Impact of local- and regional-scale restoration measures on a vulnerable rich fen in the Naardermeer nature reserve (the Netherlands)

Abstract

Restoration of rich fens is commonly attempted through local-scale measures, such as removal of sod or blockage of ditches. However, regional-scale restoration measures, that aim to re-establish the original hydrology in which rich fens developed, might have a more long-lasting effect. We investigated the effect of local- and regional-scale restoration measures on a vulnerable rich fen in the Naardermeer nature reserve in the Netherlands. We compared water quality and vegetation composition of the fen before and after the restoration measures, almost 30 years apart. Overall rich fen species increased and although this indicates the desired increased supply of fresh mineral-rich groundwater to the fen, continued succession towards poor fen vegetation has not been prevented in the entire fen. Despite sod layer removal, we observed an increase in a Polytrichum-dominated vegetation in patches that are primarily fed by rainwater. Our findings confirm results from a previous study which showed that brackish palaeo-groundwater is still contributing substantially to the water balance of the fen, especially in periods of precipitation deficit. We conclude that the local- and regional-scale restoration measures have been successful in increasing the abundance of rich fen species in parts of the fen. However, considering the pressures of climate change and high atmospheric N-deposition on the fen, it is uncertain whether rich fen species can be sustained in quite nutrient-poor conditions in the future. Therefore, there is a need for continued management that keeps the nutrient-poor and mineral-rich conditions of the fen intact.

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.…”

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

“…Enhanced pH, along with low potassium and phosphorus availability, prevention of quick recolonization of Sphagnum mosses, and transplantation of target brown mosses, might, to some extent, help restore rich fen vegetation with an abundance of brown mosses in fens dominated by S. teres or S. recurvum agg. A large area with removed Sphagnum mosses may prevent quick recolonization and increase the representation of brown mosses and low‐stature endangered rich fen species (Veeken & Wassen, 2020). Alternatively, small‐scale interventions may be applied annually or every few years.…”

“…Removal of late-successional Sphagnum taxa is occasionally done in rich fens dominated by expansive peat mosses (Beltman et al, 1995(Beltman et al, , 1996Singh et al, 2021;Veeken & Wassen, 2020). Although some conservation practitioners opt for this measure enthusiastically and do observe a positive outcome (Beltman et al, 1996;Singh et al, 2021), others are skeptical and stick to the precautionary principle (Underwood, 1997) or refer to the legal protection guidelines of all peat mosses in some countries (Singh et al, 2021).…”

“…Unfortunately, mowing or mulching is frequently done using machinery instead of traditional hand mowing. Currently, many revitalization programs have sought to reverse undesired rich fen succession through restoration measures, such as hydrological interventions, including artificial flooding or pond excavation (Kooijman et al, 2016; Verhoeven et al, 2017; Verhoeven & Bobbink, 2001), rebound mowing and grazing or other disturbances (Lamers et al, 2015), or even by removing moss, sod, shrub, or topsoil (Beltman et al, 1995; Emsens et al, 2015; Singh et al, 2021; Sundberg, 2012; Veeken & Wassen, 2020).…”