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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94<br />
4 . Behaviour <strong>of</strong> FORCLIM along a<br />
transect <strong>in</strong> <strong>the</strong> European Alps<br />
The modular structure <strong>of</strong> FORCLIM makes it possible to exam<strong>in</strong>e <strong>the</strong> behaviour <strong>of</strong> each<br />
submodel <strong>in</strong> isolation before consider<strong>in</strong>g comb<strong>in</strong>ations <strong>of</strong> <strong>the</strong> three submodels. This allows<br />
to quantify e.g. <strong>the</strong> effects <strong>of</strong> FORCLIM-E on FORCLIM-P, and to evaluate <strong>the</strong> feedback<br />
mechanisms between FORCLIM-P and FORCLIM-S. Thus, <strong>in</strong> a first step each submodel<br />
will be run on its own, ei<strong>the</strong>r for all or a selection <strong>of</strong> <strong>the</strong> sites given <strong>in</strong> Appendix<br />
III (sections 4.1 – 4.3.1). Second, two <strong>in</strong>terest<strong>in</strong>g comb<strong>in</strong>ations <strong>of</strong> submodels will be exam<strong>in</strong>ed:<br />
(1) FORCLIM-E/P, a setup correspond<strong>in</strong>g to many o<strong>the</strong>r forest gap models (section<br />
4.3.2), and (2) <strong>the</strong> full FORCLIM-E/P/S model, a setup com<strong>in</strong>g closer to a true ecosystem<br />
model (section 4.3.3). F<strong>in</strong>ally, a method for estimat<strong>in</strong>g efficiently <strong>the</strong> steady state<br />
species composition <strong>of</strong> FORCLIM will be developed (section 4.4).<br />
4.1 FORCLIM-E<br />
The FORCLIM-E model was run for <strong>the</strong> time w<strong>in</strong>dow 0…5000 years at all 12 sites<br />
(Tab. 4.1). These sites correspond to an ecological gradient from cool to warm and from<br />
ecologically wet to dry (cf. <strong>the</strong> variables uDD and uDrStr, Cleuson – Sion <strong>in</strong> Tab. 4.1).<br />
There is an emphasis on sites around uDD = 1900 °C·d (Huttwil – Basel) because <strong>the</strong>se<br />
conditions are typical for a large part <strong>of</strong> <strong>the</strong> Swiss Plateau.<br />
It is evident from Tab. 4.1 that <strong>the</strong>se sites do not correspond to a smooth gradient <strong>of</strong> <strong>the</strong><br />
drought stress <strong>in</strong>dex. For example, <strong>the</strong>re are no sites with 0.06 < uDrStr < 0.2. In fact,<br />
drought gradients are very steep <strong>in</strong> <strong>the</strong> European Alps. In central alp<strong>in</strong>e valleys<br />
precipitation decreases from around 800 mm to 600 mm over distances as small as<br />
30 km (e.g. from Martigny to Sion; Martigny has similar climatic parameters as Basel,<br />
Tab. 4.1); yet this corresponds to a strong <strong>in</strong>crease <strong>of</strong> drought stress. These gradients<br />
will be explored <strong>in</strong> more detail <strong>in</strong> chapter 5.<br />
The cross-correlation coefficients between monthly temperature means and monthly<br />
precipitation sums affect both <strong>the</strong> actual evapotranspiration (uAET) and <strong>the</strong> drought stress