Environmental Engineering Reference
In-Depth Information
partly also from the Mediterranean Sea - accumulate,
precipitation is 800-1000 mm more than in the
heart of the Alps. Evaporation rises. Critical
situations in the water balance of plants, however,
are rare, other than in special locations (those of
strong radiation, high temperature and high wind).
• Wind increases in frequency and strength with
altitude. This strongly influences the distribution
of snow in winter and thus the length of the snow-
free period and the water balance, which makes a
strong erosion effect possible in exposed locations.
Various inclinations of the sun's radiation create
differing degrees of heat.
• The difference between a north and south aspect is
increasingly greater with altitude. The micro-
climate, however, can surpass the influence of the
macroclimate and altitude.
assessments indicate that at altitudes of between 1800
and 2400 m a minimum vegetation cover of 70 - 80%
is required to avoid erosion (Stocking & Elwell 1976,
Mosimann 1984, Tasser
et al.
1999, Peratoner 2003).
Therefore, a sufficient combination of application
technique and adapted seed mixture, or plant mater-
ial, reaching the minimum requirement of sustainable
vegetation with 70-80% cover within the first two
vegetation periods, must be the main target for
restoration at high altitudes. Assessments of the veg-
etation cover of the sites showed that, under average
conditions at high altitudes, the necessary minimum
demand of cover can be achieved in the second
vegetation period at the earliest. This requires applica-
tion techniques with sufficient protection for topsoil
for the first two vegetation periods.
15.3.3 Ski runs and agricultural
utilization
15.3.2 Loss of the mother soil, loss of the
established species, and erosion
No resulting burden normally occurs in the recul-
tivated areas in the course of building protective
measures (torrent and avalanche barriers). But areas
used as ski runs in winter and/or alpine pasture in
summer are subject to very special site factors, such
as extended snow cover that is generally longer than
usual at the given altitude. The generally dense snow
cover on ski runs, often with deposits of ice layers,
hinders the exchange of oxygen between the plant
cover, the ground and the atmosphere in winter.
Mechanical disturbance factors, such as the effect of
the steel edges and chains on ski-run preparation
machinery, can have a destructive influence on
vegetation on rounded hills and steep slopes.
Low herbal vegetation growing on ski slopes also
decisively increases the influence of surface runoff
following large volumes of precipitation in high
zones. In contrast to forests and areas stocked with
dwarf shrubs, only technical measures (diagonally
running and open drainage channels) can effect a safe
disposal of the surface water.
Large areas used for agriculture are mostly burdened
by grazing in summer. This burdening can lead to a
multiplicity of damage (trampling and pressure dam-
age by animals, humans and machines, soil density,
etc.), which cause erosion and then require expensive
restoration measures. Nevertheless, the task of the
Removal of the topsoil, as is common in technical inter-
ception, means the destruction of the mother soil
specific to a site. Without this, ecologically adapted
grassland can no longer thrive. Only pioneer com-
munities can develop on stony ground lacking fine
soil, which is usually created within the sphere of
re-cultivation.
The species in the high zones of naturally present
grassland communities are adapted to an optimum
degree to the soil and weather conditions of their
habitat (short vegetation period, low provision of
nutrition). Insofar as they were previously available,
these species as well as the natural seed bank and the
vegetative organs of renewal contained in the mother
soil are generally lost during building activities.
The mastering of erosion, with all of its resulting
effects, such as increased surface drainage and loss of
topsoil, and up to the formation of karst, is one of
the main problems in re-cultivation work in alpine
environments. Average slope gradients of 30 - 45%
in the area of ski runs, and far above in the area of
natural erosion zones and avalanche barriers, make
adequate erosion protection a prerequisite for successful
restoration. Only sufficient vegetation cover stabilizes
the topsoil and reduces soil erosion to an acceptable
degree (Markart
et al.
1997). Results of several
