On the Ecology of Mountainous Forests in a Changing Climate: A ...

2 Chapter 1
Shands & Hoffman 1987, Fabian 1991, Thomasius 1991, Shugart et al. 1992), and on
the whole biosphere (e.g. Emanuel et al. 1985, Smith et al. 1992, Prentice et al. 1992,
Solomon & Shugart 1993, Cramer & Solomon 1993). The fate of forests is of particular
interest not only from a regional or national, but also from a global perspective
(Wisniewski et al. 1993): The equivalent of the entire atmospheric carbon dioxide passes
through the terrestrial biota every 7 years, with about 70% of the exchange occurring
through forests (Waring & Schlesinger 1985). Thus, climate-induced changes of primary
productivity, soil respiration or the areal extent of forests may lead to a significant biospheric
feedback to the climate system. For example, Tans et al. (1990) hypothesized that
the carbon content of temperate forests in the northern hemisphere is currently increasing,
thus removing part of the emitted CO 2 from the atmosphere (“missing sink”, Post et al.
1990).
Forests in mountainous areas have a multitude of functions: They may protect settlements
and roads from avalanches, they regulate runoff and prevent erosion, and they form a
part of the largest terrestrial biotic carbon pool. Forests and meadows make a varied landscape
and provide the environment necessary for many touristic activities, and – last but
not least – forests are exploited for fuel, pulpwood, and timber. Climatic change may
have a strong impact on all these functions (Bolin et al. 1986). Hence studies of the impact
of climatic change on mountainous forests could be of practical relevance to politicians,
foresters, and the broad public (Hostettler 1991, Tranchet et al. 1993).
One of the characteristic features of mountainous areas is their complex spatial pattern
with steep gradients over short distances. For example, in the central part of the European
Alps the distance between the lower (dry) timberline in the bottom of the Rhone valley
and the alpine (cold) timberline is in the order of 10 km only. Thus, mountainous forests
may show a broad spectrum of responses to climatic change. On the other hand, predicting
these responses is more difficult than in flat terrain and requires to study many factors
explicitly and in detail.
The major emphasis of the present study is to contribute to impact assessments of climatic
change on mountainous forests, selecting the European Alps as a case study. To achieve
this goal, the climatic and ecological factors governing the long-term dynamics of nearnatural
forest ecosystems in this area shall be elaborated first. Then the sensitivity to climatic
change of these forests shall be studied extensively by means of scenarios describing
the anticipated climatic changes.