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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Behaviour <strong>of</strong> FORCLIM along a transect <strong>in</strong> <strong>the</strong> European Alps 111<br />
Tab. 4.5: Organic matter <strong>in</strong> <strong>the</strong> litter (LOM, t/ha) and humus compartments (HOM, t/ha), total soil organic<br />
matter (SOM, t/ha), and total available nitrogen (uAvN, kg/ha) as calculated by FORCLIM-E/P/S <strong>in</strong><br />
<strong>the</strong> steady state. Cf. Tab. 4.3 with <strong>the</strong> same results from <strong>the</strong> FORCLIM-S model simulated <strong>in</strong> isolation.<br />
Site uAvN LOM HOM SOM<br />
Bever N 72.7 57.0 260.1 317.1<br />
Davos 80.5 67.4 113.4 180.9<br />
Sion 88.3 87.6 56.3 143.9<br />
Bever S 68.0 52.4 92.3 144.7<br />
Bern 137.0 111.3 85.1 196.3<br />
Locarno 142.0 119.8 81.0 200.8<br />
4.3.4 Discussion & conclusion<br />
The simulation studies with various comb<strong>in</strong>ations <strong>of</strong> submodels, all <strong>in</strong>clud<strong>in</strong>g FORCLIM-<br />
P, reveal <strong>the</strong> follow<strong>in</strong>g:<br />
The FORCLIM-P model driven by constant wea<strong>the</strong>r (section 4.3.1) produces plausible<br />
species compositions for some sites (Davos, Bern). However, under circumstances <strong>of</strong><br />
strong environmental stress, such as close to <strong>the</strong> alp<strong>in</strong>e and <strong>the</strong> dry timberl<strong>in</strong>e (Bever,<br />
Sion), average wea<strong>the</strong>r conditions do not suffice to characterize <strong>the</strong> effects <strong>of</strong> <strong>the</strong> abiotic<br />
environment on <strong>the</strong> trees. It may be concluded that <strong>the</strong> variability <strong>of</strong> <strong>the</strong> abiotic environment<br />
is at least as important as its averages (cf. Katz & Brown 1992), and that it is necessary<br />
to couple FORCLIM-E with FORCLIM-P explicitly (section 4.3.2).<br />
The nitrogen availability simulated by <strong>the</strong> submodel FORCLIM-S when coupled to FOR-<br />
CLIM-P changes strongly through time. This may have a considerable effect on <strong>the</strong> simulated<br />
species compositions. <strong>On</strong> <strong>the</strong> o<strong>the</strong>r hand, <strong>the</strong> amount <strong>of</strong> soil organic matter simulated<br />
by FORCLIM-S does not change much if <strong>the</strong> FORCLIM-P model is used to simulate litter<br />
production <strong>in</strong>stead <strong>of</strong> assum<strong>in</strong>g a constant production. Thus, <strong>the</strong> behaviour <strong>of</strong><br />
FORCLIM-S is <strong>in</strong>fluenced only weakly by FORCLIM-P, but FORCLIM-P is <strong>in</strong>fluenced<br />
more strongly by FORCLIM-S.<br />
The simulation results at <strong>the</strong> four sites (Fig. 4.6 – 4.11) suggest that <strong>the</strong> coupl<strong>in</strong>g between<br />
FORCLIM-S and FORCLIM-P is weaker than <strong>the</strong> one between FORCLIM-E and<br />
FORCLIM-P. The strength <strong>of</strong> <strong>the</strong>se coupl<strong>in</strong>gs may be used to expla<strong>in</strong> why <strong>the</strong> large majority<br />
<strong>of</strong> forest gap models constructed so far have been successful although <strong>the</strong>y ignore<br />
<strong>the</strong> dynamics <strong>of</strong> nutrients and soil organic matter (Botk<strong>in</strong> et al. 1972a,b, Shugart 1984,