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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164 Chapter 6<br />
At <strong>the</strong> site Airolo (Fig. 6.5), spruce (P. excelsa), which is characteristic <strong>of</strong> montane<br />
mixed forests, is replaced by silver fir (A. alba), beech (F. silvatica), and o<strong>the</strong>r deciduous<br />
species under both climate scenarios. Compar<strong>in</strong>g <strong>the</strong>se results to <strong>the</strong> ones by Kienast<br />
(1991) is difficult because <strong>of</strong> <strong>the</strong> large sensitivity to species parameters <strong>in</strong> <strong>the</strong> FORECE<br />
model (cf. section 5.1), and fur<strong>the</strong>r studies with <strong>the</strong> FORECE model would be required to<br />
allow for a mean<strong>in</strong>gful comparison.<br />
At <strong>the</strong> site Bern (Fig. 6.5), only slight changes occur as compared to current climatic<br />
conditions. The major features <strong>of</strong> <strong>the</strong> current forests, especially <strong>the</strong> dom<strong>in</strong>ance <strong>of</strong> beech<br />
(F. silvatica) and silver fir (A. alba), rema<strong>in</strong> characteristic also <strong>of</strong> future forests; under all<br />
scenarios, similar forest compositions are obta<strong>in</strong>ed.<br />
At Sion, major differences become evident concern<strong>in</strong>g <strong>the</strong> physiognomy <strong>of</strong> <strong>the</strong> site under<br />
climatic change: While <strong>the</strong> IPCC scenario leads to steppification, a scrawny, low-biomass<br />
forest cont<strong>in</strong>ues to exist under <strong>the</strong> Kienast scenario. Us<strong>in</strong>g FORECE, Kienast (1991)<br />
found that steppification may occur with<strong>in</strong> 50 years after <strong>the</strong> onset <strong>of</strong> climatic change.<br />
Moreover, simulation results from FORCLIM-E/P/S under <strong>the</strong> regionalized scenario (A.<br />
Fischl<strong>in</strong>, pers. comm.) also project that forests would cease to grow at Sion. Hence, accord<strong>in</strong>g<br />
to <strong>the</strong>se simulation studies <strong>the</strong>re is a considerable risk that sites close to <strong>the</strong> dry<br />
timberl<strong>in</strong>e may be confronted with forest dieback phenomena and steppification under climatic<br />
change.<br />
The behaviour <strong>of</strong> five forest models under <strong>the</strong> regionalized scenarios<br />
The simulation results from <strong>the</strong> five forest models at <strong>the</strong> sites Bever, Davos, and Bern are<br />
shown <strong>in</strong> Fig. 6.6. At <strong>the</strong> site Bever, <strong>the</strong> models produce strongly differ<strong>in</strong>g species<br />
composition under this scenario <strong>of</strong> climatic change. While <strong>the</strong> percentage similarity coefficient<br />
(PS, Eq. 2.3) between FORCLIM-E/P and E/P/S is 0.75, and PS = 0.85 between<br />
FORCLIM 1.1 and 1.3, <strong>the</strong>re is little resemblance between <strong>the</strong>se two groups and <strong>the</strong><br />
FORECE species composition (PS < 0.4). At <strong>the</strong> site Davos, <strong>the</strong>re are also considerable<br />
differences among <strong>the</strong> models, but <strong>the</strong>y are more gradual than at Bever. The forest composition<br />
at <strong>the</strong> low-elevation site Bern exhibits <strong>the</strong> smallest differences among <strong>the</strong> five<br />
models (Fig. 6.6).