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  • 1.
    Aalto, Juha
    Helsingfors universitet, matematisk-naturvetenskapliga fakulteten, institutionen för geovetenskaper och geografi.
    New perspectives on climate: Earth surface processes and thermal hydrological conditions in high latitude systems2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Climate, Earth surface processes and soil thermal hydrological conditions drive landscape development, ecosystem functioning and human activities in high latitude regions. These systems are at the focal point of concurrent global change studies as the ongoing shifts in climate regimes has already changed the dynamics of fragile and highly specialized environments across pan Arctic. This thesis aimed to 1) analyze and model extreme air temperatures, soil thermal and hydrological conditions, and the main Earth surface processes (ESP) (cryoturbation, solifluction, nivation and palsa mires) controlling the functioning of high latitude systems in current and future climate conditions; 2) identify the key environmental factors driving the spatial variation of the studied phenomena; and 3) develop methodology for producing novel high quality datasets. To accomplish these objectives, spatial analyses were conducted throughout geographical scales by utilizing multiple statistical modelling approaches, such as regression, machine learning techniques and ensemble forecasting. This thesis was based on unique datasets from the northern Fennoscandia; climate station records from Finland, Sweden and Norway, state of the art climate model simulations, fine scale field measurements collected in arctic alpine tundra and remotely sensed geospatial data. In paper I, accurate extreme air temperature maps were produced, which were notably improved after incorporating the influence of local factors such as topography and water bodies into the spatial models. In paper II, the results showed extreme variation in soil temperature and moisture over very short distances, while revealing the factors controlling the heterogeneity of ground thermal and hydrological conditions. Finally, the modelling outputs in papers III and IV provided new insights into the determination of geomorphic activity patterns across arctic alpine landscapes, while stressing the need for accurate climate data for predictive geomorphological distribution mapping. Importantly, Earth surface processes were found to be extremely climatic sensitivity, and drastic changes in geomorphic systems towards the end of 21st century can be expected. The increase of current temperature conditions by 2 ˚C was projected to cause a near complete loss of active ESPs in the high latitude study area. This thesis demonstrated the applicability of spatial modelling techniques as a useful framework in multiple key challenges of contemporary physical geography. Moreover, with the utilized model ensemble approach, the modelling uncertainty can be reduced while presenting the local trends in response variables more robustly. In future Earth system studies, it is essential to further assess the dynamics of arctic alpine landscapes under changing climatic conditions and identify potential tipping points of these sensitive systems.

  • 2. Aalto, Juha
    et al.
    le Roux, Peter C.
    Luoto, Miska
    The meso-scale drivers of temperature extremes in high-latitude Fennoscandia2014In: Climate Dynamics, ISSN 0930-7575, E-ISSN 1432-0894, Vol. 42, no 1, p. 237-252Article in journal (Refereed)
    Abstract [en]

    Extreme temperatures are key drivers controlling both biotic and abiotic processes, and may be strongly modified by topography and land cover. We modelled mean and extreme temperatures in northern Fennoscandia by combining digital elevation and land cover data with climate observations from northern Finland, Norway and Sweden. Multivariate partitioning technique was utilized to investigate the relative importance of environmental variables for the variation of the three temperature parameters: mean annual absolute minima and maxima, and mean annual temperature. Generalized additive modeling showed good performance, explaining 84–95 % of the temperature variation. The inclusion of remotely sensed variables improved significantly the modelling of thermal extremes in this system. The water cover variables and topography were the most important drivers of minimum temperatures, whereas elevation was the most important factor controlling maximum temperatures. The spatial variability of mean temperatures was clearly driven by geographical location and the effects of topography. Partitioning technique gave novel insights into temperature-environment relationship at the meso-scale and thus proved to be useful tool for the study of the extreme temperatures in the high-latitude setting.

  • 3. Aben, Ralf C. H.
    et al.
    Barros, Nathan
    van Donk, Ellen
    Frenken, Thijs
    Hilt, Sabine
    Kazanjian, Garabet
    Lamers, Leon P. M.
    Peeters, Edwin T. H. M.
    Roelofs, Jan G. M.
    de Senerpont Domis, Lisette N.
    Stephan, Susanne
    Velthuis, Mandy
    Van de Waal, Dedmer B.
    Wik, Martin
    Thornton, Brett F.
    Wilkinson, Jeremy
    DelSontro, Tonya
    Kosten, Sarian
    Cross continental increase in methane ebullition under climate change2017In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 8, no 1Article in journal (Refereed)
    Abstract [en]

    Methane (CH4) strongly contributes to observed global warming. As natural CH4 emissions mainly originate from wet ecosystems, it is important to unravel how climate change may affect these emissions. This is especially true for ebullition (bubble flux from sediments), a pathway that has long been underestimated but generally dominates emissions. Here we show a remarkably strong relationship between CH4 ebullition and temperature across a wide range of freshwater ecosystems on different continents using multi-seasonal CH4 ebullition data from the literature. As these temperature–ebullition relationships may have been affected by seasonal variation in organic matter availability, we also conducted a controlled year-round mesocosm experiment. Here 4 °C warming led to 51% higher total annual CH4 ebullition, while diffusion was not affected. Our combined findings suggest that global warming will strongly enhance freshwater CH4 emissions through a disproportional increase in ebullition (6–20% per 1 °C increase), contributing to global warming.

  • 4. Abrahamsson, T.
    Sjangeli.1978In: Fjällklubbsnytt, Vol. 23, no 3, p. 10-11Article in journal (Other academic)
  • 5.
    Ackermann, M.
    Inst. für Phys. Geogr..
    Frost- und Vegetationsmuster an einem Hang bei Abisko, Schwedisch Lappland.1988Student thesis
  • 6. Acland, C.M.
    et al.
    Maxce, V.C.
    Peakall, D.B.
    Fågelobservationer i Lappland.1956In: Fauna och flora, Vol. 51, no 4, p. 162-173Article in journal (Other academic)
  • 7. Adamek, P.M.
    Geology and mineralogy of the Kopparåsen uraninite-sulphide mineralization, Norrbotten county, Sweden.1975In: Sveriges Geologiska Undersökning Serie, Vol. C 712, no 69(4), p. 3-69Article in journal (Other academic)
  • 8. Adamčík, Slavomír
    et al.
    Slovák, Marek
    Eberhardt, Ursula
    Ronikier, Anna
    Jairus, Teele
    Hampe, Felix
    Verbeken, Annemieke
    Molecular inference, multivariate morphometrics and ecological assessment are applied in concert to delimit species in the Russula clavipes complex2016In: Mycologia, ISSN 0027-5514, E-ISSN 1557-2536, Vol. 108, no 4, p. 716-730Article in journal (Refereed)
    Abstract [en]

    Species of Russula subsect. Xerampelinae are notoriously difficult to identify and name and have not been subject to molecular study. A group of species, referred to here as the R. clavipes complex, growing in association with Salix, Betula and Populus as well as coniferous tree species from temperate to arctic and alpine habitats, were examined. Analyses of the nuc rDNA internal transcribed spacer (ITS) region and a numerical analysis of morphological characters were used. The R. clavipes complex is a monophyletic group within Russula subsect. Xerampelinae, according to molecular results. The complex includes three species: R. nuoljae is a phylogenetically and morphologically well-supported species while the other two, R. clavipes and R. pascua, are similar based on ITS data and morphology but separate based on their ecology. Russula pseudoolivascens is conspecific with R. clavipes. Several combinations of characters traditionally used in the taxonomy of R. subsect. Xerampelinae are inappropriate for species delimitation in this group and the adequacy of the ITS for species identification in this group is discussed. Detailed microscopic observations on the type collection of R. nuoljae are presented and illustrated, along with a key to the European members of R. subsect. Xerampelinae.

  • 9. Adedokun, J.A.
    et al.
    Holmgren, B.
    Acoustic sounder detection of anabatic/katabatic winds in Abisko N. Sweden.1991In: Renewable Energy, Vol. 1, no 1, p. 77-89Article in journal (Other academic)
  • 10. Adedokun, J.A.
    et al.
    Holmgren, B.
    Acoustic sounder doppler measurement of the wind fields associated with a mountain stratus transformed into a valley fog: a case study.1993In: Atmospheric Environment, Vol. 27A, no 7, p. 1091-1098Article in journal (Other academic)
  • 11. Adeyefa, Z.D.
    Spectral Investigations of Solar Irradiance under Arctic and Tropical Weather Situations.1996Student thesis
  • 12. Adeyefa, Z.D.
    et al.
    Holmgren, B.
    Adedokun, J.A.
    Spectral solar radiation measurements and turbidity: comparative studies within a tropical and a subarctic environment.1997In: Solar Energy, Vol. 60, no 1, p. 17-24Article in journal (Other academic)
  • 13.
    Aebi, M.A.
    Department of Geography. Institute of Meteorology, Climatology and Remote Sensing..
    Analysis of Critical Meteorological Conditions Essential to Snowmelt Induced Slush-Torrent Release over the Last 50 Years in the Abisko Mountains, Northern Swedish Lapland.2001Student thesis
  • 14. Aerts, R
    The freezer defrosting: global warming and litter decomposition rates in cold biomes2006In: Journal of Ecology, ISSN 0022-0477, E-ISSN 1365-2745, Vol. 94, no 4, p. 713-724Article in journal (Refereed)
    Abstract [en]

    1 Decomposition of plant litter, a key component of the global carbon budget, is hierarchically controlled by the triad: climate > litter quality > soil organisms. Given the sensitivity of decomposition to temperature, especially in cold biomes, it has been hypothesized that global warming will lead to increased litter decomposition rates, both through direct temperature effects and through indirect effects on litter quality and soil organisms. 2 A meta-analysis of experimental warming studies in cold biomes (34 site-species combinations) showed that warming resulted in slightly increased decomposition rates. However, this response was strongly dependent on the method used: open top chambers reduced decomposition rates, whereas heating lamps stimulated decomposition rates. The low responsiveness was mainly due to moisture-limited decomposition rates in the warming treatments, especially at mesic and xeric sites. This control of litter decomposition by both temperature and moisture was corroborated by natural gradient studies. 3 Interspecific differences in litter quality and decomposability are substantially larger than warming-induced phenotypic responses. Thus, the changes in the species composition and structure of plant communities that have been observed in medium-term warming studies in cold biomes will have a considerably greater impact on ecosystem litter decomposition than phenotypic responses. 4 Soil fauna communities in cold biomes are responsive to climate warming. Moreover, temperature-driven migration of the, hitherto absent, large comminuters to high-latitude sites may significantly increase decomposition rates. However, we do not know how far-reaching the consequences of changes in the species composition and structure of the soil community are for litter decomposition, as there is a lack of data on functional species redundancy and the species’ dispersal ability. 5 Global warming will lead to increased litter decomposition rates only if there is sufficient soil moisture. Hence, climate scenario and experimental studies should focus more on both factors and their interaction. As interspecific differences in potential decomposability and litter chemistry are substantially larger than phenotypic responses to warming, the focus of future research should be on the former. In addition, more light should be shed on the below-ground ‘darkness’ to evaluate the ecological significance of warming-induced soil fauna community changes for litter decomposition processes in cold biomes.

  • 15. Aerts, R
    et al.
    Cornelissen, J H C
    Dorrepaal, E
    van Logtestijn, R S P
    Callaghan, T V
    Effects of experimentally imposed climate scenarios on flowering phenology and flower production of subarctic bog species2004In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 10, no 9, p. 1599-1609Article in journal (Refereed)
    Abstract [en]

    Climate scenarios for high-latitude areas predict not only increased summer temperatures, but also larger variation in snowfall and winter temperatures. By using open-top chambers, we experimentally manipulated both summer temperatures and winter and spring snow accumulations and temperatures independently in a blanket bog in subarctic Sweden, yielding six climate scenarios. We studied the effects of these scenarios on flowering phenology and flower production of Andromeda polifolia (woody evergreen) and Rubus chamaemorus (perennial herb) during 2 years. The second year of our study (2002) was characterized by unusually high spring and early summer temperatures. Our winter manipulations led to consistent increases in winter snow cover. As a result, average and minimum air and soil temperatures in the high snow cover treatments were higher than in the winter ambient treatments, whereas temperature fluctuations were smaller. Spring warming resulted in higher average, minimum, and maximum soil temperatures. Summer warming led to higher air and soil temperatures in mid-summer (June-July), but not in late summer (August-September). The unusually high temperatures in 2002 advanced the median flowering date by 2 weeks for both species in all treatments. Superimposed on this effect, we found that for both Andromeda and Rubus, all our climate treatments (except summer warming for Rubus) advanced flowering by 1-4 days. The total flower production of both species showed a more or less similar response: flower production in the warm year 2002 exceeded that in 2001 by far. However, in both species flower production was only stimulated by the spring-warming treatments. Our results show that the reproductive ecology of both species is very responsive to climate change but this response is very dependent on specific climate events, especially those that occur in winter and spring. This suggests that high-latitude climate change experiments should focus more on winter and spring events than has been the case so far.

  • 16. Aerts, R.
    et al.
    Cornelissen, J. H. C.
    van Logtestijn, R. S. P.
    Callaghan, T. V.
    Climate change has only a minor impact on nutrient resorption parameters in a high-latitude peatland2007In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 151, no 1, p. 132-139Article in journal (Refereed)
    Abstract [en]

    Nutrient resorption from senescing plant tissues is an important determinant of the fitness of plant populations in nutrient-poor ecosystems, because it makes plants less dependent on current nutrient uptake. Moreover, it can have significant “afterlife” effects through its impact on litter chemistry and litter decomposability. Little is known about the effects of climate change on nutrient resorption. We studied the effects of climate change treatments (including winter snow addition, and spring and/or summer warming) on nutrient resorption of four dominant species in a nutrient-poor subarctic peatland. These species were Betula nana (woody deciduous), Vaccinium uliginosum (woody deciduous), Calamagrostis lapponica (graminoid) and Rubus chamaemorus (forb). After five years of treatments both mature and senesced leaf N concentrations showed a small but significant overall reduction in response to the climate treatments. However, the effects were species-specific. For example, in the controls the N concentration in senesced leaves of Calamagrostis (3.0 +/- 0.2 mg N g(-1)) was about four times lower than for Rubus (11.2 +/- 0.2 mg N g(-1)). There were no significant treatment effects on N resorption efficiency (% of the N pool in mature leaves that is resorbed during senescence). The nitrogen resorption efficiency of Calamagrostis (about 80%) was higher than in the other three species (about 60%). Thus, climate change has only a minor impact on nutrient resorption parameters. However, given the substantial interspecific differences in these parameters, substantial changes in plant-soil feedbacks may be expected as a result of the observed changes in the species composition of high-latitude vegetation. These changes are species-specific and thus difficult to predict.

  • 17. Aerts, R.
    et al.
    Wallén, B.
    Malmer, N.
    Growth-limiting nutrients in Sphagnum-dominated bogs subject to low and high atmospheric nitrogen supply.1992In: Journal of Ecology, Vol. 80, no 1, p. 131-140Article in journal (Other academic)
  • 18. Aerts, R.
    et al.
    Wallén, B.
    Malmer, N.
    Caluwe, H.de.
    Nutritional constraints on Sphagnum-growth and potential decay in northern peatlands.2001In: Journal of Ecology, Vol. 89, no 2, p. 292-299Article in journal (Other academic)
  • 19. Afzelius, K.
    Apomixis in der Gattung Arnica.1936In: Svensk Botanisk Tidskrift, Vol. 30, p. 572-579Article in journal (Other academic)
  • 20. Agrell, I.
    An objective method for characterization of animal and plant communities1945In: Kungliga Fysiografiska Sällskapets Förhandlingar, p. 1-15Article in journal (Other academic)
  • 21. Agrell, I.
    Ein Artproblem in der Collembolengattung Folsomia1939In: Kungliga Fysiografiska Sällskapets Förhandlingar, Vol. 9, no 13, p. 14-Article in journal (Other academic)
  • 22. Agrell, I.
    Ein Vergleich zwischen Isotoma bipunctata Axelson und pallida-Formen von Isotoma notabilis Schäfer1939In: Kungliga Fysiografiska Sällskapets Förhandlingar, Vol. 9, no 14, p. 4-Article in journal (Other academic)
  • 23. Agrell, I.
    Kritisches Verzeichnis der schwedischen Collembolen mit einigen Neubeschreibungen und tiergeographischen Erörterungen1943In: Opuscula Entomologica, Vol. 8, p. 123-137Article in journal (Other academic)
  • 24. Agrell, I.
    The collemboles in nests of warm-blooded animals with a method for sociological analysis1945In: Kungliga Fysiografiska Sällskapets Handlingar, NF, Vol. 56, no 10, p. 1-19Article in journal (Other academic)
  • 25. Agrell, I.
    Zur Kenntnis der schwedischen Collembolen mit Beschreibung von vier neuen Arten und einigen Varietäten1939In: Opuscula Entomologica, Vol. 4, no 3-4, p. 159-168Article in journal (Other academic)
  • 26. Agrell, I.
    Zur Ökologie der Collembolen. Untersuchungen im schwedischen Lappland1941In: Opuscula Entomologica Suppl., Vol. 3, p. 236-Article in journal (Other academic)
  • 27. Ahlberg, P.
    Early Cambrian trilobites from mount Luopakte northern Sweden.1979In: Sveriges Geologiska Undersökning Serie, Vol. C 765, no 73(6), p. 3-12Article in journal (Other academic)
  • 28. Ahlberg, P.
    Early Cambrian trilobites from northern Scandinavia.1980In: Norsk Geologisk Tidskrift, Vol. 60, p. 153-159Article in journal (Other academic)
  • 29. Ahlberg, P.
    Lower Cambrian trilobites and biostratigraphy of Scandinavia.1984Student thesis
  • 30. Ahlberg, P.
    et al.
    Bergström, J.
    Lower Cambrian ptychopariid trilobites from Scandinavia.1978In: Sveriges Geologiska Undersökning Serie, Vol. Ca 49, p. 40-Article in journal (Other academic)
  • 31. Ahlberg, P.
    et al.
    Taylor, M.E
    Ptychopariid trilobites in the Lower Cambrian of Scandinavia.1981Conference paper (Other academic)
  • 32. Ahlbom, B.
    Fågellivet i Vadvetjåkka nationalpark.1971In: Fauna och flora, Vol. 66, no 6, p. 241-248Article in journal (Other academic)
  • 33. Ahlmann, H. W:son
    Excursion 1 a, to the north of Sweden (Stockholm-Boliden-Porjus-Sjöfallet-Kiruna-Abisko-Riksgränsen).1930Report (Other academic)
  • 34. Ahlmann, H. W:son
    Excursion vers le nord de la Suède.1930Report (Other academic)
  • 35. Ahlmann, H. W:son
    Glacier variations and climatic fluctuations.1953Report (Other academic)
  • 36. Ahlmann, H. W:son
    Guide pour les excursions 1 a, au départ de Skellefteå.1930Report (Other academic)
  • 37. Ahlmann, H. W:son
    Le niveau de glaciation comme fonction de l'accumulation d'humidité sous forme solide.1924In: Geografiska Annaler, Vol. 6, no 3-4, p. 223-272Article in journal (Other academic)
  • 38. Ahlmann, H. W:son
    Le régime des glaciers. Ses éléments, ses variations.1941In: Revue de Géeographie Alpine, Vol. 29, p. 537-556Article in journal (Other academic)
  • 39. Ahlmann, H. W:son
    Projet d'un programme de recherches glaciaires.1929In: Geografiska Annaler, Vol. 11, no (3-4), p. 313-320Article in journal (Other academic)
  • 40. Ahlmann, H. W:son
    Recent Glaciological Investigations in Sweden. - Union Geodésique et Géeophysique Internationale. Association Internationale d'Hydrologie Scientifique.1948In: Résumés des Rapports Scientifique, Vol. 1948, p. 119-122Article in journal (Other academic)
  • 41. Ahlmann, H. W:son
    et al.
    Lindblad, T.
    Die Grössenveränderungen des Kårsajökels in Schwedisch-Lappland.1940In: Geografiska Annaler, Vol. 22, no 1-2, p. 80-94Article in journal (Other academic)
  • 42. Ahlmann, H. W:son
    et al.
    Tryselius, O.
    Der Kårsagletscher in Schwedisch Lappland.1929In: Geografiska Annaler, Vol. 11, no 1, p. 1-32Article in journal (Other academic)
  • 43. Alatalo, J.M.
    Climate change: Impacts on structure and biodiversity of subarctic plant communities.1998Student thesis
  • 44.
    Alatalo, J.M.
    Department of Systematic Botany.
    Reproductive biology of Silene acaulis (Caryophyllaceae): Gender expression and potential impact of climate change.1996Student thesis
  • 45. Alatalo, J.M.
    et al.
    Totland, Ø.
    Responses to simulated climatic change in an alpine and subarctic pollen-risk strategist, Silene acaulis.1997In: Global Change Biology, Vol. 3, no Supplement 1, p. 74-79Article in journal (Other academic)
  • 46. Alatalo, Juha M.
    et al.
    Jägerbrand, Annika K.
    Chen, Shengbin
    Molau, Ulf
    Responses of lichen communities to 18 years of natural and experimental warming2017In: Annals of Botany, Vol. 120, no 1, p. 159-170Article in journal (Refereed)
  • 47. Alatalo, Juha M
    et al.
    Jägerbrand, Annika K
    Juhanson, Jaanis
    Michelsen, Anders
    Ľuptáčik, Peter
    Impacts of twenty years of experimental warming on soil carbon, nitrogen, moisture and soil mites across alpine/subarctic tundra communities2017In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7Article in journal (Refereed)
    Abstract [en]

    High-altitude and alpine areas are predicted to experience rapid and substantial increases in future temperature, which may have serious impacts on soil carbon, nutrient and soil fauna. Here we report the impact of 20 years of experimental warming on soil properties and soil mites in three contrasting plant communities in alpine/subarctic Sweden. Long-term warming decreased juvenile oribatid mite density, but had no effect on adult oribatids density, total mite density, any major mite group or the most common species. Long-term warming also caused loss of nitrogen, carbon and moisture from the mineral soil layer in mesic meadow, but not in wet meadow or heath or from the organic soil layer. There was a significant site effect on the density of one mite species, Oppiella neerlandica, and all soil parameters. A significant plot-scale impact on mites suggests that small-scale heterogeneity may be important for buffering mites from global warming. The results indicated that juvenile mites may be more vulnerable to global warming than adult stages. Importantly, the results also indicated that global warming may cause carbon and nitrogen losses in alpine and tundra mineral soils and that its effects may differ at local scale.

  • 48. Alatalo, Juha M.
    et al.
    Jägerbrand, Annika K.
    Molau, Ulf
    Climate change and climatic events: community-, functional- and species-level responses of bryophytes and lichens to constant, stepwise, and pulse experimental warming in an alpine tundra2014In: Alpine Botany, ISSN 1664-2201, E-ISSN 1664-221X, Vol. 124, no 2, p. 81-91Article in journal (Refereed)
    Abstract [en]

    We experimentally imposed three different kinds of warming scenarios over 3 years on an alpine meadow community to identify the differential effects of climate warming and extreme climatic events on the abundance and biomass of bryophytes and lichens. Treatments consisted of (a) a constant level of warming with open top chambers (an average temperature increase of 1.87 °C), (b) a yearly stepwise increase of warming (average temperature increases of 1.0; 1.87 and 3.54 °C, consecutively), and (c) a pulse warming, i.e., a single first year pulse event of warming (average temperature increase of 3.54 °C only during the first year). To our knowledge, this is the first climate change study that attempts to distinguish between the effects of constant, stepwise and pulse warming on bryophyte and lichen communities. We hypothesised that pulse warming would have a significant short-term effect compared to the other warming treatments, and that stepwise warming would have a significant mid-term effect compared to the other warming treatments. Acrocarpous bryophytes as a group increased in abundance and biomass to the short-term effect of pulse warming. We found no significant effects of mid-term (third-year) stepwise warming. However, one pleurocarpous bryophyte species, Tomentypnum nitens, generally increased in abundance during the warm year 1997 but decreased in control plots and in response to the stepwise warming treatment. Three years of experimental warming (all treatments as a group) did have a significant impact at the community level, yet changes in abundance did not translate into significant changes in the dominance hierarchies at the functional level (for acrocarpous bryophytes, pleurocarpous bryophytes, Sphagnum or lichens), or in significant changes in other bryophyte or lichen species. The results suggest that bryophytes and lichens, both at the functional group and species level, to a large extent are resistant to the different climate change warming simulations that were applied.

  • 49. Alatalo, Juha M
    et al.
    Jägerbrand, Annika K
    Molau, Ulf
    Impacts of different climate change regimes and extreme climatic events on an alpine meadow community2016In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 6Article in journal (Refereed)
    Abstract [en]

    Climate variability is expected to increase in future but there exist very few experimental studies that apply different warming regimes on plant communities over several years. We studied an alpine meadow community under three warming regimes over three years. Treatments consisted of (a) a constant level of warming with open-top chambers (ca. 1.9 °C above ambient), (b) yearly stepwise increases in warming (increases of ca. 1.0, 1.9 and 3.5 °C), and (c) pulse warming, a single first-year pulse event of warming (increase of ca. 3.5 °C). Pulse warming and stepwise warming was hypothesised to cause distinct first-year and third-year effects, respectively. We found support for both hypotheses; however, the responses varied among measurement levels (whole community, canopy, bottom layer, and plant functional groups), treatments, and time. Our study revealed complex responses of the alpine plant community to the different experimentally imposed climate warming regimes. Plant cover, height and biomass frequently responded distinctly to the constant level of warming, the stepwise increase in warming and the extreme pulse-warming event. Notably, we found that stepwise warming had an accumulating effect on biomass, the responses to the different warming regimes varied among functional groups, and the short-term perturbations had negative effect on species richness and diversity

  • 50. Alatalo, Juha M.
    et al.
    Jägerbrand, Annika K.
    Molau, Ulf
    Testing reliability of short-term responses to predict longer-term responses of bryophytes and lichens to environmental change2015In: Ecological Indicators, ISSN 1470-160X, E-ISSN 1872-7034, Vol. 58, no Supplement C, p. 77-85Article in journal (Refereed)
    Abstract [en]

    Abstract Environmental changes are predicted to have severe and rapid impacts on polar and alpine regions. At high latitudes/altitudes, cryptogams such as bryophytes and lichens are of great importance in terms of biomass, carbon/nutrient cycling, cover and ecosystem functioning. This seven-year factorial experiment examined the effects of fertilizing and experimental warming on bryophyte and lichen abundance in an alpine meadow and a heath community in subarctic Sweden. The aim was to determine whether short-term responses (five years) are good predictors of longer-term responses (seven years). Fertilizing and warming had significant negative effects on total and relative abundance of bryophytes and lichens, with the largest and most rapid decline caused by fertilizing and combined fertilizing and warming. Bryophytes decreased most in the alpine meadow community, which was bryophyte-dominated, and lichens decreased most in the heath community, which was lichen-dominated. This was surprising, as the most diverse group in each community was expected to be most resistant to perturbation. Warming alone had a delayed negative impact. Of the 16 species included in statistical analyses, seven were significantly negatively affected. Overall, the impacts of simulated warming on bryophytes and lichens as a whole and on individual species differed in time and magnitude between treatments and plant communities (meadow and heath). This will likely cause changes in the dominance structures over time. These results underscore the importance of longer-term studies to improve the quality of data used in climate change models, as models based on short-term data are poor predictors of long-term responses of bryophytes and lichens.

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