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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Model applications 157<br />
6.2 Possible effects <strong>of</strong> future climatic change on forest<br />
ecosystems <strong>in</strong> <strong>the</strong> European Alps<br />
Any assessment <strong>of</strong> <strong>the</strong> possible effects <strong>of</strong> future climatic change on forest ecosystems is<br />
faced with a tw<strong>of</strong>old problem: First, <strong>the</strong>re is a considerable uncerta<strong>in</strong>ty <strong>in</strong>herent <strong>in</strong> <strong>the</strong><br />
predictions <strong>of</strong> future climate, both on <strong>the</strong> global and even more pronounced on <strong>the</strong> regional<br />
scale (Houghton et al. 1990, 1992, Wigely & Raper 1992). Second, every forest<br />
model <strong>in</strong>corporates different and highly simplified parametrizations <strong>of</strong> ecological processes;<br />
<strong>the</strong>se certa<strong>in</strong>ly conta<strong>in</strong> errors both on <strong>the</strong> quantitative and maybe even on <strong>the</strong> conceptual<br />
level (Solomon 1986, Shugart & Prentice 1992). Thus, it appears to be more<br />
promis<strong>in</strong>g to analyse <strong>the</strong> behaviour <strong>of</strong> several ecological models under several scenarios<br />
<strong>of</strong> climatic change <strong>in</strong>stead <strong>of</strong> focus<strong>in</strong>g on just one model and one scenario. This approach<br />
also emphasizes that such studies are tests <strong>of</strong> <strong>the</strong> sensitivity <strong>of</strong> forests ecosystems to climatic<br />
changes, and not predictions <strong>of</strong> <strong>the</strong>ir future structure and function<strong>in</strong>g.<br />
In this section, scenarios <strong>of</strong> climatic change will be used that refer to <strong>the</strong> year 2100, and it<br />
will be assumed that <strong>the</strong> climatic parameters reached by <strong>the</strong>n can be used to def<strong>in</strong>e a new,<br />
constant climate. It is undisputed that this assumption is unrealistic because <strong>the</strong>re is no<br />
evidence that climatic change would come to a halt by <strong>the</strong> end <strong>of</strong> <strong>the</strong> next century<br />
(Houghton et al. 1990, 1992). Aga<strong>in</strong>, it should be noted that <strong>the</strong> simulation results<br />
obta<strong>in</strong>ed like this do not constitute predictions <strong>of</strong> <strong>the</strong> future state <strong>of</strong> forests <strong>in</strong> <strong>the</strong> European<br />
Alps, but simple sensitivity tests.<br />
First, let us assume that <strong>the</strong>re was one forest model that we could favour over all <strong>the</strong><br />
o<strong>the</strong>rs. How does this model behave when it is exposed to several climate scenarios?<br />
How sensitive are <strong>the</strong> projections obta<strong>in</strong>ed from <strong>the</strong> forest model to <strong>the</strong> differences between<br />
<strong>the</strong>se climate scenarios?<br />
Second, given that <strong>the</strong>re was no uncerta<strong>in</strong>ty <strong>in</strong> <strong>the</strong> prediction <strong>of</strong> future climate, i.e. that<br />
one climate scenario could be identified unequivocally as <strong>the</strong> “best estimate”, how does<br />
<strong>the</strong> behaviour <strong>of</strong> several forest models compare under this climate scenario? Are <strong>the</strong> projections<br />
on future forest ecosystem structure sensitive to <strong>the</strong> assumptions <strong>in</strong>corporated <strong>in</strong><br />
<strong>the</strong> various forest models?<br />
Third, even if we could favour one climate scenario over <strong>the</strong> o<strong>the</strong>rs, <strong>the</strong>re is some uncerta<strong>in</strong>ty<br />
<strong>in</strong>herent <strong>in</strong> this scenario. How sensitive are <strong>the</strong> projections obta<strong>in</strong>ed from a forest<br />
model to <strong>the</strong>se uncerta<strong>in</strong>ties?