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