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  • 1. Barrio, Isabel C.
    et al.
    Lindén, Elin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Te Beest, Mariska
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Olofsson, Johan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Rocha, Adrian
    Soininen, Eeva M.
    Alatalo, Juha M.
    Andersson, Tommi
    Asmus, Ashley
    Boike, Julia
    Bråthen, Kari Anne
    Bryant, John P.
    Buchwal, Agata
    Bueno, C. Guillermo
    Christie, Katherine S.
    Denisova, Yulia V.
    Egelkraut, Dagmar
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Ehrich, Dorothee
    Fishback, LeeAnn
    Forbes, Bruce C.
    Gartzia, Maite
    Grogan, Paul
    Hallinger, Martin
    Heijmans, Monique M. P. D.
    Hik, David S.
    Hofgaard, Annika
    Holmgren, Milena
    Høye, Toke T.
    Huebner, Diane C.
    Jónsdóttir, Ingibjorg Svala
    Kaarlejärvi, Elina
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Department of Biology, Vrije Universiteit Brussel (VUB), Brussels, Belgium.
    Kumpula, Timo
    Lange, Cynthia Y. M. J. G.
    Lange, Jelena
    Lévesque, Esther
    Limpens, Juul
    Macias-Fauria, Marc
    Myers-Smith, Isla
    van Nieukerken, Erik J.
    Normand, Signe
    Post, Eric S.
    Schmidt, Niels Martin
    Sitters, Judith
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Department of Biology, Vrije Universiteit Brussel (VUB), Brussels, Belgium.
    Skoracka, Anna
    Sokolov, Alexander
    Sokolova, Natalya
    Speed, James D. M.
    Street, Lorna E.
    Sundqvist, Maja K.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. The Center for Macroecology, Evolution and Climate, The Natural History Museum of Denmark, University of Copenhagen, Copenhagen Ø, Denmark.
    Suominen, Otso
    Tananaev, Nikita
    Tremblay, Jean-Pierre
    Urbanowicz, Christine
    Uvarov, Sergey A.
    Watts, David
    Wilmking, Martin
    Wookey, Philip A.
    Zimmermann, Heike H.
    Zverev, Vitali
    Kozlov, Mikhail V.
    Background invertebrate herbivory on dwarf birch (Betula glandulosa-nana complex) increases with temperature and precipitation across the tundra biome2017In: Polar Biology, ISSN 0722-4060, E-ISSN 1432-2056, Vol. 40, no 11, p. 2265-2278Article in journal (Refereed)
    Abstract [en]

    Chronic, low intensity herbivory by invertebrates, termed background herbivory, has been understudied in tundra, yet its impacts are likely to increase in a warmer Arctic. The magnitude of these changes is however hard to predict as we know little about the drivers of current levels of invertebrate herbivory in tundra. We assessed the intensity of invertebrate herbivory on a common tundra plant, the dwarf birch (Betula glandulosa-nana complex), and investigated its relationship to latitude and climate across the tundra biome. Leaf damage by defoliating, mining and gall-forming invertebrates was measured in samples collected from 192 sites at 56 locations. Our results indicate that invertebrate herbivory is nearly ubiquitous across the tundra biome but occurs at low intensity. On average, invertebrates damaged 11.2% of the leaves and removed 1.4% of total leaf area. The damage was mainly caused by external leaf feeders, and most damaged leaves were only slightly affected (12% leaf area lost). Foliar damage was consistently positively correlated with mid-summer (July) temperature and, to a lesser extent, precipitation in the year of data collection, irrespective of latitude. Our models predict that, on average, foliar losses to invertebrates on dwarf birch are likely to increase by 6-7% over the current levels with a 1 degrees C increase in summer temperatures. Our results show that invertebrate herbivory on dwarf birch is small in magnitude but given its prevalence and dependence on climatic variables, background invertebrate herbivory should be included in predictions of climate change impacts on tundra ecosystems.

  • 2.
    Becher, Marina
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Olofsson, Johan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Berglund, Louise
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Klaminder, Jonatan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Decreased cryogenic disturbance: one of the potential mechanisms behind the vegetation change in the Arctic2018In: Polar Biology, ISSN 0722-4060, E-ISSN 1432-2056, Vol. 41, no 1, p. 101-110Article in journal (Other academic)
    Abstract [en]

    During the last few decades, the Arctic has experienced large-scale vegetation changes. Understanding the mechanisms behind this vegetation change is crucial for our ability to predict future changes. This study tested the hypothesis that decreased cryogenic disturbances cause vegetation change in patterned ground study fields (non-sorted circles) in Abisko, Sweden during the last few decades. The hypothesis was tested by surveying the composition of plant communities across a gradient in cryogenic disturbance and by reinvestigating plant communities previously surveyed in the 1980s to scrutinise how these communities changed in response to reduced cryogenic disturbance. Whereas the historical changes in species occurrence associated with decreased cryogenic disturbances were relatively consistent with the changes along the contemporary gradient of cryogenic disturbances, the species abundance revealed important transient changes highly dependent on the initial plant community composition. Our results suggest that altered cryogenic disturbances cause temporal changes in vegetation dynamics, but the net effects on vegetation communities depend on the composition of initial plant species.

  • 3. Beyens , L.
    et al.
    Ledeganck , P.
    Graae , B. J.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Nijs , I.
    Are soil biota buffered against climatic extremes? An experimental test on testate amoebae in arctic tundra (Qeqertarsuaq, West Greenland)2009In: Polar Biology, ISSN 0722-4060, E-ISSN 1432-2056, Vol. 32, p. 453-462Article in journal (Refereed)
    Abstract [en]

    Climate warming is likely to have pronounced impacts on soil biota in arctic ecosystems. In a warmer climate, heatwaves are more frequent and intense, but it is unclear to what extent soil communities are buffered against this. We studied the effects of an artificially induced heatwave on the structure of testate amoebae communities in dry heath tundra in Qeqertarsuaq (Disko Island, West Greenland) during the summer of 2003. While the heatwave was severe enough to induce significant leaf mortality in the aboveground vegetation, overall testate amoebae abundance did not react to the difference in temperature. However, in the heated plots transient shifts in species populations occurred during the exposure, followed by increases in species richness weeks after the heatwave had ended. The most important taxa appearing after the heating period belonged to bacterivorous genera, in agreement with a transient peak in bacterial colony forming units, caused by the heatwave. Lobose testate amoebae resisted the heating and its associated desiccation better than their filose counterparts.

  • 4.
    Graae, Bente Jessen
    et al.
    University of Copenhagen Arctic Station 3953 Qeqertarsuaq Greenland.
    Ejrnaes, R
    University of Copenhagen Arctic Station 3953 Qeqertarsuaq Greenland.
    Marchand, FL
    University of Antwerp, Campus Drie Eiken Research Group Plant and Vegetation Ecology, Department of Biology Universiteitsplein 1 2610 Wilrijk Belgium.
    Milbau, Ann
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Shevtsova, A
    University of Antwerp, Campus Drie Eiken Research Group Plant and Vegetation Ecology, Department of Biology Universiteitsplein 1 2610 Wilrijk Belgium.
    Beyens, L
    University of Antwerp, Campus Drie Eiken Research Group Polar Ecology, Limnology and Geomorphology, Department of Biology Universiteitsplein 1 2610 Wilrijk Belgium.
    Nijs, I
    University of Antwerp, Campus Drie Eiken Research Group Plant and Vegetation Ecology, Department of Biology Universiteitsplein 1 2610 Wilrijk Belgium.
    The effect of an early-season short-term heat pulse on plant recruitment in the Arctic2009In: Polar Biology, ISSN 0722-4060, E-ISSN 1432-2056, Vol. 32, no 8, p. 1117-1126Article in journal (Refereed)
    Abstract [en]

    Climate change will cause large-scale plant migration. Seedling recruitment constitutes a bottleneck in the migration process but is itself climate-dependent. We tested the effect of warming on early establishment of three Arctic pioneer species, while holding other environmental variables constant. Seeds and bulbils were sown in artificial gaps in dry Arctic tundra and subjected to a 13-day heating of the soil surface by 2-8°C, simulating temperature increases ranging from the general summer warming to heat waves projected to occur more frequently with global warming. All species showed decreased establishment with increasing soil surface temperature. The short-term heat pulse decreased establishment of Polygonum viviparum and Saxifraga cernua, whereas establishment of Cerastium alpinum decreased with temperature due to more permanent natural variation in micro-climate. The treatment effects increased by the quadrat of the temperature increase. Warming and in particular heat waves may result in declining establishment of Arctic plants in dry tundra regions. Electronic supplementary material The online version of this article (doi:10.1007/s00300-009-0608-3) contains supplementary material, which is available to authorized users.

  • 5. Kuparinen, J.
    et al.
    Autio, R.
    Kaartokallio, H.
    Sea ice bacterial growth rate, growth efficiency and preference for inorganic nitrogen sources in the Baltic Sea2011In: Polar Biology, ISSN 0722-4060, E-ISSN 1432-2056, Vol. 34, no 9, p. 1361-1373Article in journal (Refereed)
    Abstract [en]

    Seasonal Baltic Sea ice is structurally similar to polar sea ice and provides habitats for diverse ice organism assemblages that are integral to the biogeochemistry and ecology of the sea during winter. Temperature and inorganic nitrogen sources have been suggested to control bacterial growth, with increasing dependence on ammonium at low temperatures. To study the bacterial growth and preference for the nitrogen source, we conducted experiments at 0 and 4A degrees C, using ammonium and nitrate as nitrogen sources at two coastal fast-ice stations in the Gulf of Finland and in the Gulf of Bothnia during three successive winters. The two study sites differ markedly in relation to the allochthonous dissolved organic matter supply from the catchment area. High levels of bacterial growth were recorded at both study sites, with community generation times of 15-37 h. The measured bacterial growth efficiencies of 20-58% suggest that the Baltic sea ice brines provide a rich medium for bacterial growth and efficient functioning of bacteria-based food webs. Our experiments with sea ice samples showed a preference for ammonium at both temperatures and high potential growth in both types of nitrogen supplies. No major differences in phosphorus depletion rates were found at the two temperatures, but rates were always highest when ammonium was added to the experiments. These experiments point out that ice maturity, presumably through changes in bacterial community structure, impacts nitrogen processes and that these processes are pronounced prior to melting of the ice.

  • 6.
    Makoto, Kobayashi
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Klaminder, Jonatan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    The influence of non-sorted circles on species diversity of vascular plants, bryophytes and lichens in Sub-Arctic Tundra2012In: Polar Biology, ISSN 0722-4060, E-ISSN 1432-2056, Vol. 35, no 11, p. 1659-1667Article in journal (Refereed)
    Abstract [en]

    Non-sorted circles (NSCs), also known as frost boils, are common soil frost features that create a small-scale mosaic of vegetation zones in periglacial landscapes. The causes of variation in plant diversity within NSCs are poorly understood. This lack of understanding hampers our ability to predict how arctic plant communities respond to changing soil frost conditions. We hypothesised that plant communities of different ages develop at a micro-site scale within NSCs as soil frost periodically exposes uncolonised soil or fatally offsets plant succession. To test this hypothesis, we investigated the species diversity of plant communities (vascular plants, bryophytes and lichens) from the sparsely vegetated centre of the circles to the densely vegetated outer domain in conjunction with estimates of the age of the plant communities (inferred using lichenometry). Our results suggest that the variation in species diversity and density can largely be explained by the occurrence of progressively older plant communities from the centre towards the vegetated rim. Here, the high species diversity was observed to occur in communities having the ages approximately around 150 years. Our findings suggest that soil frost disturbances are important for maintaining successional gradients several centuries long within the arctic landscape at a small spatial scale (< 3 m). The termination of soil frost activity as a result of a warmer future winter climate is therefore most likely to result in a loss of micro-sites having young vegetation communities with high plant diversities and a subsequent establishment of mature shrub-dominated plant communities.

  • 7. Skarin, Anna
    et al.
    Danell, Öje
    Bergström, Roger
    Moen, Jon
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Reindeer movement patterns in alpine summer ranges2010In: Polar Biology, ISSN 0722-4060, E-ISSN 1432-2056, Vol. 33, no 9, p. 1263-1275Article in journal (Refereed)
    Abstract [en]

    To evaluate the movement rates of semidomesticated reindeer (Rangifer tarandus tarandus) during the bare-ground season, we used successive GPS positions from 48 female reindeer. Data were collected  during the summers of 2002 and 2003 in two Sámi reindeer herding districts in the Swedish mountains, Handölsdalen, and Sirges. The movement rates were analysed at different time periods: over the whole season, and over the sub-seasons spring, and early summer, mid summer and early autumn. Variation in movements were analysed in relation to vegetation type, altitude, terrain ruggedness, temperature, wind speed, and proximity to hiking trails. We hypothesised that the foraging quality and different weather conditions is an important factor in determining movement rates. We found that reindeer movement rates were similar between study areas and were dependent on vegetation type and on weather conditions. Studying the circadian movements, in mid summer period when daytime oestrid activity are expected to be high, the reindeer stayed at higher altitudes where food quality was low, but moved to low altitudes at night where the food quality was higher. Therefore, we suggest that oestrid activity forces the reindeer to stay in low-quality vegetation types. Reindeer movements were linked to disturbance in areas of intermediate human activity. We found that in Handölsdalen, where hikers are abundant, the movement rates of reindeer decreased closer to the trails whereas in Sirges, where hikers are less abundant, the movement rates of reindeer increased closer to the trails.

  • 8.
    Säwström, Christin
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Karlsson, Jan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Laybourn-Parry, J
    Granéli, W
    Zooplankton feeding on algae and bacteria under ice in Lake Druzhby, East Antarctica2009In: Polar Biology, ISSN 0722-4060, E-ISSN 1432-2056, Vol. 32, p. 1195-1202Article in journal (Refereed)
    Abstract [en]

    The feeding of the cladoceran Daphniopsis studeri on algae and bacteria was investigated under ice in an ultra-oligotrophic Antarctic lake from late autumn (May) to early spring (October) in 2004. D. studeri fed on both algae and bacteria with estimated filtering rates of 0.048 and 0.061 l ind−1 day−1), respectively. Algae seemed to be the major food resource for the D. studeri population, however at times of low algal densities the bacterioplankton represented an important alternative food resource. The D. studeri grazing impact on the algal and bacterial standing stock was in general low (0.6–4.6% removed per day), but during the winter period this organism can remove up to 34% of the bacterial production (BP). At times D. studeri grazing can temporarily have a significant impact on the BP rates, though their impact was relatively low when compared to viral-induced bacterial mortality in the lake.

  • 9.
    Torp, Mikaela
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Olofsson, Johan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Witzell, Johanna
    Swedish University of Agricultural Sciences, Southern Swedish Forest Research Centre, P.O. Box 49, 230 53 Alnarp, Sweden.
    Baxter, Robert
    School of Biological and Biomedical Sciences, Institute of Ecosystem Science, University of Durham, Durham, DH1 3LE, UK.
    Snow-induced changes in dwarf birch chemistry increase moth larval growth rate and level of herbivory2010In: Polar Biology, ISSN 0722-4060, E-ISSN 1432-2056, Vol. 33, no 5, p. 693-702Article in journal (Refereed)
    Abstract [en]

    Changes in snow cover might influence arctic ecosystems to the same extent as increased temperatures. Although the duration of snow cover is generally expected to decrease in the future as a result of global warming, the amounts of snow might increase in arctic areas where much of the elevated precipitation will fall as snow. We examined the effects of an increased snow cover, as a result of a snow fence treatment, on soil nitrogen mineralization, plant phenology, plant chemistry (nitrogen and potential defense compounds), the level of invertebrate herbivory, and performance of invertebrate herbivores in an arctic ecosystem, using dwarf birch (Betula nana) and the autumnal moth (Epirrita autumnata) as study organisms. An enhanced and prolonged snow cover increased the level of herbivory on dwarf birch leaves. Larvae feeding on plants that had experienced enhanced snow cover grew faster and pupated earlier than larvae fed with plant material from control plots, indicating that plants from enhanced snow-lie plots produce higher-quality food to herbivores. The increased larval growth rate was strongly correlated with higher leaf nitrogen concentration in plants subjected to snow manipulation, and also to certain phenolic acids. Snow manipulation did not change net nitrogen mineralization rates in the soil or total carbon concentration in leaves, but it altered the within-season fluctuating pattern of leaf phenolic compounds. This study demonstrates a positive relationship between increased snow cover and level of herbivory on deciduous shrubs, thus proposing a negative feedback on the climate-induced dwarf shrub expansion in arctic areas.

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