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

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1 . Introduction
1.1 Climatic change and mountainous forests
Carbon dioxide and other trace gases in the earth's atmosphere are relatively transparent
to the incoming solar radiation, but they absorb a large portion of the infrared energy radiated
back into space (Schneider 1989). This phenomenon is known as the “greenhouse
effect”. It causes the average surface temperature of the earth to be 35 °C higher than its
radiation temperature as seen from interplanetary space (Siegenthaler & Oeschger 1978).
Without the greenhouse effect, our planet simply would be too cold to support life.
With the onset of fossil fuel burning, large amounts of carbon dioxide were emitted into
the atmosphere, causing a steady increase of its concentration from the preindustrial level
of 285 ppm to 355 ppm at present (Siegenthaler & Oeschger 1987, Houghton et al.
1992). The palaeoclimatic record shows that the concentrations of carbon dioxide and
methane were closely correlated with temperature and have been changing continuously
during the last 200'000 years (Barnola et al. 1987, Kuo et al. 1990, Jouzel et al. 1993).
So why should we bother if climate changes today due to human activities?
During the last 1'500 years the 20-year means of summer temperatures in Scandinavia
oscillated less than ±1 °C around modern values (Briffa et al. 1990, 1992), with some
longer warm (e.g. Medieval Warm Epoch) as well as cool periods (e.g. Little Ice Age).
Brimblecombe & Pfister (1990) showed that such relatively small climatic changes had
major impacts on agricultural yield and, consequently, on the welfare of the human population.
Houghton et al. (1990, 1992) produced various scenarios of future greenhouse
gas emissions, and Wigley & Raper (1992) examined the implications for climate and sea
level of the latest, moderate scenarios (Houghton et al. 1992). They found that both the
magnitude and the rate of the expected global temperature change are far beyond the limits
of natural variability. Thus, future climatic change may have severe consequences for the
biosphere and its components (Bolin et al. 1986, Davis 1990).
Many studies dealt with the possible impact of climatic change on soils (Bouwman 1990,
Anderson 1992), agricultural land (Parry et al. 1988a,b), forests (Shugart et al. 1986,