| 1. |
- Bengtsson, Fia, 1986-, et al.
(författare)
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Environmental drivers of Sphagnum growth in peatlands across the Holarctic region
- 2021
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Ingår i: Journal of Ecology. - : John Wiley & Sons. - 0022-0477 .- 1365-2745. ; 109:1, s. 417-431
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Tidskriftsartikel (refereegranskat)abstract
- The relative importance of global versus local environmental factors for growth and thus carbon uptake of the bryophyte genusSphagnum-the main peat-former and ecosystem engineer in northern peatlands-remains unclear. We measured length growth and net primary production (NPP) of two abundantSphagnumspecies 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 onSphagnumgrowth. 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 denserSphagnum fuscumgrowing on hummocks had weaker responses to climatic variation than the larger and looserSphagnum magellanicumgrowing in the wetter conditions. Growth decreased with increasing vascular plant cover within a site. Between sites, precipitation and temperature increased growth forS. 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 influencedSphagnumgrowth indirectly by affecting moss shoot density. Synthesis. Our results imply that in a warmer climate,S. magellanicumwill increase length growth as long as precipitation is not reduced, whileS. fuscumis 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.
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| 2. |
- Bengtsson, Fia, et al.
(författare)
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Mechanisms behind species-specific water economy responses to water level drawdown in peat mosses
- 2020
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Ingår i: Annals of Botany. - : Oxford University Press (OUP). - 0305-7364 .- 1095-8290. ; 126:2, s. 219-230
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Tidskriftsartikel (refereegranskat)abstract
- Background and AimsThe ecosystem engineers Sphagnum (peat mosses) are responsible for sequestering a large proportion of carbon in northern peatlands. Species may respond differently to hydrological changes, and water level changes may lead to vegetation shifts in peatlands, causing them to revert from sinks to sources of carbon. We aimed to compare species-specific responses to water level drawdown within Sphagnum, and investigate which traits affect water economy in this genus.MethodsIn a mesocosm experiment, we investigated how water level drawdown affected water content (WC) in the photosynthetically active apex of the moss and maximum quantum yield of photosystem II (i.e. Fv/Fm) of 13 Sphagnum species. Structural traits were measured, and eight anatomical traits were quantified from scanning electron microscopy micrographs.Key ResultsMixed-effects models indicated that at high water level, large leaves were the most influential predictor of high WC, and at low water level WC was higher in species growing drier in the field, with larger hyaline cell pore sizes and total pore areas associated with higher WC. Higher stem and peat bulk density increased WC, while capitulum mass per area and numerical shoot density did not. We observed a clear positive relationship between Fv/Fm and WC in wet-growing species.ConclusionsWhile we found that most hummock species had a relatively high water loss resistance, we propose that some species are able to maintain a high WC at drawdown by storing large amounts of water at a high water level. Our result showing that leaf traits are important warrants further research using advanced morphometric methods. As climate change may lead to more frequent droughts and thereby water level drawdowns in peatlands, a mechanistic understanding of species-specific traits and responses is crucial for predicting future changes in these systems.
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| 3. |
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| 4. |
- Colson, Daniel W., et al.
(författare)
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Six Decades of Changes in Pool Characteristics on a Concentric-Patterned Raised Bog
- 2023
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Ingår i: Ecosystems. - 1432-9840 .- 1435-0629.
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Tidskriftsartikel (refereegranskat)abstract
- Raised bogs are wetland ecosystems which, under the right climatic conditions, feature patterns of pool hollows and hummock ridges. The relative cover and the spatial arrangement of pool and ridge microforms are thought to be influential on peatland atmosphere carbon gas fluxes and plant biodiversity. The mechanisms responsible for the formation and maintenance of pools, and the stability of these features in response to warming climates, remain topics of ongoing research. We employed historical aerial imagery, combined with a contemporary uncrewed aerial vehicle survey, to study 61 years of changes in pools at a patterned raised bog in central Sweden. We used a pool inheritance method to track individual pools between image acquisition dates throughout the time series. These data show a rapid loss of open-water pool area during the study period, primarily due to overgrowth of open-water pools by Sphagnum. We postulate that these changes are driven by ongoing climate warming that is accelerating Sphagnum colonisation. Open-water pool area declined by 26.8% during the study period, equivalent to a loss of 1001 m2 y−1 across the 150-hectare site. This is contradictory to an existing theory that states pools are highly stable, once formed, and can only convert to a terrestrial state through catastrophic drainage. The pool inheritance analysis shows that smaller pools are liable to become completely terrestrialised and expire. Our findings form part of a growing body of evidence for the loss of open-water habitats in peatlands across the boreal and elsewhere.
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| 5. |
- Evans, Christopher, et al.
(författare)
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The impact of wildfire on biogeochemical fluxes and water quality in boreal catchments
- 2021
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Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 18, s. 3243-3261
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Tidskriftsartikel (refereegranskat)abstract
- Wildfires are the major disturbance in boreal ecosystems and are of great importance for the biogeochemical cycles of carbon (C) and nutrients. However, these fire-induced impacts are hard to quantify and are rarely assessed together at an ecosystem level incorporating both aquatic and terrestrial environments. Following a wildfire in Sweden in an area with ongoing monitoring, we conducted a pre-fire (9 years) and post-fire (4 years) multi-catchment investigation of element losses (combustion and leaching) and impacts on water quality. Direct C and nitrogen (N) losses through combustion were ca. 4500 and 100 gm(-2), respectively. Net CO2 loss associated with soil and biomass respiration was similar to 150 g C m(-2) during the first year, but the ecosystem started to show net CO2 uptake in June 3 years post-fire. Aquatic C and N losses the first 12 months post-fire were 7 and 0.6 gm(-2), respectively. Hence, soil respiration comprised a non-negligible part of the post-fire C loss, whereas aquatic C losses were minor and did not increase post-fire. However, other elements (e.g. Ca, S) exhibited ecologically relevant increases in fluvial export and concentration with large peaks in the immediate post-fire period. The temporal dynamics of stream concentrations (Ca2+, Mg2+, K+,SO4-2, Cl-, NH4+, total organic N) suggest the presence of faster- and slower-release nutrient pools with half-lives of around 2 weeks and 4 months which we attribute to physicochemically and biologically mediated mobilization processes, respectively. Three years after the fire, it appears that dissolved fluxes of nutrients have largely returned to pre-fire conditions, but there is still net release of CO2.
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| 6. |
- Gustafsson, Lena, et al.
(författare)
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Burn severity and soil chemistry are weak drivers of early vegetation succession following a boreal mega-fire in a production forest landscape
- 2021
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Ingår i: Journal of Vegetation Science. - : John Wiley & Sons. - 1100-9233 .- 1654-1103. ; 32:1
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Tidskriftsartikel (refereegranskat)abstract
- Questions: Do burn severity and soil chemistry drive species and trait composition on recently burned clear-cuttings? Does the spatial distribution of common, easily dispersed colonizers vary with distance to fire perimeter?Location: A 13,000 ha production forest landscape in boreal southern Sweden burned in a wildfire in 2014.Methods: Vascular plants and bryophytes were recorded in permanent plots on clear-cuts two and five years following fire, covering a burn severity gradient. Soil carbon content (reflecting burn severity), pH and nutrients were measured at plot level. Trait data were retrieved from the BIEN and LEDA databases and analyzed using community-weighted mean (CWM) trait values. Statistical analyses included generalized linear mixed models (GLMMs), non-metric multidimensional scaling (NMDS) and multivariate ANOVA.Results: Low burn severity resulted in higher frequency of legacy species (e.g. Vaccinium myrtillus), while high burn severity facilitated colonizing species (e.g. Senecio sylvaticus). Vegetation varied with soil chemistry, expressed through pH. Species composition changed between years and deviated from unburned clear-cuts. After five years the most common taxa on burned plots were the vascular plants Chamaenerion angustifolium, Betula spp. and Populus tremula and the bryophytes Ceratodon purpureus and Polytrichum juniperinum. CWM specific leaf area (SLA) decreased markedly with time and root buds increased with total carbon content in the soil (i.e., toward less severely burned plots), while soil pH was not associated with any studied trait. Chamaenerion angustifolium decreased with distance to the fire perimeter, while Ceratodon purpureus increased.Conclusions: Burn severity and soil pH weakly drive vegetation dynamics in the early phase following fire on clear-cuts, indicating a large influence of stochastic processes. Deciduous trees are common already after five years and their further expansion will affect light and nutrient availability. To understand future vegetation trajectories on burned clear-cuts, studies need to incorporate the light factor and links between tree species' identity and soil nutrient availability.
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| 7. |
- Gustafsson, Lena, et al.
(författare)
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Disturbance interval modulates the starting point for vegetation succession
- 2021
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Ingår i: Ecology. - : John Wiley & Sons. - 0012-9658 .- 1939-9170. ; 102:9
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Tidskriftsartikel (refereegranskat)abstract
- Increased frequency and new types of disturbances caused by global change calls for deepened insights into possible alterations of successional pathways. Despite current interest in disturbance interactions there is a striking lack of studies focusing on the implication of decreasing times between disturbances. We surveyed forest-floor vegetation (vascular plants and bryophytes) in a Pinus sylvestris–dominated, even-aged production forest landscape, unique because of the presence of stands under a precisely dated disturbance interval gradient, ranging from 0 to 123 yr between clearcutting and a subsequent megafire. Despite a dominance of early-successional species in all burned stands 5 yr after fire, progression of succession was linked to time since the preceding clearcutting disturbance. This was most clearly seen in increased frequency with time since clearcutting of the dominant, late-successional dwarf shrub Vaccinium myrtillus, with surviving rhizomes as an important mechanism for postfire recovery. Our results demonstrate the role of legacy species as significant drivers of succession. We conclude that the starting point for succession is modulated by disturbance interval, so that shortened intervals risk reducing development towards late-successional stages. We suggest that a decrease in long successional sequences caused by more frequent disturbances may represent a general pattern, relevant also for other forest types and ecosystems.
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| 8. |
- Jorgensen, Karolina, et al.
(författare)
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Links between boreal forest management, soil fungal communities and below-ground carbon sequestration
- 2022
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Ingår i: Functional Ecology. - : John Wiley & Sons. - 0269-8463 .- 1365-2435. ; 36:2, s. 392-405
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Tidskriftsartikel (refereegranskat)abstract
- 1. Forest management has a potential to alter below-ground carbon storage. However, the underlying mechanisms, and the relative importance of carbon input and decomposition in regulation of soil carbon dynamics are poorly understood. 2. We examined whether interactive effects of forest fertilization and thinning on carbon stocks in the topsoil of boreal forests were linked to changes in fungal community composition, biomass and enzyme activities, in a long-term fertilization and thinning experiment distributed across 29 Pinus sylvestris forests along a 1,300 km latitudinal transect in Sweden. 3. Nitrogen fertilization increased fungal biomass, particularly towards the north and mainly by promoting root-associated Ascomycetes, but the response was moderated by thinning. Fungal biomass correlated positively with carbon stocks in the organic topsoil. However, ectomycorrhizal Cortinarius species were reduced in abundance by fertilization and correlated negatively with carbon stocks. 4. Plausibly, increased soil carbon stocks after fertilization are linked to increased input of carbon in the form of root-associated mycelium combined with the loss of ectomycorrhizal decomposers within the genus Cortinarius. These fungal responses to fertilization may mediate a natural climate solution by promoting carbon sequestration in the organic topsoil, but the effect of fertilization may also be undesired from a biodiversity perspective.
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| 9. |
- Jörgensen, Karolina, et al.
(författare)
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Forest management to increase carbon sequestration in boreal Pinus sylvestris forests
- 2021
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Ingår i: Plant and Soil. - : Springer Nature. - 0032-079X .- 1573-5036. ; 466:1-2, s. 165-178
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Tidskriftsartikel (refereegranskat)abstract
- Background and aims Forest management towards increased carbon (C) sequestration has repeatedly been suggested as a “natural climate solution”. We evaluated the potential of altered management to increase C sequestration in boreal Pinus sylvestris forest plantations.Methods At 29 forest sites, distributed along a 1300 km latitudinal gradient in Sweden, we studied interactive effects of fertilization and thinning on accumulation of C in standing biomass and the organic horizon over a 40 year period.Results Abstention from thinning increased the total C stock by 50% on average. The increase was significant (14% on average) even when C in the removed timber was included in the total ecosystem C pool. Fertilization of thinned stands increased stocks similarly regardless of including (11%) or excluding (12%) removed biomass, and fertilization combined with abstention from thinning had a synergistic effect on C stocks that generated an increase of 79% (35% when removed timber was included in the C stock). A positive effect of fertilization on C stocks was observed along the entire gradient but was greater in relative terms at high latitudes. Fertilization also reduced soil respiration rates.Conclusion Taken together, our results suggest that changed forest management practices have major potential to increase the C sink of boreal forests. Although promising, these benefits should be evaluated against the undesired effects that such management can have on economic revenue, timber quality, biodiversity and delivery of other ecosystem services.
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| 10. |
- Koronatova, Natalia G., et al.
(författare)
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Weather Factors in Different Growing Periods Determine Inter-Annual Change in Growth of Four Sphagnum Species : Evidence from an Eight-Year Study
- 2022
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Ingår i: Wetlands (Wilmington, N.C.). - : Springer Nature. - 0277-5212 .- 1943-6246. ; 42:8
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Tidskriftsartikel (refereegranskat)abstract
- The growth of peat mosses is crucial for carbon uptake and storage in high latitude peatlands. Nevertheless, little is known on how variation in specific weather conditions affect Sphagnum functional traits and productivity. Using data from an eight-year study in a mire complex in the southern taiga of Western Siberia, we investigated how a suite of within-season weather conditions relates to Sphagnum growth. We collected weather data, and data on functional traits (length increment, increment biomass, capitulum numerical density and capitulum biomass) and net primary productivity of four Sphagnum species growing in raised bogs and poor fens. Overall, the most important factors were those related moisture conditions. Growing season averages of weather variables (e.g., precipitation and mean temperature) were often as good predictors of Sphagnum functional traits and productivity as early or late seasonal averages, but not necessarily for the same variables. The most sensitive traits to weather fluctuation were length increment (for S. magellanicum agg., S. angustifolium, S. fallax) and numerical density (for S. fuscum). Primary productivity of S. fuscum and S. magellanicum agg. were the highest under warm and wet conditions with S. fuscum being less sensitive to the weather; productivity of S. angustifolium increased under cool and wet conditions; and productivity of S. fallax was the highest under dry weather. Diversity in interspecific response to weather fluctuations may result in high peatland resistance towards environmental variability, and thereby maintaining a stable Sphagnum productivity in time across the mire complex.
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