Frei, Esther

Rixen, Christian

Stöckli, Veronika

Wipf, Sonja

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EDITORIAL: VEGETATION IN COLD ENVIRONMENTS UNDER CLIMATE CHANGEFaster, higher, more? Past, present and future dynamics of alpineand arctic flora under climate changeChristian Rixen • Sonja Wipf • Esther Frei •Veronika Sto¨ckliReceived: 12 September 2014 / Accepted: 17 September 2014 / Published online: 1 October 2014 Swiss Botanical Society 2014Climate warming affects the biotic environment worldwide,and especially in cold regions such as Arctic and alpinebiomes. Enhanced plant growth, shrub encroachment andupward migration of species have been observed as a result(Myers-Smith et al. 2011; Sto¨ckli et al. 2011; Pauli et al.2012). Profound changes in ecosystem functioning andpotential losses of high-alpine and Arctic species areexpected under climate warming as cold-adapted plants maybe outcompeted by taller growing species or lost as theirhabitats vanish. Due to their endangerment in spatiallylimited habitats and low abundance, it is important to studythe dynamics of plant species in cold environments underclimate change.In the International Tundra Experiment ITEX (e.g., El-mendorf et al. 2012a), a scientific network of research teamscarried out experiments at more than 40 sites focusing on theimpact of climate change on plant species in Arctic andalpine vegetation. Similar, multi-year plant manipulationexperiments allow comparing annual variation in plantperformance with respect to phenological response to cli-mate conditions. The ITEX research combines long-termand short-term experimentations with monitoring and aimsto understand ecosystem responses and vulnerability tochange.Across all study sites, the ITEX network found the veg-etation height and abundance of growth forms to havechanged. Results of long-term changes in control plots werelargely consistent with predictions based on warmingexperiments (Elmendorf et al. 2012b). Inter-site compari-sons indicated that shrubs (particularly deciduous shrubs)were increasing over time primarily in sites that werewarming rapidly over the study period, but this pattern wasonly apparent in locations where temperatures were alreadyquite high. In contrast, the vegetation in the coldest tundrasites was relatively insensitive to climate warming.Many other research projects have addressed changes inspecies distributions and community composition in coldbiomes relative to global change. The focus has recentlybeen on vegetation of mountain regions, where upwardmigration of plant species can lead to changes in taxonomicand functional species composition. For instance, acrossEuropean summits evidence for so-called thermophilizationwas found, i.e., more warm-adapted species increasedwhereas more cold-adapted species declined (Gottfried et al.2012). In the short period between 2001 and 2008, thisupward migration has caused an increase of local speciesrichness in many boreal-temperate mountain regions, but adecrease in Mediterranean mountain regions (Pauli et al.2012). Looking at longer time scales, i.e., more than a cen-tury, the vegetation change has even accelerated in recentdecades, most likely in line with accelerated climatewarming (Wipf et al. 2013).To understand changes of Arctic and alpine plants andcommunities in response to current climatic change, it ishelpful to consider the full range of research approaches:experimental manipulations of the tundra environment,studies of long-term vegetation changes, attempts toC. Rixen  S. Wipf (&)  E. Frei  V. Sto¨ckliWSL Institute for Snow and Avalanche Research SLF,Flu¨elastrasse 11, 7260 Davos Dorf, Switzerlande-mail: wipf@slf.chPresent Address:E. FreiDepartment of Geography, University of British Columbia,Vancouver Campus, GEOG 127A, Vancouver, CanadaPresent Address:V. Sto¨ckliBergwelten 21 AG, Bahnhofstrasse 8a, 7260 Davos Dorf,SwitzerlandAlp Botany (2014) 124:77–79DOI 10.1007/s00035-014-0141-z123disentangle different environmental factors like temperatureand snow cover, studies of evolutionary changes and plas-ticity of species, and modeling approaches to predict futurevegetation. Such changes in alpine and Arctic flora underclimate change were the focus of two conferences in Sep-tember 2013 in Bergu¨n, Switzerland, with the main aim ofpresenting the state of the art in this research field. The firstconference (co-organized with Robert D. Hollister and KariKlanderud) focussed on recent work of the ITEX network(see above), while the second conference ‘‘Faster, Higher,More’’ aimed at presenting current research in climate-dri-ven changes in species distribution in alpine and Arcticenvironments. Presentations ranged from changes in speciesdistribution to phenotypic plasticity and genetic adaptationas mechanisms of change, and also included projections ofclimate change effects into the future. This special issue ofAlpine Botany presents a selection of papers from bothconferences.Climatic warming scenarios, and therefore experimentalapproaches that simulate it, usually focus on a rise in averagetemperatures. However, a short-term extreme warming mayaffect plants differently than a longer-term moderatewarming. In an experimental approach comparing the effectof different warming treatments on bryophytes in NorthernSweden (Alatalo et al. 2014, this issue), bryophytes andlichens overall were fairly resistant to different warmingscenarios. However, acrocarpous mosses showed a short-term increase in abundance after a 1-year temperatureincrease of 3.5 C, which was not apparent after a gradualincrease of temperatures over 3 years. These findings indi-cate that different types of warming scenarios can make adifference in tundra vegetation.One of the most important consequences of climatechange in cold biomes may be the change in snow cover orsnow cover duration, on which several papers in this issuefocus. Pickering et al. (2014, this issue) studied changes insnowbed vegetation in an area of the world where suchhabitats are very rare and are probably becoming increas-ingly so and hence are threatened: in the Australian Alps.Within 6 years, community trait-weighted means for plantheight and leaf area had changed in the part of the snow-patches with the longest snow-lie. This change was mostlydriven by the increase of a tall tussock grass, Poa costiniana,which was most abundant in areas with earlier snowmelt.Hence, the findings demonstrate that within a fairly shorttime, common and competitive species may migrate intohabitats that were previously dominated by snowbed spe-cialists, which highlights threats and potentially rapidchanges of formerly discrete units of alpine plant commu-nities. Similar to the study in Australia, (Carbognani et al.2014, this issue) found an increase in species richness andabundance over a 6-year period in snowbed communities inthe Italian Alps. In this case, this development did notnecessarily occur at the cost of snowbed specialists. How-ever, because of higher plant densities, species co-occurenceshifted towards higher species segregation, which indicatesmore competitive plant–plant interactions. The authorsconclude that currently, snowbed communities are in a phaseof change with competitive interactions becoming moreimportant, which might be critical for weak competitorsamong the snowbed plants in the future.When facing ongoing and future climate change, plantspecies can respond with migration, phenotypic plasticity orevolution. Bienau et al. (2014, this issue) studied trait plas-ticity of the crowberry, Empetrum hermaphroditum, under arange of different snow and climate conditions. Across twolatitudes ranging from Northern Sweden to central Norway,snow cover had highly consistent effects on growth andreproductive traits. Plants from snow-poor sites had a highernumber of flowers and fruits, but smaller ramets and lowerabove-ground biomass than plants from snow-rich habitats.The authors suggest that Empetrum hermaphroditum mayhave the potential to cope with changing snow conditionsdue to its large plasticity of traits.Mountain plant species with wide elevational ranges areexpected to be exposed to different selection pressures atlow and high elevation. Estimating the extent of geneticpopulation differentiation contributes to our understandingof selective forces shaping phenotypic variation of plants inresponse to changing climate conditions. A comparison ofquantitative trait differentiation with neutral genetic differ-entiation of Ranunculus bulbosus populations in the SwissAlps showed evidence for divergent selection across popu-lations (Frei et al. 2014, this issue). The differing levels oftrait differentiation at high and low elevation indicated dif-ferent selective forces across elevations, which suggests thatselection regimes might alter under climate change. Alsochanges in richness, community and trait composition ofalpine habitats may respond differently to climate changedepending on their elevation. In their resurvey study,Rosbakh et al. (2014, this issue) found that over the past50 years, richness increased and functional and taxonomicvegetation composition changed most at lowest sites in thesubalpine, while the high-alpine sites showed a decrease inrichness and few changes in composition. Potentially, per-mafrost thaw and thus, increasing soil instability at thehighest sites may foster this seemingly counter-intuitiveresult. It illustrates that vegetation changes may vary at thelocal scale, and that understanding complex interactionsbetween environmental drivers is crucial to understandecosystem processes in complex alpine terrain. Conse-quently, it is useful to investigate community compositionalong environmental gradients to understand possibleresponses to climate change. Wehn et al. (2014) studiedvegetation changes along a gradient from the coast to theinland of Norway, analyzed effects of snow cover duration78 Alp Botany (2014) 124:77–79123and aspect on plant diversity and predicted future vegetationbased on the existing gradients. The authors found that plantdiversity was mostly influenced by the coast–inland gradi-ent, and, beyond that, modified by snow cover duration andaspect. The increase in species richness was mostly drivenby increases in dwarf shrubs and graminoids. The predic-tions showed that species richness is likely to increase in thefuture, and most in areas with medium to long snow coverduration.The selection of papers in this Special Issue of AlpineBotany highlights the focus of ongoing research approachesand gives directions of future research needs. Discussions atthe conferences suggested that our understanding of vege-tation changes in cold biomes will benefit greatly fromfuture studies that focus on (1) the relative importance ofenvironmental factors such as climate, land-use, nutrientinput, etc., (2) different levels of biodiversity, i.e., speciesand genetic diversity, functional traits, etc., (3) the rate ofadaptive processes in relation to climate and global change,including evolutionary adaptation, migration, or range shift,(4) factors defining the distributional limits of cold-adaptedspecies both at the ‘‘leading’’ (cold) and at the ‘‘trailing’’(warm) edge. The organizers of the conferences are gratefulfor the discussions and presentations, and look forward tomore research that was stimulated by the conferences.ReferencesAlatalo JM, Ja¨gerbrand AK, Molau U (2014) Climate change andclimatic events: community-, functional- and species-levelresponses of bryophytes and lichens to constant, stepwise, andpulse experimental warming in an alpine tundra. Alp Botany124(2). doi:10.1007/s00035-014-0133-zBienau MJ et al. (2014) Snow cover consistently affects growth andreproduction of Empetrum hermaphroditum across latitudinaland local climatic gradients. Alp Botany 124(2). doi:10.1007/s00035-014-0137-8Carbognani M, Tomaselli M, Petraglia A (2014) Current vegetationchanges in an alpine late snowbed community in the south-eastern Alps (N-Italy). Alp Botany 124(2). doi:10.1007/s00035-014-0135-xElmendorf SC et al (2012a) Global assessment of simulated climatewarming on tundra vegetation: heterogeneity over space andtime. Ecol Lett 15Elmendorf SC et al (2012b) Plot-scale evidence of tundra vegetationchange and links to recent summer warming. Nat Clim Change 2Frei ER, Hahn T, Ghazoul J, Pluess AR (2014) Divergent selection inlow and high elevation populations of a perennial herb in theSwiss Alps. Alp Botany 124(2). doi:10.1007/s00035-014-0131-1Gottfried M et al (2012) Continent-wide response of mountainvegetation to climate change. Nat Clim Change 2Myers-Smith IH et al (2011) Shrub expansion in tundra ecosystems:dynamics, impacts and research priorities. Environ Res Lett 6Pauli H et al (2012) Recent plant diversity changes on Europe’sMountain Summits. Science 336Pickering C, Green K, Barros AA, Venn S (2014) A resurvey of late-lying snowpatches reveals changes in both species and functionalcomposition across snowmelt zones. Alp Botany 124(2). doi:10.1007/s00035-014-0140-0Rosbakh S, Bernhardt-Ro¨mermann M, Poschlod P (2014) Elevationmatters: contrasting effects of climate change on the vegetationdevelopment at different elevations in the Bavarian Alps. AlpBotany 124(2). doi:10.1007/s00035-014-0139-6Sto¨ckli V, Wipf S, Nilsson C, Rixen C (2011) Using historical plantsurveys to track biodiversity on mountain summits. Plant EcolDivers 4Wehn S, Lundemo S, Holten JI (2014) Alpine vegetation alongmultiple environmental gradients and possible consequences ofclimate change. Alp Botany 124(2). doi:10.1007/s00035-014-0136-9Wipf S, Sto¨ckli V, Herz K, Rixen C (2013) The oldest monitoring siteof the Alps revisited: accelerated increase in plant speciesrichness on Piz Linard summit since 1835. Plant Ecol Divers 6Alp Botany (2014) 124:77–79 79123

Faster, higher, more? Past, present and future dynamics of alpine and arctic flora under climate change

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Faster, higher, more? Past, present and future dynamics of alpine and arctic flora under climate change

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