Abstract
Main conclusionEvergreen plants are more vulnerable than grasses and birch to snow and temperature variability in the sub-Arctic.Most Arctic climate impact studies focus on single factors, such as summer warming, while ecosystems are exposed to changes in all seasons. Through a combination of field and laboratory manipulations, we compared physiological and growth responses of dominant sub-Arctic plant types to midwinter warming events (6 °C for 7 days) in combination with freezing, simulated snow thaw and nitrogen additions. We aimed to identify if different plant types showed consistent physiological, cellular, growth and mortality responses to these abiotic stressors. Evergreen dwarf shrubs and tree seedlings showed higher mortality (40–100%) following extreme winter warming events than Betula pubescens tree seedlings and grasses (0–27%). All species had growth reductions following exposure to − 20 °C, but not all species suffered from − 10 °C irrespective of other treatments. Winter warming followed by − 20 °C resulted in the greatest mortality and was strongest among evergreen plants. Snow removal reduced the biomass for most species and this was exacerbated by subsequent freezing. Nitrogen increased the growth of B. pubescens and grasses, but not the evergreens, and interaction effects with the warming, freezing and snow treatments were minor and few. Physiological activity during the winter warming and freezing treatments was inconsistent with growth and mortality rates across the plants types. However, changes in the membrane fatty acids were associated with reduced mortality of grasses. Sub-Arctic plant communities may become dominated by grasses and deciduous plants if winter snowpack diminishes and plants are exposed to greater temperature variability in the near future.
Highlights
The Arctic is experiencing more extreme weather events due to climate change, causing high mortality rates among species when events surpass survival thresholds (Post et al 2009; Liston and Hiemstra 2011)
Plant mortality can result from loss of frost hardiness due to physiological activity induced by the winter warming event (Strimbeck et al 1995; Beck et al 2004; Buchner and Neuner 2011; Pagter and Arora 2013) or increased freeze–thaw cycles and lower freezing temperature from the reduced snow cover (Lund and Livingston 1999)
Minimum temperature was lower (− 12 °C) in some of the other snow removal treatments due to a few days with colder frost during which both control plots were still covered by snow (Fig. 1b–d)
Summary
The Arctic is experiencing more extreme weather events due to climate change, causing high mortality rates among species when events surpass survival thresholds (Post et al 2009; Liston and Hiemstra 2011). Loss of snow cover during a midwinter melt can induce plant physiological activity, while the plants are generally dormant (Ögren 1996; Schaberg et al 1996; Bokhorst et al 2010). Evergreen plants have more ‘alive’ green tissue aboveground and can potentially respond more strongly to abiotic cues making them more susceptible to damage, whereas deciduous plants have dormant buds which may take longer to develop and respond to midwinter warming events. Plant mortality can result from loss of frost hardiness due to physiological activity induced by the winter warming event (Strimbeck et al 1995; Beck et al 2004; Buchner and Neuner 2011; Pagter and Arora 2013) or increased freeze–thaw cycles and lower freezing temperature from the reduced snow cover (Lund and Livingston 1999). Identifying the drivers behind plant vulnerability allows for a better understanding of sub-Arctic vegetation changes, as the predictions of winter climate and snow conditions vary across circumpolar regions (Liston and Hiemstra 2011)
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