Environmental Engineering Reference
In-Depth Information
Figure 15.1
Average changes of important phenological and climatic parameters according to altitude. (Modifi ed from
Krautzer
et al
. 2003 .)
months. During winter, Arctic regions have a compa-
rably long dark period, in which the sun remains per-
manently below the horizon. Accordingly, the Arctic
has not only a distinct temperature climate but also a
markedly seasonally light climate. Mountains also are
frequent in the Arctic regions, which creates altitudi-
nal climatic gradients similar to those in alpine regions.
As a result, Arctic environments are often character-
ized by a fi ne-grained mosaic of local altitudinal and
regional latitudinal climatic gradients.
year in high altitudes; at the beginning and end of the
vegetation period, an interchanging frost climate gen-
erally predominates (Arenson 2002). The relatively
low soil temperatures in alpine environments strongly
reduce the rate of soil microbiological activity and thus
also nutrient cycling. Decomposition of dead organic
mass, and thus the provision of basic mineral nutrition
to plants, is thereby inhibited. The subterranean
habitat is thus limited - contrary to the warmer, lower
zones - to the most strongly warmed, humus-rich and
generally acidic and intensively rooted upper layers of
the ground.
Precipitation generally increases with altitude, while
evaporation rate also rises. Critical situations in the
water balance of plants, however, are rare, other than
in special locations like those exposed to strong radia-
tion, high temperature or strong winds. In general,
wind speed and frequency also increase with altitude.
Wind infl uences alpine plant growth not only directly
but also indirectly due to its impact on snow distribu-
tion pattern during winter. Snow depth may have a
signifi cant impact on, among other things, the length
of the vegetation growth period, soil temperature and
soil humidity. Various inclinations of the sun's radia-
tion create differing degrees of heat. The ecological
signifi cance of differences between a northern and
southern exposition generally increases with altitude.
15.1.2
Specifi c alpine characteristics
Plants at high altitudes are often subject to frequent
and often rough changes of climatic factors. The tran-
sition from one season to the next often takes place
very quickly. With increasing altitude, the vegetation
period is around 1 week shorter per 100 m of rising
altitude (Reisigl & Keller 1994). The differentiation of
the macroclimate from the microclimate, dependent
on altitude and location is important. The most impor-
tant differences depending on altitude can be briefl y
characterized by the factors described below (see also
Figure 15.1 ).
Air temperature generally decreases by 0.6°C per
100 m of altitude. Frost may occur at all times of the
