Abstract
Snow is one of the most important factors driving vegetation in mountain areas of the temperate climate zone. With increasing global warming, the creation of artificial snow gains importance to guarantee the ski season and it might even increase in future, since temperatures are expected to rise further both in winter and in summer.
The increasing air temperatures observed during the last decades, alterations in the precipitation regime, and the resulting high variability in the snow cover duration are already impacting the winter tourism. The number of naturally snow-reliable ski areas is dropping, and is forcing ski area operators to an intensive use of artificial snow. Artificial snow may have chemical and physical characteristics that differ from those of the natural snow, and its duration is generally prolonged, influencing the plant development and regulating the species distribution. In fact, differences in species composition on ski slopes respect to the natural surroundings, and a lower abundance of early flowering species because of the late snowmelt of the compacted artificial snow are reported. Furthermore, as natural snow cover is decreasing, this may also affect soil and vegetation. In fact, snow plays a crucial role in the alpine-subalpine and mountain environment in generating adequate conditions for plant development, controlling soil temperature and moisture.
In South Tyrol (Southern Alps, N Italy), two different ski management practices coexist, i.e. (1) there are large and medium ski resorts, which have enough economic and human resources to extend the ski season up to 5 months, and (2) there are small local ski resorts, whose limited resources do not allow a ski season longer than 2-3 months.
In the first study, I was interested in (1) assessing the impact of the ski piste on the chemical and physical properties of the snow, on the soil and on grassland vegetation and (2) testing if this impact would be different between medium and small ski resorts. Snow and soil physico-chemical characteristics were measured. Additionally, the biodiversity of the vegetation was investigated, together with the plant biomass and the plants’ functional groups. For all the studies, we used a pairwise design of plots on grasslands of the ski pistes and control plots on grasslands outside the pistes for direct comparison, in South Tyrol, N Italy.
The first study took place in a medium and in three small ski resorts, all lying on dolomitic rocks. The results indicated that 1) The lack of snow outside the pistes allows for ground freezing to the same extent as under artificial snow and 2) ski management practices affect grassland vegetation, in terms of a decrease in the species’ number and in the functional groups’ composition, but the effects in the small ski areas are more restrained, probably due to the more limited use of artificial snow in a shorter ski season.
The second study, instead, was performed only in the medium ski resort. The ecophysiology of the dominant plants under the snow cover was investigated using stable isotope analyses of carbon (13C/12C) and oxygen (18O/16O) of plants’ leaves, in order to determine the water use efficiency (iWUE) of the dominant species on the ski piste and outside, in a year when the natural snow was particularly scarce. The isotopes’ composition was used also to test if the two kinds of snowmelt water (natural vs artificial) had a different source or different properties, respectively. Furthermore, leaves’ carbon (C), nitrogen (N), leaves’ pigments content, leaf dry matter content and the specific leaf area of the vegetation under the snow cover were measured to assess if the ski piste management caused changes in the plant performance between the plants on the ski piste and those outside. We found that the iWUE of the plants on the ski piste was higher than that of the plants outside, probably because the similar-flooding conditions on ski pistes, due to the artificial snow input, lead the investigated plants to regulate their stomata more than the plants outside the ski pistes, but the responses are species-specific.
This work represents finally an attempt to monitor the impact of ski pistes by working at multiple levels, from the snow properties (hydrosphere) to the soil properties (lithosphere) up to the vegetation (biosphere), questioning if the type of ski piste management, i.e. medium-sized high intensity resorts and small, local low intensity ones, makes a difference in the impact to ecosystems. It is a study particularly interesting in a province as South Tyrol, where the ski tourism plays a fundamental role for the economy and where considerable investments in artificial (technical) snow systems are made.