| 1. |
- Bosiö, Julia
(författare)
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A green future with thawing permafrost mires? : a study of climate-vegetation interactions in European subarctic peatlands
- 2013
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Climate projections indicate that Arctic and sub-Arctic regions are facing a significant change in climate during the 21st century. With warmer temperatures precipitation is also expected to increase, and in particular winter precipitation. These changes are likely to have large impacts on the Arctic and subarctic environment, and extensive research has focused on ecosystem-climate interactions in Arctic and sub-Arctic environments, but still the environmental response to such changes is not fully understood. This thesis presents the work and outcomes of my research on climate-vegetation interactions in permafrost (ground that remains frozen for two or more consecutive years) mires in subarctic Fennoscandia. In this region permafrost mires demarks the outer border of lowland permafrost existence, where a combination of climatological and environmental conditions allows for the ground to remain frozen year round, making the permafrost particularly sensitive to changes. By combining field observations of vegetation patterns in permafrost mires throughout the study region with spatial data of the present (2008) and projected future climate in subarctic Fennoscandia the future vegetational patterns of these permafrost mires were modeled. Further, the impact of increased snow cover on plant photosynthesis in these environments was assessed through field experiments on a subarctic permafrost mire, where the snow cover was manipulated during seven winters using snow fences. The results suggest that a rapid transition from dry heath tundra vegetation to moist tussock tundra vegetation is to be expected in these permafrost mires with the warmer climate and increased precipitation projected for the studied region. The snow manipulation experiments suggest that even a moderate increase in snow cover thickness increases plant photosynthesis on the long term. This increase in photosynthesis is attributed to the observed shift in plant species composition where moist tussock vegetation is likely to be favored by increased soil moisture, soil temperature and nutrient availability. However, the increased carbon uptake through higher photosynthesis rates is may be completely offset by increased methane emissions from increased wetness in the thawing peatlands.
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| 2. |
- Bosiö, Julia, et al.
(författare)
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Future vegetation changes in thawing subarctic mires and implications for greenhouse gas exchange-a regional assessment
- 2012
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Ingår i: Climatic Change. - : Springer Science and Business Media LLC. - 0165-0009 .- 1573-1480. ; 115:2, s. 379-398
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Tidskriftsartikel (refereegranskat)abstract
- One of the major concerns regarding climate change in high latitudes is the potential feedback from greenhouse gases (GHG) being released from thawing peat soils. In this paper we show how vegetational patterns and associated GHG fluxes in subarctic palsa (peat mounds with a permanently frozen core) mires can be linked to climate, based on field observations from fifteen palsa sites distributed in northern Fennoscandia. Fine resolution (100 m) land cover data are combined with projections of future climate for the 21st century in order to model the potential future distribution of palsa vegetation in northern Fennoscandia. Site scale climate-vegetational relationships for two vegetation types are described by a climate suitability index computed from the field observations. Our results indicate drastic changes in the palsa vegetational patterns over the coming decades with a 97 % reduction in dry hummock areas by 2041-2060 compared to the 1961-1990 areal coverage. The impact of these changes on the carbon balance is a decrease in the efflux of CO2 from 130 kilotonnes C y(-1) to a net uptake of 11 kilotonnes C y(-1) and a threefold increase in the efflux of CH4 from 6 to 18 kilotonnes C y(-1) over the same period and over the 5,520 km(2) area of palsa mires. The combined effect is equivalent to a slight decrease in CO2-C emissions, from 182 to 152 kilotonnes C y(-1). Main uncertainties involve the ability of the vegetation community to adapt to new conditions, and long-term changes in hydrology due to absence of ice and frost heaving.
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| 3. |
- Bosiö, Julia, et al.
(författare)
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Increased photosynthesis compensates for shorter growing season in subarctic tundra - 8 years of snow accumulation manipulations
- 2014
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Ingår i: Climatic Change. - : Springer Science and Business Media LLC. - 0165-0009 .- 1573-1480. ; 127:2, s. 321-334
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Tidskriftsartikel (refereegranskat)abstract
- This study was initiated to analyze the effect of increased snow cover on plant photosynthesis in subarctic mires underlain by permafrost. Snow fences were used to increase the accumulation of snow on a subarctic permafrost mire in northern Sweden. By measuring reflected photosynthetic active radiation (PAR) the effect of snow thickness and associated delay of the start of the growing season was assessed in terms of absorbed PAR and estimated gross primary production (GPP). Six plots experienced increased snow accumulation and six plots were untreated. Incoming and reflected PAR was logged hourly from August 2010 to October 2013. In 2010 PAR measurements were coupled with flux chamber measurements to assess GPP and light use efficiency of the plots. The increased snow thickness prolonged the duration of the snow cover in spring. The delay of the growing season start in the treated plots was 18 days in 2011, 3 days in 2012 and 22 days in 2013. Results show higher PAR absorption, together with almost 35 % higher light use efficiency, in treated plots compared to untreated plots. Estimations of GPP suggest that the loss in early season photosynthesis, due to the shortening of the growing season in the treatment plots, is well compensated for by the increased absorption of PAR and higher light use efficiency throughout the whole growing seasons. This compensation is likely to be explained by increased soil moisture and nutrients together with a shift in vegetation composition associated with the accelerated permafrost thaw in the treatment plots.
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| 4. |
- Johansson, Margareta, et al.
(författare)
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Rapid responses of permafrost and vegetation to experimentally increased snow cover in sub-arctic Sweden
- 2013
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Ingår i: Environmental Research Letters. - : IOP Publishing. - 1748-9326. ; 8:3
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Tidskriftsartikel (refereegranskat)abstract
- Increased snow depth already observed, and that predicted for the future are of critical importance to many geophysical and biological processes as well as human activities. The future characteristics of sub-arctic landscapes where permafrost is particularly vulnerable will depend on complex interactions between snow cover, vegetation and permafrost. An experimental manipulation was, therefore, set up on a lowland peat plateau with permafrost, in northernmost Sweden, to simulate projected future increases in winter precipitation and to study their effects on permafrost and vegetation. After seven years of treatment, statistically significant differences between manipulated and control plots were found in mean winter ground temperatures, which were 1.5 degrees C higher in manipulated plots. During the winter, a difference in minimum temperatures of up to 9 degrees C higher could be found in individual manipulated plots compared with control plots. Active layer thicknesses increased at the manipulated plots by almost 20% compared with the control plots and a mean surface subsidence of 24 cm was recorded in the manipulated plots compared to 5 cm in the control plots. The graminoid Eriophorum vaginatum has expanded in the manipulated plots and the vegetation remained green longer in the season.
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