequent absences of aquatic molluscs in samples. We tested the relationships between the magnitude of composition change (BrayCurtis dissimilarities between the old and new samples), individual environmental factors and indexes (Extremity Index, Extremity & Management Index) using the linear regressions. The significance of regression models was tested using the F-statistic, and percentage of the explained variation was

expressed as adjusted R2. In the cases of multiple testing, the p-values were adjusted using the Holm’s correction (Holm 1979). The analyses were performed in R 3.4.0 (R Core Team, 2017), using the ‘vegan’ (Oksanen et al., 2017), ‘labdsv’ (Roberts, 2016), and ‘ggplot2’ (Wickham, 2016) packages.

3. Results

3.1 Observations in the field

All study fen communities have persisted throughout the study period. Based on the visual evaluation, most of them have kept the original sedge-moss vegetation structure, although at some of them, we observed the increasing representation of herbs or tree saplings. Two of them (no. 19, and 29, see Appendix 1) have changed substantially, and are now represented by the tall-herb-willow rather than the sedge-moss communities. In few cases (no. 4, and 11) the study plot was encroached by more tall herbs and woody plants, yet the fen as a whole still contained the sedge-moss patches similar to the structure of the old plot, perhaps as a consequence of a shift in the spring position or decrease in the number of sedge-moss patches. On the other hand, in some sites, the original study plot has preserved the same structure, while a substantial change was observed in the plot surroundings, more distant from the mainspring. The area of well-preserved sedge-moss fen was hence reduced, although the resampling results indicate a low or no change (no. 14, and 17). In one site (no. 12), the study patch itself showed a lower representation of grassland and higher representation of fen species because of an obvious hydrological change (blocked runoff), while the rest of the fen was heavily affected by reed expansion.

3.2 Species richness and composition changes

For all three studied groups of organisms, the db-RDA showed a significant, yet subtle, effect of sampling period on the species composition when the effect of the main ecological gradients was

controlled for (see Methods). Period (old versus new samples) explained 3.8% (p = 0.007), 2.5% (p = 0.018) and 2.7% (p = 0.037) of the compositional variation for molluscs, vascular plants, and bryophytes, respectively. Between the two sampling periods, the median number of all vascular plants per plot increased from 25.0 to 31.5 (p << 0.001). The matrix-derived species largely drove this change, increasing from 13.0 to 17.5 species per plot (p << 0.001). The number of matrix-derived bryophytes slightly increased as well (p = 0.002). The median numbers of specialists did not change significantly, except for a slight increase in vascular plants (from 13.0 to 14.5; p = 0.012; though this result was no longer significant at adjusted p-values). Median number of aquatic molluscs decreased from 4.0 to 2.5 (p < 0.006). The unweighted mean of EIVs for nutrient availability significantly increased (p < 0.001), while the unweighted mean of EIVs for moisture significantly decreased (p = 0.001) since the first sampling period. For the results of all paired tests, see Table 2 and Fig. 2. Indicator species analysis showed that the aquatic bivalve Pisidium casertanum, and the lightdemanding moss Bryum pseudotriquetrum, were the only species that significantly (p < 0.05) characterised the first sampling period. The group of species characterising the second sampling period was more numerous. It consisted mostly of matrix-derived species of more productive habitats. The examples are the ubiquitous land snail Semilimax semilimax, wet-grassland and hummockdwelling nutrient-demanding moss Brachythecium mildeanum, spruce (Picea abies) saplings, short nutrient-demanding grass Festuca rubra (showing the highest significance of all species; p = 0.001), short herb of moderately-rich fen grasslands Epilobium palustre, and two nutrient-demanding tall herbs Filipendula ulmaria and Valeriana officinalis s. str. (Table 3). We interpreted the principal MDS gradients of vascular plants and bryophytes as shifts from sedge-moss strongly calcareous fens to fens harbouring more grassland and shrubland species (the fento-grassland/shrubland gradient; Fig. 3b,c). This interpretation is based on species compositions of the plots at the opposite ends of the gradient, and species counts/EIVs projected into the ordination space. In bryophytes, the fen-to-grassland/shrubland gradient also stretched along the second axis. This pattern reflects the difference between fen grasslands with (upper part of the diagram) or without (lower part of the diagram) calcium-tolerant Sphagnum species (Fig. 3c). In molluscs, the principal

axis was driven by the representation of aquatic species. It hence reflects the differences in water level, while the second axis reflects the fen-to-grassland/shrubland gradient, which was important mainly for the fens with less aquatic species (Fig. 3a). Contrary to bryophytes and molluscs, the second axis was no longer ecologically meaningful in vascular plants according to the Broken-stick model (not shown). The vectors connecting old and new samples showed that the directions from fens towards grassland/shrubland communities visually clearly prevailed over the other directions in all studied groups (Fig. 3). The median site score values along the first MDS axis significantly differed between the pairs of old and new samples for all study groups (Table 4), suggesting community shifts towards grasslands (in plants) or drier conditions (in molluscs). However, these shifts were generally quite small, with only a few sites showing a great compositional turnover from one to the opposite end of the gradient (Fig. 3).

3.3 The effect of multiple stress factors on a compositional change

Most tested relationships between the individual stress factors and the magnitude of compositional change (Bray-Curtis dissimilarities) were non-significant or weakly significant (Table 5). However, the relationships between the species composition dissimilarities and the Extremity & Management Index (a value considering multiple stress factors, i.e. carbonate precipitation, water level, soil water content, nutrient availability and management intensity) were negative and significant for all study groups of taxa (Table 6, Fig. 4). The highest fit obtained for bryophytes (adj. R2 = 50.0%, p << 0.001). These results suggest that with the higher environmental stress and management intensity, the change in the species composition throughout the sampling periods becomes lower. When the Extremity Index (without management intensity considered) was tested, the relationships were only marginally significant, or not significant at all with the Holm-adjusted p-values. The relationship remained relatively strong only for land snails (Table 6). This result suggests that the management intensity strongly conditioned the effect of environmental stress factors. Bryophytes showed the largest difference in the magnitude of compositional change explained by the Extremity Index and Extremity & Management Index (a decrease in the explained variation by 38.6% when

management intensity was excluded). In contrast, for both all molluscs and land snails the exclusion of the management intensity lowered the explained variation by only 2.4% and 5.1%, respectively. The result obtained for vascular plants was intermediate (14.2%).

4. Discussion

4.1 Small yet significant changes: good news, or warning?

For all study taxa, we detected subtle yet statistically significant change in the overall species composition between the first and second sampling periods. The numbers of habitat specialists, a critical measure of habitat deterioration, have however not decreased. Such results may seem overly optimistic in times of apparent global and regional changes in environment and climate, and especially in the light of analogous resurvey studies that report a strong decline and substantial transformation of calcareous and base-rich fens in Great Britain (Fojt & Harding 1995, Menichino et al. 2016), German and Dutch lowlands (van Belle et al. 2006, Seer & Schrautzer 2014, Koch & Jurasinski, 2015), Swiss pre-Alps (Bergamini et al. 2009, Moradi et al. 2012), Bohemian Massif in the Czech Republic (Hájek et al. 2015, Navrátilová et al. 2017) or even Scandinavia (Kapfer et al. 2011, Pedrotti et al. 2014). What, then, makes the situation of Western Carpathian fens different and seemingly more optimistic? It appears that the extreme environmental conditions of the Western Carpathian fens, along with the conservation management in some sites, have – for the time being – helped to maintain a relatively stable species composition. Calcium carbonate precipitation is an important stabilising factor due to its ability to bind superfluous phosphorus (Boyer & Wheeler 1989, Corman et al. 2015), thus preventing a succession of fens towards more productive ecosystems (Wassen et al. 2005). Maintaining or restoring active calcium carbonate precipitation should hence be an ultimate conservation and restoration aim (Grootjans et al. 2015). When calcium carbonate is not precipitating at all, other local conditions such as undisturbed hydrology may stabilise fen ecosystems as well (Jabłońska et al. 2019). Carbonate precipitation along with a stable, deep groundwater circulation, has determined a long-time persistence of wooded or open sedge-moss calcareous fens in the study area spanning even the entire Holocene

period (Hájková et al. 2015) and allowing a survival of numerous relicts from the Late Glacial and Early Holocene times (Hájek et al. 2011, Dítě et al. 2018). The two sites that have undergone the most obvious changes towards tall-herb grasslands and shrublands are small in size and show a shallow peat layer. They are further not associated with deep groundwater circulation. It, therefore, seems that our results cannot be generalised beyond the study region of the Inner Western Carpathians where the fens are mostly old and ancient. Horsák et al. (2007) and Hájek et al. (2011) have demonstrated a striking difference in the species composition and history between fens in the Inner and the Outer Western Carpathians. Rather high stability of calcareous fens may be hence only a matter of the Inner Western Carpathians. Our observations from the Outer Western Carpathians indeed suggest that the loss of calcareous fens is rapid there, and the persistence of the last remnants greatly depends on the conservation management such as regular mowing (Hájková et al. 2009), similarly as in other analogous regions (Billeter et al. 2007, Menichino et al. 2016). In addition to the significant effect of sampling period, other signs of successional shifts towards grasslands and shrublands were detected in our resurvey study. The number of aquatic mollusc species decreased, and the number of matrix-derived species increased, suggesting a water level decline and surface homogenisation due to a disappearance of small shallow pools. Some nutrient-demanding species such as Festuca rubra, Valeriana officinalis, Filipendula ulmaria and Epilobium palustre have increased their frequency and abundance. Their increase may indicate an accelerated decomposition rate due to climate warming and desiccation (Bragazza et al. 2009, Lamers et al. 2015, Emsens et al. 2016), and/or nitrogen deposition and nutrient input from the surrounding agricultural land (Koerselman et al. 1990, Lamers et al. 2015, Hille et al. 2018). The change towards drier and nutrient-richer conditions is also evidenced by statistically significant changes in EIVs for moisture and nutrient availability. As a consequence, the number of matrix-derived vascular plant species increased about ca. 25% during the last two decades. The number of vascular plant specialists nevertheless did not decrease, perhaps because of a clonal nature of most species, making them partially resistant to changes in water level. The increase of plant species richness in fens over the last few decades has been currently reported also from other regions (Bergamini et al. 2009, Stix & Erschbamer 2018). Moreover, the

number of mostly generalist vascular plant species has been recently observed to increase in another island-like ecosystem of extreme conditions, i.e. mountain summits, as a consequence of climate warming (Czortek et al. 2018, Steinbauer et al. 2018). The ongoing global change hence alleviates the level of environmental stress and habitat extremity (Gutiérrez-Cánovas et al. 2019), changes biotic interactions among species (Michalet et al. 2014, Olsen et al. 2016), and leads to the decreasing contrast between the habitat islands and the surrounding landscape matrix (Horsáková et al. 2018). This development ultimately causes the disappearance of the habitat from the landscape.

4.2 Conservation management as an environmental change mitigation

The trend detected in our study calls for the continuation or even extension of active conservation measures even in fens that have persisted for millennia. Although the need for conservation management in natural ecosystems may sound odd, the current species composition of calcareous fen grasslands has largely formed as late as since the times of human deforestation and subsequent management of fen basins (Hájková et al. 2015). Even in the boreal zone of Europe, where fens are natural and even semi-zonal, Ross et al. (2019) reported mowing as the main tool to mitigate the undesired effects of global environmental change. With humans severely affecting the Earth system, it would be naive to expect natural habitats to persist in the same way as they would under pristine conditions. On the other hand, our results seemingly contradict those from Poland (Kotowski et al. 2013, Kozub et al. 2019) that report a negative effect of mowing on pristine fen ecosystems, such as surface homogenisation, peat compression and disappearance of some specialists. The main difference is related to the machinery used. While tracked mowers were used to manage the Polish fens, hand brush cutters mowed most of the fens in our study. Other differences might also be related to hydrology and history. Soligenous rather than topogenous fens prevail in our study area, and they have been mostly transformed from wooded fens as a consequence of deforestation and mowing since the Iron Age (Hájková et al. 2012, 2015).

A good piece of news for regional nature conservancy authorities is that the magnitude of environmental changes in our study area is still not high enough to suppress the mitigating effect of the conservation management. In some other central European regions, calcareous fens are changing even when the prescribed disturbance by mowing is not interrupted (Bergamini et al. 2009, Moradi et al. 2012, Hájek et al. 2015). The reason is that either the environmental change is already so intense, or habitat conditions are less extreme. Analogous results are also reported from North America, where even a short-term cessation of disturbance triggers fast successional change towards grassland-like fens (Merriam et al. 2018). Another good piece of news is that the number of specialised species has not decreased yet. We even confirmed the presence – yet in few individuals – of the most important diagnostic species (e.g. Hamatocaulis vernicosus, Equisetum variegatum and Vertigo geyeri) in the fens which have visually changed the most. Restoration of conservation-oriented disturbances in the most heavily affected fens would hence lead to the rescue of local fen communities at the eleventh hour. And finally, we have shown that we can prioritise the management needs by applying an abiotic indicator system, such as the Extremity Index, with less environmentally extreme fens requiring more intense conservation management.

4.3 Active conservation needs for bryophytes

Bryophyte calcareous fen communities showed the strongest need for active conservation management to maintain their long-term stability in the current landscape. The local stress factors such as high calcium carbonate precipitation, high water content and low nutrient availability appeared to be insufficient. Bryophytes act as important ecosystem engineers and may indicate incipient successional changes in fen ecosystem and maintenance of their original composition often requires prescribed disturbances (Hájek et al. 2015, Singh et al. 2019). Major functional groups of bryophytes, so-called brown mosses and Sphagnum mosses, differ in their effect on the biogeochemical and hydrological conditions in fen surface (Gornall et al. 2007; Crowley & Bedford 2011), on the successional trajectories (Vicherová et al. 2017), and especially on the germination and recruitment of different vascular plant species (Ohlson et al. 2001, Lett et al. 2018, Singh et al. 2019). They respond

very rapidly to environmental changes and may have high growth rates (Udd et al. 2016), being able to dominate the ecosystem faster than vascular plants. Some of our revisited fens indeed became strongly dominated by generalist act as important ecosystem engineers, species such as Calliergonella cuspidata (site no. 14), Plagiomnium elatum (site no. 19) or monodominant carpets of Sphagnum warnstorfii (sites no. 9, and 21). All these changes may dramatically change not only other bryophyte species, such as a calcareous fen specialist Scorpidium cossonii and recently rapidly declining relict species such as Meesia triquetra, Pseudocalliergon trifarium, Catoscopium nigritum, Paludella squarrosa and Scorpidium scorpioides (Hájková et al. 2018), but also current vascular plant and mollusc communities. The expansion of Sphagnum mosses and other fast-growing bryophytes may endanger less clonal and non-clonal vascular plants such as Primula farinosa, Triglochin palustris, Pedicularis palustris and Saxifraga hirculus (Singh et al. 2019) as well as land snail habitat specialists such as Vertigo geyeri, V. angustior and Pupilla alpicola (e.g. Hájek et al. 2006, Schenková et al. 2012). When the bryophyte layer is changed entirely, it may alter the functioning of a fen ecosystem. Our results optimistically demonstrate that the early establishment of conservation management may help prevent undesired succession in the bryophyte layer, which would potentially have far-reaching and detrimental consequences for the entire fen ecosystem.

5. Conclusions

Despite the ongoing rapid fen deterioration currently reported across temperate Europe, we found small yet statistically significant differences in the overall species composition of molluscs, vascular plants and bryophytes in 30 calcareous fens of the Western Carpathians over almost two decades. According to the EIVs for vascular plants and changing representation of aquatic molluscs, the compositional change may be explained by decreasing soil moisture and increasing nutrient availability. We reported a significantly increasing species richness, driven by the increase in matrixderived, usually generalist species. Successional shift towards grasslands and shrublands was more apparent in less environmentally extreme and less intensively managed fens. Nevertheless, rare and

low competitive fen specialists have persisted at most abandoned sites, providing a chance that the original sedge-moss fen communities may be restored when management will be re-established. Our data show that the local habitat extremity – compared to the character of the surrounding habitats – can successfully mitigate the effect of contemporary climate and environmental changes. However, this mitigating effect acts only when the extremity of local conditions is high enough, and only when multiple stress factors come into play, with an active conservation management having the key role in preventing the species composition changes from fens towards grassland and shrubland communities. Our results point out that the management intensity should be optimised to reflect the level of environmental extremity of individual sites, with less extreme fens requiring more intense conservation management.

Acknowledgements We thank M. Pavonič and L. Petr for conducting the laboratory analyses, O. Hájek for the map preparation, anonymous reviewers for constructive comments and nature conservancy authorities for providing us the data about the conservation management applied in the study fens.

Funding: This work was supported by the Czech Science Foundation [grant number 19-01775S]. PH was partially supported by the long-term developmental project of the Czech Academy of Sciences (RVO 67985939).

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Table 1. Descriptive statistics for environmental variables measured at the 30 study sites (either directly in the field, or in the water and soil samples in the laboratory), and numbers of mollusc, bryophyte and vascular plant species, and unweighted means of Ellenberg Indicator Values (EIVs) for moisture and nutrient availability. Note that while the species counts are available for both periods, exact measurements of environmental data were conducted during the resurvey period only.

A. Environmental variables Resurvey (2018)

Minimum

1st

value

quartile

Median

Mean

3rd

Maximum

quartile

value

Water pH

6.5

7.1

7.4

7.3

7.6

8.2

Water conductivity (μS/cm)

68

462

507

568

675

1702

Adjusted pH

5.8

7.4

7.6

7.5

7.9

8.9

Ca (mg/l)

7.2

54.1

72.4

78.4

87.8

206.6

Mg (mg/l)

2.0

10.8

14.7

20.2

21.0

111.1

K (mg/l)

0.2

1.0

1.5

2.8

2.7

11.8

Fe (mg/l)

0.01

0.11

0.54

1.74

1.95

17.19

Total N (mg/l)

0.16

0.55

1.12

1.50

1.76

5.53

0.001

0.001

0.007

0.009

0.012

0.066

Total organic C (mg/l)

5.6

8.8

18.6

19.4

23.3

65.6

Total inorganic C (mg/l)

0.0

0.1

17.4

32.8

62.8

96.1

Soil water content (%)

42.5

75.5

84.6

80.7

88.0

92.8

Water table depth (cm)

3.0

5.3

10.0

11.8

15.0

50.0

Phosphates (mg/l)

B. Species counts First survey (2001-2005)

Minimum

1st

value

quartile

Median

Mean

3rd

Maximum

quartile

value

Molluscs

7

13

17

16

20

25

Land snails

3

10

13

13

16

22

Aquatic molluscs

0

3

4

4

5

6

Mollusc specialists

0

3

3

3

4

8

Mollusc matrix spp.

5

10

14

13

16

21

All vascular plants

19

22

25

27

29

47

All bryophytes

3

6

7

8

10

18

Vascular plant specialists

7

11

13

13

15

21

Vascular plant matrix spp.

5

8

13

14

17

32

Bryophyte specialists

1

4

5

5

7

10

Bryophyte matrix spp.

0

1

2

2

3

6

Molluscs

9

13

17

16

18

24

Land snails

8

10

13

13

15

22

Aquatic molluscs

0

1

3

3

4

6

Mollusc specialists

1

2

4

3

4

6

Mollusc matrix spp.

6

10

13

12

14

20

All vascular plants

23

28

32

33

38

52

All bryophytes

3

7

9

9

12

17

Vascular plant specialists

7

13

15

14

16

23

Vascular plant matrix spp.

9

15

18

19

22

34

Bryophyte specialists

0

3

5

5

6

11

Bryophyte matrix spp.

1

2

3

3

4

8

Resurvey (2018)

C. Ellenberg Indicator Values First survey (2001-2005)

Minimum

1st

value

quartile

Median

Mean

3rd

Maximum

quartile

value

EIVs moisture

6.96

7.74

7.91

7.84

8.00

8.42

EIVs nutrient availability

2.68

3.08

3.25

3.36

3.65

4.49

EIVs moisture

6.60

7.46

7.68

7.64

7.88

8.22

EIVs nutrient availability

2.67

3.45

3.65

3.61

3.83

4.52

Resurvey (2018)

Table 2. Wilcoxon signed-rank tests for the differences between the pairs of the old (2001-2005) and new (2018) samples, in terms of the species richness of molluscs, vascular plants and bryophytes, and unweighted means of Ellenberg Indicator Values (EIVs) for moisture and nutrient availability. Significant results (p < 0.05) are marked with asterisks, and results that are significant after Holm’s correction are shown in bold.

Wilcoxon signed-

W-

rank tests All species

value Molluscs

Matrix-derived sp.

EIVs

Median

p-Holm

(2001-05)

(2018)

198

0.575

1.000

17

16.5

129.5

0.566

1.000

12.5

13

Aquatic molluscs

211

0.006*

0.046

4

2.5

Vascular plants

34.5 <0.001*

<0.001

25

31.5

Bryophytes

96.5

0.076

0.455

7

8.5

Molluscs

68.5

0.715

1.000

3

3.5

Vascular plants

69.5

0.012*

0.085

13

14.5

Bryophytes

92.5

0.646

1.000

4.5

5

219.5

0.470

1.000

13.5

12.5

Vascular plants

49.5 <0.001*

0.002

13

17.5

Bryophytes

52.5

0.002*

0.014

2

3

347.0

0.001*

0.001

7.91

7.68

55.5 <0.001*

0.001

3.25

3.65

Land snails

Specialists

p

Median

Molluscs

Moisture Nutrient availability

Table 3. Indicator species analysis showing mollusc, bryophyte and vascular plant species significantly associated with samples from either the first (2001-2005), or second (2018) sampling periods. For the significant (p < 0.05) indicator species, the indicator values based on the relative frequency and relative sqrt-transformed average abundance of the species in samples of a particular period, and significance of the result are shown. Species are ordered decreasingly according to their indicator value. The abbreviations in parentheses: m = mollusc, v = vascular plant, b = bryophyte.

First survey (2001-2005)

IndVal

p

Pisidium casertanum (m)

0.74

0.007

Bryum pseudotriquetrum (b)

0.74

0.048

Festuca rubra (v)

0.71

0.001

Picea abies (v)

0.59

0.003

Semilimax semilimax (m)

0.59

0.014

Epilobium palustre (v)

0.53

0.006

Filipendula ulmaria (v)

0.50

0.044

Brachythecium mildeanum (b)

0.48

0.012

Valeriana officinalis (v)

0.41

0.050

Resurvey (2018)

Table 4. Wilcoxon signed-rank tests for the differences between the pairs of the old (2001-2005) and new (2018) samples, in terms of their position (site scores) on the 1st axis of the MDS ordinations (for details see Fig. 3). A significant difference means a significant and directional shift along the principal MDS axis, driven by the species composition change. Significant results (p < 0.05) are marked with asterisks, and results that are significant after Holm’s correction are shown in bold.

Wilcoxon signed-

W-

rank tests MDS1 site scores

value

Median

Median

(2001-05)

(2018)

p value

p-Holm

383

0.001*

0.002

0.008

-0.064

Vascular plants

73

0.001*

0.002

-0.064

0.012

Bryophytes

42

<0.001*

<0.001

0.116

-0.006

Molluscs

Table 5. Linear regressions between the magnitude of species composition change (expressed as BrayCurtis dissimilarities between the old and new samples with sqrt-transformed abundance data) and all individual stress factors, as well as factors combined into the Extremity and Extremity & Management Index. Values of F-statistic and p-values were calculated separately for all molluscs, land snails, bryophytes and vascular plants. Significant results (p < 0.05) are marked with an asterisk, and results that are significant after Holm’s correction are shown in bold. Detailed results for the Extremity and Extremity & Management Indexes, as the only variables significant for all study taxa, are shown in Table 6.

Molluscs F

Land snails

p

F

p

Vascular plants F

Bryophytes

p

F

p

Water pH

0.54

0.469

1.15

0.293

0.33

0.573

0.37

0.550

Water conductivity (μS/cm)

1.13

0.297

2.99

0.095

1.58

0.220

0.34

0.567

Adjusted pH

1.09

0.306

3.32

0.079

0.29

0.596

0.86

0.363

Ca (mg/l)

0.29

0.596

1.40

0.247

0.48

0.493

0.66

0.424

Mg (mg/l)

0.73

0.399

1.72

0.200

0.00

0.952

1.44

0.240

K (mg/l)

0.42

0.523

0.16

0.694

2.63

0.116

0.03

0.856

Fe (mg/l)

0.92

0.345

0.86

0.361

0.36

0.552

0.62

0.439

Total N (mg/l)

4.70 0.039*

2.86

0.102

0.42

0.522

1.76

0.195

Phosphates (mg/l)

5.06 0.033*

3.32

0.079

0.10

0.752

2.58

0.119

Total organic C (mg/l)

1.69

0.205

2.92

0.099

1.14

0.294

1.74

0.197

Total inorganic C (mg/l)

1.16

0.291

3.47

0.073

3.53

0.071

11.80

0.002*

Soil water content (%)

0.58

0.451

0.33

0.571

0.05

0.828

4.44

0.044*

Water table depth (cm)

2.01

0.168

7.07 0.013*

5.07 0.032*

0.13

0.725

Management

0.03

0.862

0.09

1.09

0.306

7.84

0.009*

Extremity Index

5.35 0.028* 11.40 0.002*

11.87 0.002*

30.02

<0.001*

0.768

Table 6. A. Linear regressions between the magnitude of species composition change (expressed as Bray-Curtis dissimilarities between the old and new samples with sqrt-transformed abundance data) and the Extremity & Management Index. Percentage of explained variation (R2 and Adj R2), values of F-statistic, p-values, and p-values adjusted using the Holm’s correction were calculated separately for all molluscs, land snails, bryophytes and vascular plants. Significant results (p < 0.05) are marked with an asterisk, and results that are significant after Holm’s correction are shown in bold; B. The same analyses for the Extremity Index (without management).

A. Extremity & Management Index*

R2

Adj R2

F-statistic

p

p-Holm

Molluscs

16.05

13.05

5.35

0.028*

0.452

Land snails

28.93

26.39

11.40

0.002*

0.035

Vascular plants

29.77

27.26

11.87

0.002*

0.029

Bryophytes

51.74

50.01

30.02

<0.001*

<0.001

p

p-Holm

B. Extremity Index**

R2

Adj R2

F-statistic

Molluscs

13.75

10.67

4.46

0.044*

0.568

Land snails

23.97

21.26

8.83

0.006*

0.090

Vascular plants

16.11

13.11

5.38

0.028*

0.419

Bryophytes

14.49

11.43

4.74

0.038*

0.494

* including carbonate precipitation, water level, soil water content, nutrient availability, and management intensity ** including all the above, except for management intensity

Figure 1. Geographic location of the 30 study fen grasslands. All sites were first sampled in 20012005 and revisited in 2018.

Figure 2. Box-and-whisker plots of unweighted Ellenberg Indicator Values for moisture and nutrient availability calculated for the old (2001-2005) and new (2018) samples of vascular plants. The difference in EIVs between the two sampling periods was tested using the Wilcoxon signed-rank test (see Table 2). The central line of each box refers to the median value, box height to the interquartile range and whiskers to the non-outlier range (i.e. 1.5 times the interquartile range on each side).

Figure 3. MDS ordination analysis of the 30 study sites, based on the Bray-Curtis dissimilarity matrix of sqrt-transformed abundance data, with the position of samples along the first and second ordination axes. Each site was sampled twice, i.e. during the first (2001-2005) and second (2018) survey periods, and the pairs of the old and new samples are connected with arrows (oriented towards the new samples). The arrows suggesting a shift from fen towards grassland or shrubland communities are shown in bold. Selected species with the highest fit to the main ordination axes (GAMs, p < 0.001, lntransformed abundances of species occurring in more than ten samples) were shown in the ordination diagrams. Species counts and EIVs with a significant fit to the main ordination axes were passively projected into the ordination space as well (“envfit” function in the “vegan” package, p < 0.05, 9999 permutations). Abbreviations: Sp moll/vasc/bryo = number of specialist land snail/vascular plant/bryophyte species, MD moll/vasc/bryo = number of matrix-derived land snail/vascular plant/bryophyte species, Aq moll = number of aquatic molluscs, Moist = EIVs for moisture, Nutr = EIVs for nutrient availability. For the abbreviations of species names see Appendix 2.

Figure 4. Linear regressions of the species composition changes (expressed as Bray-Curtis dissimilarities between the old and new samples with sqrt-transformed abundance data), in relation to the Extremity & Management Index (i.e. a value combining carbonate precipitation, water level, soil water content, nutrient availability, and management intensity). Regression lines, 95% confidence intervals, Adj R2 values and p-values (Holm’s correction) are shown. For details, see Table 6.

Appendix 1. List of 30 study fen grasslands, which were first sampled between 2001 and 2005, and revisited in 2018.

Altitude No.

Site name

Lat (°N)

Lon (°E)

1

NPR Rakšianské rašelinisko

48.87917

18.89000

2

PR Rojkovské rašelinisko

49.14861

3

PR Močiar

4

(m a.s.l.)

Habitat

Vegetation

514

small-sedge calcareous spring fen

C.davallianae (Cd

19.15560

435

small-sedge calcareous spring fen

C.davallianae (Cd

49.15344

19.15293

438

tufa-forming calcareous spring fen

C.davallianae (Sch

Stankovany

49.15755

19.15051

492

tufa-forming calcareous spring fen

C.davallianae (Sch

5

Švošov

49.12542

19.21636

486

small-sedge calcareous spring fen

C.davallianae (Cd

6

Studničná

49.13102

19.26311

822

small-sedge calcareous spring fen

C.davallianae (Cd

7

Demänová

49.04527

19.57916

661

small-sedge calcareous spring fen

C.davallianae (Cd

8

Jalovec, Bariny

49.13306

19.62775

673

small-sedge rich fen

Sphagno-Toment

9

Pribylina

49.10969

19.81083

789

small-sedge rich fen

Sphagno-Toment

10

Brezové

49.05083

20.02833

892

small-sedge calcareous spring fen

C.davallianae (Cd

11

Krivošova lúka

49.06842

19.99935

810

small-sedge calcareous spring fen

C.davallianae (Cd

12

Spišská Teplica

49.04417

20.24407

699

small-sedge calcareous spring fen

C.davallianae (Sch

13

Železná voda

49.08746

20.04524

903

small-sedge rich fen

Sphagno-Toment

14

Tatransky Lieskovec

49.09068

20.05548

913

small-sedge calcareous spring fen

C.davallianae (Cd

15

Vysoká Bazička

49.22055

20.37444

692

small-sedge calcareous spring fen

C.davallianae (Cd

16

PR Belianské lúky

49.21457

20.39055

678

small-sedge calcareous spring fen

C.davallianae (Cd

17

Hozelec

49.04525

20.33419

671

tufa-forming calcareous spring fen

C.davallianae (Cd

18

Velké Borové

49.19334

19.52224

816

small-sedge calcareous spring fen

C.davallianae (Cd

19

Malé Borové

49.21805

19.54583

814

small-sedge extremely rich fen

C.davallianae (V-C

20

Zuberec

49.27151

19.66185

808

tall-sedge extremely rich fen

C.davallianae (V-C

21

Peciská

49.29108

19.74456

825

tall-sedge extremely rich fen

Sphagno-Toment

22

Kościelisko, Bialy potok

49.28416

19.84694

902

small-sedge rich fen

Sphagno-Toment

23

Trstená-Krivý kút

49.36000

19.56250

633

tufa-forming calcareous spring fen

C.davallianae (C f

24

Trstená-Zimník

49.39333

19.66295

661

tall-sedge extremely rich fen

C.davallianae (Cam

25

Oravská polhora

49.52138

19.47277

748

small-sedge extremely rich fen

C.davallianae (V-C

26

Biela farma

49.53773

19.40007

734

small-sedge extremely rich fen

C.davallianae (V-C

27

PR Mútňanská píla

49.47023

19.28680

782

tall-sedge rich fen

Sphagno-Toment

28

PR Beňadovské rašelinisko

49.42138

19.32888

698

tall-sedge extremely rich fen

C.davallianae (Cam

29

Beňadovo

49.40447

19.33267

685

small-sedge extremely rich fen

C.davallianae (V-C

30

Ťaskovka

49.45400

19.46110

749

small-sedge calcareous spring fen

C.davallianae (C f

Appendix 2. Species abbreviations in MDS ordination diagrams (Fig. 3): Molluscs – AniLeu = Anisus leucostoma, CarTri = Carychium tridentatum, CocLub = Cochlicopa lubrica, PisCas = Pisidium casertanum, PisObt = Pisidium obtusale, PisPer = Pisidium personatum, PunPyg = Punctum pygmaeum, SemSem = Semilimax semilimax, ValPul = Vallonia pulchella, VerAng = Vertigo angustior, VerSub = Vertigo substriata; vascular plants – AngSyl = Angelica sylvestris, BriMed = Briza media, CalPal = Caltha palustris, CarDav = Carex davalliana, CarDio = Carex dioica, CarFla = Carex flacca, CarLep = Carex lepidocarpa, CarNig = Carex nigra, CarPan = Carex panicea, CirRiv = Cirsium rivulare, CrePal = Crepis paludosa, EquPal = Equisetum palustre, EriLat = Eriophorum latifolium, FesRub = Festuca rubra, GalUli = Galium uliginosum, MenTri = Menyanthes trifoliata, MolCoe = Molinia caerulea, ParPal = Parnassia palustris, PinVul = Pinguicula vulgaris, PriFar = Primula farinosa, ValSim = Valeriana simplicifolia; bryophytes – AulPal = Aulacomnium palustre, BryPse = Bryum pseudotriquetrum, CalCus = Calliergonella cuspidata, CamSte = Campylium stellatum, CliDen = Climacium dendroides, CraCom = Cratoneuron commutatum, DreCos = Drepanocladus cossonii, HomNit = Homalothecium nitens, PhiCal = Philonotis calcarea, PlaAff = Plagiomnium affine agg., SphWar = Sphagnum warnstorfii.

Highlights



Ongoing environmental changes threaten island-like unproductive fen ecosystems



Extremity (tufa, water, lack of nutrients) and management stabilise fen communities



Less extreme calcareous fens are more prone to shifts into grasslands and shrublands



Conservation mowing can compensate for low extremity



Management is more important for bryophytes than for vascular plants and snails