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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180 Chapter 8<br />
Several problems rema<strong>in</strong> when attempt<strong>in</strong>g to use FORCLIM to study <strong>the</strong> impact <strong>of</strong> climatic<br />
change on near-natural forests: First, such applications basically deal with extrapolations<br />
<strong>in</strong> time and beyond current ecological conditions. The fact that FORCLIM – although<br />
developed for European conditions – provides plausible descriptions <strong>of</strong> forest dynamics<br />
also <strong>in</strong> eastern North America may provide a clue that such extrapolations may be legitimate.<br />
However, it would be highly desirable to conduct validation experiments under<br />
conditions <strong>of</strong> climatic change, e.g. <strong>in</strong> <strong>the</strong> early Holocene (cf. Solomon et al. 1980, 1981,<br />
Solomon & Tharp 1985, Solomon & Bartle<strong>in</strong> 1993). Although few suitable palaeoecological<br />
records are available and it is difficult to derive <strong>in</strong>dependent climatic data to<br />
drive FORCLIM, such experiments would be important to <strong>in</strong>crease our confidence that <strong>the</strong><br />
model is appropriate for study<strong>in</strong>g some possible impacts <strong>of</strong> climatic change on forests.<br />
Second, some factors that are important <strong>in</strong> mounta<strong>in</strong>ous terra<strong>in</strong> are not considered <strong>in</strong><br />
FORCLIM, such as soil erosion and landslides, which may occur after forest dieback phenomena<br />
and may render large areas <strong>in</strong>appropriate for forest growth. Moreover, air pollution<br />
<strong>in</strong> conjunction with climatic change may lead to unexpected synergistic effects, such<br />
as an <strong>in</strong>creased sensitivity <strong>of</strong> forests to climatic change (e.g. Schulze et al. 1989), and<br />
herbivores could also modify <strong>the</strong> response <strong>of</strong> forests to climatic change (e.g. Fajer et al.<br />
1989). F<strong>in</strong>ally, <strong>in</strong> FORCLIM it is assumed that seeds <strong>of</strong> every species are always available.<br />
In reality, migration <strong>of</strong> trees is slow (e.g. Fenner 1985, Roberts 1989, Leck et al.<br />
1989), and <strong>the</strong> growth <strong>of</strong> new species at a given site <strong>of</strong>ten would start later than predicted<br />
by FORCLIM because <strong>of</strong> delayed immigration. Thus, <strong>the</strong> changes <strong>of</strong> community composition<br />
projected by FORCLIM <strong>of</strong>ten are too fast and may overestimate <strong>the</strong> recovery rates especially<br />
after forest dieback phenomena.<br />
In spite <strong>of</strong> <strong>the</strong>se restrictions, which have to be taken <strong>in</strong>to account especially when <strong>in</strong>terpret<strong>in</strong>g<br />
<strong>the</strong> results obta<strong>in</strong>ed from FORCLIM, it is concluded that this model yields realistic<br />
results when applied along climate gradients and thus can be considered to be appropriate<br />
for assess<strong>in</strong>g <strong>the</strong> impact <strong>of</strong> climatic change on <strong>the</strong> species composition <strong>of</strong> near-natural<br />
forests <strong>in</strong> large parts <strong>of</strong> central Europe and eastern North America.<br />
Implications for impact assessments <strong>of</strong> climatic change<br />
The study <strong>of</strong> forest dynamics for <strong>the</strong> last 500 years at a site representative <strong>of</strong> <strong>the</strong> Swiss<br />
Plateau, us<strong>in</strong>g reconstructed monthly temperature and precipitation data to drive <strong>the</strong><br />
model, showed that <strong>the</strong>se historical climate variations have no impact on <strong>the</strong> simulated