Faster, higher, more? Past, present and future dynamics of alpine and arctic flora under climate change
Christian Rixen
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Sonja Wipf
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Esther Frei
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Veronika Stockli
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Present Address: V. Stockli Bergwelten 21 AG, Bahnhofstrasse 8a, 7260 Davos Dorf,
Switzerland
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Present Address: E. Frei Department of Geography, University of British Columbia
, Vancouver Campus, GEOG 127A,
Vancouver, Canada
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C. Rixen S. Wipf (&) E. Frei V. Stockli WSL Institute for Snow and Avalanche Research SLF
, Fluelastrasse 11, 7260 Davos Dorf,
Switzerland
Climate warming affects the biotic environment worldwide, and especially in cold regions such as Arctic and alpine biomes. Enhanced plant growth, shrub encroachment and upward migration of species have been observed as a result (Myers-Smith et al. 2011; Stockli et al. 2011; Pauli et al. 2012). Profound changes in ecosystem functioning and potential losses of high-alpine and Arctic species are expected under climate warming as cold-adapted plants may be outcompeted by taller growing species or lost as their habitats vanish. Due to their endangerment in spatially limited habitats and low abundance, it is important to study the dynamics of plant species in cold environments under climate change. In the International Tundra Experiment ITEX (e.g., Elmendorf et al. 2012a), a scientific network of research teams carried out experiments at more than 40 sites focusing on the impact of climate change on plant species in Arctic and alpine vegetation. Similar, multi-year plant manipulation experiments allow comparing annual variation in plant performance with respect to phenological response to climate conditions. The ITEX research combines long-term and short-term experimentations with monitoring and aims
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to understand ecosystem responses and vulnerability to
change.
Across all study sites, the ITEX network found the
vegetation height and abundance of growth forms to have
changed. Results of long-term changes in control plots were
largely consistent with predictions based on warming
experiments (Elmendorf et al. 2012b). Inter-site
comparisons indicated that shrubs (particularly deciduous shrubs)
were increasing over time primarily in sites that were
warming rapidly over the study period, but this pattern was
only apparent in locations where temperatures were already
quite high. In contrast, the vegetation in the coldest tundra
sites was relatively insensitive to climate warming.
Many other research projects have addressed changes in
species distributions and community composition in cold
biomes relative to global change. The focus has recently
been on vegetation of mountain regions, where upward
migration of plant species can lead to changes in taxonomic
and functional species composition. For instance, across
European summits evidence for so-called thermophilization
was found, i.e., more warm-adapted species increased
whereas more cold-adapted species declined (Gottfried et al.
2012). In the short period between 2001 and 2008, this
upward migration has caused an increase of local species
richness in many boreal-temperate mountain regions, but a
decrease in Mediterranean mountain regions (Pauli et al.
2012). Looking at longer time scales, i.e., more than a
century, the vegetation change has even accelerated in recent
decades, most likely in line with accelerated climate
warming (Wipf et al. 2013).
To understand changes of Arctic and alpine plants and
communities in response to current climatic change, it is
helpful to consider the full range of research approaches:
experimental manipulations of the tundra environment,
studies of long-term vegetation changes, attempts to
disentangle different environmental factors like temperature
and snow cover, studies of evolutionary changes and
plasticity of species, and modeling approaches to predict future
vegetation. Such changes in alpine and Arctic flora under
climate change were the focus of two conferences in
September 2013 in Bergun, Switzerland, with the main aim of
presenting the state of the art in this research field. The first
conference (co-organized with Robert D. Hollister and Kari
Klanderud) focussed on recent work of the ITEX network
(see above), while the second conference Faster, Higher,
More aimed at presenting current research in
climate-driven changes in species distribution in alpine and Arctic
environments. Presentations ranged from changes in species
distribution to phenotypic plasticity and genetic adaptation
as mechanisms of change, and also included projections of
climate change effects into the future. This special issue of
Alpine Botany presents a selection of papers from both
conferences.
Climatic warming scenarios, and therefore experimental
approaches that simulate it, usually focus on a rise in average
temperatures. However, a short-term extreme warming may
affect plants differently than a longer-term moderate
warming. In an experimental approach comparing the effect
of different warming treatments on bryophytes in Northern
Sweden (Alatalo et al. 2014, this issue), bryophytes and
lichens overall w (...truncated)