Restoration of rare bryophytes in degraded rich fens: The effect of sod-and-moss removal
Graphical abstract
Introduction
Biodiverse base-rich fens became a highly endangered European habitat. The main causes of their reduction are acidification, eutrophication, groundwater pollution, hydrological deterioration, climate change or cessation of traditional management (Chytrý et al., 2019; Essl et al., 2012; Hájek et al., 2015; Janssen et al., 2016; Kooijman, 2012; Kooijman & Paulissen, 2006; Rion et al., 2018; Wassen et al., 2005). These processes triggered a shift from typical sedge-moss base-rich fen vegetation to more common vegetation types such as wet meadows with a dominance of tussock-forming grasses such as Deschamspia cespitosa, Molinia caerulea agg. (Diemer et al., 2009; Hájková et al., 2009; Rion et al., 2018), reed-bed or woodland species (Güsewell, 2003; Jabłońska et al., 2019; Koch & Jurasinski, 2015; Middleton et al., 2006) or to acidified poor-fen communities dominated by fast-growing Sphagnum species (Beltman et al., 2001; Granath et al., 2010; Kooijman, 2012; Lamers et al., 2015; Paulissen et al., 2014). This vegetation shift has frequently resulted in biodiversity loss.
Rich fens are out of all peatlands one of the most biodiverse habitats, encompassing a significant proportion of specialised plant species (Bedford & Godwin, 2003; Peterka et al., 2017; Wheeler, 1988). A substantial part of the ground is occupied by fen-specialised bryophytes such as so-called brown mosses, i.e. non-sphagnaceous weft-forming bryophytes from family Amblystegiaceae, e.g. Campylium stellatum or family Calliergonaceae, e.g. Hamatocaulis vernicosus and calcium tolerant species, e.g. Sphagnum contortum or S. warnstorfii (Vitt et al., 1995). Their dominance may affect fen functioning. Brown mosses grow laterally and often create extensive mats, covering most of the ground, alleviate harsh environmental conditions and facilitate seedling emergence and survival (Clapham, 1940; Crowley, 2009). However, even in seemingly well-preserved fens, brown moss patches virtually disappeared in some regions (Hájek et al., 2015) which may also affect endangered vascular plants (Singh et al., 2019). One of the reasons of brown moss disappearance is the expansion of fast-growing calcifuge Sphagnum species and nutrient-demanding vascular plants, which act as competitors and often overgrow small-stature bryophytes, vascular plants or their seedlings (Hájek et al., 2015; Juutinen, 2011; Neuhäusl, 1975; Nordbakken et al., 2004; Ohlson et al., 2001; Paulissen et al., 2014). Sphagnum mosses, protected legally in some countries and being major global peat-formers and carbon sinkers, here paradoxically act as mediators of biodiversity loss.
Most of the current temperate fens are semi-natural ecosystems, grazed since the Neolithic Era and supplying hay since the Iron Age (Cromsigt, 2000; Middleton, 1999). During the pre-industrial period, many fens were drained due to increasing hay-yield demand in densely populated regions. In addition, new fen grasslands have appeared after cutting of alder or spruce fen woodlands (Hájková et al., 2012; Jamrichová et al., 2018). Despite the fen drainage and susceptibility to secondary succession, haymaking (scything and raking), combined with occasional grazing and litter/moss raking for bedding, sustained mosaic heterogeneity typical for sedge-moss fen vegetation. This traditional management maintained high fen biodiversity for decades through slowing down the natural succession (Grootjans et al., 2006; Hájek et al., 2015; Verhoeven & Bobbink, 2001). However, since the 1950s the traditional land use of fens was abandoned, due to intensified agriculture which led to rapid successional shift and loss of characteristic fen-specialised plant species (Hájková et al., 2009; Koch & Jurasinski, 2015; Middleton et al., 2006; Moen et al., 1999; Peintinger & Bergamini, 2006; Tyler, 1984).
Rich fens have undergone a significant decline in Western, West-Central and Southern Europe. They are virtually extinct in several regions where only their last remnants can be found. Their deterioration was mainly caused by agricultural and industrial development (Bragg & Lindsay, 2003; Grzybowski & Glińska-Lewczuk, 2020; Janssen et al., 2016). Similar influences have negatively affected rich fens also in East-Central Europe, including our study area. Yet, losses have so far been less severe, and the region still harbours rich fen types that are virtually extinct further west and have great importance for the maintenance of the continent’s biodiversity (Bragg & Lindsay, 2003).
Management measures such as scything, mowing, grazing or burning are recommended to tackle successional shift (Billeter et al., 2003; Hansson & Fogelfors, 2000; Hogg et al., 1995; Middleton et al., 2006; Mitlacher et al., 2002; Øien & Moen, 2001; van Belle et al., 2006; Van Diggelen et al., 1996). However, over the past decades, we observed a loss of fen specialists and the increase in nutrient-demanding generalists, even despite prescribed conservation-oriented haymaking or grazing in Central Europe (Bergamini et al., 2009; Hájek et al., 2015, 2020). Rich fens are protected at the European level under Habitats Directive Annex I (Directive, 1992). Besides, rich fens belong currently to overall 10 % of the most endangered, red-listed habitats within European Union countries based on a decline over the past 50 years and more long-term historical times (Janssen et al., 2016). In the Czech Republic, the current state of rich fens is critical. They cover, in different stages of conditions, the last 566 ha (expert estimate - AOPK ČR, 2018), which, in total, is less than 0.01 % of the area of the Czech Republic. According to IUCN criteria, they belong to a few critically endangered habitats in the Czech Republic according to the A1 and A3 criteria (reduction in quantity >90 %; Chytrý et al., 2019). In the lowlands, many fens have been either completely transformed to arable land or substantially degraded due to hydrological change and eutrophication (Bragg & Lindsay, 2003). Successional changes after cessation of traditional management are one of the most critical threatening factors of Czech habitats (Chytrý et al., 2019).
Remaining Czech rich fens are mown by nature conservation authorities that maintain treeless fen nature and reduce litter accumulation. However, annual mowing is failing to restore small-scale heterogeneity, which is necessary for the existence of sedge-moss rich-fen vegetation. It further seems not to prevent the expansion of acidophilous Sphagnum species, which cause a shift to poor-fen communities (Hájek et al., 2015; Singh et al., 2019).
Top-soil removal (also referred to as peat or sod-stripping) is an invasive technique often used to rehabilitate deeply drained and eutrophicated peatlands, i.e. former agricultural areas. The removal of degraded peat layer may quickly remove nutrients, achieve wetter conditions, and enhance the influence of groundwater in the upper soil layer, and consequently improve local biodiversity. However, it has a high initial cost, due to the requirement of the excavators for deep soil removal, and is not suited for the peatlands where natural communities rich in specialists still occur (Emsens et al., 2015; Klimkowska et al., 2010, 2015; Patzelt et al., 2001; Ramseier, 2000; Smolders et al., 2008; Van Duren et al., 1998; Verhagen et al., 2001; Zak et al., 2018).
We aim to test a rarely used and relatively low-cost fen restoration measure, the removal of a shallow upper layer of sod and moss, performed mechanically by rakes, in fens near to natural state, but heavily encroached by few fast-growing Sphagnum mosses and tussock graminoids (Beltman et al., 2001; Mälson & Rydin, 2007). We applied this treatment on six minerotrophic fens in the Czech Republic, which harbour the remnant populations of fen-specialised bryophytes being suppressed by expanding acidicole Sphagnum species. We aim to create a heterogeneous ground layer to initiate the development of the original sedge-moss structure of rich fens.
Section snippets
Selection of study area
We proceeded the sod-and-moss removal in six minerotrophic fens, which are isolated habitats under nature protection in an unprotected agricultural landscape (pH 5.7–6.7, conductivity [EC] 104–315 μS.cm-1) located in the western part of the Bohemian Massif (Fig. 1, Table 1). These localities are sloping fens or a combination of sloping and basin fens (Charman, 2002) with similar water regime, i.e. slightly fluctuating water level in the root zone creating desirable conditions for
Community-level analyses
Detrended Correspondence Analysis sorted samples from the first and the last sampling period along the two principal gradients (Fig. 3). The first one stretches from samples with expansive Sphagnum species (S. palustre, S. flexuosum) to samples with target bryophytes. The second principal gradient sorts samples predominantly on the positive end of the first axis (i.e., samples with fen-specialised bryophytes), plausibly according to calcium tolerance, with brown mosses of calcium-rich habitats (
Increasing yet a low abundance of fen-specialised bryophytes after the sod-and-moss removal
Our study addressed the question of whether prescribed removal of sod and moss in rich fens undergoing succession to poor fens or tussock grasslands would support the communities of fen-specialised bryophytes and suppress expansive Sphagnum species. The plots initially dominated by expansive Sphagnum species (S. flexuosum, S. palustre, S. teres) shifted to early successional stages with the occurrence of target bryophytes. The total cover of target bryophytes was, however, low after one and a
Conclusion
The sod-and-moss removal applied in deteriorated rich fens, strongly dominated by expansive Sphagnum species or vascular plants, seems to be a promising tool to restore rich fen patches with brown mosses and other specialised fen bryophytes, but has certain limitations. In our study, the total cover of fen-specialised bryophytes was low after one and a half years since the treatment application, while a cover of expansive Sphagnum species started to recover insignificantly. Yet, only a few
Data accessibility statement
The primary data that support the findings of this study are available from the corresponding author, [PS], upon reasonable request.
CRediT authorship contribution statement
Patrícia Singh: Formal analysis, Writing - original draft, Writing - review & editing. Ester Ekrtová: Conceptualization, Investigation, Writing - review & editing. Eva Holá: Conceptualization, Investigation, Writing - review & editing, Formal analysis. Táňa Štechová: Conceptualization, Investigation, Writing - review & editing. Stanislav Grill: Formal analysis. Michal Hájek: Writing - review & editing, Funding acquisition.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgement
The data processing and preparation of the paper was funded by the Czech Science Foundation (project no. 19-01775S). The funding of sod-and-moss removal itself was arranged by J. Janová, A. Hofhanzl, and V. Kodet. We thank all colleagues who made the realisation of the sod-and-moss removal possible. We are grateful to T. Velehradská and F. Lysák for inspiration to carry out sod-and-moss removal, P. Šmilauer for developing the software computing for the transition matrix and M. Štech for
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