On the Ecology of Mountainous Forests in a Changing Climate: A ...

112 Chapter 4
Botkin 1993), but most of them include a stochastic weather generator (one prominent
exception is FORSKA-2, Prentice et al. 1991, 1993).
At the sites Bever and Sion, the availability of nitrogen simulated by FORCLIM-S does
not have a strong influence on the simulated species composition. At the other two sites,
the simulated effect of nitrogen availability on forest succession is debatable: At Davos,
the biomass peak of 600 t/ha, which is made up mainly of L. decidua, appears little
plausible for a subalpine site that should be characterized by low-biomass forests (Fig.
4.10). At the site Bern, the simulated nitrogen availability leads to a considerable increase
of the biomass of Quercus spp. (Fig. 4.11), which may be questionable because
Quercus spp. should reach large biomass only under warm and dry conditions, for which
the site Bern is not characteristic (Ellenberg & Klötzli 1972).
Based on these considerations it is concluded that the model variant FORCLIM-E/P/S is
not more trustworthy than the model variant FORCLIM-E/P and does not offer clear advantages
over the variant E/P. Thus, in the subsequent investigations the variant
FORCLIM-E/P will be used as the standard model setup. The steady-state species compositions
simulated by this model variant at all the sites along the transect in the European
Alps are given in Fig. 4.12. Typical examples of the transient behaviour of FORCLIM-
E/P at subalpine sites are given in Fig. 4.8 (Bever, Davos). Fig. 4.13 shows the
transient behaviour of the model at the montane site Airolo, which will be used in the sensitivity
analysis of FORCLIM. The behaviour typical of low-elevation sites is given in
Fig. 4.9 (Bern) together with that of a dry central alpine site (Sion, Fig. 4.9). The
steady-state species composition simulated at the insubrian site Locarno (Fig. 4.12) does
not differ strongly from the one simulated at the site Bern, which may be questionable
(Ellenberg 1986). The same goes for the species composition simulated at the site
Montana (Fig. 4.12). The reasons for this behaviour will be elaborated in detail in
section 5.3.
Finally, it may be concluded that the FORCLIM model produces species compositions that
are as plausible as the ones obtained from its predecessor model FORECE (Kienast 1987).
At low-elevation sites (e.g. Bern), the FORCLIM simulation results are even more plausible
(Ellenberg & Klötzli 1972, Ellenberg 1986). Further tests of the performance of
both models will be conducted in section 5.3.