Impacts and Risks of Global Change - Impact of Global Changes on Mountains: Responses and Adaptation - page 38

layer, (iv) destabilization of frozen debris slopes as well as (v) rock-fall
and rock avalanches from frozen rock faces (Kääb et al. 2006). Human life
and settlements as well as infrastructure for high mountain tourism (huts,
buildings, ski-lifts, hiking trails, climbing routes, etc.) and hydropower
plants (buildings, dams, reservoirs) are potentially threatened by these
events (Krainer et al. 2007).
The occurrence of permafrost as such does not present a danger, but
permafrost is inherently a transitory phenomenon. Given this situation,
detailed knowledge of the distribution of permafrost-related slope activity
on a local scale is fundamental to any statement about the potential of
permafrost hazards and for developing strategies by decision makers in
natural hazard management (Monreal and Stötter 2010).
Recently the analysis of multi-temporal laserscan data sets, allowed
a fi rst quantifi cation of area-wide permafrost melting (see Sailer et al.
accepted). As a result of the general lowering of permafrost underlain
high mountain areas, the losses of subsurface ice could thus be calculated.
For the last decade melting rates average out at 5-10 cm per year can be
observed (Fig. 3.3).
Impact on biodiversity
Initial indications of warming-induced migration of species, especially in
the nival zone, date back to the beginning of the 20th century (Klebelsberg
1913). In the 1950s, Braun-Blanquet (1958) confi rmed an increase in species
richness on selected summits above 3000 m in the Rhaetian Alps. Grabherr
et al. (1994) showed this to be a general trend in this region and beyond,
even if some of the 25 summits studied, for which old and reliable records
existed, presented no pronounced increase in species richness. Walther et
al. (2005) reported that in the recent, very warm, decades the process of
upward movement has accelerated. Meanwhile, effects of climate warming
on alpine plants have been recorded for other mountain regions as well.
The current status of evidence-based climate impact research on
mountain vegetation at cold-determined ecotones can be summarized as
follows:
• the tree line ecotone has become denser (e.g., Urals; Moiseev and
Shiyatov 2003; Fig. 3.4) and its upper limits are moving up; this trend
had been reversed during cooler periods (1960s/1970s) as Kullmann
(2007) showed for the tree line of birch forests in the Scandinavian
Mountains;
• the total number of species on mountain summits, especially in the
nival zone, has risen and implies an upwards move of species (e.g.,
Alps: Grabherr et al. 1994, Walther et al. 2005);