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

176 Chapter 7
year 2100 (Houghton et al. 1990, 1992). Hence these results do not mean that future climatic
change will not affect these forests drastically, but that they are buffered better
against climatic change than forests that are subject to environmental stress already under
current climate (Bugmann & Fischlin 1994).
The comparison of the behaviour of five forest gap models under one scenario of climatic
change shows that the models disagree most sharply at sites close to the alpine timberline.
Thus, under these conditions the models are sensitive to climatic parameters as well as to
the formulation of ecological factors. Although there is less divergence at the other sites
and it is felt that FORCLIM-E/P and FORCLIM-E/P/S are the most trustworthy of all the
five models studied, it is daunting to see the differences the five models produce. Moreover,
there is no clue that future versions of FORCLIM will be robust in their projections.
For example, ongoing research (Perruchoud 1994) is aimed at providing an improved
version of FORCLIM-S, which again may lead to projections about future forests differing
strongly from the present ones. Thus, there is a serious problem concerning the number
of factors to be included in forest ecosystem models and their exact formulation (cf.
Bonan 1993).
Even if the best scenario of climatic change could be unequivocally identified, there
would remain some uncertainty in it. The investigation of the propagation of the uncertainties
inherent in a state-of-the-art scenario obtained from large-scale GCM data
(Gyalistras et al. 1994) showed that, again mainly at sites close to the timberline, a bewildering
array of possible future forest compositions is obtained. Thus also such a climate
scenario does not currently match the precision requirements of forest ecosystem models,
corroborating the findings by Fischlin et al. (1994), which were based on a different climate
scenario.
FORCLIM was developed to include reliable formulations of the influence of temperature
and precipitation on ecological processes. Thus it may be hypothesized that the model is
trustworthy enough to assess the possible impact of climatic change on forest ecosystems
in the European Alps. However, as discussed above little confidence can be placed in its
projections both for climatological and ecological reasons. Yet, even if we are not able to
give precise information on the potential future species composition at a given location,
this does not mean that no statements could be made at all: The strength of the application
of forest gap models in impact assessments of climatic change lies in determining the sensitivity
of the simulated species composition to changes of climatic parameters. In this
sense and under the assumption of a constant climate corresponding to the climate at the