Alleviation of Plant Stress Precedes Termination of Rich Fen Stages in Peat Profiles of Lowland Mires

Abstract

Mesotrophic rich fens, that is, groundwater-fed mires, may be long-lasting, as well as transient ecosystems, displaced in time by poor fens, bogs, forests or eutrophic reeds. We hypothesized that fen stability is controlled by plant stress caused by waterlogging with calcium-rich and nutrient-poor groundwater, which limits expansion of hummock mosses, tussock sedges and trees. We analysed 32 European Holocene macrofossil profiles of rich fens using plant functional traits (PFTs) which indicate the level of plant stress in the environment: canopy height, clonal spread, diaspore mass, specific leaf area, leaf dry matter content, Ellenberg moisture value, hummock-forming ability, mycorrhizal status and plant functional groups. Six PFTs, which formed long-term significant trends during mire development, were compiled as rich fen stress indicator (RFSI). We found that RFSI values at the start of fen development were correlated with the thickness of subsequently accumulated rich fen peat. RFSI declined in fens approaching change into another mire type, regardless whether it was shifting into bog, forest or eutrophic reeds. RFSI remained comparatively high and stable in three rich fens, which have not terminated naturally until present times. By applying PFT analysis to macrofossil data, we demonstrated that fens may undergo a gradual autogenic process, which lowers the ecosystem's resistance and enhances shifts to other mire types. Long-lasting rich fens, documented by deep peat deposits, are rare. Because autogenic processes tend to alleviate stress in fens, high levels of stress are needed at initial stages of rich fen development to enable its long persistence and continuous peat accumulation.

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

“…When these anthropogenic interventions are heavy, they cause a rapid expansion of tussock‐forming grasses such as Deschampsia cespitosa and Molinia caerulea agg. (Diemer et al, 2001; Hájková et al, 2009; Rion et al, 2018) or even reed bed, shrub, or woodland species (Barbaro et al, 2001; Jabłońska et al, 2020; Koch & Jurasinski, 2015; Middleton et al, 2006). Fens can persist when interventions are moderate, but succession proceeds toward communities with calcium‐tolerant peat mosses.…”

Assessment and Spatial Planning for Peatland Conservation and Restoration: Europe’s Trans-Border Neman River Basin as a Case Study

“…The evolution of peatland ecosystems is controlled by regional climate, landscape topography, water supply, nutrient, natural (e.g., fire, flooding) and anthropogenic (grazing, mowing, draining) disturbances, and autogenic processes associated with aging of individual peatlands [53,[83][84][85]. The aim of peatland restoration is to re-establish the desired vegetation and initiate self-regulatory mechanisms [86].…”

“…There are several trajectories of historic development of different peatlands types [84]. Fens are usually composed of large homogeneous patches with well-marked zonation from the waterlogged areas of riverbeds and oxbow lakes to the elevated edge-on parts of the valley that are not subject to inundation [38].…”

“…Interrelation between the sites to be re-wetted and preserved may optimize a large-scale facilitation of nutrient retention in wetland buffer zones [111]. One should also consider that the costs of restoring wetland buffer zones are expected to be lower than the values of gains expressed as ecosystem services provided by the restored sites [84]. For instance, Valasiuk et al [68] showed that citizens in Belarus are willing to pay a substantial amount of money for peatland habitat conservation, restoration, and maintenance for wetland birds, such as the aquatic warbler.…”

Reflections on the Use of Ecological Attributes and Traits in Quaternary Botany

“…Rather surprisingly, traits have not been widely studied for plant-macrofossil assemblages (Birks, 2014) except for Bhagwat and Willis (2008; see above) and Jabłońska et al (2019). The latter study centered on mesotrophic rich-fens and tested the hypothesis that fen stability is controlled by plant stress induced by waterlogging with calcium-rich but nutrient-poor groundwater.…”