The Effect of Climate Change at Different Tem-poral Scales on Vaccinium Myrtillus

The Arctic’s plant growth, soil temperatures, and season length are dependent on snow cover. Snow characteristics and snowmelt timing will change with a warmer climate. In warmer winters, a lot of the precipitation falls as rain resulting in earlier spring. Rixen et al. (2010) observed year rings and shoot growth of the dwarf shrub bilberry (Vaccinium myrtillus) in response to early or late snowmelt in the Central Alps. With a temperature rise of 1.3 oC in the 20th century, changes in ecosystem structure and function that are attributed to snow cover have already become apparent in tundra ecosystems. The authors measured radial and shoot growth increments of the bilberry and the species abundances of the vegetation in response to different types of snow cover. The comparison of ramet age and ring widths from different sites allows for a comparison of growing conditions under different snow regimes over as much as two decades. Clara Lyashevsky
 Rixen, C., Schwoerer, C., Wipf, S., 2010. Winter climate change at different temporal scales in Vaccinium myrtillus, an Arctic and alpine dwarf shrub. Ecological Monographs 29, 85–94.

The experiments were done at the Central Alps in Switzerland, where the mean temperature in winter is 2.0 oC, the snow cover lasts on average from 18 October to 26 May, and the main vegitation type is dwarf shrub heath (Empetro-Vaccinietum cetrarietosum).
Plots of vegetation were established in four different subsets varying in timescale of the snow manipulations, in order to assess the impact of the snowmelt date on the vegetation. The first subset consisted of plots on an ongoing snow manipulation experiment, the second had plots that were chosen along snow fences that were built 30 years ago, the third subset had plots that were established along a natural snow gradient, and the fourth subset had plots at two different altitudes in order to identify the effect of snowmelt date on the growth performance of vegetation at different elevations. The data were collected between June and October.
Advanced snowmelt was simulated in nine plots by removing most of the snow in Spring, nine other plots were used as controls. The vegetation along the natural snowmelt gradient was analyzed by plots established at nine sites in close vicinity to the experimental plots; eighteen additional plots were established at two different elevations. The authors analyzed xylem ring width, shoot length, and species abundance of the vegitation. The differences in age distribution between plots were tested with chi-square tests to see whether treatments affected the age structure of ramet populations. The xylem ring widths were analyzed separately for each year. The relationships of xylem ring width with climate variables were tested with single and multiple linear regression techniques. Subtracting the mean xylem ring widths of late melting plots from the mean xylem ring widths of the early melting plots identified the effect of temperature on the plots.
In very warm summers, plants at high elevation produced larger rings than plants at lower elevation, indicating more favorable conditions. Year rings were generally wider at sites with late snowmelt at the natural snow gradient. Comparing snow fences and natural snow gradients that did not differ in altitude, colder summers had small year ring width whereas warmer summers year ring growth was enhanced by early snowmelt. The shoot length in 2006 was greater after early snowmelt in all plot types. Shoot length was greater after early snowmelt in the natural snow gradient, along the snow fences, and in the snow manipulation experiment.

Analysis of xylem ring width is a valuable tool in investigating growth across elevation and snow gradients. Xylem ring width was greater in plots with late snowmelt than in plots with early snowmelt along the natural snowmelt gradient, which is true in years with relatively cold summers. Climate change can be detrimental to the age of vegetation because of the potential for colder summers. In years with colder summers, growth rings were larger at lower elevation than at higher elevation. Climate change also caused species abundance to change because of higher temperatures

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