Climate change effects on freezing damage in three subarctic bryophytes : A snow manipulation field experiment in a tundra ecosystem in Abisko, Sweden
Climate change is expected to have a large impact on northern ecosystems. Increased temperatures and altered precipitation and snow cover patterns will have a great impact on subarctic tundra. Bryophytes form an important component of tundra ecosystems because of their high abundance and their importance in many ecological processes. The effect of elevation and snow cover on freezing damage in shoots of three subarctic bryophytes: Ptilidium ciliare, Hylocomium splendens and Sphagnum fuscum, was studied in a snow manipulation field experiment at different elevations in Abisko, Sweden, during early spring. The treatments included snow addition, snow removal and control. In addition, bryophyte healthiness at the plot scale was determined by image analysis using colour selection, and soil temperature and moisture data were collected. Freezing damage differed significantly among bryophyte species with P. ciliare having the lowest freezing damage. There was a decrease in freezing damage over time due to the increase in temperature as spring progressed. Counter expectation, freezing damage was higher at low elevation although the mean daily minimum temperature was lower at higher elevation, which might be due to adaptation effects. Snow treatment had only a minor effect on freezing damage, but it did have an effect on proportion of undamaged tissue at the plot scale which increased with increasing snow cover at high elevation, but decreased with increasing snow cover at low elevation. Soil moisture content was also affected by snow treatment. The number of freeze-thaw cycles was less for S. fuscum and H. splendens compared to bare soil plots, which indicates insulating capacities of these bryophytes. Freezing damage could not be explained by the measured climate variables alone; therefore, it is likely the result of a complex set of factors, possibly including solar radiation and disturbance by herbivores.
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