Absence of snow cover reduces understory plant cover and alters plant community composition in boreal forests
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Snow regimes affect biogeochemistry of boreal ecosystems and are altered by climate change. The effects on plant communities, however, are largely unexplored despite their influence on relevant processes. Here, the impact of snow cover on understory community composition and below-ground production in a boreal Picea abies forest was investigated using a long-term (8-year) snow cover manipulation experiment consisting of the treatments: snow removal, increased insulation (styrofoam pellets), and control. The snow removal treatment caused longer (118 vs. 57 days) and deeper soil frost (mean minimum temperature −5.5 vs. −2.2°C) at 10 cm soil depth in comparison to control. Understory species composition was strongly altered by the snow cover manipulations; vegetation cover declined by more than 50% in the snow removal treatment. In particular, the dominant dwarf shrub Vaccinium myrtillus (−82%) and the most abundant mosses Pleurozium schreberi (−74%) and Dicranum scoparium (−60%) declined strongly. The C:N ratio in V. myrtillus leaves and plant available N in the soil indicated no altered nitrogen nutrition. Fine-root biomass in summer, however, was negatively affected by the reduced snow cover (−50%). Observed effects are attributed to direct frost damage of roots and/ or shoots. Besides the obvious relevance of winter processes on plant ecology and distribution, we propose that shifts in the vegetation caused by frost damage may be an important driver of the reported alterations in biogeochemistry in response to altered snow cover. Understory plant performance clearly needs to be considered in the biogeochemistry of boreal systems in the face of climate change.
KeywordsWinter climate change Snow manipulation experiment Soil frost Svartberget LTER Hylocomium splendens
This research was supported by a grant from the German Science Foundation (DFG KR 3309/4-1) to J.K. and by grants from the Swedish Research Council (VR-2005-4257), Future Forest and Formas-ForWater (230-2010-89) to H.L. We also thank Mikaell Ottosson-Löfvenius for providing us with climate data, and two anonymous referees and the editors for constructive comments on an earlier version of this manuscript.
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