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  • 1.
    Aunapuu, Maano
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Dahlgren, Jonas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Oksanen, Tarja
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Grellmann, Doris
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Oksanen, Lauri
    Olofsson, Johan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Rammul, Ullar
    Schneider, Michael
    Johansen, Bernt
    Hygen, Hans Olav
    Spatial patterns and dynamic responses of arctic food webs corroborate the exploitation ecosystems hypothesis (EEH)2008Ingår i: American Naturalist, ISSN 0003-0147, E-ISSN 1537-5323, Vol. 171, nr 2, s. 249-262Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    According to the exploitation ecosystems hypothesis (EEH), productive terrestrial ecosystems are characterized by community‐level trophic cascades, whereas unproductive ecosystems harbor food‐limited grazers, which regulate community‐level plant biomass. We tested this hypothesis along arctic‐alpine productivity gradients at the Joatka field base, Finnmark, Norway. In unproductive habitats, mammalian predators were absent and plant biomass was constant, whereas herbivore biomass varied, reflecting the productivity of the habitat. In productive habitats, predatory mammals were persistently present and plant biomass varied in space, but herbivore biomass did not. Plant biomass of productive tundra scrublands declined by 40% when vegetation blocks were transferred to predation‐free islands. Corresponding transfer to herbivore‐free islands triggered an increase in plant biomass. Fertilization of an unproductive tundra heath resulted in a fourfold increase in rodent density and a corresponding increase in winter grazing activity, whereas the total aboveground plant biomass remained unchanged. These results corroborate the predictions of the EEH, implying that the endotherm community and the vegetation of the North European tundra behaves dynamically as if each trophic level consisted of a single population, in spite of local co‐occurrence of >20 plant species representing different major taxonomic groups, growth forms, and defensive strategies.

  • 2. Barrio, I. C.
    et al.
    Bueno, C. G.
    Gartzia, M.
    Soininen, E. M.
    Christie, K. S.
    Speed, J. D. M.
    Ravolainen, V. T.
    Forbes, B. C.
    Gauthier, G.
    Horstkotte, Tim
    Hoset, K. S.
    Høye, T. T.
    Jónsdóttir, I. S.
    Lévesque, E.
    Mörsdorf, M. A.
    Olofsson, Johan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Wookey, P. A.
    Hik, D. S.
    Biotic interactions mediate patterns of herbivore diversity in the Arctic2016Ingår i: Global Ecology and Biogeography, ISSN 1466-822X, E-ISSN 1466-8238, Vol. 25, nr 9, s. 1108-1118Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Aim: Understanding the forces shaping biodiversity patterns, particularly for groups of organisms with key functional roles, will help predict the responses of ecosystems to environmental changes. Our aim was to evaluate the relative role of different drivers in shaping the diversity patterns of vertebrate herbivores, a group of organisms exerting a strong trophic influence in terrestrial Arctic ecosystems. This biome, traditionally perceived as homogeneous and low in biodiversity, includes wide variation in biotic and physical conditions and is currently undergoing major environmental change. Location: The Arctic (including the High Arctic, Low Arctic and Subarctic) MethodsWe compiled available data on vertebrate (birds and mammals) herbivore distribution at a pan-Arctic scale, and used eight variables that represent the most relevant hypotheses for explaining patterns of species richness. We used range maps rasterized on a 100kmx100km equal-area grid to analyse richness patterns of all vertebrate herbivore species combined, and birds and mammalian herbivores separately. Results: Overall, patterns of herbivore species richness in the Arctic were positively related to plant productivity (measured using the normalized difference vegetation index) and to the species richness of predators. Greater species richness of herbivores was also linked to areas with a higher mean annual temperature. Species richness of avian and mammalian herbivores were related to the distance from the coast, with the highest avian richness in coastal areas and mammalian richness peaking further inland. Main conclusions: Herbivore richness in the Arctic is most strongly linked to primary productivity and the species richness of predators. Our results suggest that biotic interactions, with either higher or lower trophic levels or both, can drive patterns of species richness at a biome-wide scale. Rapid ongoing environmental changes in the Arctic are likely to affect herbivore diversity through impacts on both primary productivity and changes in predator communities via range expansion of predators from lower latitudes.

  • 3. Barrio, Isabel C.
    et al.
    Lindén, Elin
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    te Beest, Mariska
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Olofsson, Johan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Rocha, Adrian
    Soininen, Eeva M.
    Alatalo, Juha M.
    Andersson, Tommi
    Asmus, Ashley
    Boike, Julia
    Brathen, Kari Anne
    Bryant, John P.
    Buchwal, Agata
    Bueno, C. Guillermo
    Christie, Katherine S.
    Denisova, Yulia V.
    Egelkraut, Dagmar
    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.
    Jonsdottir, Ingibjorg Svala
    Kaarlejärvi, Elina
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Department of Biology, Vrije Universiteit Brussel (VUB), Pleinlaan 2, 1050 Brussels, Belgium.
    Kumpula, Timo
    Lange, Cynthia Y. M. J. G.
    Lange, Jelena
    Levesque, Esther
    Limpens, Juul
    Macias-Fauria, Marc
    Myers-Smith, Isla
    van Nieukerken, Erik J.
    Normand, Signe
    Post, Eric S.
    Schmidt, Niels Martin
    Sitters, Judith
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Department of Biology, Vrije Universiteit Brussel (VUB), Pleinlaan 2, 1050 Brussels, Belgium.
    Skoracka, Anna
    Sokolov, Alexander
    Sokolova, Natalya
    Speed, James D. M.
    Street, Lorna E.
    Sundqvist, Maja K.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. The Center for Macroecology, Evolution and Climate, The Natural History Museum of Denmark, University of Copenhagen, Universitetsparken 5, 2100 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.
    Publisher Correction to: Background invertebrate herbivory on dwarf birch (Betula glandulosa-nana complex) increases with temperature and precipitation across the tundra biome (vol 40, pg 2265, 2017)2018Ingår i: Polar Biology, ISSN 0722-4060, E-ISSN 1432-2056, Vol. 41, nr 8, s. 1653-1654Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The above mentioned article was originally scheduled for publication in the special issue on Ecology of Tundra Arthropods with guest editors Toke T. Hoye . Lauren E. Culler. Erroneously, the article was published in Polar Biology, Volume 40, Issue 11, November, 2017. The publisher sincerely apologizes to the guest editors and the authors for the inconvenience caused.

  • 4. Barrio, Isabel C.
    et al.
    Lindén, Elin
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Te Beest, Mariska
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Olofsson, Johan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    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 universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    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 universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. 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 universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. 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 universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. 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 biome2017Ingår i: Polar Biology, ISSN 0722-4060, E-ISSN 1432-2056, Vol. 40, nr 11, s. 2265-2278Artikel i tidskrift (Refereegranskat)
    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.

  • 5.
    Barthelemy, Helene
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Stark, Sari
    Rovaniemi, Finland.
    Olofsson, Johan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Strong Responses of Subarctic Plant Communities to Long-Term Reindeer Feces Manipulation2015Ingår i: Ecosystems (New York. Print), ISSN 1432-9840, E-ISSN 1435-0629, Vol. 18, nr 5, s. 740-751Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Deposition of feces is a key mechanism by which herbivores influence soil nutrient cycling and plant production, but the knowledge about its importance for plant production and community structure is still rudimental since experimental evidence is scarce. We thus performed a 7-year long reindeer feces manipulation experiment in two tundra vegetation types with contrasting nutrient availability and analyzed effects on plant community composition and soil nutrient availability. Despite feces being fairly nutrient poor, feces manipulation had strong effect on both the nutrient-poor heath and the nutrient-rich meadow. The strongest effect was detected when feces were added at high density, with a substantial increase in total vascular plant productivity and graminoids in the two communities. Doubling natural deposition of reindeer feces enhanced primary production and the growth of deciduous shrubs in the heath. By contrast, removal of feces decreased only the production of graminoids and deciduous shrubs in the heath. Although the response to feces addition was faster in the nutrient-rich meadow, after 7 years it was more pronounced in the nutrient-poor heath. The effect of feces manipulation on soil nutrient availability was low and temporarily variable. Our study provides experimental evidence for a central role of herbivore feces in regulating primary production when herbivores are abundant enough. Deposition of feces alone does, however, not cause dramatic vegetation shifts; to drive unproductive heath to a productive grass dominated state, herbivore trampling, and grazing are probably also needed.

  • 6.
    Barthelemy, Hélène
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Dorrepaal, Ellen
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Olofsson, Johan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Defoliation of a grass is mediated by the positive effect of dung deposition, moss removal and enhanced soil nutrient contents: results from a reindeer grazing simulation experiment2019Ingår i: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 128, nr 10, s. 1515-1524Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Herbivory is one of the key drivers shaping plant community dynamics. Herbivores can strongly influence plant productivity directly through defoliation and the return of nutrients in the form of dung and urine, but also indirectly by reducing the abundance of neighbouring plants and inducing changes in soil processes. However, the relative importance of these processes is poorly understood. We, therefore, established a common garden experiment to study plant responses to defoliation, dung addition, moss cover, and the soil legacy of reindeer grazing. We used an arctic tundra grazed by reindeer as our study system, and Festuca ovina, a common grazing-tolerant grass species as the model species. The soil legacy of reindeer grazing had the strongest effect on plants, and resulted in higher growth in soils originating from previously heavily-grazed sites. Defoliation also had a strong effect and reduced shoot and root growth and nutrient uptake. Plants did not fully compensate for the tissue lost due to defoliation, even when nutrient availability was high. In contrast, defoliation enhanced plant nitrogen concentrations. Dung addition increased plant production, nitrogen concentrations and nutrient uptake, although the effect was fairly small. Mosses also had a positive effect on aboveground plant production as long as the plants were not defoliated. The presence of a thick moss layer reduced plant growth following defoliation. This study demonstrates that grasses, even though they suffer from defoliation, can tolerate high densities of herbivores when all aspects of herbivores on ecosystems are taken into account. Our results further show that the positive effect of herbivores on plant growth via changes in soil properties is essential for plants to cope with a high grazing pressure. The strong effect of the soil legacy of reindeer grazing reveals that herbivores can have long-lasting effects on plant productivity and ecosystem functioning after grazing has ceased.

  • 7.
    Barthelemy, Hélène
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Dorrepaal, Ellen
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Olofsson, Johan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Defoliation, soil grazing legacy, dung and moss cover influence growth and nutrient uptake of the common grass species, Festuca ovinaManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    Herbivores can strongly influence plant growth directly through defoliation and the return of nutrients in the form of dung and urine but also indirectly by reducing the abundance of neighbouring plants and inducing changes in soil processes. The relative importance of these driving mechanisms of plant response to herbivory are still poorly understood. In a common garden experiment, we studied the aboveground and belowground responses of Festuca ovina, a grazing tolerant grass common in arctic secondary grassland, to defoliation, reindeer dung addition, changes in soil microclimate induced by the presence or the absence of a moss cover, and soil grazing legacy. Defoliation strongly reduced shoot and root growth and plant nutrient uptake. Plants did thus not compensate for the tissue lost due to defoliation, even at a higher nutrient availability. By contrast, defoliation enhanced plant N concentration and decreased plant C to N ratio. Soil from heavily grazed sites and dung addition increased plant production, plant N concentrations and nutrient uptake, although the effects of dung addition were only small. Mosses had a strong negative effect of root biomass and reduced plant compensatory growth after defoliation. Interestingly mosses also had facilitative effects on aboveground plant growth in absence of defoliation and on plant nutrient uptake and N concentrations. Although plants suffered severely from defoliation, they were also strongly favoured by the increased nutrient availability associated with herbivory. After two years, plants produced as much biomass when all positive and negative effects of herbivores were considered (defoliation, soil communities and nutrient availability under heavily grazing, dung addition and no moss cover) as in the ungrazed conditions (no defoliation, soil communities and nutrient availability under lightly grazing, no dung addition, a thick moss cover). This study indicates that graminoids can tolerate high densities of herbivores, although it suffer from defoliation directly, and suggests that changes in plant quality following defoliation and grazing-induced changes in soil processes are two key mechanisms through which herbivores can control plant productivity in arctic secondary grasslands. Plant tolerance to herbivory will depends on how herbivores utilise a pasture area and on the balance between the positive and the negative effects of grazing on plant growth.

  • 8.
    Barthelemy, Hélène
    et al.
    Department of Biological Science, University of Bergen, Bergen, Norway.
    Nobel, Liv Alexa
    Department of Biology, Terrestrial Ecology, University of Copenhagen, Copenhagen, Denmark; Center for Permafrost (CENPERM), University of Copenhagen, Copenhagen, Denmark.
    Stark, Sari
    Arctic Centre, University of Lapland, Rovaniemi, Finland.
    Väisänen, Maria
    Arctic Centre, University of Lapland, Rovaniemi, Finland; Ecology and Genetics Research Unit, University of Oulu, Oulu, Finland.
    Olofsson, Johan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Michelsen, Anders
    Department of Biology, Terrestrial Ecology, University of Copenhagen, Copenhagen, Denmark; Center for Permafrost (CENPERM), University of Copenhagen, Copenhagen, Denmark.
    Short- and long-term plant and microbial uptake of 15N-labelled urea in a mesic tundra heath, West Greenland2024Ingår i: Polar Biology, ISSN 0722-4060, E-ISSN 1432-2056, Vol. 47, nr 1, s. 1-15Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Terrestrial animals are key elements in the cycling of elements in the Arctic where nutrient availability is low. Waste production by herbivores, in particular urine deposition, has a crucial role for nitrogen (N) recycling, still, it remains largely unexplored. Also, experimental evidence is biased toward short-term studies and Arctic regions under high herbivore pressure. In this study, we aimed to examine the fate of N derived from urine in a nutrient poor tundra heath in West Greenland, with historical low level of herbivory. We performed a pulse labelling with 15N-urea over the plant canopy and explored ecosystem N partition and retention in the short-term (2 weeks and 1 year) and longer-term (5 years). We found that all vascular plants, irrespective of their traits, could rapidly take up N-urea, but mosses and lichens were even more efficient. Total 15N enrichment was severely reduced for all plants 5 years after tracer addition, with the exception of cryptogams, indicating that non-vascular plants constituted a long-term sink of 15N-urea. The 15N recovery was also high in the litter suggesting high N immobilization in this layer, potentially delaying the nutrients from urine entering the soil compartment. Long-term 15N recovery in soil microbial biomass was minimal, but as much as 30% of added 15N remained in the non-microbial fraction after 5 years. Our results demonstrate that tundra plants that have evolved under low herbivory pressure are well adapted to quickly take advantage of labile urea, with urine having only a transient effect on soil nutrient availability.

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  • 9.
    Barthelemy, Hélène
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Stark, Sari
    Arctic Center, University of Lapland, Rovaniemi, Finland.
    Kytöviita, Minna-Maarit
    Department of Biological and Environmental Science, University of Jyväskylä, Finland.
    Olofsson, Johan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Grazing decreases N partitioning among coexisting plant species2017Ingår i: Functional Ecology, ISSN 0269-8463, E-ISSN 1365-2435, Vol. 31, nr 11, s. 2051-2060Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    1. Herbivores play a key role in shaping ecosystem structure and functions by influencing plant and microbial community composition and nutrient cycling.

    2. This study investigated the long-term effects of herbivores on plant resource acquisition. We explored differences in the natural delta N-15 signatures in plant, microbial and soil N pools, and examined mycorrhizal colonization in two tundra sites that have been either lightly or heavily grazed by reindeer for more than 50 years. The study examined changes in nutrient acquisition in five common tundra plants with contrasting traits and mycorrhiza status; the mycorrhizal dwarf shrubs, Betula nana, Vaccinium myrtillus and Empetrum hermaphroditum; a mycorrhizal grass, Deschampsia flexuosa, and a non-mycorrhizal sedge, Carex bigelowii.

    3. There were large variations in delta N-15 among coexisting plant species in the lightly grazed sites. This variation was dramatically reduced in the heavily grazed sites. At an individual species level, delta N-15 was higher in E. hermaphroditum and lower in C. bigelowii in the heavily grazed sites. Mycorrhizal colonization in B. nana and E. hermaphroditum roots were also lower in the heavily grazed sites. The delta N-15 signatures of the total soil N pool and of the microbial N pools were higher in the heavily grazed sites.

    4. Since the strong delta N-15 differentiation among plant species has been interpreted as a result of plants with different mycorrhizal types using different sources of soil nitrogen, we suggest that the lower variation in delta N-15 in heavily grazed sites indicates a lower niche differentiation in nitrogen uptake among plants. Reduced mycorrhizamediated nitrogen uptake by some of the species, a shift towards a more mineral nutrition due to higher nutrient turnover, and uptake of labile nitrogen from dung and urine in the heavily grazed sites could all contribute to the changes in plant delta N-15.

    5. We conclude that herbivores have the potential to influence plant nutrient uptake and provide the first data suggesting that herbivores decrease nutrient partitioning on the basis of chemical N forms among plant species. Reduced niche complementarity among species is potentially important for estimates of the effects of -herbivory on plant nutrient availability and species coexistence.

  • 10.
    Barthelemy, Hélène
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Stark, Sari
    Arctic Center, University of Lapland Rovaniemi, Finland.
    Michelsen, Anders
    Department of Biology, Terrestrial Ecology, University of Copenhagen 2. 4Center for Permafrost (CENPERM), University of Copenhagen.
    Olofsson, Johan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Effect of herbivory on the fate of added 15N-urea in a grazed Arctic tundraManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    Mammalian herbivores can strongly influence nitrogen cycling and herbivore urine could be an important component of the nutrient cycle in grazed ecosystems. Despite its potential role for ecosystem productivity and soil processes, the distribution of N from urine in the different ecosystem compartments is poorly understood. This study investigates the fate of 15N enriched urea applied above the plant canopy in two tundra sites either heavily or lightly grazed by reindeer for the last 50 years. We explored the fate of the 15N in the different ecosystem N pools at 2 weeks and 1 years following tracer addition. We hypothesized that cryptogams would take up most N under light grazing, but graminoids most N under heavy grazing. The 15N-urea was rapidly incorporated in cryptogams and aboveground parts of vascular plants, while the soil microbial pool and plant roots sequestered only a marginal proportion of the labelled N applied. Hence, urine addition supports a higher primary production in tundra since most of the nutrients released from urine could be assimilated by the aboveground components with little N reaching the belowground compartments. Mosses and lichens still constituted the largest sink of the 15N-urea 1 year after tracer addition at both levels of grazing intensity demonstrating their large ability to capture and retain N  from urine. Deciduous and evergreen shrubs were just as efficient as graminoids in taking up the 15N-urea. The total recovery of the labelled urea was lower in the heavily grazed sites, suggesting that reindeer reduce the N retention in the system. Rapid incorporation of the applied 15N-urea indicates that arctic plants can take advantage of a pulse of incoming N in the form of urea, which supports a higher primary production. However, whether urine also maintains a high production of forage plants depend on plant community composition, since most urea was recovered in non-forage plants for reindeer.

  • 11.
    Barthelemy, Hélène
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Stark, Sari
    Michelsen, Anders
    Olofsson, Johan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Urine is an important nitrogen source for plants irrespective of vegetation composition in an Arctic tundra: Insights from a N-15-enriched urea tracer experiment2018Ingår i: Journal of Ecology, ISSN 0022-0477, E-ISSN 1365-2745, Vol. 106, nr 1, s. 367-378Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    1. Mammalian herbivores can strongly influence nitrogen (N) cycling and herbivore urine could be a central component of the N cycle in grazed ecosystems. Despite its potential role for ecosystem productivity and functioning, the fate of N derived from urine has rarely been investigated in grazed ecosystems. 2. This study explored the fate of N-15-enriched urea in tundra sites that have been either lightly or intensively grazed by reindeer for more than 50years. We followed the fate of the N-15 applied to the plant canopy, at 2weeks and 1year after tracer addition, in the different ecosystem N pools. 3. N-15-urea was rapidly incorporated in cryptogams and in above-ground parts of vascular plants, while the soil microbial pool and plant roots sequestered only a marginal proportion. Furthermore, the litter layer constituted a large sink for the N-15-urea, at least in the short term, indicating a high biological activity in the litter layer and high immobilization in the first phases of organic matter decomposition. 4. Mosses and lichens still constituted the largest sink for the N-15-urea 1year after tracer addition at both levels of grazing intensity demonstrating their large ability to capture and retain N from urine. Despite large fundamental differences in their traits, deciduous and evergreen shrubs were just as efficient as graminoids in taking up the N-15-urea. The total recovery of N-15-urea was lower in the intensively grazed sites, suggesting that reindeer reduce ecosystem N retention. 5. Synthesis. The rapid incorporation of the applied N-15-urea indicates that arctic plants can take advantage of a pulse of incoming N from urine. In addition, N-15 values of all taxa in the heavily grazed sites converged towards the N-15 values for urine, bringing further evidence that urine is an important N source for plants in grazed tundra ecosystems.

  • 12.
    Becher, Marina
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Olofsson, Johan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Berglund, Louise
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Klaminder, Jonatan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Decreased cryogenic disturbance: one of the potential mechanisms behind the vegetation change in the Arctic2018Ingår i: Polar Biology, ISSN 0722-4060, E-ISSN 1432-2056, Vol. 41, nr 1, s. 101-110Artikel i tidskrift (Övrigt vetenskapligt)
    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.

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  • 13.
    Becher, Marina
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Olofsson, Johan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Klaminder, Jonatan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Cryogenic disturbance and its impact on carbon fluxes in a subarctic heathland2015Ingår i: Environmental Research Letters, E-ISSN 1748-9326, Vol. 10, nr 11, artikel-id 114006Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Differential frost heave, along with the associated cryogenic disturbance that accompanies it, is an almost universal feature of arctic landscapes that potentially influences the fate of the soil carbon (C) stored in arctic soils. In this study, we quantify how gross ecosystem photosynthesis (GEP), soil respiration (Re) and the resulting net ecosystem exchange (NEE) vary in a patterned ground system (non-sorted circles) at plot-scale and whole-patterned ground scales in response to cryogenic disturbances (differential heave and soil surface disruption). We found that: (i) all studied non-sorted circles (n=15) acted as net CO2 sources (positive NEE); (ii) GEP showed a weaker decrease than Re in response to increased cryogenic disturbance/decreased humus cover, indicating that undisturbed humus-covered sites are currently the main source of atmospheric CO2 in the studied system. Interestingly, Re fluxes normalized to C pools indicated that C is currently respired more rapidly at sites exposed to cryogenic disturbances; hence, higher NEE fluxes at less disturbed sites are likely an effect of a more slowly degrading but larger total pool that was built up in the past. Our results highlight the complex effects of cryogenic processes on the C cycle at various time scales. 

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  • 14. Beer, Christian
    et al.
    Zimov, Nikita
    Olofsson, Johan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Porada, Philipp
    Zimov, Sergey
    Protection of Permafrost Soils from Thawing by Increasing Herbivore Density2020Ingår i: Scientific Reports, E-ISSN 2045-2322, Vol. 10, nr 1, artikel-id 4170Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Climate change will cause a substantial future greenhouse gas release from warming and thawing permafrost-affected soils to the atmosphere enabling a positive feedback mechanism. Increasing the population density of big herbivores in northern high-latitude ecosystems will increase snow density and hence decrease the insulation strength of snow during winter. As a consequence, theoretically 80% of current permafrost-affected soils (<10 m) is projected to remain until 2100 even when assuming a strong warming using the Representative Concentration Pathway 8.5. Importantly, permafrost temperature is estimated to remain below -4<degrees>C on average after increasing herbivore population density. Such ecosystem management practices would be therefore theoretically an important additional climate change mitigation strategy. Our results also highlight the importance of new field experiments and observations, and the integration of fauna dynamics into complex Earth System models, in order to reliably project future ecosystem functions and climate.

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  • 15. Berg, Anna
    et al.
    Östlund, Lars
    Moen, Jon
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Olofsson, Johan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    A century of logging and forestry in a reindeer herding area in northern Sweden2008Ingår i: Forest Ecology and Management, ISSN 0378-1127, E-ISSN 1872-7042, Vol. 256, s. 1009-1020Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Boreal forest ecosystems are generally highly sensitive to logging and other forestry activities. Thus, commercial forestry has had major effects on the forests and landscape structure in northern Sweden since the middle of the 19th Century, when it rapidly extended across the region. Lichens (which constitute up to 80% of reindeer forage in winter and early spring) have often been amongst the most severely affected ecosystem components. The overall aim of the present study was to analyze how forestry has influenced the potential supply of ground-growing lichens as winter forage for the reindeer in this region over the past ca. 100 years. For this purpose, we analysed changes in forest and stand structure in Scots pine-dominated (Pinus sylvestris L.) reindeer wintering areas in the southern part of the county Norrbotten (covering ca. 58,000 ha) using detailed historical forest inventories and management plans. We found that the amount of the forest types considered potentially good pasture (mainly middleaged and old pine forests) decreased during the first part of the 20th Century. However, the quality of grazing grounds was improved by forestry during this time mainly because selective logging made the forests more open which benefits lichen growth. During the last part of the 20th century forestry impaired the quality of grazing grounds in several ways, e.g. by clear-cutting and intensified use of various silviculturalmeasures. We conclude that ca. 30–50% of the winter grazing grounds have been lost in the study area because of intensive forest management during the last century. The spatially precise historical information about the affects of forestry on lichen pasture provided in this study can be used to direct forest management which will facilitate and promote reindeer herding in the future.

  • 16.
    Berner, Logan T.
    et al.
    School of Informatics, Computing, and Cyber Systems, Northern Arizona University, Flagstaff, United States.
    Orndahl, Kathleen M.
    School of Informatics, Computing, and Cyber Systems, Northern Arizona University, Flagstaff, United States.
    Rose, Melissa
    School of Informatics, Computing, and Cyber Systems, Northern Arizona University, Flagstaff, United States.
    Tamstorf, Mikkel
    Department of Ecoscience, Aarhus University, Aarhus, Denmark.
    Arndal, Marie F.
    Department of Ecoscience, Aarhus University, Aarhus, Denmark.
    Alexander, Heather D.
    College of Forestry, Wildlife, and Environment, Auburn University, Auburn, United States.
    Humphreys, Elyn R.
    Department of Geography and Environmental Studies, Carleton University, Ottawa, Canada.
    Loranty, Michael M.
    Department of Geography, Colgate University, Hamilton, United States.
    Ludwig, Sarah M.
    Department of Earth and Environmental Sciences, Columbia University, Palisades, United States.
    Nyman, Johanna
    Jeb E. Brooks School of Public Policy, Cornell University, Ithaca, United States.
    Juutinen, Sari
    Climate System Research, Finnish Meteorological Institute, Helsinki, Finland.
    Aurela, Mika
    Finnish Meteorological Institute, Helsinki, Finland.
    Happonen, Konsta
    Finnish Youth Research Society, Helsinki, Finland.
    Mikola, Juha
    Bioeconomy and Environment Unit, Natural Resources Institute Finland, Helsinki, Finland.
    Mack, Michelle C.
    Center for Ecosystem Science and Society, Northern Arizona University, Flagstaff, United States; Department of Biological Sciences, Northern Arizona University, Flagstaff, United States.
    Vankoughnett, Mathew R.
    Applied Research, Nova Scotia Community College, Middleton, Canada.
    Iversen, Colleen M.
    Climate Change Science Institute, Oak Ridge National Laboratory, Oak Ridge, United States.
    Salmon, Verity G.
    Climate Change Science Institute, Oak Ridge National Laboratory, Oak Ridge, United States; Environmental Science Division, Oak Ridge National Laboratory, Oak Ridge, United States.
    Yang, Dedi
    Environmental Science Division, Oak Ridge National Laboratory, Oak Ridge, United States.
    Kumar, Jitendra
    Environmental Science Division, Oak Ridge National Laboratory, Oak Ridge, United States.
    Grogan, Paul
    Department of Biology, Queen’s University, Kingston, Canada.
    Danby, Ryan K.
    Department of Geography and Planning, Queen’s University, Kingston, Canada.
    Scott, Neal A.
    Department of Geography and Planning, Queen’s University, Kingston, Canada.
    Olofsson, Johan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Siewert, Matthias B.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Deschamps, Lucas
    Département des sciences de l’environnement, Université du Québec à Trois-Rivières, Trois-Rivières, Canada.
    Lévesque, Esther
    Département des sciences de l’environnement, Université du Québec à Trois-Rivières, Trois-Rivières, Canada.
    Maire, Vincent
    Département des sciences de l’environnement, Université du Québec à Trois-Rivières, Trois-Rivières, Canada.
    Morneault, Amélie
    Département des sciences de l’environnement, Université du Québec à Trois-Rivières, Trois-Rivières, Canada.
    Gauthier, Gilles
    Centre d’Études Nordiques, Université Laval, Québec, Canada; Department of Biology, Université Laval, Québec, Canada.
    Gignac, Charles
    Centre d’Études Nordiques, Université Laval, Québec, Canada; Department of Plant Science, Université Laval, Québec, Canada.
    Boudreau, Stéphane
    Department of Biology, Université Laval, Québec, Canada.
    Gaspard, Anna
    Department of Biology, Université Laval, Québec, Canada.
    Kholodov, Alexander
    Geophysical Institute, University of Alaska Fairbanks, Fairbanks, United States.
    Bret-Harte, M. Syndonia
    Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, United States.
    Greaves, Heather E.
    Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, United States.
    Walker, Donald
    Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, United States.
    Gregory, Fiona M.
    Alberta Biodiversity Monitoring Institute, University of Alberta, Edmonton, Canada.
    Michelsen, Anders
    Department of Biology, University of Copenhagen, København, Denmark.
    Kumpula, Timo
    Department of Geographical and Historical Studies, University of Eastern Finland, Joensuu, Finland.
    Villoslada, Miguel
    Department of Geographical and Historical Studies, University of Eastern Finland, Joensuu, Finland; Institute of Agriculture and Environmental Sciences, Estonian University of Life Sciences, Tartu, Estonia.
    Ylänne, Henni
    School of Forest Sciences, University of Eastern Finland, Joensuu, Finland.
    Luoto, Miska
    Department of Geosciences and Geography, University of Helsinki, Helsinki, Finland.
    Virtanen, Tarmo
    Ecosystems and Environment Research Program, University of Helsinki, Helsinki, Finland.
    Forbes, Bruce C.
    Arctic Centre, University of Lapland, Rovaniemi, Finland.
    Hölzel, Norbert
    Institute of Landscape Ecology, University of Münster, Münster, Germany.
    Epstein, Howard
    Department of Environmental Science, University of Virginia, Charlottesville, United States.
    Heim, Ramona J.
    Department of Evolutionary Biology and Environmental Studies, University of Zurich, Zürich, Switzerland.
    Bunn, Andrew
    Department of Environmental Sciences, Western Washington University, Bellingham, United States.
    Holmes, Robert M.
    Woodwell Climate Research Center, Falmouth, United States.
    Hung, Jacqueline K. Y.
    Woodwell Climate Research Center, Falmouth, United States.
    Natali, Susan M.
    Woodwell Climate Research Center, Falmouth, United States.
    Virkkala, Anna-Maria
    Woodwell Climate Research Center, Falmouth, United States.
    Goetz, Scott J.
    School of Informatics, Computing, and Cyber Systems, Northern Arizona University, Flagstaff, United States; Bioeconomy and Environment Unit, Natural Resources Institute Finland, Helsinki, Finland.
    The Arctic plant aboveground biomass synthesis dataset2024Ingår i: Scientific Data, E-ISSN 2052-4463, Vol. 11, nr 1, artikel-id 305Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Plant biomass is a fundamental ecosystem attribute that is sensitive to rapid climatic changes occurring in the Arctic. Nevertheless, measuring plant biomass in the Arctic is logistically challenging and resource intensive. Lack of accessible field data hinders efforts to understand the amount, composition, distribution, and changes in plant biomass in these northern ecosystems. Here, we present The Arctic plant aboveground biomass synthesis dataset, which includes field measurements of lichen, bryophyte, herb, shrub, and/or tree aboveground biomass (g m−2) on 2,327 sample plots from 636 field sites in seven countries. We created the synthesis dataset by assembling and harmonizing 32 individual datasets. Aboveground biomass was primarily quantified by harvesting sample plots during mid- to late-summer, though tree and often tall shrub biomass were quantified using surveys and allometric models. Each biomass measurement is associated with metadata including sample date, location, method, data source, and other information. This unique dataset can be leveraged to monitor, map, and model plant biomass across the rapidly warming Arctic.

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  • 17. Bjorkman, Anne D.
    et al.
    Myers-Smith, Isla H.
    Elmendorf, Sarah C.
    Normand, Signe
    Rueger, Nadja
    Beck, Pieter S. A.
    Blach-Overgaard, Anne
    Blok, Daan
    Cornelissen, J. Hans C.
    Forbes, Bruce C.
    Georges, Damien
    Goetz, Scott J.
    Guay, Kevin C.
    Henry, Gregory H. R.
    HilleRisLambers, Janneke
    Hollister, Robert D.
    Karger, Dirk N.
    Kattge, Jens
    Manning, Peter
    Prevey, Janet S.
    Rixen, Christian
    Schaepman-Strub, Gabriela
    Thomas, Haydn J. D.
    Vellend, Mark
    Wilmking, Martin
    Wipf, Sonja
    Carbognani, Michele
    Hermanutz, Luise
    Levesque, Esther
    Molau, Ulf
    Petraglia, Alessandro
    Soudzilovskaia, Nadejda A.
    Spasojevic, Marko J.
    Tomaselli, Marcello
    Vowles, Tage
    Alatalo, Juha M.
    Alexander, Heather D.
    Anadon-Rosell, Alba
    Angers-Blondin, Sandra
    te Beest, Mariska
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Berner, Logan
    Bjork, Robert G.
    Buchwal, Agata
    Buras, Allan
    Christie, Katherine
    Cooper, Elisabeth J.
    Dullinger, Stefan
    Elberling, Bo
    Eskelinen, Anu
    Frei, Esther R.
    Grau, Oriol
    Grogan, Paul
    Hallinger, Martin
    Harper, Karen A.
    Heijmans, Monique M. P. D.
    Hudson, James
    Huelber, Karl
    Iturrate-Garcia, Maitane
    Iversen, Colleen M.
    Jaroszynska, Francesca
    Johnstone, Jill F.
    Jorgensen, Rasmus Halfdan
    Kaarlejärvi, Elina
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Klady, Rebecca
    Kuleza, Sara
    Kulonen, Aino
    Lamarque, Laurent J.
    Lantz, Trevor
    Little, Chelsea J.
    Speed, James D. M.
    Michelsen, Anders
    Milbau, Ann
    Nabe-Nielsen, Jacob
    Nielsen, Sigrid Scholer
    Ninot, Josep M.
    Oberbauer, Steven F.
    Olofsson, Johan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Onipchenko, Vladimir G.
    Rumpf, Sabine B.
    Semenchuk, Philipp
    Shetti, Rohan
    Collier, Laura Siegwart
    Street, Lorna E.
    Suding, Katharine N.
    Tape, Ken D.
    Trant, Andrew
    Treier, Urs A.
    Tremblay, Jean-Pierre
    Tremblay, Maxime
    Venn, Susanna
    Weijers, Stef
    Zamin, Tara
    Boulanger-Lapointe, Noemie
    Gould, William A.
    Hik, David S.
    Hofgaard, Annika
    Jonsdottir, Ingibjorg S.
    Jorgenson, Janet
    Klein, Julia
    Magnusson, Borgthor
    Tweedie, Craig
    Wookey, Philip A.
    Bahn, Michael
    Blonder, Benjamin
    van Bodegom, Peter M.
    Bond-Lamberty, Benjamin
    Campetella, Giandiego
    Cerabolini, Bruno E. L.
    Chapin, F. Stuart, III
    Cornwell, William K.
    Craine, Joseph
    Dainese, Matteo
    de Vries, Franciska T.
    Diaz, Sandra
    Enquist, Brian J.
    Green, Walton
    Milla, Ruben
    Niinemets, Ulo
    Onoda, Yusuke
    Ordonez, Jenny C.
    Ozinga, Wim A.
    Penuelas, Josep
    Poorter, Hendrik
    Poschlod, Peter
    Reich, Peter B.
    Sande, Brody
    Schamp, Brandon
    Sheremetev, Serge
    Weiher, Evan
    Plant functional trait change across a warming tundra biome2018Ingår i: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 562, nr 7725, s. 57-+Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The tundra is warming more rapidly than any other biome on Earth, and the potential ramifications are far-reaching because of global feedback effects between vegetation and climate. A better understanding of how environmental factors shape plant structure and function is crucial for predicting the consequences of environmental change for ecosystem functioning. Here we explore the biome-wide relationships between temperature, moisture and seven key plant functional traits both across space and over three decades of warming at 117 tundra locations. Spatial temperature-trait relationships were generally strong but soil moisture had a marked influence on the strength and direction of these relationships, highlighting the potentially important influence of changes in water availability on future trait shifts in tundra plant communities. Community height increased with warming across all sites over the past three decades, but other traits lagged far behind predicted rates of change. Our findings highlight the challenge of using space-for-time substitution to predict the functional consequences of future warming and suggest that functions that are tied closely to plant height will experience the most rapid change. They also reveal the strength with which environmental factors shape biotic communities at the coldest extremes of the planet and will help to improve projections of functional changes in tundra ecosystems with climate warming.

  • 18.
    Blume-Werry, Gesche
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Experimental Plant Ecology, Institute of Botany and Landscape Ecology, University of Greifswald, Soldmannstraße, Greifswald, Germany.
    Krab, Eveline J
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Swedish University of Agricultural Sciences, Department of Soil and Environment, Uppsala, Sweden.
    Olofsson, Johan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Sundqvist, Maja K.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Department of Earth Sciences, University of Gothenburg, Gothenburg, Sweden.
    Väisänen, Maria
    Klaminder, Jonatan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Invasive earthworms unlock arctic plant nitrogen limitation2020Ingår i: Nature Communications, E-ISSN 2041-1723, Vol. 11, nr 1Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Arctic plant growth is predominantly nitrogen (N) limited. This limitation is generally attributed to slow soil microbial processes due to low temperatures. Here, we show that arctic plant-soil N cycling is also substantially constrained by the lack of larger detritivores (earthworms) able to mineralize and physically translocate litter and soil organic matter. These new functions provided by earthworms increased shrub and grass N concentration in our common garden experiment. Earthworm activity also increased either the height or number of floral shoots, while enhancing fine root production and vegetation greenness in heath and meadow communities to a level that exceeded the inherent differences between these two common arctic plant communities. Moreover, these worming effects on plant N and greening exceeded reported effects of warming, herbivory and nutrient addition, suggesting that human spreading of earthworms may lead to substantial changes in the structure and function of arctic ecosystems. Arctic plant growth is predominantly nitrogen limited, where the slow nitrogen turnover in the soil is commonly attributed to the cold arctic climate. Here the authors show that the arctic plant-soil nitrogen cycling is also constrained by the lack of larger detritivores like earthworms.

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  • 19.
    Blume-Werry, Gesche
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Semenchuk, Philipp
    Department of Arctic Biology, UNIS – The University Centre in Svalbard, Longyearbyen, Norway.
    Ljung, Karin
    Department of Forest Genetics and Plant Physiology, Umeå Plant Science Centre, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Milbau, Ann
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Novak, Ondrej
    Department of Forest Genetics and Plant Physiology, Umeå Plant Science Centre, Swedish University of Agricultural Sciences, Umeå, Sweden; Laboratory of Growth Regulators, Faculty of Science, Palacký University & Institute of Experimental Botany of the Czech Academy of Sciences, Olomouc, Czech Republic.
    Olofsson, Johan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Brunoni, Federica
    Department of Forest Genetics and Plant Physiology, Umeå Plant Science Centre, Swedish University of Agricultural Sciences, Umeå, Sweden; Laboratory of Growth Regulators, Faculty of Science, Palacký University & Institute of Experimental Botany of the Czech Academy of Sciences, Olomouc, Czech Republic.
    In situ seasonal patterns of root auxin concentrations and meristem length in an arctic sedge2024Ingår i: New Phytologist, ISSN 0028-646X, E-ISSN 1469-8137, Vol. 242, nr 3, s. 988-999Artikel i tidskrift (Refereegranskat)
    Abstract [en]
    • Seasonal dynamics of root growth play an important role in large-scale ecosystem processes; they are largely governed by growth regulatory compounds and influenced by environmental conditions. Yet, our knowledge about physiological drivers of root growth is mostly limited to laboratory-based studies on model plant species.
    • We sampled root tips of Eriophorum vaginatum and analyzed their auxin concentrations and meristem lengths biweekly over a growing season in situ in a subarctic peatland, both in surface soil and at the permafrost thawfront.
    • Auxin concentrations were almost five times higher in surface than in thawfront soils and increased over the season, especially at the thawfront. Surprisingly, meristem length showed an opposite pattern and was almost double in thawfront compared with surface soils. Meristem length increased from peak to late season in the surface soils but decreased at the thawfront.
    • Our study of in situ seasonal dynamics in root physiological parameters illustrates the potential for physiological methods to be applied in ecological studies and emphasizes the importance of in situ measurements. The strong effect of root location and the unexpected opposite patterns of meristem length and auxin concentrations likely show that auxin actively governs root growth to ensure a high potential for nutrient uptake at the thawfront.
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  • 20.
    Bognounou, Fidele
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Hulme, Philip E.
    Oksanen, Lauri
    Suominen, Otso
    Olofsson, Johan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Role of climate and herbivory on native and alien conifer seedling recruitment at and above the Fennoscandian tree line2018Ingår i: Journal of Vegetation Science, ISSN 1100-9233, E-ISSN 1654-1103, Vol. 29, nr 4, s. 573-584Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Questions: We investigated the importance of climate and herbivory on native and alien conifer colonization of the birch-dominated Fennoscandian tree line by addressing the following questions: (a) are tree line and tundra habitats similarly suitable for conifer seedling recruitment; (b) do ungulate and rodent herbivores differentially impact seedling recruitment; and (c) how does the role of habitat and herbivory on seedling recruitment vary across a marked climate gradient?

    Location: Northern Fennoscandia, Sweden (Vassijaure and Paddus), and Norway (Joatka and Seiland).

    Methods: We conducted an experiment to assess the emergence rate, survival probability and height development of Norway spruce (Picea abies), Scots pine (Pinus sylvestris) and Siberian larch (Larix sibirica) seedlings. Three experimental plots (i.e., open control, reindeer exclosure and complete vertebrate exclosure) were established in both tree line and tundra habitats at each of the four locations. Seeds of the three conifer species were sown in each plot in June 1999 during three consecutive years. The surviving seedlings were counted in August to September 1999, 2000, 2001, 2002 and 2007. The height of all seedlings was measured in 2007.

    Results: Our study reveals that Norway spruce, Scots pine and Siberian larch can regenerate from seed at and above the current tree line in northern Fennoscandia. Their performance was generally higher above tree line in tundra than at tree line, but depended on species identity, climate aridity and mammal herbivory, particularly by rodents. These results suggest that the species composition and latitudinal limit of the tree line in the future might depend not only on direct effects of the future climate on the current tree line species, but also on the intensity of alien and native conifer introductions, as well as changes in herbivore populations.

    Conclusion: If sufficient seeds of Norway spruce, Scots pine and Siberian larch should reach the current tree line, their performances will increase with a warmer and wetter climate, and this effect will be markedly modulated by herbivores (particularly rodents). Further work is required to extend these results to determine the ability of these conifers to become tree line-forming species in the future.

  • 21. Brooker, R.W.
    et al.
    Maestre, F.T.
    Callaway, R.M.
    Lortie, C.L.
    Cavieres, L.A.
    Kunstler, G.
    Liancourt, P.
    Tielborger, K.
    Travis, J.M.J.
    Anthelme, F.
    Armas, C.
    Coll, L.
    Corcket, E.
    Delzon, S.
    Forey, E.
    Kikvidze, Z.
    Olofsson, Johan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Pugnaire, F.
    Quiroz, C.L.
    Saccone, P.
    Schiffers, K.
    Seifan, M.
    Touzard, B.
    Michalet, R.
    Facilitation in plant communities: the past, the present, and the future2008Ingår i: Journal of Ecology, ISSN 0022-0477, E-ISSN 1365-2745, Vol. 96, nr 1, s. 18-34Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    1. Once neglected, the role of facilitative interactions in plant communities has received considerable attention in the last two decades, and is now widely recognized. It is timely to consider the progress made by research in this field.

    2. We review the development of plant facilitation research, focusing on the history of the field, the relationship between plant–plant interactions and environmental severity gradients, and attempts to integrate facilitation into mainstream ecological theory. We then consider future directions for facilitation research.

    3. With respect to our fundamental understanding of plant facilitation, clarification of the relationship between interactions and environmental gradients is central for further progress, and necessitates the design and implementation of experiments that move beyond the clear limitations of previous studies.

    4. There is substantial scope for exploring indirect facilitative effects in plant communities, including their impacts on diversity and evolution, and future studies should connect the degree of non-transitivity in plant competitive networks to community diversity and facilitative promotion of species coexistence, and explore how the role of indirect facilitation varies with environmental severity.

    5. Certain ecological modelling approaches (e.g. individual-based modelling), although thus far largely neglected, provide highly useful tools for exploring these fundamental processes.

    6. Evolutionary responses might result from facilitative interactions, and consideration of facilitation might lead to re-assessment of the evolution of plant growth forms.

    7. Improved understanding of facilitation processes has direct relevance for the development of tools for ecosystem restoration, and for improving our understanding of the response of plant species and communities to environmental change drivers.

    8. Attempts to apply our developing ecological knowledge would benefit from explicit recognition of the potential role of facilitative plant–plant interactions in the design and interpretation of studies from the fields of restoration and global change ecology.

    9. Synthesis: Plant facilitation research provides new insights into classic ecological theory and pressing environmental issues. Awareness and understanding of facilitation should be part of the basic ecological knowledge of all plant ecologists.

  • 22.
    Buckland, Philip I
    et al.
    Umeå universitet, Humanistiska fakulteten, Arkeologi och samiska studier.
    Johan, Olofsson
    Umeå universitet, Humanistiska fakulteten, Arkeologi och samiska studier.
    Engelmark, Roger
    Umeå universitet, Humanistiska fakulteten, Arkeologi och samiska studier.
    SEAD: Strategic Environmental Archaeology Database, planning report2006Rapport (Övrigt vetenskapligt)
    Abstract [en]

    This document lays out a strategy for the development of SEAD – A Strategic Environmental Archaeology Database, which will facilitate the digitisation and accessibility augmentation of MAL’s existing data from nearly thirty years of work in the fields of archaeology and environmental science. SEAD will also provide a framework for the entry of data from all future research and consultancy work at MAL, and allow guest researchers and external partners to contribute to, and work with the same data. The planned system will be implemented at both local and internet levels, and be designed with an aim towards broadening its scope with external partners in the future. SEAD will be made available online in order to increase the ease of access to environmental archaeology data and encourage an expansion of both the discipline and Sweden’s role in it. This is inline with current EU strategies on enhancing research infrastructure, and providing a greater insight into human-environment interactions for long term planning.

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  • 23. Callaghan, Terry V
    et al.
    Jonasson, Christer
    Thierfelder, Tomas
    Yang, Zhenlin
    Hedenas, Henrik
    Johansson, Margareta
    Molau, Ulf
    Van Bogaert, Rik
    Michelsen, Anders
    Olofsson, Johan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Gwynn-Jones, Dylan
    Bokhorst, Stef
    Phoenix, Gareth
    Bjerke, Jarle W
    Tommervik, Hans
    Christensen, Torben R
    Hanna, Edward
    Koller, Eva K
    Sloan, Victoria L
    Ecosystem change and stability over multiple decades in the Swedish subarctic: complex processes and multiple drivers2013Ingår i: Philosophical Transactions of the Royal Society of London. Biological Sciences, ISSN 0962-8436, E-ISSN 1471-2970, Vol. 368, nr 1624Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The subarctic environment of northernmost Sweden has changed over the past century, particularly elements of climate and cryosphere. This paper presents a unique geo-referenced record of environmental and ecosystem observations from the area since 1913. Abiotic changes have been substantial. Vegetation changes include not only increases in growth and range extension but also counterintuitive decreases, and stability: all three possible responses. Changes in species composition within the major plant communities have ranged between almost no changes to almost a 50 per cent increase in the number of species. Changes in plant species abundance also vary with particularly large increases in trees and shrubs (up to 600%). There has been an increase in abundance of aspen and large changes in other plant communities responding to wetland area increases resulting from permafrost thaw. Populations of herbivores have responded to varying management practices and climate regimes, particularly changing snow conditions. While it is difficult to generalize and scale-up the site-specific changes in ecosystems, this very site-specificity, combined with projections of change, is of immediate relevance to local stakeholders who need to adapt to new opportunities and to respond to challenges. Furthermore, the relatively small area and its unique datasets are a microcosm of the complexity of Arctic landscapes in transition that remains to be documented.

  • 24.
    Castaño, Carles
    et al.
    Department of Forest Mycology and Plant Pathology, Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Hallin, Sara
    Department of Forest Mycology and Plant Pathology, Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Egelkraut, Dagmar
    Department of Biological Sciences, University of Bergen, Bergen, Norway.
    Lindahl, Björn D.
    Department of Soil and Environment, Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Olofsson, Johan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Clemmensen, Karina Engelbrecht
    Department of Forest Mycology and Plant Pathology, Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Contrasting plant–soil–microbial feedbacks stabilize vegetation types and uncouple topsoil C and N stocks across a subarctic–alpine landscape2023Ingår i: New Phytologist, ISSN 0028-646X, E-ISSN 1469-8137, Vol. 238, nr 6, s. 2621-2633Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Global vegetation regimes vary in belowground carbon (C) and nitrogen (N) dynamics. However, disentangling large-scale climatic controls from the effects of intrinsic plant–soil–microbial feedbacks on belowground processes is challenging. In local gradients with similar pedo-climatic conditions, effects of plant–microbial feedbacks may be isolated from large-scale drivers. Across a subarctic–alpine mosaic of historic grazing fields and surrounding heath and birch forest, we evaluated whether vegetation-specific plant–microbial feedbacks involved contrasting N cycling characteristics and C and N stocks in the organic topsoil. We sequenced soil fungi, quantified functional genes within the inorganic N cycle, and measured 15N natural abundance. In grassland soils, large N stocks and low C : N ratios associated with fungal saprotrophs, archaeal ammonia oxidizers, and bacteria capable of respiratory ammonification, indicating maintained inorganic N cycling a century after abandoned reindeer grazing. Toward forest and heath, increasing abundance of mycorrhizal fungi co-occurred with transition to organic N cycling. However, ectomycorrhizal fungal decomposers correlated with small soil N and C stocks in forest, while root-associated ascomycetes associated with small N but large C stocks in heath, uncoupling C and N storage across vegetation types. We propose that contrasting, positive plant–microbial feedbacks stabilize vegetation trajectories, resulting in diverging soil C : N ratios at the landscape scale.

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  • 25.
    Dahlgren, Jonas
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Oksanen, Lauri
    Oksanen, Tarja
    Olofsson, Johan
    Trophic cascades and direct herbivore impacts in a low arctic scrublandManuskript (preprint) (Övrigt vetenskapligt)
  • 26.
    Dahlgren, Jonas
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Oksanen, Lauri
    Department of Biology, Section of Ecology, University of Turku, Turku, Finland.
    Oksanen, Tarja
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Olofsson, Johan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Hambäck, Peter A
    Department of Botany, Stockholm University, Stockholm, Sweden.
    Lindgren, Åsa
    Department of Botany, Stockholm University, Stockholm, Sweden.
    Plant defences to no avail?: Responses of plants of varying edibility to food web manipulations in a low arctic scrubland2009Ingår i: Evolutionary Ecology Research, ISSN 1522-0613, E-ISSN 1937-3791, Vol. 11, s. 1189-1203Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Background: According to the Green World Hypothesis of Hairston, Smith, and Slobodkin,all plants are edible for some herbivores. Hence, the copious abundance of plant biomass,typical for terrestrial ecosystems, depends on the collective regulatory action of predators on the herbivore guild. According to the counterarguments of Polis and Strong, the defensive traits of terrestrial plants attenuate terrestrial trophic cascades to species-specific trickles,so elimination of predators might lead to increased abundance of inedible plants but will not influence community-level plant biomass.

    Question: Does the elimination of predators from a low arctic scrubland, with high-quality forage plants and poorly edible evergreen ericoids, lead to a reduction of community-level plant biomass or to an increased abundance of well-defended evergreen ericoids?

    Methods: In 1991, we introduced grey-sided voles (Myodes rufocanus) to islands, initially harbouring dense scrubland vegetation, and established permanent plots there. In 2000, we transplanted vegetation blocks from a large three-trophic-level island with voles and predators,to two-trophic-level islands with introduced voles but without resident predators, and also to vole-free one-trophic-level islands, and back to the three-trophic-level island. Vole densities were monitored by semi-annual live trapping. Vegetation was monitored by the point-frequency method.

    Results: In the absence of predators, vole densities increased 3.7-fold and the communitylevel plant biomass was decimated. The least palatable plant group, evergreen ericoids,suffered especially heavily, whereas palatable herbaceous plants increased in abundance. However, all three functional plant groups responded positively to the elimination of grey-sided voles.

    Conclusions: Our results corroborate the Green World Hypothesis, indicating that in the absence of predators, plant defences do not prevent runaway consumption of the vegetation.

  • 27.
    Dahlgren, Jonas
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Oksanen, Lauri
    Department of Biology, Section of Ecology, University of Turku, Turku, Finland.
    Olofsson, Johan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Oksanen, Tarja
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Plant defense at no cost?: The recovery of tundra scrubland following heavy grazing by grey-sided voles (Myodes rufocanus)2009Ingår i: Evolutionary Ecology Research, ISSN 1522-0613, E-ISSN 1937-3791, Vol. 11, s. 1205-1216Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Background: Evergreen ericaceous dwarf shrubs form a dominating component of low arctic and low alpine vegetation. They typically produce high contents of secondary chemicals such as phenolics. The primary function of these chemicals may be to defend the shrubs by making them less palatable to herbivores. Question: Does the production of secondary chemicals carry a fitness cost in terms of low growth rate and, therefore, low capacity to recover from past herbivory?

    Methods: In 2000, we constructed vole-proof exclosures on low arctic islands where vegetation had, since 1991, been heavily impacted by grey-sided voles. In 2000 and 2003,we surveyed the vegetation of the exclosures, of unfenced plots on the same islands, and of control plots on a vole-free island. We used the point-frequency method for vegetation surveys.

    Results: In the exclosures, the biomasses of most plant species increased, by and large, at the same pace. The two woody species, which increased most rapidly, were the maximally palatable bilberry (Vaccinium myrtillus) and the phenolics-laden, maximally unpalatable northern crowberry (Empetrum nigrum ssp. hermaprhoditum). The recovery rates of these species were similar.

    Conclusions: The high concentrations of phenolics typical for evergreen arctic dwarf shrubs do not carry any obvious cost in the form of reduced capacity for compensatory growth. The principle of trade-offs does not help to explain the variation in plant palatability.

  • 28.
    Dahlgren, Jonas
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Oksanen, Lauri
    Sjödin, Maria
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Ekologi och geovetenskap.
    Olofsson, Johan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Ekologi och geovetenskap.
    Interactions between gray-sided voles (Clethrionomys rufucanus) and bilberry (Vaccinium myrtillus), their main winter food plant2007Ingår i: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 152, nr 3, s. 525-532Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We compared the abundance, population structure and palatability of bilberry ramets on vole-free islands, islands with voles but no predators (predator-free islands) and mainland sites with both voles and predators. As expected, bilberry biomass was strongly correlated with the herbivory pressure exerted by the voles, since it was significantly lower on the mainland, and much (>80%) lower on the predator-free islands, than on the vole-free islands. However, another finding, which conflicts with hypotheses postulating that herbivory generally induces plant defenses, was that voles preferred ramets from predator-free islands. Bilberry plants were fairly tolerant to grazing since they compensated for some of the lost tissue by producing more new ramets. This response should promote stability in the plant–herbivore interaction by reducing the impact of past grazing on current food production and thus minimizing time delays in the interactions that could potentially generate population cycles.

  • 29.
    de la Barreda-Bautista, Betsabe
    et al.
    School of Biosciences, University of Nottingham, Sutton Bonington, Loughborough, United Kingdom; School of Geography, University of Nottingham, University Park, Nottingham, United Kingdom.
    Boyd, Doreen S.
    School of Geography, University of Nottingham, Nottingham, United Kingdom.
    Ledger, Martha
    School of Biosciences, University of Nottingham, Sutton Bonington, Loughborough, United Kingdom.
    Siewert, Matthias B.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Chandler, Chris
    School of Geography, University of Nottingham, Nottingham, United Kingdom.
    Bradley, Andrew V.
    Department of Chemical and Environmental Engineering, Faculty of Engineering, Nottingham Geospatial Institute, Nottingham, United Kingdom.
    Gee, David
    Department of Chemical and Environmental Engineering, Faculty of Engineering, University of Nottingham, Nottingham, United Kingdom.
    Large, David J.
    Department of Chemical and Environmental Engineering, Faculty of Engineering, Nottingham Geospatial Institute, Nottingham, United Kingdom; Department of Chemical and Environmental Engineering, Faculty of Engineering, University of Nottingham, Nottingham, United Kingdom.
    Olofsson, Johan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Sowter, Andrew
    Terra Motion Ltd, Ingenuity Centre, Nottingham, United Kingdom.
    Sjögersten, Sofie
    School of Biosciences, University of Nottingham, Sutton Bonington, Loughborough, United Kingdom.
    Towards a Monitoring Approach for Understanding Permafrost Degradation and Linked Subsidence in Arctic Peatlands2022Ingår i: Remote Sensing, E-ISSN 2072-4292, Vol. 14, nr 3, artikel-id 444Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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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  • 30.
    Egelkraut, Dagmar
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Aronsson, Kjell-Åke
    Ájtte, Swedish Mountain and Sami Museum, Jokkmokk, Sweden.
    Allard, Anna
    Department of Forest Resource Management, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Åkerholm, Marianne
    Department of Forest Resource Management, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Stark, Sari
    Arctic Centre, University of Lapland, Rovaniemi, Finland.
    Olofsson, Johan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Multiple feedbacks contribute to a centennial legacy of reindeer on tundra vegetation2018Ingår i: Ecosystems (New York. Print), ISSN 1432-9840, E-ISSN 1435-0629, Vol. 21, nr 8, s. 1545-1563Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Historical contingency is the impact of past events, like the timing and order of species arrival, on community assembly, and can sometimes result in alternative stable states of ecological communities. Large herbivores, wild and domestic, can cause profound changes in the structure and functioning of plant communities and therefore probably influence historical contingency; however, little empirical data on the stability of such shifts or subsequent drivers of stability are available. We studied the centennial legacy of reindeer (Rangifer tarandus) pressure on arctic tundra vegetation by considering historical milking grounds (HMGs): graminoid- and forb-dominated patches amid shrub-dominated tundra, formed by historical Sami reindeer herding practices that ended approximately 100 years ago. Our results show that the core areas of all studied HMGs remained strikingly stable, being hardly invaded by surrounding shrubs. Soil nitrogen concentrations were comparable to heavily grazed areas. However, the HMGs are slowly being reinvaded by vegetative growth of shrubs at the edges, and the rate of ingrowth increased with higher mineral N availability. Furthermore, our data indicate that several biotic feedbacks contribute to the stability of the HMGs: increased nutrient turnover supporting herbaceous vegetation, strong interspecific competition preventing invasion and herbivore damage to invading shrubs. In particular, voles and lemmings appear to be important, selectively damaging shrubs in the HMGs. We concluded that HMGs provide clear evidence for historical contingency of herbivore effects in arctic ecosystems. We showed that several biotic feedbacks can contribute to subsequent vegetation stability, but their relative importance will vary in time and space.

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  • 31.
    Egelkraut, Dagmar
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Umeå University.
    Barthelemy, Hélène
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Olofsson, Johan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Reindeer trampling causes vegetation changes in tundra heathlands: results from a simulation experimentManuskript (preprint) (Övrigt vetenskapligt)
  • 32.
    Egelkraut, Dagmar
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Department of Biological Sciences, University of Bergen, Bergen, Norway.
    Barthelemy, Hélène
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Olofsson, Johan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Reindeer trampling promotes vegetation changes in tundra heathlands: Results from a simulation experiment2020Ingår i: Journal of Vegetation Science, ISSN 1100-9233, E-ISSN 1654-1103, Vol. 31, nr 3, s. 476-486Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Question: Herbivores exert strong influences on vegetation through activities such as trampling, defoliation, and fertilization. The combined effect of these activities on plant performance may cause dramatic vegetation shifts. Because herbivore pressures and the relative importance of their different activities are not equally distributed across the landscape, it is important to understand their isolated effect. One example of an herbivore‐induced vegetation shift is the reindeer‐driven transition from a subarctic tundra vegetation dominated by dwarf shrubs into a more productive, graminoid‐dominated state. Here, we asked how each of the grazing activities by reindeer separately and combined shape vegetation composition.

    Location: Nordreisa, Norway.