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

Conclusions 181
species composition of near-natural forests (section 6.1). However, future climatic
change is likely to affect the species compositon of these forests (section 6.2). Hence not
only the magnitude and rate of future climatic change (Wigely & Raper 1992), but also
the biotic responses to these changes are beyond the limits of natural variability and deserve
to be studied in detail.
The simulation experiments conducted with several forest gap models under several scenarios
of climatic change for the year 2100 (chapter 6) reveal a common pattern: The effects
of the anticipated climatic change on forest ecosystems differ strongly depending on
the geographical location considered. Specifically, forests that are subject to considerable
environmental stress under current conditions, such as close to the alpine and the dry timberline,
are likely to undergo major changes, whereas sites at mid altitudes appear to be
buffered rather well to these climatic changes. However, forests at mid altitudes may be
affected as well if climatic change should exceed that projected for the year 2100, which
is quite probable (Houghton et al. 1990, 1992, Wigely & Raper 1992).
At some sites, the forests simulated by one model under various scenarios of climatic
change have little in common except that they are different from current forests. It is not
possible to identify unequivocally which of these scenarios describes the future climate
best and to ignore the others. Hence we have to conclude that the precision of the forecasts
of future climatic change falls short relative to the sensitivity of the forest models,
and it is therefore not possible to predict the potential natural vegetation at a given time
and a given place in the future. Moreover, there are marked differences between the projections
obtained from various forest models under the same scenario of climatic change.
Hence there is also a considerable uncertainty concerning the number of ecological factors
to be included in forest gap models and, even more pronunced, their specific formulation.
However, these restrictions do not mean that no statements can be made at all. The
strength of the application of forest gap models for impact assessments is that they provide
us with statements on the sensitivity of the current potential natural vegetation to climatic
change. The present study shows that many forest ecosystems in the European
Alps are sensitive to climatic parameters. Already under the climatic change anticipated
for the year 2100 dieback phenomena could occur in some forests, possibly with irreversible
consequences for the structure and functioning of these ecosystems. These findings
strongly suggest that it is important to implement abatement policies to fight the increase
of greenhouse gas concentrations in the atmosphere on the global as well as the national
scale.