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

Abstract

An undesired succession of rich fens leads to the formation of dense Sphagnum carpets that outcompete brown mosses and some vascular plants, resulting in biodiversity loss in fen habitats of high conservation importance. Small‐scale Sphagnum removal is a rarely implemented conservational measure, whose success may depend on soil alkalinity and fertility (i.e., nutrient availability). Therefore, characterizing the effects of pH and fertility levels would potentially allow for the development of better Sphagnum removal strategies. Two experiments were conducted across 24 rich fens of different alkalinity and fertility located in an area of ~32,000 km2 spanning from the Bohemian Massif to the Western Carpathians (Europe). We hypothesized that high alkalinity and low fertility support the restoration of rich fen vegetation after Sphagnum removal. Our study focused on four different Sphagnum groups. In Experiment 1, the treatment plots remained unfenced. In Experiment 2, the treatment plots were fenced off and target brown mosses were transplanted from the surroundings to overcome dispersal limitations. A repeated‐measures design was used, with vegetation composition recorded over a 5‐year period. High alkalinity rather than fertility facilitated species richness and the appearance of target brown mosses. High alkalinity generally hindered Sphagnum recovery, whereas high fertility supported the recurrence of S. teres and S. recurvum agg. Under high pH conditions, enhanced fertility further correlated with the spread of nonsphagnaceous generalist bryophytes of low conservation value. Despite sustaining a significant overall reduction, all Sphagnum taxa began to recover throughout the experiment, albeit less obviously in fens with S. warnstorfii. Sphagnum removal may reverse biodiversity loss and allow for the restoration of brown mosses in rich fens where Sphagnum cover had increased due to slight eutrophication, acidification, or a decrease in the water table. In alkaline and nutrient‐poor conditions (e.g., S. warnstorfii fens), the effect is evident and long lasting and the intervention may not be extensive. In fens dominated by S. teres or S. recurvum agg., repeated or large‐scale removal may be needed if high nutrient availability (potassium, phosphorus) or low alkalinity supports Sphagnum recolonization. Treatment plots with S. subgenus Sphagnum exhibited the least promising brown‐moss restoration prospects.

Water level drawdown makes boreal peatland vegetation more responsive to weather conditions

“…It is known that the disconnection from the lateral flow of minerogenic water reduces nutrient availability and decreases pH levels (Laine et al, 2004) and therein lowers the toxic effect of calcium, and this in turn increases the growth of Sphagnum mosses (Clymo, 1973). Similarly, to our results, such an effect of lowered WT on the growth of Sphagnum has been reported in Sweden (Granath et al, 2010), Netherlands (Diggelen et al, 1996; Veeken & Wassen, 2020), the United States (Borkenhagen & Cooper, 2018) and Central Europe (Singh et al, 2022; Vicherová et al, 2017). In the poor fen and bog the apparent lack of moss growth response to WLD was more likely achieved by species‐specific growth responses that counteracted the impact of each other.…”

Habitat‐based biodiversity responses to macroclimate and edaphic factors in European fen ecosystems

“…This is partially explained not only by the higher number of macroclimatic variables used in the models but also by the spatial mismatch between the groundwater pH (calculated at 1 km 2 ) and the local scale in which fens are found. Indeed, different habitat types may co‐occur in the same landscape, sometimes in local‐scale successional stages (Singh et al, 2022), which are further facilitated by increasing summer temperature and precipitation (Vicherová et al, 2017).…”