Research articles


78. Ylänne, H.,  Olofsson, J., Oksanen, L., and Stark, S. (2017). Consequences of grazer-induced vegetation transitions on ecosystem carbon storage in the tundra. Functional Ecology, in press.

Bottom-line: We show that the heavily grazed graminoid-dominated areas stored less C aboveground compared to the lightly grazed shrub-dominated areas. Yet, the consequences of grazing belowground varied between the sites: grazing did not alter organic soil C stocks at one of the sites, whereas at the other site, heavy grazing increased organic soil C stocks. Our results indicate that despite the negative impacts of grazers on aboveground C storage, their impact on belowground C may even be positive. We suggest that the site specific responses of organic soil C stocks to grazing are explained by the dominant plant functional types, and that the grazing-induced replacement of deciduous shrubs by graminoids could increase soil C sequestration.

77. Horstkotte, T., Utsi, T.Å, Larsson-Blind, A.,Bruggess, P., Johansen, P., Käyhkö, J., Oksanen, L. and Forbes, B.C. (2017). Human-animal agency in reindeer management: Sami herders’ perspectives on vegetation dynamics under climate change. Ecosphere 8(9):e01931.10.1002/ecs2.1931.

Bottom-line: Where the tree line has risen in elevation and/or latitude, herding practices have by necessity adapted to these changes. Exploiting the capacity of reindeer impacts on vegetation as a conservation tool offers time-tested adaptive strategies of ecosystem management to counteract a potential encroachment of the tundra by woody plants. However, novel solutions in environmental governance involve difficult trade-offs for ecologically sustainable, economically viable, and socially desirable management strategies.

76. Vuorinen, K.E.M., Oksanen, L.,  Oksanen, T.,  Pyykönen, A., Olofsson. J.,  and  Virtanen, R. 2017. Open tundra persist, but arctic features decline: vegetation changes in the warming Fennoscandian tundra. Global Change Biol. 2017: 1 –14. DOI: 10.1111/gcb.13710.

Bottom-line: The novel climate seems to favour competitive clonal species and species thriving in closed vegetation, creating a community hostile for seedling establishment, but equally hostile for many arctic species, too. Preventing trees and shrubs from invading the tundra is thus not sufficient for conserving arctic biota in the changing climate. The only dependable cure is to stop the global warming.

75. Hoset, K.H, Ruffino, L., Tuomi, M., Oksanen, T., Oksanen, L., Mäkynen, A., Johansen, B. and Moe, T. (2017). Changes in the spatial configuration and strength of trophic control across a productivity gradient during a massive rodent outbreak. Ecosystems

Bottom-line: Our results showed that spatio-temporal variation in trophic control also occurs in ecosystems structured according to the Exploitation Ecosystems Hypothesis, and emphasise the importance of long-term studies to capture non-linear and stochastic features that shape ecosystem functioning. In this context, the temporary release from top-down regulation in productive habitats caused strong grazing impacts that may be crucial for the resilience of tundra ecosystems under the threat of climate-change driven shrub encroachment.

74. Vindstad, O.P.L, Jepsen, J.U., Klinghardt, M., Ek, M. and Ims, R.A. (2017). Salvage logging of mountain birch after geometric outbreaks: Ecological context determines management outcomes. Forest Ecology and Management, 405 (2017), 8191.

Bottom-line: Logging may stimulate damaged mountain birch stands to recover by means of basal sprouting, but that the positive effects of logging may be reduced by browsing in some areas. Logging should also be practiced with care in rich meadow type stands, which have limited capacity for sprouting.


73. Jepsen, J.U., Vindstad, O.P.L, Barraquand, F., Ims, R.A., and Yoccoz, N.G. (2016). Continental scale travelling waves in forest geometrids in Europe: an evaluation of the evidence. J. Anim. Ecol. 85: 385390.

Bottom-line: A recent paper claims the presence of continental scale SE-NW travelling waves in geometrid moth outbreaks across Europe, and argue that the outbreak dynamics of moth in Fennoscandia, at the western end of the proposed wave, cannot be understood without taking this large-scale wave into account. In this Forum paper we strongly oppose this and argue that such large-scale travelling waves in European geometrids are unlikely. We further show that methodological pitfalls in the paper claiming such waves will have served to exaggerate the reported spatial patterns.

72. Virtanen, R., Oksanen, L., Oksanen, T., Cohen, J., Forbes, B.C., Johansen, B., Käyhkö, J., Olofsson, J., Pulliainen, J., and Tømmervik, H. (2016). Where do the treeless tundra areas of northern highlands fit in the global biome system: toward an ecologically natural subdivision of the tundra biome. Ecology and Evolution 6 (1): 143158. DOI: 10.1002/ece3.1837.

Bottom-line: Our analyses reveal that ecologically meaningful January–February snow and thermal conditions differ between different types of tundra. High precipitation and mild winter temperatures prevail on middle-latitude mountains, low precipitation and usually cold winters prevail on high-latitude tundra, and Scandinavian mountains show intermediate conditions. Additionally, our analyses based on climate and vegetation criteria thus seem to resolve the long-standing biome delimitation problem, help in consistent characterization of research sites, and create a basis for further biogeographic and ecological research in global tundra environments.

71. Keskitalo, E.C.H, Horstkotte, T., Kivinen, S., Forbes, B., and Käyhkö, J. (2016). "Generality of mis-fit"? The real-life difficulty of matching scales in an interconnected world. Ambio. DOI: 10.1007/s13280-015-0757-2.

Bottom-line: We illustrate the complexities inherent in the management of social-ecological systems (SES), which are composed of a multitude of scales and their hierarchical levels, especially when several land users with different priorities are involved. We suggest that a ‘generality of mis-fit’ between these scales and their levels are a rule rather than the exception in the governance of SES. The dilemma of “managing mis-fit” could be a more realistic governance challenge, rather than efforts to create idealistic outcomes.

70. Ruffino, L., Oksanen, T., Hoset, K.S., Tuomi, M., Oksanen, L., Korpimäki, E., Bugli, A., Hobson, K.A., Johansen, B., and Mäkynen A. (2016). Predator-rodent-plant interactions along a coast-inland gradient in Fennoscandian tundra. Ecography. DOI: 10.1111/ecog.01758.

Bottom-line: During a massive rodent outbreak in northern Fennoscandia, rodent grazing impact on tundra vegetation (including dwarf shrubs) was uniformly strong along a coast-inland gradient (0-35 km), suggesting that the input of marine subsidies to rodent predators in coastal tundra areas did not trigger a trophic cascade and cause variation in the strength of rodent-plant interactions between coastal and inland tundra areas.


69. Ménard, C.B., Ikonen, J., Rautiainen, R., Aurela, M., Arslan, A.N., and Pulliainen, J. (2015). Effects of Meteorological and Ancillary Data, Temporal Averaging, and Evaluation Methods on Model Performance and Uncertainty in a Land Surface Model. Journal of Hydrometeorology, 16 (6): 2559–2576.DOI:

Bottom-line: Meteorological data are the largest source of uncertainty; differences in ancillary data have little effect on model results. Although generally informative and representative, aggregated performance metrics fail to identify “right results for the wrong reasons”; to do so, scrutinizing of time series and of interactions between variables is necessary.

68. Kvist, L., Aminian, L., Rouger, R., Kreivi, M., Laurila, M., Hyvärinen, M., Aspi, J., and Markkola, A.M. (2015). A climatic relict or a long distance disperser: conservation genetics of an Arctic disjunct polyploid plant. Conservation Genetics (in press).

Bottom-line: The Primula sibirica group is a set of a dozen Arctic, taxonomically unrelated plant species that share a similar disjunct distribution on the shores of the Arctic Ocean and the northernmost part of the Baltic Sea. We found that the Bothnian Bay population of the graminoid Puccinellia phryganodes is differentiated from the geographically closest populations on the shores of the Arctic Ocean and the White Sea. Puccinellia phryganodes is more likely a climatic relict in the Bothnian Bay than a long-distance disperser.  Endangered Bothnian Bay population should be considered as an evolutionary significant unit rather than a mere representative of the main population.

67. Markkola A.M., Saravesi K., Aikio, S., Taulavuori, E., and Taulavuori, K. (2015). Light-driven host-symbiont interactions under hosts' range shifts caused by global warming: A review. Environmental and Experimental Botany (in press). DOI: 10.1016/j.envexpbot.2015.05.009.

Bottom-line: We highlight the importance of a changing light environment in plant range shifts under conditions of global warming. Although distinct clinal responses to light quality have not been earlier reported, some studies have shown that northern ecotypes are more sensitive to changes in light quality. Northern light environment may significantly modify competition between plant species and within photoperiodic ecotypes, if predicted rapid range shifts of forest trees are realized. Southern photoperiodic ecotypes of forest trees migrating northward will encounter both changed light quality and a different photoperiod. Our special focus is on carbon economy and biomass partitioning between the autotrophic hosts and heterotrophic ectomycorrhizal fungal (EMF) symbionts, reciprocally dependent on each other.

66. Saccone P. and Virtanen R. (2015). Extrapolating multi-decadal plant community changes based on medium-term experiments can be risky: evidence from high-latitude tundra. Oikos. DOI: 10.1111/oik.02399.

Bottom-line: This paper is a novel contribution about the risk of misinterpretation of the results from short-term experiments. The monitoring of tundra heath composition under press experimental treatments showed that both treatment effects and plant response can operate at different time scales making the short and even medium term experiment poor predictors of long-term community responses.

65. Stark, S. and Ylänne H. (2015). Grazing in Arctic peatlands – an unknown agent in the global carbon budget. Environmental Research Letters, 10: 051002. DOI: 10.1088/1748-9326/10/5/051002.

Bottom-line: This perspective aims to sum up studies on the consequences of grazing on peatland carbon balance. The perspective presents different scenarios how warming or grazing may alter the fixing and release of carbon dioxide and methane through altering the abundance of certain plant functional groups.

64. Ylänne, H., Stark, S., and Tolvanen, A. (2015). Vegetation shift from deciduous to evergreen dwarf shrubs in response to selective herbivory offsets carbon losses: evidence from 19 years of warming and simulated herbivory in the sub-arctic tundra. Global Change Biology, 21: 3696–3711.

Bottom-line: On nutrient poor sites increased herbivore pressure does not alter the warming induced increase in total ecosystem C stocks. However, through a vegetation shift from deciduous to evergreen shrubs, selective herbivory increased C allocation from below-ground stocks to vegetation in a warmer tundra climate.

63. Björkman, C. and Niemelä, P., eds. (2015). Climate Change and Insect Pests. CABI Climate Change Series 7. 279 pp.

Bottom line: Climate change and insect pests sums up present knowledge regarding both agricultural and forest insect pests and climate change in order to identify future research directions.

62. Saravesi, K., Aikio, S., Wäli, P.R., Ruotsalainen, A.L., Kaukonen, M., Huusko, K., Suokas, M., Brown, S.P., Jumpponen, A., Tuomi, J., and Markkola, A.M. (2015). Moth outbreaks alter root-associated fungal communities in subarctic mountain birch forests. Microbial Ecology 69(4): 788797. DOI: 10.1007/s00248-015-0577-8.

Bottom line: Moth outbreaks caused profound changes in functional and taxonomic community composition of root-associated fungi of the host tree, mountain birch.
Most severe defoliation during several growing seasons reduced biotrophic mycorrhizal fungi by 70–80 %, while saprotrophic and endophytic fungi increased. Moth herbivory also reduced dominance of Basidiomycota in the roots due to loss of basidiomycete EMF and increases in functionally unknown Ascomycota. Our results demonstrate the top-down control of belowground fungal communities by moth herbivory and suggest a marked reduction in the carbon flow from plants to soil fungi following defoliation.

61. Vindstad, O.P.L., Jepsen, J.U. and Ims, R.A. (2015). Resistance of a sub-arctic bird community to severe forest damage caused by geometrid moth outbreaks. European Journal of Forest Research 134(4): 725–736. DOI:10.1007/s10342-015-0886-y.

Bottom line:
This study shows that the abundance and species richness of passerine birds differs little between mountain birch forest that has suffered extensive mortality due to geometrid moth outbreaks and healthy undamaged forest. This suggests that bird communities have high resistance to the habitat disturbance caused by outbreaks.

60. Kaarlejärvi, E., Hoset, K.S. and Olofsson, J. (2015). Mammalian herbivores confer resilience of Arctic shrub-dominated ecosystems to changing climate. Global Change Biology, DOI:10.1111/gcb.12970.

Bottom line:
This paper shows that herbivores can facilitate resilience of forest-tundra ecosystems by returning shrub-dominated vegetation back to its original low-biomass regime after a warm period, while in absence of herbivores shrub biomass continued to increase even over a subsequent colder period.


59. Saccone, P., Pyykkönen, T., Eskelinen, A., and Virtanen R. (2014). Environmental perturbation, grazing pressure and soil wetness jointly drive mountain tundra toward alternative states. Journal of Ecology, 102: 16611672. DOI: 10.1111/1365-2745.12316.

Bottom line:
paper highlights the importance of multiple drivers for plant community responses to environmental changes. The long-term divergence of tundra heath communities under contrasted level of grazing pressure in different environmental conditions was analyzed through the lens of Alternative Stable States framework. The results showed that the joint effects of multiple drivers can lead tundra heath toward alternative trajectories and equilibrium.

58. Kaarlejärvi E. & Olofsson J. (2014). Concurrent biotic interactions influence plant performance at their altitudinal distribution margins. Oikos, 123: 943–952.
Bottom line: Large mammalian grazers may counteract the anticipated warming-induced distribution shifts by reducing competition at the lower margins of high-altitude tundra forbs.
57. Väisänen M., Ylänne H., Kaarlejärvi E., Sjögersten S., Olofsson J., Crout N. & Stark S. (2014). Consequences of warming on tundra carbon balance determined by reindeer grazing history. Nature Climate Change, 4, 384–388.
Bottom line: Heavily grazed tundra dominated by graminoids is weaker sink of carbon compared to lightly grazed shrub dominated tundra. Warming decreased C sink of shrub dominated tundra, but had no effect on heavily grazed tundra.
56. Ruffino, L. & Oksanen, T. (2014). Coevolution of jaegers (Stercorarius spp.) and arctic lemmings (Dicrostonyx spp. and Lemmus spp.) and the formation of the jaeger guild: an hypothesis. Evolutionary Ecology Research 16: 121–132.
Bottom line: Similarities between long-tailed and Pomarine jaegers can be understood as consequences of convergent evolution when the ancestors of these species shifted from purely cleptoparasitic (long-tailed jaeger) or predatory (Pomarine jaeger) niches to a niche combining cleptoparasitism in non-breeding season with predation on lemmings in breeding season.
55. Saccone, P., Pyykkönen, T., Eskelinen, A. & Virtanen, R. (2014). Environmental perturbation, grazing pressure and soil wetness jointly drive mountain tundra toward divergent alternative states. Journal of Ecology (in press). DOI:10.1111/1365-2745.12316.
Bottom line: Our long-term experiment reveals that environmental perturbation, grazing and soil wetness exhibit joint effects that induce divergent trajectories of tundra plant communities. We suggest that a strong environmental perturbation triggers mountain tundra heath community to move away from its equilibrium state. The outcome of this shift depends on the interplay between grazing pressure and soil wetness that drive tundra plant communities toward divergent alternative states.
54. Vindstad, O.P.L., Schultze. S., Jepsen, J.U., Biuw, M., Kapari, L., Sverdrup-Thygeson, A. & Ims, R.A. (2014). Numerical Responses of Saproxylic Beetles to Rapid Increases in Dead Wood Availability following Geometrid Moth Outbreaks in Sub-Arctic Mountain Birch Forest. Plos One 9: DOI:10.1371/journal.pone.0099624.
Bottom line: The paper addresses the cascading effects of the massive moth outbreaks and resulting birch forest death, on one of the most important groups of dead wood decomposers; saproxylic beetles. Five years after the moth outbreak the numeric response of saproxylics remains weak possibly due to satiation effects. This suggests that saproxylic beetles so far play a minor role in decomposing the enormous quantities of dead wood left by moth outbreaks in this system, and places a correspondingly greater emphasis on the role of microbial decomposers.
53. Biuw, M., Jepsen J.U., Cohen, J., Markkola, A., Aikio, S., Ahonen, S., Wäli, P.R., Tejesvi, M., Vindstad, O.P.L., Niemelä, P. & Ims, R.A. (2014). Long-term impacts of contrasting management of large ungulates in the arctic tundra-forest ecotone: Ecosystem structure and climate feedback. Ecosystems 17 (5): 890–905.
Bottom line: The long-standing differences in reindeer herding practices in Norway and Finland modify forest and shrub layer structure in treeline habitat to an extent that is sufficient to significantly influence the surface energy balance through changes in snow cover, spring season albedo and summer NDVI.
52. Taulavuori K., Taulavuori, E. & Sheppard, L. J. (2014) Truths or myths, fact or fiction, setting the record straight concerning nitrogen effects on levels of frost hardiness. Environmental and Experimental Botany 106:132–137.
Bottom line: This paper reviews on nitrogen effects on plants frost hardiness, and indicates that nitrogen may have positive effects on it. The myth is broken!
51. Kivinen, S. and Rasmus, S. (2014). Observed cold season changes in a past Fennoscandian fell area over the past three decades.   AMBIO: a journal of the human environment, DOI:10.1007/s13280-014-0541-8.
Bottom line: Shortened duration of snow cover may facilitate reindeer grazing, whereas potentially more frequent formation of ice layers and mold growth on pastures in the future is disadvantageous for reindeer husbandry.
50. Ménard, C.B., Essery, R. and Pomeroy, J. (2014). Modelled sensitivity of the snow regime to topography, shrub fraction and shrub height. Hydrology and Earth System Sciences, 18, 23752392.
Bottom line: To avoid overestimating the effect of shrub expansion on the energy budget of the Arctic, future large-scale investigations should consider wind redistribution of snow, shrub bending and emergence, and sub-grid topography as they affect the variability of snow cover.
49. Hoset, K.S., Kyrö, K., Oksanen, T., Oksanen, L. and Olofsson, J. (2014). Spatial variation in vegetation damage relative to primary productivity, small rodent abundance and predation. – Ecography 37 (9): 894–901, DOI:10.1111/ecog.00791.
Bottom line: Predators influence the plant community via a trophic cascade in a spatial pattern that support the exploitation ecosystems hypothesis. The responses to grazing also differ between plant functional groups, with implications for short and long-term consequences for plant communities.
48. Hunter, M.D., Kozlov, M.V., Itämies, J., Pulliainen, E., Bäck, J., Kyrö, E.-M. and Niemelä, P. (2014). Current temporal trends in moth abundance are counter to predicted effects of climate change in an assemblage of subarctic forest moths. – Global Change Biology, 20 (6): 1723–1737.
Bottom line: Populations of subarctic forest moths in Finland are performing better than expected, and their populations appear buffered at present from potential deleterious effects of climate change by other ecological forces.
47. Kaarlejärvi, E. (2014). The role of herbivores in mediating responses of tundra ecosystems to climate change. – PhD thesis, Umeå University (Sweden).
Bottom line: Herbivores counteract the effects of climate warming by slowing down or preventing vegetation changes in tundra.
46. Olofsson, J., Oksanen, L., Oksanen, T., Tuomi, M., Hoset, K.S., Virtanen, R. and Kyrö, K. (2014). Long-term experiments reveal strong interactions between lemmings and plants in the Fennoscandian highland tundra. - Ecosystems, OnlineFirst.
Bottom line: Palatability is a poor predictor of long-term responses of plants to excluding herbivores.
45. Iversen, M., Fauchald, P., Langeland, K., Ims, R.A., Yoccoz, N.G. & Bråthen, K.A. (2014). Phenology and Cover of Plant Growth Forms Predict Herbivore Habitat Selection in a High Latitude Ecosystem. PlosOne 9 (6) DOI:10.1371/journal.pone.0100780.
Bottom line: This paper examines seasonal reindeer habitat use as a function of forage quality and quantity measured as phenology and cover of growth forms of varying palatability. Reindeer show a diminishing selectivity in habitat use from being governed primarily by forage quality (early phenology) early in the  season, to foreage quantity (cover) late in the season.
44. Ravolainen, V.T., Kolstrøm, J., Bråthen, K.A., Yoccoz, N.G., and Ims, R.A., (2014). Complementary impacts of small rodents and ungulates limit tall shrub expansion in tundra. Ravolainen, V.T., Kolstrøm, J., Bråthen, K.A., Yoccoz, N.G., and Ims, R.A., (2014). Complementary impacts of small rodents and ungulates limit tall shrub expansion in tundra. Journal of Applied Ecology 51: 234–241.
Bottom line: Sympatric populations of reindeer and rodents have strongly complementary impacts on shrub recruits and may limit the expansion of shrubs even in the most productive habitats of arctic tundra.
43. Soininen, E. M.,  Ehrich, D., Lecomte, N.,Yoccoz, N.G.,  Tarroux, A.,  Berteaux, D., Gauthier,G., Gielly, L., Brochmann, C., Gussarova, G. & Ims, R.A. (2014). Sources of variation in small rodent trophic niche: new insights from DNA metabarcoding and stable isotope analysis. Isotopes in Environmental and Health Studies, 50: 361–381.
Bottom line: The paper addresses the effects of competition on the trophic niche of rodents in tundra habitats. It was found that the main effect of competition was an increased use of secondary habitats, rather than an expansion of the trophic niche in primary habitats.
42. Legagneux, P., Gauthier, G., Lecomte, N., Schmidt, N.M, Reid, D., Cadieux, M-C., Berteaux, D., Bêty, J., Krebs, C.J., Ims, R.A., Yoccoz, N.G., Morrison, R.I.G., Leroux. S.J., Loreau, M. & Gravel, D. (2014). Climate and body-size shape structure and functioning of arctic ecosystems. Nature Climate Change 4: 379–383.
Bottom line: This circumpolar study examines the effects of climate on tundra primary productivity, food-web structure and species interaction strength. Temperature significantly influenced both intensity of predation and species interactions. This highlights the potential for a climate change induced switch from bottom-up to top-down regulation of herbivores in tundra ecosystems.


41. Callaghan, T.V., Jonasson, C., Thierfelder, T., Zhenlin, Y., Hedenås, H., Johansson, M., Molau, U., Van Bogaert, R., Michelsen, A., Olofsson, J., Gwynn-Jones, D., Bokhorst, S., Phoenix, G., Bjerke, J.W., Tømmervik, H., Christensen, T.R., Edward, H., Koller, E. and Sloan, V.L. (2013). Ecosystem change and stability over multiple decades in the Swedish sub-Arctic: complex processes and multiple drivers. – Philosophical Transactions of the Royal Society B-Biological Sciences, 2013, 368, 20120488; DOI:10.1098/rstb.2012.0488.
Bottom line: Reindeer grazing regimes and landuse changes contribute to many of the vegetation changes that have been recorded during the last century in the Abisko region.
40. Cohen, J., Pulliainen, J., Ménard, C.B., Johansen, B., Oksanen, L., Luojus, K. and Ikonen, J. (2013). Effect of reindeer grazing on snowmelt, albedo and energy balance based on satellite data analyses. – Remote Sensing of Environment 135: 107117.
Bottom line: The impact of summer grazing by reindeer on tundra vastly increases surface albedo in March-May, delaying snow melt and counteracting global warming.

39. Huttunen, L., Ayres, M.P., Niemelä, P., Heiska, S., Tegelberg, R., Rousi, M. and Kellomäki, S. (2013). Interactive effects of defoliation and climate change on compensatory growth of silver birch seedlings. – Silva Fennica, 47 (3): article id 964.
Bottom line: Under warmer growing conditions, lower early-season leaf and fine root carbohydrate concentrations of previously defoliated trees cannot be used as indicators of aboveground growth.
38. Huttunen, L., Blade, J.D., Li, T., Rousi, M. and Klemola, T. (2013). Effects of warming climate on early-season carbon allocation and height growth of defoliated mountain birches. – Plant Ecology, 214: 373383.
Bottom line: Thermal sum accumulation does not greatly promote the recovery of mountain birches, Althoug damaged trees produced more leaves at warmer growing sites, this did not increase their height growth or carbohydrate gain.
37. Huttunen, L., Markkola A-M., Saravesi, K. and Niemelä, P. (2013). Do elevations in temperature, CO2, and nutrient availability modify belowground carbon gain and root morpohology in artifically defiliated silver birch seedlings? – Ecology and Evolution 9: 27832794.
Bottom line: Under a realistic scenario of concurrent increases in temperature and CO2, as well as nutrient availability, the effect of defoliation on belowground carbon gain in silver birch seedlings is marginal.
36. Jepsen, J.U., Biuw, M., Ims, R.A., Kapari, L., Schott, T., Vindstad, O.P.L., and Hagen, S.B. (2013). Ecosystem impacts of a range expanding forest defoliator at the forest-tundra ecotone. – Ecosystems 16: 561575.
Bottom line: Moth outbreaks at the forest-tundra ecotone change field layer from dwarf-shrub dominated to grass-dominated. The shift in the understory vegetation causes cascading impact on herbivores; the abundance of grass eating rodents is facilitated, whereas reindeer avoid impacted forests.
35. Johansen, B. and Tømmervik, H. (2013). The relationship between phytomass, NDVI and vegetation communities on Svalbard. – Int. J. Appl. Earth Observ. Geoinf. 27: 2030.
Bottom line: We established a linear relationship between NDVI and field-recorded phytomass on Svalbard, Arctic Norway and used it to estimate the total plant phytomass for the entire Nordenskjöld peninsula.
34. Kaarlejärvi, E., Eskelinen, A. and Olofsson, J. (2013). Herbivory prevents positive responses of lowland plants to warmer and more fertile conditions at high altitudes. – Functional Ecology, 27: 12441253.
Bottom line: Reindeer grazing can prevent thermophilic species from expanding to higher altitudes.
33. Karlsen, S.R., Jepsen, J.U., Odland, A., Ims, R.A. and Elvebakk, A. (2013). State-dependent shifts in plant communities following an insect outbreak range expansion across the birch forest-tundra ecotone in northern Fennoscandia. – Oecologia 173: 859870.
Bottom line: Moth outbreaks at the forest-tundra ecotone cause drastic vegetation state changes from dwarf-shrub dominated to grass-dominated communities. The extent of change depends on the initial state of the forest and will have implications for ecosystem productivity.
32. Kaukonen, M., Ruotsalainen, A.L., Wäli, P.R., Männistö, M., Setälä, H., Saravesi, K., Huusko, K. and Markkola, A-M. (2013). Moth herbivory enhances resource turnover in subarctic mountain birch forests? – Ecology 94: 267272.
Bottom line: Massive moth herbivory in subarctic mountain birch forests is suggested to enhance resource turnover and provide an early-season shortcut for carbon and nutrients from green foliage to soil organisms. This shortcut largely bypasses the main routes of carbon from trees to soil via mycorrhizal and litter-decomposing fungi.
31. Kauppinen, M., Raveala, K, Wäli, P.R. and Ruotsalainen, A.L. (2013). Contrasting preferences of arbuscular mycorrhizal and dark septate fungi colonizing Avenella flexuosa. – Mycorrhiza, OnlineFirst 24 (3): 171–177, DOI:10.1007/s00572-013-0526-7.
Bottom line: AM and DSE root fungal colonizations of the grass Avenella flexuosa responded differently to site conditions (boreal vs. subarctic, humus thickness, openness).
30. Oksanen T., Oksanen L., Söderbacka G., Hoset K.S., Ruffino L. and Tuomi M. (2013). Impact of marine-subsidized predators on lemming-plant oscillations. – Ecology Research 15: 124.
Bottom line: Marine-based predators can modify lemming-plant oscillations; their impact varies geographically and also infleunces the survival strategies of lemmings.
29. Olofsson, J., te Beest, M. and Ericson, L. (2013). Complex biotic interactions drive long-term vegetation dynamics in a subarctic ecosystem. – Philosophical Transactions of the Royal Society B-Biological Sciences 368: 20120486.
Bottom line: Vegetation changes in subarctic tundra are primarily driven by herbivores (reindeer, moth, rodents) not by direct climatic effects.
28. Taulavuori, K., Laine, K. and Taulavuori, E. (2013). A review: Experimental studies on Vaccinium species in relation to air pollution and global change. – Environmental and Experimental Botany 87: 191196.
Bottom line: Objective was to make an overview of studies of abiotic stress related to global change on the above species, and discuss the reported effects of these environmental factors. These issues include nitrogen, heavy metals, radionuclides, salt, ozone, carbon dioxide, warming climate, declining snow cover, periodic droughts, fire and elevated UV radiation. The findings suggest that both species are relatively tolerant to many abiotic environmental stresses. However, the reports demonstrated that both have species-specific areas of weakness: (1) V. myrtillus is susceptible to stress caused by warming winter, and (2) frost hardiness of V. vitis-idaea may be reduced under enhanced UV radiation.
27. Tejesvi, M.V., Sauvola, T., Pirttilä, A.M. and Ruotsalainen, A.L. (2013). Neighbouring Deschampsia flexuosa and Trientalis europaea harbor contrasting root fungal endophyte communities. – Mycorrhiza 23: 110.
Bottom line: Despite their co-occurrence, two forest understory plants harbor distinctively different root fungal endophytic communities. This may be attributed to different host life-cycles. Although this study is made in boreal zone, these plants are common tundra plants, and this work increases the basic knowledge on the ecology and role of their root-associated symbionts.
26. Virtanen, R., Grytnes, J.-A., Lenoir, J., Oksanen, J., Oksanen, L., and Svenning, J.-C. (2013). Productivity-diversity patterns in arctic tundra vegetation. – Ecography 36: 331341.
Bottom line: High arctic communities are characterized by high botanical diversity, whereas the southernmost subzone of the tundra has low diversity in all spatial scales; hence already the change from open swards to low arctic scrublands would spell the demise of arctic botanical biodiversity.

25. Wäli, P.P., Wäli, P.R., Saikkonen, K. and Tuomi, J. (2013). Is the Pathogenic Ergot Fungus a Conditional Defensive Mutualist for Its Host Grass? – PlosOne 8(7): e69249, DOI:10.1371/journal.pone.0069249.
Bottom line: Ergot fungus may serve as a conditional defensive mutualist in grasses against mammal grazing; pathogenic interaction may range from antagonistic to mutualistic.
24. Xu, L., Myneni, R.B., Chapin III,F.S., Callaghan, T.V., Pinzon, J.E., Tucker, C.J., Zhu, Z., Bi1, J., Ciais, P., Tømmervik, H., Euskirchen, E.S., Forbes, B.C., Piao, S.L., Anderson, B.T., Ganguly, S., Nemani, R.R., Goetz, S.J., Beck, P.S.A., Bunn, A.G., Cao, C. and Stroeve, J.C. (2013). Temperature and vegetation seasonality diminishment over northern lands. – Nature Climate Change, DOI:10.1038/NCLIMATE1836.
Bottom line: Analysis of circumpolar NDVI data reveals a latitudinal shift equatorward of temperature and seasonanilty during the past 30 years equivalent to be between 4° and 7°. Thus the key parameters differentiating summer and winter conditions at high northern latitudes are diminishing fast.
23. Zeng, H., Jia, G.S. and Forbes, B.C. (2013). Response of phenological shifts to climate and anthropogenic factors as detected from multi-satellite data. – Environmental Research Letters, DOI:10.1088/1748-9326/8/3/035036.
Bottom line: Results from the latest NDVI3g data set show that during 20002010 on Yamal Peninsula, West Siberia, there has been an earlier start of the growing season, later end of the growing season, longer length of the growing season, and greater MaxNDVI from north to south in the region.



22. Bosiö, J., Johansson, M., Callaghan, T.V., Johansen, B. and Christensen, T.R (2012). Future vegetation changes in thawing subarctic mires and implications for greenhouse gas exchange - a regional assessment. – Climatic Change 115: 379398, DOI:10.1007/s10584-012-0445-1.
Bottom line: Palsa mires will change rapidly over the coming decades with a 97 % reduction in dry hummock areas by 2041–2060, which will increase the release of greenhouse gasses.
21. Ehrich, D., Henden, J.A. and Ims, R.A. (2012). The importance of willow thickets for ptarmigan and hares in shrub tundra: the more the better? – Oecologia 168: 141151.
Bottom line: Across the Eurasian tundra zone medium-sized herbivores (hares and willow ptarmigan) differ in occurrence in willow shrub habitats in response to willow shrub cover and configuration (a functional response). This highlights the need for large-scale assessments for understanding the cascading impacts of shrub expansion in tundra ecosystems.
20. Eskelinen, A., Harrison, S. and Tuomi, M. (2012). Plant traits mediate consumer and nutrient control on plant community productivity and diversity. – Ecology 93: 27052718.
Bottom line: Plant traits provide improved understanding of the impact of consumers and nutrients on plant community productivity and diversity.
19. Huttunen, L., Niemelä, P., Ossipov, V., Rousi, M. and Klemola, T. (2012). Do warmer growing seasons ameliorate the recovery of mountain birches after winter moth outbreak? – Trees 26: 809819.
Bottom line: Thermal sum accumulation does not greatly promote the recovery of mountain birches.
18. Ims, R.A. and Henden, J.A. (2012). Collapse of an arctic bird community resulting from ungulate-induced loss of erect shrubs. – Biol. Cons. 149: 25.
Bottom line: Changes in the extent of thicket-forming shrubs in tundra habitats have direct implications for the species richness in arctic tundra bird communities.
17. Kaarlejärvi, E., Baxter, R., Hofgaard, A., Hytteborn, H., Khitun, O., Molau, U., Sjögersten, S., Wookey, P. and Olofsson, J. (2012). Effects of warming on shrub abundance and chemistry drive ecosystem level changes in a forest-tundra ecotone. – Ecosystems 15: 12191233.
Bottom line: Shrub abundance will increase with warming, and resultant alterations in plant community composition will decrease in community-level nutrient concentrations.
16. Kapfer, J., Virtanen, R. and Grytnes, J.-A. (2012). Changes in Arctic vegetation on Jan Mayen Island over 19 and 80 years. – Journal of Vegetation Science 23: 771781.
Bottom line: Recent climate warming has caused shifts in tundra plant communities in past few decades and show tendecies for increased dominance of arctic woody plants, where herbaceous species linked to tundra snowbeds decreased.
15. Karlsen, S.R, Ramfjord, H., Høgda, K.A., Johansen, B., Danks, F. and Brobakk, T.E. (2012). A satellite-based map of onset of birch (Betula) flowering in Norway. – Aerobiologia 25(1): 1525.
Bottom line: There are large differences in the timing of birch flowering along the north–south and altitude gradients in Norway.
14. Lenoir, J., Virtanen, R., Oksanen, J., Oksanen, L., Luoto, M., Grytnes, J.-A., and Svenning, J.-C. (2012). Dispersal ability links to cross-scale species diversity patterns across the Eurasian arctic tundra. – Global Ecology and Biogeography 21: 851860.
Bottom line: Arctic plants have vastly different abilities to disperse to suitable sites; bryophytes and lichens are good dispersers, whereas most vascular plants are not, making them much vulnerable to climate change.
13. le Roux, P.C., Virtanen, R., Heikkinen, R.K, and Luoto, M. (2012). Biotic interactions affect the elevational ranges of high-latitude plant species. – Ecography 35: 10481056.
Bottom line: Climate warming impacts of tundra plant distributions depend on interspecific interactions.
12. Macias Fauria, M., Forbes, B.C., Zetterberg, P. and Kumpula, T. (2012). Eurasian Arctic greening reveals teleconnections and the potential for structurally novel ecosystems. – Nature Climate Change 2: 613–618.
Bottom line: Erect willow and alder shrubs that avoid heavy ungulate browsing have grown to the height of small trees (2 to 2.5 m) in the past 30+ years, representing an in situ transition of low scrubland to deciduous woodland.
11. Menard, C. B., Essery, R., Pomeroy, J., Marsh, P. and Clark, D. B. (2012). A shrub bending model to calculate the albedo of shrub-tundra. – Hydrological Processes, DOI:10.1002/hyp.9582.
Bottom line: A physical model to describe the albedo of shrub-tundra was developed. The model is further applied to the analysis of vegetation effects to energy balance in the Tundra project.
10. Metsämäki, S., Mattila, O.-P., Pulliainen, J., Niemi, K., Luojus, K. and Böttcher, K. (2012). An optical reflectance model-based method for fractional snow cover mapping applicable to continental scale. – Remote Sensing of Environment 123: 508521.
Bottom line: Presentation and performance assessment of satellite data retrieval methodology applied in the determination of snow melt in paper Cohen et al. (2013) for the analysis of reindeer herding practices to tundra energy balance.
9. Olofsson, J., Tommervik, H. and Callaghan, T.V. (2012). Vole and lemming activity observed from space. – Nature Climate Change 2: 880883.
Bottom line: Voles and lemmings drive cycles in plant abundance, strong enough to be recorded from satellites. This is important for understanding how strong the counteracting effect of herbivory on climatic changes can be.
8. Pajunen, A., Virtanen, R. and Roininen, H. (2012). Browser mediated impacts of shrub canopy on understorey vegetation. – Oikos 121: 15441552.
Bottom line: Tundra shrub abundance is linked with plant diversity. Forb abundance was positively associated with shrubs; low growing lichens and bryophytes decline if shrubs increase.
7. Rautiainen, K., Lemmetyinen, J., Pulliainen, J., Vehviläinen, J., Drusch, M., Kontu, A., Kainulainen, J. and Seppänen, J. (2012). BL-Band radiometer observations of soil processes at boreal and sub-arctic environments. – IEEE Transactions on Geoscience and Remote Sensing 50: 14831497.
Bottom line: Development of methodology to map soil frost and thaw processes for arctic to boreal regions using satellite data. Time-series of circumpolar behavior of soil frost will be provided for the Tundra project using the developed methodology.
6. Saikkonen, K., Taulavuori, K., Hyvönen, T., Gundel, P.E., Hamilton, C.E., Vänninen, I., Nissinen, A. and Helander, M. (2012). Climate change-driven species' range shifts filtered by photoperiodism. – Nature Climate Change 2: 15.
Bottom line: Adaptations to photoperiods may result in mistiming of phenology, and thus constraining the climate change driven species' range shifts.
5. Taulavuori, K., Taulavuori, E., Suokanerva, Lakkala, K.H., Huttunen, S. and Laine, K. (2012). Decreased frost hardiness of Vaccinium vitis-idaea in reponse to UV-A radiation. – Physiologia Plantarum 145: 516526.
Bottom line: Studies from several years were collected to compare responses different life forms (deciduous and evergreen tree; deciduous and evergreen dwarf shrub). The results provide evidence that frost hardiness of Vaccinium vitis-idaea is suffering from UV radiation, especially UV-A radiation.
4. Tømmervik, H., Bjerke, J.W., Gaare, E., Johansen, B. and Thannheisser, D. (2012). Rapid recovery of recently overexploited winter grazing pastures for reindeer in Northern Norway. – Fungal Ecology 5(1): 3–15.
Bottom line: Fluctuation in lichen vegetation from dense lichen carpets to severely depleted ground and back again to flourishing lichen-dominated vegetation document high capacity of lichens to respond to changes in grazing pressure.


3. Estes, J.A., Terborgh, J., Brashares, J.S., Power, M.E., Berger, J., Bond, W.J. Carpenter, S.R., Essington, T.E., Holt, R.D., Jackson, J.B.C., Marquis, R.J., Oksanen, L., Oksanen, T., Paine, R.T., Pikitch, E.K., Ripple, W.J., Sandin, S.A., Scheffer, M. Schoener, T.W., Shurin, J.B., Sinclair, A.R.E., Soule, M.E., Virtanen, R. and Wardle, D.A. (2011). Trophic Downgrading of Planet Earth. – Science 333: 301306.
Bottom line: All kinds of food chains are characterized by strong, cascading connections between the top and the basal organisms. Thus, food chain manipulations are a viable option to preserve open landscapes with prostrate vegetation.
2. Olofsson, J., Ericson, L, Torp, M., Stark, S. & Baxter, R. (2011). Carbon balance of Arctic tundra under increased snow cover mediated by a plant pathogen. – Nature Climate Change 1: 220223.
Bottom line: Vegetation changes caused by a changing climate may be primarily driven by plant diseases. This is important for knowing which changes to adapt to and what changes to counteract.
1. Pajunen, A., Oksanen, J. and Virtanen, R. (2011). Impact of shrub canopies on understorey vegetation in western Eurasian tundra. – Journal of Vegetation Science 22: 837846.
Bottom line: Tundra shrub abundance is linked with tundra plant diversity. Cover of forbs was positively associated with shrubs whereas low growing lichens and bryophytes likely decline if tundra shrubs increase.

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