| 1. |
- Björk, Robert G., 1974, et al.
(author)
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Long-term warming effects on carbon and nitrogen dynamics in tundra soils
- 2012
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In: 20th Anniversary ITEX Workshop, El Paso, USA, 17–21 January 2012.
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Conference paper (other academic/artistic)abstract
- During IPY 2008 we used the ITEX experiment in Latnjajaure (northern Sweden), established during the early years of the program, to investigate long-term warming effects on ecosystem respiration (ER), carbon (C) and nitrogen (N) pool (including d13C and d15N), soil organic C (SOC) chemical composition, and N mineralization among plant communities. After 12 to 15 years of open top chamber (OTC) treatment no statistical effect was found on the soil temperature (10 cm soil depth), although the was an overall increase in all OTC by +0.2°C. However, the soil moisture decreased significantly by 3-14%, depending on plant community, in the OTCs compared to ambient conditions. Preliminary, there was a 19-61% non-significant increase in annual growing season ER in the OTC compared to the ambient plots over the growing season. The were distinct differences in the SOM functional composition among plant communities with c 10% more O-alkyls stored in tussock tundra than in dry meadow. The OTCs did not consistently alter the SOM composition among the vegetation types but clearly showed a trend for reduced aliphatic and O-alkyl C in the OTCs suggesting increased decomposition (or reduced inputs) of these compounds. Thus, the non-significantly higher ER may in some communities be of plant origin linked to greater plant biomass in the OTCs, and in other (e.g. tussock tundra) from increased decomposition rates. In conclusion, this study showed that 12-15 years of OTC treatment had a modest effects impact C and N dynamics in tundra soils specific to distinct plant communities.
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| 2. |
- de la Barreda-Bautista, Betsabe, et al.
(author)
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Towards a Monitoring Approach for Understanding Permafrost Degradation and Linked Subsidence in Arctic Peatlands
- 2022
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In: Remote Sensing. - : MDPI. - 2072-4292. ; 14:3
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Journal article (peer-reviewed)abstract
- Permafrost thaw resulting from climate warming is threatening to release carbon from high latitude peatlands. The aim of this research was to determine subsidence rates linked to permafrost thaw in sub-Arctic peatlands in Sweden using historical orthophotographic (orthophotos), Unoccupied Aerial Vehicle (UAV), and Interferometric Synthetic Aperture Radar (InSAR) data. The orthophotos showed that the permafrost palsa on the study sites have been contracting in their areal extent, with the greatest rates of loss between 2002 and 2008. The surface motion estimated from differential digital elevation models from the UAV data showed high levels of subsidence (maxi-mum of −25 cm between 2017 and 2020) around the edges of the raised palsa plateaus. The InSAR data analysis showed that raised palsa areas had the greatest subsidence rates, with maximum subsidence rates of 1.5 cm between 2017 and 2020; however, all wetland vegetation types showed sub-sidence. We suggest that the difference in spatial units associated with each sensor explains parts of the variation in the subsidence levels recorded. We conclude that InSAR was able to identify the areas most at risk of subsidence and that it can be used to investigate subsidence over large spatial extents, whereas UAV data can be used to better understand the dynamics of permafrost degradation at a local level. These findings underpin a monitoring approach for these peatlands.
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| 3. |
- Monsimet, Jérémy, et al.
(author)
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UAV data and deep learning : efficient tools to map ant mounds and their ecological impact
- 2024
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In: Remote Sensing in Ecology and Conservation. - : John Wiley & Sons. - 2056-3485.
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Journal article (peer-reviewed)abstract
- High-resolution unoccupied aerial vehicle (UAVs) data have alleviated the mismatch between the scale of ecological processes and the scale of remotely sensed data, while machine learning and deep learning methods allow new avenues for quantification in ecology. Ant nests play key roles in ecosystem functioning, yet their distribution and effects on entire landscapes remain poorly understood, in part because they and their mounds are too small for satellite remote sensing. This research maps the distribution and impact of ant mounds in a 20 ha treeline ecotone. We evaluate the detectability from UAV imagery using a deep learning model for object detection and different combinations of RGB, thermal and multispectral sensor data. We were able to detect ant mounds in all imagery using manual detection and deep learning. However, the highest precision rates were achieved by deep learning using RGB data which has the highest spatial resolution (1.9 cm) at comparable UAV flight height. While multispectral data were outperformed for detection, it allows for novel insights into the ecology of ants and their spatial impact on vegetation productivity using the normalized difference vegetation index. Scaling up, this suggests that ant mounds quantifiably impact vegetation productivity for up to 4% of our study area and up to 8% of the Betula nana vegetation communities, the vegetation type with the highest abundance of ant mounds. Therefore, they could have an overlooked role in nutrient-limited tundra vegetation, and on the shrubification of this habitat. Further, we show the powerful combination UAV multi-sensor data and deep learning for efficient ecological tracking and monitoring of mound-building ants and their spatial impact.
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| 4. |
- Myrsky, Eero, et al.
(author)
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Higher vascular plant abundance associated with decreased ecosystem respiration after 20 years of warming in the forest–tundra ecotone
- 2024
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In: Functional Ecology. - : British Ecological Society. - 0269-8463 .- 1365-2435. ; 38:1, s. 219-232
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Journal article (peer-reviewed)abstract
- The on-going climate warming is promoting shrub abundance in high latitudes, but the effect of this phenomenon on ecosystem functioning is expected to depend on whether deciduous or evergreen species increase in response to warming. To explore effects of long-term warming on shrubs and further on ecosystem functioning, we analysed vegetation and ecosystem CO2 exchange after 20 years of warming in the forest–tundra ecotone in subarctic Sweden. A previous study conducted 9 years earlier had found increased evergreen Empetrum nigrum ssp. hermaphroditum in the forest and increased deciduous Betula nana in the tundra. Following current understanding, we expected continued increase in shrub abundance that would be stronger in tundra than in forest. We expected warming to increase ecosystem respiration (Re) and gross primary productivity (GPP), with a greater increase in Re in tundra due to increased deciduous shrub abundance, leading to a less negative net ecosystem exchange and reduced ecosystem C sink strength. As predicted, vascular plant abundances were higher in the warmed plots with a stronger response in tundra than in forest. However, whereas B. nana had increased in abundance since the last survey, E. hermaphroditum abundance had declined due to several moth and rodent outbreaks during the past decade. In contrast to predictions, Re was significantly lower in the warmed plots irrespective of habitat, and GPP increased marginally only in the forest. The lower Re and a higher GPP under warming in the forest together led to increased net C sink. Re was negatively associated with the total vascular plant abundance. Our results highlight the importance of disturbance regimes for vegetation responses to warming. Climate warming may promote species with both a high capacity to grow under warmer conditions and a resilience towards herbivore outbreaks. Negative correlation between Re and total vascular plant abundance further indicate that the indirect impacts of increased plants on soil microclimate may become increasingly important for ecosystem CO2 exchange in the long run, which adds to the different mechanisms that link warming and CO2 fluxes in northern ecosystems. Read the free Plain Language Summary for this article on the Journal blog.
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| 5. |
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| 6. |
- Sjögersten, Sofie, et al.
(author)
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Depth distribution of net methanotrophic activity at a mountain birch forest-tundra heath ecotone, northern Sweden
- 2007
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In: Arctic, Antarctic and Alpine research. - 1523-0430 .- 1938-4246. ; 39:3, s. 477-480
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Journal article (peer-reviewed)abstract
- Methanotrophy (the bacterial oxidation of CH4) in soils is the major biological sink for atmospheric CH4. Here we present results from a study designed to quantify the role of the physical diffusion barrier to CH4, through surface soils, as a factor affecting methanotrophy. We used the mountain birch forest-tundra heath ecotone in subarctic northern Sweden as our study system. Our results show that, although CH4 fluxes were generally low (around -20 mu mol m(-2) h(-1); a net flux from atmosphere to soil), the two adjacent communities responded in contrasting ways to in situ experimental reduction of the diffusion barrier (removal of the top 50 mm of soil): Uptake increased by 40% in forest soil in association with the removal, whereas it decreased marginally (by 10%) in tundra heath. Investigations of the depth-distribution of CH4 oxidation in vitro revealed maximum rates at the top of the mineral soil for the forest site, whereas at the tundra heath this was more evenly spread throughout the organic horizon. The contrasting physicochemical properties and methanotroph activity in the organic horizons together explain the contrasting responses to the removal treatment. They also illustrate the potential role of vegetation for methane oxidation around this ecotone, exerted through its influence on the depth and properties of the organic horizons in these subarctic soils.
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| 7. |
- Sjögersten, Sofie, et al.
(author)
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Optical and radar Earth observation data for upscaling methane emissions linked to permafrost degradation in sub-Arctic peatlands in northern Sweden
- 2023
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In: Biogeosciences. - : Copernicus Publications. - 1726-4170 .- 1726-4189. ; 20:20, s. 4221-4239
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Journal article (peer-reviewed)abstract
- Permafrost thaw in Arctic regions is increasing methane (CH4) emissions into the atmosphere, but quantification of such emissions is difficult given the large and remote areas impacted. Hence, Earth observation (EO) data are critical for assessing permafrost thaw, associated ecosystem change and increased CH4 emissions. Often extrapolation from field measurements using EO is the approach employed. However, there are key challenges to consider. Landscape CH4 emissions result from a complex local-scale mixture of micro-topographies and vegetation types that support widely differing CH4 emissions, and it is difficult to detect the initial stages of permafrost degradation before vegetation transitions have occurred. This study considers the use of a combination of ultra-high-resolution unoccupied aerial vehicle (UAV) data and Sentinel-1 and Sentinel-2 data to extrapolate field measurements of CH4 emissions from a set of vegetation types which capture the local variation in vegetation on degrading palsa wetlands. We show that the ultra-high-resolution UAV data can map spatial variation in vegetation relevant to variation in CH4 emissions and extrapolate these across the wider landscape. We further show how this can be integrated with Sentinel-1 and Sentinel-2 data. By way of a soft classification and simple correction of misclassification bias of a hard classification, the output vegetation mapping and subsequent extrapolation of CH4 emissions closely matched the results generated using the UAV data. Interferometric synthetic-aperture radar (InSAR) assessment of subsidence together with the vegetation classification suggested that high subsidence rates of palsa wetland can be used to quantify areas at risk of increased CH4 emissions. The transition of a 50 ha area currently experiencing subsidence to fen vegetation is estimated to increase emissions from 116 kg CH4 per season to emissions as high as 6500 to 13 000 kg CH4 per season. The key outcome from this study is that a combination of high- and low-resolution EO data of different types provides the ability to estimate CH4 emissions from large geographies covered by a fine mixture of vegetation types which are vulnerable to transitioning to CH4 emitters in the near future. This points to an opportunity to measure and monitor CH4 emissions from the Arctic over space and time with confidence.
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| 9. |
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| 10. |
- Sjögersten, Sofie, 1975-
(author)
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Soil Organic Matter Dynamics and Methane Fluxes at the Forest – Tundra Ecotone in Fennoscandia
- 2003
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Doctoral thesis (other academic/artistic)abstract
- This thesis presents results from several studies that have focused on the carbon and nutrient dynamics in soils at the forest – tundra ecotone in Fennoscandia. The main objectives of the study were: (i) to investigate the links between the physical environment, above-ground vegetation communities, soil carbon storage, nutrient status and the chemical composition of the soil organic matter (SOM), and (ii) to quantify trace gas fluxes (methane and carbon dioxide) between mesic soils and the atmosphere. Four main field areas spanning an 8 degree latitudinal gradient were established at the ecotone in 1998 and studied for four years. In addition to the natural gradients we also established a warming treatment. Decomposition rates (i.e. carbon dioxide efflux and litter decomposition) were higher at our forest sites. This was linked principally to the more favourable physical environment at the forest sites, rather than to SOM quality, despite some indications of higher SOM quality at forest sites based upon conventional chemical analysis and 13C NMR techniques. Tundra soils stored large amounts of potentially labile carbon that could readily be accessed by microorganisms when transferred to a forest environment. The interrelation between increased soil temperature and reduced soil moisture content is likely to moderate the response of decomposition rates to increased temperatures. Generally, these mesic soils showed net methane uptake from the atmosphere, which was enhanced by the warming treatment. No differences between forest or tundra soils could be detected.The major conclusions presented here are that (1) soil carbon storage is likely to be reduced if mountain birch forest replaces tundra heath and (2), methane uptake in mesic soils in the Fennoscandian mountains represents a negative feedback to further environmental change in a warmer climate.
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| 11. |
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| 12. |
- Stark, Sari, et al.
(author)
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Decreased soil microbial nitrogen under vegetation 'shrubification' in the subarctic forest–tundra ecotone : the potential role of increasing nutrient competition between plants and soil microorganisms
- 2023
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In: Ecosystems. - : Springer Nature. - 1432-9840 .- 1435-0629. ; 26:7, s. 1504-1523
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Journal article (peer-reviewed)abstract
- The consequences of warming-induced ‘shrubification’ on Arctic soil carbon storage are receiving increased attention, as the majority of ecosystem carbon in these systems is stored in soils. Soil carbon cycles in these ecosystems are usually tightly coupled with nitrogen availability. Soil microbial responses to ‘shrubification’ may depend on the traits of the shrub species that increase in response to warming. Increase in deciduous shrubs such as Betula nana likely promotes a loss of soil carbon, whereas the opposite may be true if evergreen shrubs such as Empetrum hermaphroditum increase. We analyzed soil organic matter stocks and 13C NMR fractions, microbial CO2 respiration, biomass, extracellular enzyme activities (EEAs), and their association with shrub density in northern Sweden after 20 years of experimental warming using open top chambers (OTCs). Our study sites were located in a tundra heath that stores high soil carbon quantities and where the OTCs had increased deciduous shrubs, and in a mountain birch forest that stores lower soil carbon quantities and where the OTCs had increased evergreen shrubs. We predicted that organic matter stocks should be lower and respiration and EEAs higher inside the OTCs than untreated plots in the tundra, whereas no effect should be detected in the forest. Soil organic matter stocks and 13C NMR fractions remained unaffected at both sites. When expressed as per gram microbial biomass, respiration and EEAs for carbohydrate and chitin degradation were higher inside the OTCs, and contrasting our prediction, this effect was stronger in the forest. Unexpectedly, the OTCs also led to a substantially lower microbial biomass carbon and nitrogen irrespective of habitat. The decline in the microbial biomass counteracted increased activities resulting in no effect of the OTCs on respiration and a lower phenol oxidase activity per gram soil. Microbial biomass nitrogen correlated negatively with evergreen shrub density at both sites, indicating that ‘shrubification’ may have intensified nutrient competition between plants and soil microorganisms. Nutrient limitation could also underlie increased respiration per gram microbial biomass through limiting C assimilation into biomass. We hypothesize that increasing nutrient immobilization into long-lived evergreen shrubs could over time induce microbial nutrient limitation that contributes to a stability of accumulated soil organic matter stocks under climate warming.
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| 13. |
- Valman, Samuel, et al.
(author)
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InSAR-measured permafrost degradation of palsa peatlands in northern Sweden
- 2024
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In: The Cryosphere. - : Copernicus Publications. - 1994-0416 .- 1994-0424. ; 18:4, s. 1773-1790
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Journal article (peer-reviewed)abstract
- Climate warming is degrading palsa peatlands across the circumpolar permafrost region. Permafrost degradation may lead to ecosystem collapse and potentially strong climate feedbacks, as this ecosystem is an important carbon store and can transition to being a strong greenhouse gas emitter. Landscape-level measurement of permafrost degradation is needed to monitor this impact of warming. Surface subsidence is a useful metric of change in palsa degradation and can be monitored using interferometric synthetic-aperture radar (InSAR) satellite technology. We combined InSAR data, processed using the ASPIS algorithm to monitor ground motion between 2017 and 2021, with airborne optical and lidar data to investigate the rate of subsidence across palsa peatlands in northern Sweden. We show that 55% of Sweden's eight largest palsa peatlands are currently subsiding, which can be attributed to the underlying permafrost landforms and their degradation. The most rapid degradation has occurred in the largest palsa complexes in the most northern part of the region of study, also corresponding to the areas with the highest percentage of palsa cover within the overall mapped wetland area. Further, higher degradation rates have been found in areas where winter precipitation has increased substantially. The roughness index calculated from a lidar-derived digital elevation model (DEM), used as a proxy for degradation, increases alongside subsidence rates and may be used as a complementary proxy for palsa degradation. We show that combining datasets captured using remote sensing enables regional-scale estimation of ongoing permafrost degradation, an important step towards estimating the future impact of climate change on permafrost-dependent ecosystems.
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