Pistes - the science bit...Pistes are increasingly having their snow cover guaranteed by the use of artificial snow for the entire season but only a few investigations have been carried out systematically to specifiy the environmental impacts.
Rixen et al made a study in 2003 about the ecological implications of ski piste preparation and of artificial snow production. They found that main direct impacts of ski piste preparation on the vegetation were related to the compaction of the snow cover caused by the piste grooming; namely the induction of soil frost, the formation of ice layers, mechanical damage and a delay in plant development. The vegetation reacts with changes in species composition and a decrease in biodiversity. However, artificial snow modifies some of these impacts; the soil frost is mitigated due to an increased insulation of the snow pack and the mechanical impacts of snow-grooming vehicles are mitigated due to the deeper snow cover. The deeper snow cover reduces the disturbance to the vegetation below. The snow melt of the piste is postponed through a combination of compression and artificial snow and thus vegetation development is delayed though not damaged. Furthermore, they found that artificial snow induces new impacts to the alpine environment. The longer artificial snow had been used on ski pistes the higher the moisture and nutrient levels. Changes in indicator values for soil nutrients and moisture could be considered beneficial for plant growth. Artificial snow is often made from river water with a high mineral content; when it melts it increases the input of water and ions to ski pistes, which can have a fertilizing effect and hence change the plant species composition. Increasingly, snow additives made of potentially phytopathogenic bacteria are used in artificial snow and they enhance ice crystal formation due to their ice nucleation activity. Although sterilised, additives affected the growth of some alpine plant species in laboratory experiments, although it is inconclusive whether this impact is negative. No effects of artificial snow on plant productivity could be detected. The impact of artificial snow on diversity was ambiguous. Salts are applied to improve the snow quality for ski races. The environmental impacts of most salts have not yet been investigated, but a commonly used nitrate salt has intense fertilising properties. Again this could be non-beneficial to the vegetation; however, this has yet to be clarified. Rixen et al made another study in 2004 to investigate snow depth and density from groomed ski pistes with compacted snow and their effects on ground temperatures and timing of snowmelt. They analysed groomed pistes with and without artificial snow as well as adjacent ungroomed off-piste control plots beside the piste. On pistes with natural snow, the thin and compacted snow cover led to severe and long lasting seasonal soil frost. On pistes with artificial snow, soil frost occurred less frequently because of increased insulation due to the greater snow depth. However, due to the greater snow mass, the beginning of the snow-free season was delayed by more than 2 weeks. Average winter ground temperatures under a continuous snow cover were decreased by approximately 1°C on both piste types compared with off-piste control plots. The results suggest that the heat balance of alpine soils is changed by both piste types, either by an extensive heat loss on pistes with natural snow or by prolonged snow cover on pistes with artificial snow. They did not conclude whether the impact was positive or negative – merely that there was a difference. Keller et al 2004 conducted a similar study in central Switzerland to analyse whether the soil below groomed ski slopes with artificial snow may be subjected to more pronounced cooling than the soil below a natural snowpack. They found that snow density, snow hardness and thermal conductivity were significantly higher on the ski slope than in the natural snowpack. However, these differences did not affect the cooling of the soil, since no difference was observed between the ski slope and the natural snow cover. This might be because cold periods were rare and short and thus any snowpack could protect the soil from freezing. The major impact of the ski-slope grooming was a 4 week delay in snowmelt and soil warming at the end of the season. The study demonstrates that there is no site-independent answer as to whether a groomed snowpack affects the thermal conditions in the soil. In Cairngorm, Scotland, during the construction phase in the 1960s and 1970s lift pylons and buildings were taken onto the site by tracked vehicles and pistes were bulldozed into the mountainside removing boulders, topsoil and vegetation. The removal of vegetation led to negative impacts on the fauna and an increase in flash floods up to the early 1980s which also caused sediment to be deposited elsewhere on otherwise unspoilt vegetation (Holden 1999b). Rolando et al (2007) studied the effects of piste preparation on alpine grassland bird communities in the Italian Alps. They investigated the differences between three different plots; away from pistes, adjacent to pistes and on new pistes which had been created in the last year through machine scraping and grading and artificially reseeded with herbs. It was found that the plots away from the pistes had the greatest bird species richness and diversity and the greatest grassland species diversity and those on pistes had the lowest. Plots beside the pistes did not support lower numbers of species but had significant lower density. Richness and abundance of arthropods were significantly lower on ski pistes than on other plot types; given that many invertebrates are preyed upon by birds, low food availability on ski runs may be one of the factors reducing the attractiveness of these patches to birds. Machine grading universally seems to be high impact and detrimental causing particularly severe and lasting impacts on alpine vegetation which are mitigated neither by time nor revegetation measures. Wipf et al (2005) found that pistes which had been machine graded had lower vegetation cover, productivity, species diversity and abundance of early flowering species and higher proportions of bare ground leading to surface run off and erosion. However, it is not the case that machine grading has to be so invasive. It is possible for the topsoil to be removed (like turf), the ground works completed and the topsoil turf to be replaced. This maintains the ecosystem exactly as it was and overcomes the difficulties experienced with reseeding/ revegetating at altitude which almost universally fails to a certain degree. None of the above studies have examined pistes created in this manner; this is an area that requires further study. Naturally, cutting through forest, particularly where it is old growth, is a major negative environmental impact and one which is vigorously opposed, particularly in North America, where many resorts lie completely below the tree line. The removal of trees in this manner can cause severe erosion and loss of habitat. However, not all impacts of piste creation are negative; some types of disturbance can increase biodiversity by suppressing dominant species or create favourable conditions for new habitat. The clearing of trees to make way for pistes in Lake Louise in Canada greatly improved the habitat for grizzly bears by providing excellent conditions for crowberry and buffalo berry production (Hudson 2002). In their studies of the negative impacts of skiing around Banff, UTSB Research noted that soil erosion had occurred as a result of tree clearance to create pistes and the slope alterations had changed drainage patterns. Additionally they noted harm to wildlife species that relied on forest cover and which were displaced or had their movement corridors restricted. Thus, it can be seen that there is no clear answer. All types of ski piste management cause deviations from the natural structure and composition, however it is inconclusive whether the impacts are positive or negative. The impacts of ski pistes in general and of artificial snow in particular appear comparatively moderate, but are by no means negligible. Conclusions to be drawn are that machine grading without the protection of the top soil should be avoided at all costs and tree clearance should only be conducted with an environmental impact analysis to balance the loss of one habitat with the gain of another. Artificial snow should be created with renewable energy sources, using water from sustainable sources that do not impact the biodiversity in natural streams and planned with care to not litter the mountainside with equipment. Long term snow production should be banned in areas where any increase in the supply of nutrients and water is a concern and pistes should not be allowed where any changes in composition or decrease in species richness cannot be tolerated. Return to The Ski Factors - Pistes |
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