Rapid responses of permafrost and vegetation to experimentally increased snow cover in sub-arctic Sweden

Abstract

Increased snow depth already observed, and that predicted for the future are of critical importance to many geophysical and biological processes as well as human activities. The future characteristics of sub-arctic landscapes where permafrost is particularly vulnerable will depend on complex interactions between snow cover, vegetation and permafrost. An experimental manipulation was, therefore, set up on a lowland peat plateau with permafrost, in northernmost Sweden, to simulate projected future increases in winter precipitation and to study their effects on permafrost and vegetation. After seven years of treatment, statistically significant differences between manipulated and control plots were found in mean winter ground temperatures, which were 1.5 • C higher in manipulated plots. During the winter, a difference in minimum temperatures of up to 9 • C higher could be found in individual manipulated plots compared with control plots. Active layer thicknesses increased at the manipulated plots by almost 20% compared with the control plots and a mean surface subsidence of 24 cm was recorded in the manipulated plots compared to 5 cm in the control plots. The graminoid Eriophorum vaginatum has expanded in the manipulated plots and the vegetation remained green longer in the season.

Increased photosynthesis compensates for shorter growing season in subarctic tundra—8 years of snow accumulation manipulations

“…(~20 cm and 10 cm respectively) (Johansson et al 2013). Between 2011 and 2013 the thicker snow cover, caused by the snow fences hindering snow drift, prolonged the duration of snow cover in the treated plots.…”

“…The thicker active layer allows roots to penetrate deeper into the soil substrate and thus increases nutrient uptake (Schimel et al 2004). According to Johansson et al (2013) the treated plots at Storflaket have significantly higher soil temperatures than control plots at both 15 and 50 cm depth during winter (NovemberApril). We hypothesize that the combined effects of increased moisture and temperature promotes nutrient availability and graminoid growth.…”

“…were selected randomly for comparison. For detailed description of the site and the experimental setup, see Johansson et al (2013).…”

“…it acts as insulating layer during winter, preventing soil temperatures to drop as low as under ambient conditions. Increased snow depth has induced permafrost thawing and associated ground subsidence in + Snow with water table closer to (and sometimes above) ground level and thicker active layer (Johansson et al 2013). In tundra regions, where plants are adapted to short growing seasons but often are moisture limited (Keuper et al 2012a), the timing of snowmelt and the availability of water during the peak growing season are important factors regulating plant growth and annual carbon balance (Aurela et al 2004).…”

“…Plant biomass decreased over the observation periods due to higher herbivore leaf damage and plant diseases (Larsen et al 2007;Torp et al 2010). After 3 years of snow manipulation at a lowland permafrost site Johansson et al (2013) could observe increased soil wetness on the manipulated plots, especially after snowmelt. However, no statistically significant difference in plant species composition could be observed although the vegetation on the manipulated plots showed an increased "greening" by the end of the growing season.…”