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 167<br />
ta<strong>in</strong>ty <strong>in</strong>herent <strong>in</strong> one climate scenario: At Davos, <strong>the</strong> smallest PS between <strong>the</strong> species<br />
composition simulated under <strong>the</strong> “best estimate” regionalized scenario (Tab. 6.2) and<br />
those simulated under <strong>the</strong> scenarios correspond<strong>in</strong>g to <strong>the</strong> lower and upper end <strong>of</strong> <strong>the</strong> uncerta<strong>in</strong>ty<br />
range (Tab. 6.3) is 0.73, and <strong>the</strong> average PS is 0.82. At Bern, <strong>the</strong> smallest PS<br />
is 0.84, while <strong>the</strong> average PS amounts to 0.89. At <strong>the</strong> site Bever, however, account<strong>in</strong>g<br />
for <strong>the</strong> uncerta<strong>in</strong>ty <strong>in</strong>herent <strong>in</strong> <strong>the</strong> downscal<strong>in</strong>g scenario produces a wide array <strong>of</strong> forest<br />
compositions (Fig. 6.7): The lowest PS is 0.25, and <strong>the</strong> average PS amounts to 0.51<br />
only. Thus, some <strong>of</strong> <strong>the</strong> simulated forests have hardly anyth<strong>in</strong>g <strong>in</strong> common (Fig. 6.7).<br />
Moreover, <strong>the</strong> simulated total aboveground biomass (Fig. 6.7) varies from 338 t/ha (T-<br />
P-) to 419 t/ha (T+P-); thus <strong>the</strong>re is also a large uncerta<strong>in</strong>ty concern<strong>in</strong>g <strong>the</strong> aboveground<br />
carbon storage <strong>of</strong> <strong>the</strong>se potential future forests. These results also corroborate <strong>the</strong> f<strong>in</strong>d<strong>in</strong>gs<br />
by Fischl<strong>in</strong> et al. (1994), which were based on <strong>the</strong> IPCC scenario for <strong>the</strong> year 2030.<br />
Sensitivity <strong>of</strong> FORCLIM to assumptions on <strong>the</strong> course <strong>of</strong> transient climatic change<br />
The transient simulation results based on scenarios <strong>of</strong> step, ramp, and sigmoid climatic<br />
change reveal that <strong>the</strong>re are no large differences at any site. At <strong>the</strong> site Bever, <strong>the</strong> largest<br />
differences between <strong>the</strong> three scenarios <strong>of</strong> transient climatic change occur (Fig. 6.8).<br />
This is because at Bever <strong>the</strong> difference between <strong>the</strong> steady-state species compositions under<br />
current and regionalized scenarios <strong>of</strong> climatic change is larger than at <strong>the</strong> o<strong>the</strong>r sites<br />
(Fig. 6.5).<br />
The evaluation <strong>of</strong> <strong>the</strong> percentage similarity (PS) coefficients from <strong>the</strong> simulation years<br />
700 through 1300 suggests that <strong>the</strong>re is a short period (from <strong>the</strong> years 820-860) where<br />
<strong>the</strong> disagreement between <strong>the</strong> step and <strong>the</strong> ramp scenario is large (PS 840 = 0.33); this is<br />
due to <strong>the</strong> fact that <strong>in</strong> <strong>the</strong> step scenario <strong>the</strong> breakdown <strong>of</strong> <strong>the</strong> community takes place immediately<br />
after <strong>the</strong> year 800, whereas <strong>in</strong> <strong>the</strong> ramp scenario it starts a few decades later and<br />
proceeds more gradually. The fast breakdown <strong>of</strong> <strong>the</strong> community <strong>in</strong> <strong>the</strong> step scenario <strong>in</strong>creases<br />
light availability markedly, which enables <strong>the</strong> establishment and enhanced growth<br />
<strong>of</strong> light-demand<strong>in</strong>g species like Larix decidua and Quercus robur; however, <strong>the</strong>se species<br />
do not become dom<strong>in</strong>ant and are outcompeted dur<strong>in</strong>g <strong>the</strong> follow<strong>in</strong>g centuries.<br />
<strong>On</strong> <strong>the</strong> o<strong>the</strong>r hand, <strong>the</strong>re is hardly any difference between <strong>the</strong> species composition simulated<br />
with <strong>the</strong> ramp and <strong>the</strong> sigmoid scenario (PS = 0.84 <strong>in</strong> <strong>the</strong> year 860, <strong>in</strong> all o<strong>the</strong>r<br />
years PS > 0.93). Thus, for a climatic change <strong>of</strong> <strong>the</strong> anticipated magnitude tak<strong>in</strong>g place<br />
dur<strong>in</strong>g <strong>the</strong> relatively short time <strong>of</strong> one century, assumptions about how <strong>the</strong> climate