Anna M. Laine

Wetland chronosequence as a model of peatland development: Vegetation succession, peat and carbon accumulation

Model validation experiments are fundamental to ensure that the peat growth models correspond with the diversity in nature. We evaluated the Holocene Peatland Model (HPM) simulation against the field observations from a chronosequence of peatlands and peat core data. The ongoing primary peatland formation on the isostatically rising coast of Finland offered us an exceptional opportunity to study the peatland succession along a spatial continuum and to compare it with the past succession revealed by vertical peat sequences. The current vegetation assemblages, from the seashore to a 3000 year old bog, formed a continuum from minerotrophic to ombrotrophic plant communities. A similar sequence of plant communities was found in the palaeovegetation. The distribution of plant functional types was related to peat thickness and water-table depth (WTD) supporting the assumptions in HPM, though there were some differences between the field data and HPM. Palaeobotanical evidence from the oldest site showed a rapid fen–bog transition, indicated by a coincidental decrease in minerotrophic plant functional types and an increase in ombrotrophic plant functional types. The long-term mean rate of carbon (C) accumulation varied from 2 to 34 g C/m2 per yr, being highest in the intermediate age cohorts. Mean nitrogen (N) accumulation varied from 0.1 to 3.9 g N/m2 per yr being highest in the youngest sites. WTD was the deepest in the oldest sites and its variation there was temporally the least but spatially the highest. Evaluation of the HPM simulations against the field observations indicated that HPM reasonably well simulates peatland development, except for very young peatlands.

Vegetation and environmental variation in an Atlantic blanket bog in South-western Ireland

A vegetation survey was carried out in a relatively intact Atlantic blanket bog in Southwest Ireland to study the vegetation patterns in relation to environmental variation, and to quantify the effect of artificial and natural borders on compositional variation. The data were analysed using canonical correspondence analysis. In terms of both vegetation and water chemistry, the study site can be categorized as typical of Atlantic blanket bogs in the maritime regions of North-western Europe. The distribution of plant species was explained mainly by depth of the water table. The distribution of bryophytes was secondarily explained by the pH of the bog water, while the distribution of vascular plants was secondarily explained by concentrations of ammonia. The vegetation distribution exhibited little variation between the central sector of the peatland and its disturbed edges (hill-grazing and restoration areas), but a substantial variation was observed between the area along a natural edge (stream) and the areas close to the other peatland borders or centre. Similarly, the internal variation within each sector (centre, hill-grazing edge and restoration area edge) was small, but substantial vegetation variation was observed within the area located along the stream. The area along the stream was associated with relatively deep water table, shallow peat depth, high water colour, pH and NH4+ concentrations, and low Cl− concentrations in the bog water. Our results suggest the existence of strong centre-natural margin gradients, as in raised bogs, and indicate that human or animal disturbance do not give rise to the marked transition zones that often characterize natural margins of mire systems. This indicates that even small areas and remnants of Atlantic blanket bogs are worthy of conservation and that their conservation value would benefit from the inclusion of sectors close to the natural peatland borders, which would increase the plant biodiversity of the conserved area.

Sphagnum growth and ecophysiology during mire succession

Sphagnum mosses are widespread in areas where mires exist and constitute a globally important carbon sink. Their ecophysiology is known to be related to the water level, but very little is currently known about the successional trend in Sphagnum. We hypothesized that moss species follow the known vascular plant growth strategy along the successional gradient (i.e., decrease in production and maximal photosynthesis while succession proceeds). To address this hypothesis, we studied links between the growth and related ecophysiological processes of Sphagnum mosses from a time-since-initiation chronosequence of five wetlands. We quantified the rates of increase in biomass and length of different Sphagnum species in relation to their CO2 assimilation rates, their photosynthetic light reaction efficiencies, and their physiological states, as measured by the chlorophyll fluorescence method. In agreement with our hypothesis, increase in biomass and CO2 exchange rate of Sphagnum mosses decreased along the successional gradient, following the tactics of more intensely studied vascular plants. Mosses at the young and old ends of the chronosequence showed indications of downregulation, measured as a low ratio between variable and maximum fluorescence (Fv/Fm). Our study divided the species into three groups; pioneer species, hollow species, and ombrotrophic hummock formers. The pioneer species S. fimbriatum is a ruderal plant that occurred at the first sites along the chronosequence, which were characterized by low stress but high disturbance. Hollow species are competitive plants that occurred at sites with low stress and low disturbance (i.e., in the wet depressions in the middle and at the old end of the chronosequence). Ombrotrophic hummock species are stress-tolerant plants that occurred at sites with high stress and low disturbance (i.e., at the old end of the chronosequence). The three groups along the mire successional gradient appeared to be somewhat analogous to the three primary strategies suggested by Grime.

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.

Northern wetlands with organic soil i.e., mires are significant carbon storages. This key ecosystem service may be threatened by anthropogenic activities and climate change, yet we still lack a consensus on how these major changes affects their carbon sink capacities. We studied how forestry drainage and restoration combined with experimental warming, impacts greenhouse gas fluxes of wetlands with peat. We measured CO2 and CH4 during two and N2O fluxes during one growing season using the chamber method. Gas fluxes were primarily controlled by water table, leaf area and temperature. Land use had a clear impact of on CO2 exchange. Forestry drainage increased respiration rates and decreased field layer net ecosystem CO2 uptake (NEE) and leaf area index (LAI), while at restoration sites the flux rates and LAI had recovered to the level of undrained sites. CH4 emissions were exceptionally low at all sites during our study years due to natural drought, but still somewhat lower at drained compared to undrained sites. Moderate warming triggered an increase in LAI across all land use types. This was accompanied by an increase in cumulative seasonal NEE. Restoration appeared to be an effective tool to return the ecosystem functions of these wetlands as we found no differences in LAI or any gas flux components (PMAX, Reco, NEE, CH4 or N2O) between restored and undrained sites. We did not find any signs that moderate warming would compromise the return of the ecosystem functions related to C sequestration.