| Summary: | Non-sorted circles (NSCs) are important landscape components of Arctic tundra ecosystems as they determine small-scale vegetation patterns and regulate the buildup of carbon in deep soil layers. Lack of vegetation cover and insulation through snow cover in winter play key roles in the formation of these patterns as they regulate frost heave and freeze-thaw cycles (FTCs) in the soil. Winter climate and snow cover changes are expected in the future, but the implications for plant performance and nutrient dynamics on NSCs are poorly understood. This hampers our ability to predict the responses of Arctic plant communities to changing soil frost conditions. Therefore, an experimental manipulation was set up on a NSC field in sub-arctic Sweden. Snow fences and artificial fleece insulation were used to simulate future snow and temperature patterns. Plant performance and soil nutrient responses were measured after two years of manipulation. Mean winter soil temperature was increased by 0.9 – 1.8 °C in the snow treatment, whereas the fleece treatment increased spring soil temperatures by 0.81 – 1.26 °C. FTCs were reduced in the snow treatment and showed variable responses to the fleece manipulation. Leaf green-up began roughly one week earlier under increased spring temperatures. Shoot growth, biomass and frost damage responses to the manipulations differed among species. Vaccinium vitis-idaea responded positively to the snow treatment with enhanced shoot growth, increased biomass and reduced leaf frost damage. Betula nana and Empetrum nigrum showed mostly negligible but sometimes negative responses to the treatments. The results suggest enhanced performance of V. vitis-idaea in NSCs under future snow conditions, leading to a shift in vegetation community composition. Changing vegetation patterns under climate change could therefore induce a shift into a new state of equilibrium in NSC ecosystems.
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