Search

Climate warming is leading to permafrost thaw in northern peatlands, and current predictions suggest that thawing will drive greater surface wetness and an increase in methane emissions. Hydrology largely drives peatland vegetation composition, which is a key element in peatland functioning and thus in carbon dynamics. These processes are expected to change. Peatland carbon accumulation is determined by the balance between plant production and peat decomposition. But both processes are expected to accelerate in northern peatlands due to warming, leading to uncertainty in future peatland carbon budgets. Here, we compile a dataset of vegetation changes and apparent carbon accumulation data reconstructed from 33 peat cores collected from 16 sub-arctic peatlands in Fennoscandia and European Russia. The data cover the past two millennia that has undergone prominent changes in climate and a notable increase in annual temperatures towards present times. We show a pattern where European sub-Arctic peatland microhabitats have undergone a habitat change where currently drier habitats dominated by Sphagnum mosses replaced wetter sedge-dominated vegetation and these new habitats have remained relatively stable over the recent decades. Our results suggest an alternative future pathway where sub-arctic peatlands may at least partly sustain dry vegetation and enhance the carbon sink capacity of northern peatlands.

Climate change and the related increases in evapotranspiration threaten to make northern peatlands drier. The carbon sink function in peatlands is based on the delicate balance between the photosynthesis and decomposition. However, little is known about how existing and invading plant species will photosynthesize under drier conditions. The aim of this study is to quantify the long-term consequences of climate change-induced drying for peatland photosynthesis in the level of individual species and vegetation community. We measured the species-level photosynthesis of vascular plants and mosses characteristic for the three peatland types (rich fen, poor fen, bog) within a 16-year water level drawdown (WLD) experiment. Measurements were made in the laboratory from mesocosms collected from the field within the same day. We applied nonlinear mixed-effects models to test the impact of WLD on hyperbolic photosynthetic light response curve parameters. The model was then used to upscale photosynthesis to site-level. WLD impacted site-level photosynthesis through two mechanisms: species turnover and changes in species-level photosynthesis rate. The rich fen was the most sensitive and underwent major changes through both mechanisms; the vascular plant community shifted to woody plant dominance with higher rate of photosynthesis than the pre-treatment vegetation, and the rate of species-level photosynthesis increased significantly. The bog had a stable plant community with little change in photosynthesis, while the poor fen was an intermediate of the three peatland types. Our results suggest that vascular plants are the main drivers of site-level productivity changes, while mosses are more resistant to change. The change seems proportional to the availability of mineral nutrients, with higher nutrient status supporting vascular plant expansion.

Peatlands are carbon dioxide (CO2) sinks that, in parallel, release methane (CH4). The peatland carbon (C) balance depends on the interplay of decomposer and CH4-cycling microbes, vegetation, and environmental conditions. These interactions are susceptible to the changes that occur along a successional gradient from vascular plant-dominated systems to Sphagnum moss-dominated systems. Changes similar to this succession are predicted to occur from climate change. Here, we investigated how microbial and plant communities are interlinked with each other and with ecosystem C cycling along a successional gradient on a boreal land uplift coast. The gradient ranged from shoreline to meadows and fens, and further to bogs. Potential microbial activity (aerobic CO2 production; CH4 production and oxidation) and biomass were greatest in the early successional meadows, although their communities of aerobic decomposers (fungi, actinobacteria), methanogens, and methanotrophs did not differ from the older fens. Instead, the functional microbial communities shifted at the fen–bog transition concurrent with a sudden decrease in C fluxes. The successional patterns of decomposer versus CH4-cycling communities diverged at the bog stage, indicating strong but distinct microbial responses to Sphagnum dominance and acidity. We highlight young meadows as dynamic sites with the greatest microbial potential for C release. These hot spots of C turnover with dense sedge cover may represent a sensitive bottleneck in succession, which is necessary for eventual long-term peat accumulation. The distinctive microbes in bogs could serve as indicators of the C sink function in restoration measures that aim to stabilize the C in the peat.

QUESTIONS: Peatland ecosystems are a globally important carbon storage that is predicted to turn into a carbon source due to water level drawdown (WLD) associated with climate change. The predictions assume stable plant communities but how realistic is this assumption? If the vegetation is not stable, what are the nature and rate of changes? LOCATION: Peatland complex in Southern Finland. METHODS: We conducted a water level drawdown (WLD of ~10 cm) experiment over 17 years in three peatland types differing in their fertility. On each peatland type, we included an adjacent forestry drained (FD, with water table ca. 40 cm lower than in control) area for comparison. RESULTS: Peatland type had a clear impact on the response to WLD: at the ecosystem level, the two minerotrophic fens underwent rapid species turnover, while the vegetation in nutrient‐poor bog was more resilient to change. In nutrient‐rich sites, WLD initiated tree canopy development and created understorey conditions that strengthened impact of WLD. In nutrient‐poor site, tree establishment was seen only in the FD area. In addition to high nutrient level, high wetness accelerated change at the plant community level, where we found three types of responses: accelerating change, decelerating change, and stability. Succession resulted in an overall loss of community heterogeneity. CONCLUSIONS: Interaction between hydrology, nutrient availability, and biological factors in boreal peatlands is important: the drop in water table required to achieve the shift from open peatland to forested system is inversely proportional to the nutrient level of the system. The results suggest that predictive models of peatland functions under climate change should consider compositional change for fens and their diverse plant communities but are more realistic for bogs. The response of bog vegetation to climate change may, however, be more dependent on changes in rainfall regime and therefore needs to be further addressed.

Northern peatlands form a major soil carbon (C) stock. With climate change, peatland C mineralization is expected to increase, which in turn would accelerate climate change. A particularity of peatlands is the importance of soil aeration, which regulates peatland functioning and likely modulates the responses to warming climate. Our aim is to assess the impacts of warming on a southern boreal and a sub-arctic sedge fen carbon dioxide (CO2) exchange under two plausible water table regimes: wet and moderately dry. We focused this study on minerotrophic treeless sedge fens, as they are common peatland types at boreal and (sub)arctic areas, which are expected to face the highest rates of climate warming. In addition, fens are expected to respond to environmental changes faster than the nutrient poor bogs. Our study confirmed that CO2 exchange is more strongly affected by drying than warming. Experimental water level draw-down (WLD) significantly increased gross photosynthesis and ecosystem respiration. Warming alone had insignificant impacts on the CO2 exchange components, but when combined with WLD it further increased ecosystem respiration. In the southern fen, CO2 uptake decreased due to WLD, which was amplified by warming, while at northern fen it remained stable. As a conclusion, our results suggest that a very small difference in the WLD may be decisive, whether the C sink of a fen decreases, or whether the system is able to adapt within its regime and maintain its functions. Moreover, the water table has a role in determining how much the increased temperature impacts the CO2 exchange. This article is protected by copyright. All rights reserved.

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. (C) 2018 Elsevier B.V. All rights reserved.

Peatlands constitute a significant soil carbon (C) store, yet the C gas flux components show distinct spatial variation both between and within peatlands. Determining the controls on this variability could aid in our understanding of the response of peatlands to global changes. In this study, we assess the usefulness of different vegetation related parameters to explain spatial variation in peatland C gas flux components. We hypothesise that spatial variation is best explained by trait-based indices (similarly to other terrestrial ecosystems), and that the impact of soil physicochemical properties, such as nitrogen (N) content or water level, can be manifested through the traits. Furthermore, we expect that the spatial variability associated with each of the C gas flux components can be explained by a distinct set of traits. To address our aim, we used a successional peatland chronosequence from wet meadows to a bog, along which all variables were recorded with similar methods and under similar climatic conditions. We observed spatial variability with all measured gas fluxes, with carbon dioxide (CO

1. The relative importance of global versus local environmental factors for growth and thus carbon uptake of the bryophyte genus Sphagnum—the main peat‐former and ecosystem engineer in northern peatlands—remains unclear. 2. We measured length growth and net primary production (NPP) of two abundant Sphagnum species across 99 Holarctic peatlands. We tested the importance of previously proposed abiotic and biotic drivers for peatland carbon uptake (climate, N deposition, water table depth and vascular plant cover) on these two responses. Employing structural equation models (SEMs), we explored both indirect and direct effects of drivers on Sphagnum growth. 3. Variation in growth was large, but similar within and between peatlands. Length growth showed a stronger response to predictors than NPP. Moreover, the smaller and denser Sphagnum fuscum growing on hummocks had weaker responses to climatic variation than the larger and looser Sphagnum magellanicum growing in the wetter conditions. Growth decreased with increasing vascular plant cover within a site. Between sites, precipitation and temperature increased growth for S. magellanicum. The SEMs indicate that indirect effects are important. For example, vascular plant cover increased with a deeper water table, increased nitrogen deposition, precipitation and temperature. These factors also influenced Sphagnum growth indirectly by affecting moss shoot density. 4. Synthesis. Our results imply that in a warmer climate, S. magellanicum will increase length growth as long as precipitation is not reduced, while S. fuscum is more resistant to decreased precipitation, but also less able to take advantage of increased precipitation and temperature. Such species‐specific sensitivity to climate may affect competitive outcomes in a changing environment, and potentially the future carbon sink function of peatlands.

1. Most of the carbon accumulated into peatlands is derived from Sphagnum mosses. During peatland development, the relative share of vascular plants and Sphagnum mosses in the plant community changes, which impacts ecosystem functions. Little is known on the successional development of functional plant traits or functional diversity in peatlands, although this could be a key for understanding the mechanisms behind peatland resistance to climate change. Here we aim to assess how functionality of successive plant communities change along the autogenic peatland development and the associated environmental gradients, namely peat thickness and pH, and to determine whether trait trade-offs during peatland succession are analogous between vascular plant and moss communities. 2. We collected plant community and trait data on successional peatland gradients from post-glacial rebound areas in coastal Finland, Sweden and Russia, altogether from 47 peatlands. This allowed us to analyse the changes in community-weighted mean trait values and functional diversity (diversity of traits) during peatland development. 3. Our results show comparative trait trade-offs from acquisitive species to conservative species in both vascular plant and Sphagnum moss communities during peatland development. However, mosses had higher resistance to environmental change than vascular plant communities. This was seen in the larger proportion of intraspecific trait variation than species turnover in moss traits, while the proportions were opposite for vascular plants. Similarly, the functional diversity of Sphagnum communities increased during the peatland development, while the opposite occurred for vascular plants. Most of the measured traits showed a phylogenetic signal. More so, the species common to old successional stages, namely Ericacae and Sphagna from subgroup Acutifolia were detected as most similar to their phylogenetic neighbours. 4. Synthesis. During peatland development, vegetation succession leads to the dominance of conservative plant species accustomed to high stress. At the same time, the autogenic succession and ecological engineering of Sphagna leads to higher functional diversity and intraspecific variability, which together indicate higher resistance towards environmental perturbations.

Methane (CH4) emissions from northern peatlands are projected to increase due to climate change, primarily because of projected increases in soil temperature. Yet, the rates and temperature responses of the two CH4 emission-related microbial processes (CH4 production by methanogens and oxidation by methanotrophs) are poorly known. Further, peatland sites within a fen-bog gradient are known to differ in the variables that regulate these two mechanisms, yet the interaction between peatland type and temperature lacks quantitative understanding. Here, we investigated potential CH4 production and oxidation rates for 14 peatlands in Finland located between c. 60 and 70 degrees N latitude, representing bogs, poor fens, and rich fens. Potentials were measured at three different temperatures (5, 17.5, and 30celcius) using the laboratory incubation method. We linked CH4 production and oxidation patterns to their methanogen and methanotroph abundance, peat properties, and plant functional types. We found that the rich fen-bog gradient-related nutrient availability and methanogen abundance increased the temperature response of CH4 production, with rich fens exhibiting the greatest production potentials. Oxidation potential showed a steeper temperature response than production, which was explained by aerenchymous plant cover, peat water holding capacity, peat nitrogen, and sulfate content. The steeper temperature response of oxidation suggests that, at higher temperatures, CH4 oxidation might balance increased CH4 production. Predicting net CH4 fluxes as an outcome of the two mechanisms is complicated due to their different controls and temperature responses. The lack of correlation between field CH4 fluxes and production/oxidation potentials, and the positive correlation with aerenchymous plants points toward the essential role of CH4 transport for emissions. The scenario of drying peatlands under climate change, which is likely to promote Sphagnum establishment over brown mosses in many places, will potentially reduce the predicted warming-related increase in CH4 emissions by shifting rich fens to Sphagnum-dominated systems.

Recent paleoecological studies have demonstrated an ongoing drying trend in temperate and boreal peatlands in Europe and in Canada. This drying is likely to alter vegetation and carbon gas exchange with atmosphere. However, to revel the expected change in carbon gas dynamics associated with decrease in water level experimental studies and long-term monitoring are needed. In here we present results from long term experiment in Finland where the impact of water level drawdown (WLD) of ~10 cm on three different peatland sites, two fens and a bog, has been studied since year 2000. Response to WLD differed between the three ecosystem types. In the nutrient rich fen WLD initiated rapid directional succession from sedge dominated system to the dominance of woody species. In the poor fen changes were less drastic: Initially WLD benefitted dwarf scrubs already present at the site, later they were overtaken by pines. Sedges as a group hold their position but Carex species were replaced by Eriophorum. Similarly to sedges, in the moss layer proportions of different Sphagnum moss species changed. Bog vegetation was more stable than fen vegetation. In all the ecosystems methane emissions decreased directly after WLD. In contrast, the response of CO2 dynamics was more complex. While long term net ecosystem exchange decreased to lower level than in controls in all studied ecosystems, the response of photosynthesis and respiration differed between the three ecosystems and between short term and long term. Results show how the response of peatlands to climate change is diverse and emphasize the need to understand what factors regulate the stability and resilience of peatland functioning.

In boreal peatlands felling and tree harvest are commonly carried out as part of peatland restoration. Stem‐only harvest is the principal harvest method and it leaves the live crown material (felling residue) containing most tree nutrients at the site. Whole‐tree harvest, where felling residue is removed, is not favored due to higher transport costs, although it might better promote the recovery of nutrient‐poor peatlands towards pristine conditions. We investigated whether initial differences in N mineralization and decomposition rates observed between tree harvest methods continued out to 6 years after restoration and whether the spatial variation in water table (WT) level and water nutrient concentrations parallels with the observed pattern in mineralization and decomposition rates. The study was done at 15 peatland sites in Natura 2000 protection areas in Finland during 2007–2013. Concentration of ammonium in soil water was higher in the stem‐only harvest treatment compared to that of the whole‐tree harvest treatment, whereas the previously observed differences in net N mineralization and decomposition rates had leveled out by the sixth year after restoration. The spatial variation created by the ditch network still affected the hydrology and peatland functions so that the nutrient concentrations were higher near ditches than in other locations, implying potential risk for nutrient leaching. Based on this study, there is no reason to prefer either harvest method over the other in nutrient‐poor drained peatlands with low tree volumes, which constitute the majority of available peatland restoration area in Finland.

It is well established that in ombrotrophic bogs, water-table depth (WTD) is the primary environmental control on testate amoeba distribution. However, the environmental controls on testate amoebae in minerotrophic fens are less well known and successional change in their assemblages associated with fen-bog peatland development has been scarcely investigated. Here we investigate a peatland space-for-time sequence resulting from postglacial rebound on the west coast of Finland, to assess successional patterns in testate amoeba communities and their relationships with environmental variables during peatland development. Sample sites along a 10-km transect from coast to inland ranged from a recently emerged wet meadow to a mature bog. Environmental variables (e.g., peat thickness, carbon and nitrogen content, pH, WTD and vegetation) were measured alongside testate amoeba samples. Results showed that even though the distribution of testate amoebae was to some extent determined by the succession stage, many taxa had wide WTD and pH ranges. The primary environmental control for many taxa changed along the succession. In conclusion, the ecological constraints on testate amoebae in minerotrophic systems are more complex than in bogs. The detected patterns also complicate the use of testate amoebae as a primary proxy in palaeoecological reconstructions where fen-to-bog shifts occur. (C) 2018 Elsevier GmbH. All rights reserved.

Calcareous spring fens are among the rarest and most endangered wetland types worldwide. The majority of these ecosystems can be found at high latitudes, where they are affected by above average rates of climate change. Particularly winter temperatures are increasing, which results in decreased snow cover. As snow provides an insulating layer that protects ecosystems from subzero temperatures, its decrease is likely to induce stress to plants. To investigate the sensitivity of the bryophyte community – key to the functioning of calcareous spring fens – to changing climatic conditions, we studied the annual variation in ecophysiology of two dominant bryophytes: Campylium stellatum and Scorpidium scorpioides. Further, a snow removal experiment was used to simulate the effect of changing winter conditions. In both species, we observed lowest efficiency of photosystem II (Fv/Fm) in spring, indicating physiological stress, and highest chlorophyll-a, -b and carotenoid concentrations in autumn. Snow removal exacerbated physiological stress in bryophytes. Consequently Fv/Fm, pigment concentrations and chlorophyll to carotenoids ratios declined, while chlorophyll-a to -b ratios increased. Moreover, these effects of winter climate change cascaded to the growing season. C. stellatum, a low hummock inhabitor, suffered more from snow removal (annual mean decline in Fv/Fm 7.7% and 30.0% in chlorophyll-a) than S. scorpioides, a hollow species (declines 5.4% and 14.5%, respectively). Taken together, our results indicate that spring fen bryophytes are negatively impacted by winter climate change, as a result of longer frost periods and increased numbers of freeze-thaw cycles in combination with higher light intensity and dehydration.

Current peatland models generally lack dynamic feedback between the plant community structure and the environment, although the vegetation dynamics and ecosystem functioning are tightly linked. Realistic projections of peatland response to climate change requires including vegetation dynamics in ecosystem models. In peatlands, Sphagnum mosses are key engineers. The species composition in a moss community varies primarily following habitat moisture conditions. Hence, modelling the mechanisms in controlling the habitat preference of Sphagna is a good first step for modelling the community dynamics in peatlands. In this study, we developed the Peatland Moss Simulator (PMS), a process-based model, for simulating community dynamics of the peatland moss layer that results in habitat preferences of Sphagnum species along moisture gradients. PMS employed an individual-based approach to describe the variation of functional traits among shoots and the stochastic base of competition. At the shoot-level, growth and competition were driven by net photosynthesis, which was regulated by hydrological processes via capitulum water retention. The model was tested by predicting the habitat preferences of S. magellanicum and S. fallax, two key species representing dry (hummock) and wet (lawn) habitats in a poor fen peatland (Lakkasuo, Finland). PMS successfully captured the habitat preferences of the two Sphagnum species, based on observed variations in trait properties. Our model simulation further showed that the validity of PMS depended on the interspecific differences in capitulum water retention being correctly specified. Neglecting the water-retention differences led to the failure of PMS to predict the habitat preferences of the species in stochastic simulations. Our work highlights the importance of capitulum water retention to the dynamics and carbon functioning of Sphagnum communities in peatland ecosystems. Studies of peatland responses to changing environmental conditions thus need to include capitulum water processes as a control on the vegetation dynamics. For that our PMS model could be used as an elemental design for the future development of dynamic vegetation models for peatland ecosystems.

Vegetation and hydrology are important controlling factors in peatland methane dynamics. This study aimed at investigating the role of vegetation components – sedges, dwarf-shrubs, and Sphagnum mosses – in methane fluxes of a boreal fen under natural and experimental water level drawdown conditions. We measured the fluxes during four growing seasons using static chamber technique in a field experiment where the role of the ecosystem components was assessed via plant removal treatments. The first year was a calibration year after which the water level drawdown and vegetation removal treatments were applied. Under natural water level conditions, plant-mediated fluxes comprised 68–78 % of the mean growing season flux (1.95 ± 0.21 g CH4 m−2 month−1 from June to September), of which Sphagnum mosses and sedges accounted for 1/4 and 3/4, respectively. The presence of dwarf shrubs, on the other hand, had a slightly attenuating effect on the fluxes. In water level drawdown conditions, the mean flux was close to zero (0.03 ± 0.03 g CH4 m−2 month−1) and the presence/absence of the plant groups had a negligible effect. In conclusion, water level acted as a switch; only in high water level conditions vegetation regulated the net fluxes. The results are relevant for assessing the response of peatland fluxes in changing climatic conditions, as water level drawdown and the consequent vegetation succession are the major projected impacts of climate change on northern peatlands.

Previous studies have shown that atmospheric nitrogen (N) deposition is detrimental to sphagna, which are a group of mosses that are important for carbon cycling in northern peatlands. Little is known about species interactions, such as relative responses of tall moss Polytrichum strictum Menzies ex Brid. and sphagna. We studied the effects of N deposition on growth, abundance, and CO2 exchange of the moss species Sphagnum capillifolium (Ehrh.) Hedw. and Polytrichum strictum in an experiment at a temperate bog. Sphagnum growth and cover decreased significantly with high-dose N treatment (6.4 g N·m−2·year−1) in years 4 and 5 of treatment, whereas the same parameters increased for Polytrichum compared with the control. Net CO2 exchange, gross photosynthesis (Pg), and dark respiration (R) in the intact moss cores, which were measured in year 5 of treatment, were elevated in the cores that had been treated with the high-dose of N, compared with the control, and this was associated with increased abundance of Polytrichum. The moss cores where Polytrichum was removed, however, had increased mass-based R with the high-dose N treatment. Our results showed that S. capillifolium at Mer Bleue may be close to N saturation, as 5 years of high-dose N loading (6.4 g N·m−2·year−1 + background) was harmful to this species, possibly as a result of increased respiratory cost. Polytrichum strictum had a competitive advantage, at least in the short-term, through allocating excess N to growth. This change in moss layer composition deserves further attention, as a shift to more easily decomposable litter, without corresponding increases in plant production, could reduce the carbon sequestration of the bog.

Northern peatlands form a major soil carbon (C) stock. With climate change, peatland C mineralization is expected to increase, which in turn would accelerate climate change. A particularity of peatlands is the importance of soil aeration, which regulates peatland functioning and likely modulates the responses to warming climate. Our aim is to assess the impacts of warming on a southern boreal and a sub-arctic sedge fen carbon dioxide (CO

Question Measurements of ecosystem carbon (C) exchange are usually labour-intensive and expensive. In peatlands, these temporally and spatially limited measurements are often up-scaled over comparable ecosystems, such as ombrotrophic bogs, to provide an estimate for ecosystem level carbon dioxide (CO2) fluxes. Peatlands typically have moisture variations reflected in the presence of microforms (e.g. hummocks and hollows), each with characteristic plant life forms. However, so far the applicability of peatland type (e.g. bog, fen) or microforms for up-scaling has not been assessed. Does the vegetation composition or function of associated species differ so greatly between the same types of peatland that up-scaling is impossible? Location Five ombrotrophic bogs in Northern Europe; in Ireland, Finland and western Russia. Methods We described the variation in vegetation of microforms within and between ombrotrophic bogs using multivariate analyses. Thereafter, we measured CO2 exchange at different microforms and evaluated the relationship between vegetation structure and the light response of photosynthesis. Results Our results show that the community composition of hummocks, lawns and hollows was rather uniform at the plant life-form level. The photosynthetic capacity per leaf area unit was quite similar within microform classes over the different bogs. The observed differences between sites in capacity were mainly related to variation in leaf area. Conclusions A reliable estimate of ecosystem-level photosynthesis requires knowledge of the proportion of different microforms in an area and the leaf area characteristics for each microform in the year(s) in question. Assessments of ecosystem-level photosynthesis are important with regard to current and future changes in climate, as the most dramatic changes in peatlands involve water level drawdown, which in turn is likely to lead to changes in the relative proportions of microforms within peatlands.

Questions Sphagnum fuscum (Schimp.) Klinggr. is a characteristic species of the later stages of mire development. It is hypothesized that competition limits its success in earlier successional stages where higher mineral nutrient availability and wetter conditions favour species with a higher production rate and, therefore, a stronger ability to compete. We aim to quantify the importance of different site factors and the effect of neighbouring plants on the performance of S. fuscum. Location A mire chronosequence from a land uplift coast towards inland on the Finnish side of Bothnia Bay, Baltic Sea. Methods We transplanted S. fuscum to seven sites along a mire chronosequence for a period of two growing seasons. Neighbouring plants were removed from half of the locations/transplants. We measured several growth-related parameters, such as rate of photosynthesis, chlorophyll fluorescence (Fv/Fm) and abundance of mosses. Results Sphagnum fuscum samples did not survive in the recently exposed sandy shore stage and in fen flarks with extensive sedge cover. Photosynthesis and abundance of transplanted S. fuscum were highest in the wet meadows, the stages that immediately follow the sandy shore stage. Photosynthetic rate and Fv/Fm were low in the late succession bog site compared to the younger successional sites. The occurrence of neighbouring plants decreased the abundance of the transplanted mosses but improved the physiological state. The impact was similar throughout the successional chronosequence. Conclusions The site factors favourable for rapid Sphagnum growth in general also favoured S. fuscum. The low photosynthesis, respiration and Fv/Fm of intact S. fuscum growing in its natural habitat compared to the surviving transplants in the younger sites suggests that in order to occur in its natural habitat, S. fuscum needs to allocate resources for photoprotective mechanisms. Our results indicate that under better environmental conditions, these resources can be allocated to the photosynthetic apparatus to increase growth.

[1] Northern forests and peatlands are globally significant elements in carbon (C) cycling. Recent research has also highlighted the role of aquatic ecosystems in landscape C budgets. We measured contemporary carbon dioxide (CO2) and methane (CH4) exchange, lateral C transfer (dissolved organic carbon (DOC), CO2, CH4), and long-term C accumulation in a peatland-stream-lake-continuum in north boreal Finland. On an annual scale the peatland, a rich fen, was a relatively strong C sink (27 g C m−2 a−1). The stream that traversed through the fen had high CO2 and CH4 effluxes (on average 480 and 12 g C m−2 a−1, respectively) to the atmosphere, while the small oligotrophic lake was a small C gas source per unit area (15 g C m−2 a−1). A catchment C budget was compiled by supplementing these measured values with literature values for the forests. The aquatic C fluxes equaled ~13% of the net C input by the forest and peatlands in the catchment, and the largest component was the downstream transfer of DOC. This study supports the proposition that ignoring the aquatic component would result in an overestimated regional C uptake. The contemporary net C input estimate for the fen, after accounting for the C transfer, was larger than the long-term C accumulation rate based on peat cores (22 versus 6.3–16.0 g C m−2 a−1). This study provides reference values for both the contemporary C exchange and long-term C accumulation history, and the terrestrial-aquatic linkage from the boreal-subarctic ecotone, which is vulnerable to ongoing climatic change.

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.

Introduction Restoration of afforested peatlands was initially driven by recognition of the high biodiversity value and increasing scarcity of peatlands in their natural state. Now we recognise that peatlands also play an important role in climate regulation, raising the question: should we be restoring afforested peatlands on a large scale as a climate change mitigation measure? This needs careful consideration because it involves sacrificing the initial investment in afforestation and taking land out of economic production. And what if we realise when it's too late that the peatland forests were benefiting us in previously unrecognised ways? We need to consider all the goods and services that afforested peatlands provide and weigh these up against those they will supply if we restore them. This chapter provides the background to the restoration of afforested peatlands, looks at the scientific evidence on how afforestation and restoration affect ecosystem services, summarises lessons learned from practical projects and attempts to answer the question: should we be doing more of this in future? The chapter focuses on temperate and boreal peatlands. Tropical peatlands are dealt with in Chapter 14 of this book. This chapter deals with the restoration of naturally forested peatlands that have had the growth of their natural tree cover boosted by forest drainage (forestry-drained peatlands) and naturally treeless peatlands that have been afforested by planting (afforested peatlands). Much of it also applies to peatlands that have become forested naturally as a result of drainage or peat cutting (sometimes also termed ‘afforested’). There are two main contexts reflecting differing degrees of natural tree cover on mires and different peatland forestry practices. In the northern coniferous forest or boreal zone, some mire types have a natural cover of slow-growing trees. During the twentieth century, in Finland, Sweden, Norway, the Baltic countries, Russia, and to a lesser extent in Canada and the United States, forest drainage was undertaken on these wooded peatlands to stimulate growth of the existing tree cover and thus form productive forest stands. Drainage for forestry has been the most extensive use of boreal peatlands, affecting more than 15 million hectares, 90% of which is in Scandinavia or Russia (Paavilainen and Paivanen 1995).

Growing public interest in conserving peatlands has created a need for restoration and rapid indicators of progress in peat formation. Vegetation and hydrological indicators are commonly assessed, but changes in mineralization and decomposition rates might better indicate when peat formation is underway in restored peatlands. In Finland, we investigated differences in mineralization and decomposition in the upper peat layer of five undrained and eight drained Pinus-dominated fens from 2006 to 2009. Forestry-drained fens were restored in 2007 by harvesting either whole trees or only stems, and by damming and filling ditches. Before restoration, net N mineralization rate was slightly higher in the drained than in undrained fens, whereas soil pH and Betula leaf litter decomposition rate were lower. After restoration, net N mineralization rate was similar for the undrained and restored fens, except near ditches after stem harvest. Also, soil pH and decomposition rate of Betula leaf litter became similar for undrained and restored fens. We conclude that whole tree harvest is a more suitable method for peatland restoration than stem harvest and that mineralization and decomposition rates are suitable indicators for peat formation after restoration.

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.

We compared the amount and composition of different aboveground biomass (BM) fractions of four mires with their net ecosystem CO2exchange (NEE) measured by eddy covariance. We found clear differences in response of green biomass (GBM) of plant functional types (PFTs) to water table (WT), which resulted in larger spatial variation in GBM within a mire than variation between mires. GBM varied between mires from 126 ± 7 to 336 ± 16 g·m–2(mean ± SE), while within mire variation at largest was from 157 ± 17 to 488 ± 20 g·m–2(mean ± SE). GBM of dominant PFTs appeared to be better in explaining the peak growing season NEE than the total BM or GBM of a mire. The differences in photosynthetic capacity between PTFs had a major role, and thus a smaller GBM with different species composition could result in higher NEE than larger GBM. Vascular plant GBM, especially that of sedges, appeared to have a high impact on NEE. Eleven PFTs, defined here, appeared to capture well the internal variation within mires, and the differences in GBM between communities were explained by the water table response of PFTs. Our results suggest the use of photosynthesizing BM, separated into PFTs, in modelling ecosystem carbon exchange instead of using just total BM.

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 CO(2) 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 CO(2) 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 (F(v)/F(m)). 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.

Question: How does restoration affect the hydrology and the understorey vegetation of managed pine fens? Location: Oligotrophic pine fens in Natura 2000 areas in Kainuu, eastern Finland. Methods: Eleven managed pine fens and eight pristine reference pine fens were chosen for the study in 2005. The managed fens, which had been drained for forestry during the 1970s and 1980s, were restored in 2007. The water table was monitored in all fens over four growing seasons during 2006 to 2009, and vegetation was surveyed from permanent sample plots in 2006 and 2009. Results: Before restoration in 2006, the water table was at a significantly lower level in the managed fens compared with the pristine fens. Immediately after restoration, the water table rose to the same level as in the pristine fens, and this change was permanent. Forest drainage had had little impact on the understorey vegetation of the managed fens in the three decades before restoration, with species typical of pristine fens still dominating the sites. Forest dwarf shrubs and feather mosses had started to increase in cover, but mire dwarf shrubs and Sphagnum mosses still dominated the managed fens. Only the typical hollow species Sphagnum majus, Sphagnum balticum and Scheuzeria palustris were missing from the managed fens. Two years after restoration, the changes in species composition were also marginal, with increased cover of mire dwarf shrubs and sedges being the only significant change. Conclusions: The success of restoration of oligotrophic pine fens seems likely, given that changes in hydrological functioning occurred rapidly, and since little change has occurred in the vegetation composition after draining. Speeding up the regeneration process in these peatland types by restoration may, therefore, be recommended, especially if the drainage effect extends to nearby pristine mires and influences their biodiversity.

Questions: What impact do a wet and a dry growing season have on CO2 dynamics of mire plant communities along a primary succession gradient from the initiation stage to the bog stage? Location: Mires on a land uplift coast, Finland. Methods: We measured CO2 dynamics and vascular plant green area development on five mires that form a sequence of mire succession. TWINSPAN was used to define successional mire plant communities and regression analyses were used to explore the temporal variation in CO2 dynamics of the communities. Results: CO2 dynamics of successional plant communities reacted differently to a wet and a dry growing season. The net CO2 uptake rate of the earlier successional communities decreased in the dry growing season due to a decrease in photosynthesizing leaf area. Concurrently, CO2 uptake of the later successional communities moderately increased or did not change. Generally, the difference in net ecosystem exchange (NEE) between a dry and a wet year resulted from the altered rate of gross photosynthesis (PG) rather than ecosystem respiration (RE). Conclusions: Critical factors for the more stable carbon (C) gas dynamics in the later stages of mire succession were (1) higher autogenic control of the physical environment and (2) an increase in the number of factors regulating the PG rate. These factors may buffer mire ecosystems (in terms of the C sink function) from extreme and unfavourable variations in environmental conditions.

Chamber method is commonly used to measure the CO 2 exchange from plant communities. Due to low time resolution, actual measurements reflect only momentary CO 2 exchange rates. Therefore, a common way to derive seasonal or annual estimates is to establish models describing the response of CO 2 exchange to environmental variables, and then to reconstruct the CO 2 exchange over the desired time period. There are several alternative ways to obtain the CO 2 balance for the entire mire: models can be parameterized by individual sample plots, plant communities or the entire site. Similarly, the CO 2 balance can be reconstructed by plots, plant communities or the entire site. We tested how the choice of the modelling and reconstruction approach influences the CO 2 exchange estimates for the entire mire and for individual sample plots and plant communities. We measured the CO 2 exchange in a spatially heterogeneous sedge-dominated northern aapa mire for two growing seasons. We observed high spatial variation in CO 2 balance between the plant communities. We noticed that when the CO 2 balances of individual sample plots or plant communities are of interest, using a model appropriate for the entire site may result in biased estimates. In worst case the different modelling approaches may turn the CO 2 balance of an individual sample plot from positive to negative. Further, while using the whole ecosystem approach in modelling, the superior ability of chamber method in acknowledging spatial variation is lost. While the modelled growing season CO 2 balance of the mire ranged from 232 to 625 g CO 2 m −2 depending on the chosen modelling and reconstruction approach, the average estimates still remained within the uncertainty range of one another. Acknowledgement of the spatial variation in plant community level makes the areal estimate more robust to varying weather conditions. Further, the reliability of estimates is improved by explicit formulation of the choices behind the modelling and reconstruction units reflecting the study objectives.

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.

Pristine peatlands are a significant source of atmospheric methane (CH4). Large spatio–temporal variation has been observed in flux rates within and between peatlands. Variation is commonly associated with water level, vegetation structure, soil chemistry and climatic variability. We measured spatial and temporal variation in CH4 fluxes in a blanket bog during the period 2003–2005. The surface of the bog was composed of different vegetation communities (hummocks, lawns and hollows) along a water level gradient. CH4 fluxes were measured in each community using a chamber method. Regression modelling was used to relate the fluxes with environmental variables and to integrate fluxes over the study period. Water level was the strongest controller of spatial variation; the average flux rate was lowest in hummocks and highest in hollows, ranging from 3 to 53 mg CH4 m−2 day−1. In vegetation communities with a permanently high water level, the amount and species composition of vegetation was also a good indicator of flux rate. We observed a clear seasonal variation in flux that was chiefly controlled by temperature. The annual average flux (6.2 g CH4 m−2 year−1) was similar to previous estimates from blanket bogs and continental raised bogs. No interannual variation was observed.

The surface of bogs is commonly patterned and composed of different vegetation communities, defined by water level. Carbon dioxide (CO2) dynamics vary spatially between the vegetation communities. An understanding of the controls on the spatial variation of CO2 dynamics is required to assess the role of bogs in the global carbon cycle. The water level gradient in a blanket bog was described and the CO2 exchange along the gradient investigated using chamber based measurements in combination with regression modelling. The aim was to investigate the controls on gross photosynthesis (PG), ecosystem respiration (RE) and net ecosystem CO2 exchange (NEE) as well as the spatial and temporal variation in these fluxes. Vegetation structure was strongly controlled by water level. The species with distinctive water level optima were separated into the opposite ends of the gradient in canonical correspondence analysis. The number of species and leaf area were highest in the intermediate water level range and these communities had the highest PG. Photosynthesis was highest when the water level was 11 cm below the surface. Ecosystem respiration, which includes decomposition, was less dependent on vegetation structure and followed the water level gradient more directly. The annual NEE varied from −115 to 768 g CO2 m−2, being lowest in wet and highest in dry vegetation communities. The temporal variation was most pronounced in PG, which decreased substantially during winter, when photosynthetic photon flux density and leaf area were lowest. Ecosystem respiration, which is dependent on temperature, was less variable and wintertime RE fluxes constituted approximately 24% of the annual flux.

Net ecosystem exchange (NEE) was measured in a patterned peatland with eddy covariance (EC) and chamber methods during a 12-month period. The peatland surface was composed of microforms characterized by a difference in water level and vegetation composition. The distribution of microforms varied spatially within the peatland. To achieve correspondent half-hourly EC and chamber NEE estimates, we modelled microform level chamber fluxes, estimated them at each instance of weather recordings and integrated them over the year. We then scaled the fluxes up to the EC footprint. On a half-hourly time scale the correlation coefficient ( R ) of the NEE between the methods was 0.80 and the slope of regression 0.91. Measurements made in summer and during daylight were more highly correlated than measurements made in winter and during darkness. When integrated on a monthly time scale the methods agreed better, with R of 0.98 and slope of regression 1.00. The annual NEE for the EC and chamber methods were 206 and 242 g(CO 2 ) m −2 , respectively. The study confirmed that the surface pattern of the EC footprint in the blanket bog was sufficiently homogeneous, that the changing wind direction did not influence the half-hourly NEE. However, the chamber estimates found that the annual NEE of the driest area within the footprint was 130% larger than that in the wettest area, indicating that large spatial variation can be found in NEE.