How similar or different are Arctic and alpine regions in terms of climate system, species responses to change, and social-economic conditions?
The session began with Nick Pepin discussing Arctic amplification and elevation dependant warming (EDW), and suggesting that mountain systems are spatially more complex than the Arctic. Other influences might be driving warming trends in alpine regions. IPCC Assessments have largely ignored mountains and it is a challenge to clearly see the influence of elevational amplification in model scenarios. Nevertheless, there is growing evidence for EDW, and this amplification could by the result of albedo feedback, cloud feedback, intensification of the hydrological cycle, energy balance at low temperatures and/or aerosols. Nick noted that we are currently lacking local data on mountain climate and a network of mountain observatories is needed to understand the causes of enhanced warming in mountains.
Several subsequent talks explored the relationship between climate warming and tundra vegetation. Arctic and alpine regions can be defined in terms of land cover, with typically treeless vegetation covering some 8% (5% Arctic, 3% alpine) of the terrestrial surface of the globe (11M km^2), from 80°N to 67°S and reaching elevations of more than 6000 m on subtropical mountains. These cold environments contain about 4% of the global flora (10 000 alpine and 1500 arctic lowland species); 3-4% of the world’s animal species; and account for about 14% of stored terrestrial carbon.
Anne Björkman discussed the relationship between plant traits and ecosystem function, and presented an analysis showing how plant traits vary with climate using the International Tundra Experiment (ITEX) database, expanding both Arctic and alpine regions (in this case 35,000 trait observations for 318 species of tundra plants). The results showed that specific leaf area (SLA) increased at warmer temperature among species, but there was no effect within species. Plant height showed the opposite effect. Understanding how plant traits vary in response to climate will help make more accurate predictions of warming impacts on tundra plant communities.
Janet Prevey continued to this discussion of plant responses to climate change by examining patterns of phenology from the ITEX database. Changes in phenology are among the most visible response of plants to warming and Janet and her colleagues tested the hypothesis that late-flowering plants respond to warming more than early-flowing plants. They compared plants from within open-topped chambers to plants in control plots and long-term changes for alpine and Arctic sites with c. 20 years of phenology records. Overall the results supported their hypothesis, and the mean responses of Arctic and alpine plants were generally similar. However Arctic plants may senesce later in the season than alpine plants, and flowering may be slightly more advanced on dry alpine sites.
Christian Rixen introduced the possibility of monitoring plant phenology using measurements from ultrasonic snow-depth sensors from meteorological stations in the Swiss Alps. They observed a quasi-linear relationship on phenology determined by the timing of snow melt and temperature (measured as growing degree days >0 C). Elevation along was a poor predictor of phenology and there was no compelling evidence for photoperiod limitation of growth for tall alpine plants. Responses in Arctic systems might be similar, and the potential exists to address these questions by expanding the analyses of snow-depth sensors to other sites in the Arctic.
Shrub-snow interactions are being examined in alpine shrub communities in SE Australian mountains. Susanna Venn presented some preliminary results describing the role of six species of alpine shrubs in trapping snow, and the differences in both snow depth and snow water equivalent density on the lee or windward side of individual shrubs. Only one species (the tallest of the shrubs) showed a difference in accumulation of snow between early and late season.
Nigel Yoccoz compared the demography of vole species that need to cope with long winters and snow by comparing long-term data from the Alps, northern Norway and Svalbard. Populations of voles living alpine sites were stable and typically had low turnover and high overwinter survival. In contrast, voles living in Svalbard had large population fluctuations driven by winter Rain-on-Snow events that caused significant mortality. Voles in northern Norway, at a sub-arctic alpine site, showed intermediate characteristics with typically had cyclical populations, where survival was alternatively either high or low! Changes in alpine weather patterns may lead to changes in population dynamics of small mammals, but demographic variation imposes limitations to the strategies that can be adopted.
Finally, Matthew Klick compared Arctic and mountain regions in terms of social and human characteristics, including economic development, social conditions, political organization and climate change. The role of adaptation strategies and resilience are variable, but in general Arctic communities appear to be more effective in organizing themselves to mitigate against some of the most damaging potential changes (past, present, future). Mountain communities are more isolated, more marginalized and suffer from even greater inequities than people living in the Arctic.
There were also several posters that contrasted alpine and Arctic environments, and we will try to provide a summary of these contributions separately.