Vegetation structure and photosynthesis respond rapidly to restoration in young coastal fens

Abstract

Young coastal fens are rare ecosystems in the first stages of peatland succession. Their drainage compromises their successional development toward future carbon (C) reservoirs. We present the first study on the success of hydrological restoration of young fens. We carried out vegetation surveys at six young fens that represent undrained, drained, and restored management categories in the Finnish land uplift coast before and after restoration. We measured plant level carbon dioxide (CO2) assimilation and chlorophyll fluorescence (Fv/Fm) from 17 most common plant species present at the sites. Within 5 years of restoration, the vegetation composition of restored sites had started to move toward the undrained baseline. The cover of sedges increased the most in response to restoration, while the cover of deciduous shrubs decreased the most. The rapid response indicates high resilience and low resistance of young fen ecosystems toward changes in hydrology. Forbs had higher photosynthetic and respiration rates than sedges, deciduous shrubs, and grasses, whereas rates were lowest for evergreen shrubs and mosses. The impact of management category on CO2 assimilation was an indirect consequence that occurred through changes in plant species composition: Increase in sedge cover following restoration also increased the potential photosynthetic capacity of the ecosystem. Synthesis and applications. Restoration of forestry drained young fens is a promising method for safeguarding them and bringing back their function as C reservoirs. However, their low resistance to water table draw down introduces a risk that regeneration may be partially hindered by the heavy drainage in the surrounding landscape. Therefore, restoration success is best safeguarded by managing the whole catchments instead of carrying out small‐scale projects.

Impacts of drainage, restoration and warming on boreal wetland greenhouse gas fluxes

“…We selected six primary mires belonging to three land use categories: two undrained (UD1, UD2), two forestry drained in (D1, D2), and two drained (197 ) sites restored in 2008 (R1, R2). The drainage of site D2 had not resulted in effective regime shift towards forested ecosystem, and the water table was clearly higher than at D1 (see Laine et al 2016).…”

“…At the forestry-drained state, which is the starting point for restoration, the LAI of field layer vegetation was lower than at undrained state. This difference was mostly caused by a decrease of sedge cover greater than the increase of shrub cover, indicating secondary succession towards forest vegetation (the changes in species composition are shown at Laine et al 2016). During secondary succession following drainage, the closing tree canopy increases the competition for light and decreases the biomass of field layer vegetation, especially in minerotrophic mires (Laine et al 1995;Minkkinen et al 1999).…”

“…Primary mires are successionally young wetlands that, under suitable climatic conditions, will develop into deep peat mires (Tuittila et al 2013;Joosten et al 2017) and they are known to rapidly respond to climatic variation (Laitinen et al 2008;Leppälä et al 2011a). Four of the sites have experienced long-term water table drawdown due to ditching for forestry in the 1970s, while restoration of two of these sites in 2008 raised water table levels back to the same level as in the two undrained (control) sites (see Laine et al 2016). Open top chambers (OTC)…”

<i>Sphagnum</i>-associated methanotrophs – a resilient CH₄ biofilter in pristine and disturbed peatlands

“…Firstly, the WT level needs to be returned through blocking of the drainage ditches and, in the case of the forested sites, possible removal of the tree-stand (Tarvainen et al 2013). With submerged conditions, the peatland vegetation may return either spontaneously (Tuittila et al 2000b;Maanavilja et al 2014;Laine et al 2016) or through artificial reintroduction through transplantations: Especially in Northern America, addition of Sphagnum diaspores on the extracted peat basin is a typical way to enhance the restoration process (Rochefort et al 2003, Chimner et al 2017. Based on CH4 emission measurements, the CH4 production may re-activate relatively rapidly after the initiation of a higher WT and re-vegetation, but the recovery rate depends for example on the peatland type and the degree of disturbance (Tuittila et al 2000a, Waddington andDay 2007;Abdalla et al 2016).…”

“…It has been a target of several other studies as well (e.g. Merilä et al 2006;Tuittila et al 2013;Laine et al 2016). The aim was to collect several Sphagnum samples from various successional stages for the analysis of which type of MOB are active in the mosses in general and to see the effect of successional stage and Sphagnum species on the activity and diversity of the SAM.…”