On the Ecology of Mountainous Forests in a Changing Climate: A ...
On the Ecology of Mountainous Forests in a Changing Climate: A ...
On the Ecology of Mountainous Forests in a Changing Climate: A ...
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176 Chapter 7<br />
year 2100 (Houghton et al. 1990, 1992). Hence <strong>the</strong>se results do not mean that future climatic<br />
change will not affect <strong>the</strong>se forests drastically, but that <strong>the</strong>y are buffered better<br />
aga<strong>in</strong>st climatic change than forests that are subject to environmental stress already under<br />
current climate (Bugmann & Fischl<strong>in</strong> 1994).<br />
The comparison <strong>of</strong> <strong>the</strong> behaviour <strong>of</strong> five forest gap models under one scenario <strong>of</strong> climatic<br />
change shows that <strong>the</strong> models disagree most sharply at sites close to <strong>the</strong> alp<strong>in</strong>e timberl<strong>in</strong>e.<br />
Thus, under <strong>the</strong>se conditions <strong>the</strong> models are sensitive to climatic parameters as well as to<br />
<strong>the</strong> formulation <strong>of</strong> ecological factors. Although <strong>the</strong>re is less divergence at <strong>the</strong> o<strong>the</strong>r sites<br />
and it is felt that FORCLIM-E/P and FORCLIM-E/P/S are <strong>the</strong> most trustworthy <strong>of</strong> all <strong>the</strong><br />
five models studied, it is daunt<strong>in</strong>g to see <strong>the</strong> differences <strong>the</strong> five models produce. Moreover,<br />
<strong>the</strong>re is no clue that future versions <strong>of</strong> FORCLIM will be robust <strong>in</strong> <strong>the</strong>ir projections.<br />
For example, ongo<strong>in</strong>g research (Perruchoud 1994) is aimed at provid<strong>in</strong>g an improved<br />
version <strong>of</strong> FORCLIM-S, which aga<strong>in</strong> may lead to projections about future forests differ<strong>in</strong>g<br />
strongly from <strong>the</strong> present ones. Thus, <strong>the</strong>re is a serious problem concern<strong>in</strong>g <strong>the</strong> number<br />
<strong>of</strong> factors to be <strong>in</strong>cluded <strong>in</strong> forest ecosystem models and <strong>the</strong>ir exact formulation (cf.<br />
Bonan 1993).<br />
Even if <strong>the</strong> best scenario <strong>of</strong> climatic change could be unequivocally identified, <strong>the</strong>re<br />
would rema<strong>in</strong> some uncerta<strong>in</strong>ty <strong>in</strong> it. The <strong>in</strong>vestigation <strong>of</strong> <strong>the</strong> propagation <strong>of</strong> <strong>the</strong> uncerta<strong>in</strong>ties<br />
<strong>in</strong>herent <strong>in</strong> a state-<strong>of</strong>-<strong>the</strong>-art scenario obta<strong>in</strong>ed from large-scale GCM data<br />
(Gyalistras et al. 1994) showed that, aga<strong>in</strong> ma<strong>in</strong>ly at sites close to <strong>the</strong> timberl<strong>in</strong>e, a bewilder<strong>in</strong>g<br />
array <strong>of</strong> possible future forest compositions is obta<strong>in</strong>ed. Thus also such a climate<br />
scenario does not currently match <strong>the</strong> precision requirements <strong>of</strong> forest ecosystem models,<br />
corroborat<strong>in</strong>g <strong>the</strong> f<strong>in</strong>d<strong>in</strong>gs by Fischl<strong>in</strong> et al. (1994), which were based on a different climate<br />
scenario.<br />
FORCLIM was developed to <strong>in</strong>clude reliable formulations <strong>of</strong> <strong>the</strong> <strong>in</strong>fluence <strong>of</strong> temperature<br />
and precipitation on ecological processes. Thus it may be hypo<strong>the</strong>sized that <strong>the</strong> model is<br />
trustworthy enough to assess <strong>the</strong> possible impact <strong>of</strong> climatic change on forest ecosystems<br />
<strong>in</strong> <strong>the</strong> European Alps. However, as discussed above little confidence can be placed <strong>in</strong> its<br />
projections both for climatological and ecological reasons. Yet, even if we are not able to<br />
give precise <strong>in</strong>formation on <strong>the</strong> potential future species composition at a given location,<br />
this does not mean that no statements could be made at all: The strength <strong>of</strong> <strong>the</strong> application<br />
<strong>of</strong> forest gap models <strong>in</strong> impact assessments <strong>of</strong> climatic change lies <strong>in</strong> determ<strong>in</strong><strong>in</strong>g <strong>the</strong> sensitivity<br />
<strong>of</strong> <strong>the</strong> simulated species composition to changes <strong>of</strong> climatic parameters. In this<br />
sense and under <strong>the</strong> assumption <strong>of</strong> a constant climate correspond<strong>in</strong>g to <strong>the</strong> climate at <strong>the</strong>