To mow or not to mow? Plant functional traits help to understand management impact on rich fen vegetation

Abstract

Questions:Fens are important conservation targets in temperate Europe. When hydrologically undisturbed, fens remain open for millennia. However, unaltered fens are scarce, and today their biodiversity largely depends on conservational mowing applied to prevent successional shifts. However, the effects on community structure and conservation values are uncertain, and management might not always be needed where it is a priori applied by managers. Thus, within the presented study, we ask the following questions: (a) How is the species and functional composition of fens influenced by mowing? (b) Does mowing increase the conservation value of fen ecosystems? Location: Lowland fens, northern Poland. Methods: The sample consisted of 27 pairs of mown and unmown plots, located within ten sites. Ordination methods were used to assess the influence of mowing on species composition. Functional traits related to competitiveness, flowering time, mycorrhizal associations and functional groups were used to characterize plant communities and species richness, and the number of specialist and red-listed species was used to evaluate conservation values. Differences between mown and unmown plots were assessed using linear mixed-effect models and the effect size approach. Results: Management of fens suppresses the growth of trees, shrubs and highly competitive herbaceous species and inhibits the encroachment of Sphagnum mosses. At the same time, it enhances the establishment of species from other ecosystems (grasses, ruderal species, species of drier sites) within fens and alters the microtopography of the fen surface.Conclusions: Mowing can enhance species richness and the presence of rich fen specialists in transformed sites, but it can lead to fen ecosystem deterioration towards managed meadow communities within sites sustaining many typical fen species and functional characteristics. K E Y W O R D S functional traits, mowing, mycorrhiza, nature conservation, Poland, red-list species, rich fen, species richness, Sphagnum 28 | Applied Vegetation Science KOZUB et al.

Changes in functional, phylogenetic and taxonomic diversities of lowland fens under different vegetation and disturbance levels

“…Despite the importance of habitat filtering and interspecific competition in influencing plant diversity (Díaz et al 1998), disturbance caused by management intervention (e.g. mowing, grazing) can interact with environmental filters and alter plant-environment relationships in fens (Kozub et al 2019). The apparent erosion of functional diversity in the annually mown and grazed sites (sedge fen and rush pasture, respectively) may be due to the dominance of species with a specific set of traits well adapted to mechanised mowing and grazing pressure that can affect fens through surface homogenisation and peat compression (Kotowski et al 2013).…”

“…Plant diversity of fen peatlands can vary significantly and be influenced by a myriad of factors, including soil fertility (Øien et al 2018), soil water level and chemistry (Navrátilová et al 2017) and changes to hydrological conditions like drainage and rewetting (Mälson et al 2008). Vegetation management practices like mowing (Kozub et al 2019) and grazing (Merriam et al 2018) can also affect fen plant diversity, since the abandonment of fens may result in changes to vegetation composition (Navrátilová et al 2017) and the encroachment of shrubs over herb fens (Wheeler and Shaw 1995). Regular mowing and grazing and the maintenance of water and nutrient levels can have positive effects on the long-term survival of characteristic open fen vegetation (Stammel et al 2003).…”

Can Sphagnum removal reverse the undesired succession of rich fens under different alkalinity and fertility levels?

“…Repeated disturbances may be easily implemented via regular grazing or hand mowing. Hand mowing creates smaller and more regularly distributed vegetation gaps than machinery mowing (Barbaro et al, 2001;Kozub et al, 2019). The same applies to grazing, yet grazing may continue to increase potassium and phosphorus availability, and, if it is ceased, undesired succession may start quickly (Bart, 2021;Merriam et al, 2018).…”

Combining bioenergy and nature conservation: An example in wetlands

“…It has been assumed that grazing better supports the conservation value of various semi-natural wet grasslands than does mowing [68], but in some cases grazing has been reported to degrade fen wetlands beyond recovery [69]. Mowing, on the other hand, has been supposed to develop plant species' richness and to create wetland specialist habitats [70,71]. For specific habitat creation, it is sometimes important to organise, in addition to a periodic large-area harvest, a network of small meadow patches to preserve the characteristic plant species [72].…”