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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112 Chapter 4<br />
Botk<strong>in</strong> 1993), but most <strong>of</strong> <strong>the</strong>m <strong>in</strong>clude a stochastic wea<strong>the</strong>r generator (one prom<strong>in</strong>ent<br />
exception is FORSKA-2, Prentice et al. 1991, 1993).<br />
At <strong>the</strong> sites Bever and Sion, <strong>the</strong> availability <strong>of</strong> nitrogen simulated by FORCLIM-S does<br />
not have a strong <strong>in</strong>fluence on <strong>the</strong> simulated species composition. At <strong>the</strong> o<strong>the</strong>r two sites,<br />
<strong>the</strong> simulated effect <strong>of</strong> nitrogen availability on forest succession is debatable: At Davos,<br />
<strong>the</strong> biomass peak <strong>of</strong> 600 t/ha, which is made up ma<strong>in</strong>ly <strong>of</strong> L. decidua, appears little<br />
plausible for a subalp<strong>in</strong>e site that should be characterized by low-biomass forests (Fig.<br />
4.10). At <strong>the</strong> site Bern, <strong>the</strong> simulated nitrogen availability leads to a considerable <strong>in</strong>crease<br />
<strong>of</strong> <strong>the</strong> biomass <strong>of</strong> Quercus spp. (Fig. 4.11), which may be questionable because<br />
Quercus spp. should reach large biomass only under warm and dry conditions, for which<br />
<strong>the</strong> site Bern is not characteristic (Ellenberg & Klötzli 1972).<br />
Based on <strong>the</strong>se considerations it is concluded that <strong>the</strong> model variant FORCLIM-E/P/S is<br />
not more trustworthy than <strong>the</strong> model variant FORCLIM-E/P and does not <strong>of</strong>fer clear advantages<br />
over <strong>the</strong> variant E/P. Thus, <strong>in</strong> <strong>the</strong> subsequent <strong>in</strong>vestigations <strong>the</strong> variant<br />
FORCLIM-E/P will be used as <strong>the</strong> standard model setup. The steady-state species compositions<br />
simulated by this model variant at all <strong>the</strong> sites along <strong>the</strong> transect <strong>in</strong> <strong>the</strong> European<br />
Alps are given <strong>in</strong> Fig. 4.12. Typical examples <strong>of</strong> <strong>the</strong> transient behaviour <strong>of</strong> FORCLIM-<br />
E/P at subalp<strong>in</strong>e sites are given <strong>in</strong> Fig. 4.8 (Bever, Davos). Fig. 4.13 shows <strong>the</strong><br />
transient behaviour <strong>of</strong> <strong>the</strong> model at <strong>the</strong> montane site Airolo, which will be used <strong>in</strong> <strong>the</strong> sensitivity<br />
analysis <strong>of</strong> FORCLIM. The behaviour typical <strong>of</strong> low-elevation sites is given <strong>in</strong><br />
Fig. 4.9 (Bern) toge<strong>the</strong>r with that <strong>of</strong> a dry central alp<strong>in</strong>e site (Sion, Fig. 4.9). The<br />
steady-state species composition simulated at <strong>the</strong> <strong>in</strong>subrian site Locarno (Fig. 4.12) does<br />
not differ strongly from <strong>the</strong> one simulated at <strong>the</strong> site Bern, which may be questionable<br />
(Ellenberg 1986). The same goes for <strong>the</strong> species composition simulated at <strong>the</strong> site<br />
Montana (Fig. 4.12). The reasons for this behaviour will be elaborated <strong>in</strong> detail <strong>in</strong><br />
section 5.3.<br />
F<strong>in</strong>ally, it may be concluded that <strong>the</strong> FORCLIM model produces species compositions that<br />
are as plausible as <strong>the</strong> ones obta<strong>in</strong>ed from its predecessor model FORECE (Kienast 1987).<br />
At low-elevation sites (e.g. Bern), <strong>the</strong> FORCLIM simulation results are even more plausible<br />
(Ellenberg & Klötzli 1972, Ellenberg 1986). Fur<strong>the</strong>r tests <strong>of</strong> <strong>the</strong> performance <strong>of</strong><br />
both models will be conducted <strong>in</strong> section 5.3.