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

18 Chapter 2
Swiss Plateau, which are much richer both in terms of species composition, total biomass,
and soil fertility (cf. Appendix III for the location and climatic data of the sites).
The additional site-specific parameters required by FORECE for the two sites are given in
Tab. 2.2. The simulations covered 12'000 years at each site.
Emanuel et al. (1978) used spectral analysis to evaluate the behaviour of the FORET
model (Shugart & West 1977). They found that up to 0.05 cycles per year account for a
considerable portion of the spectral energy, corresponding to cycles with a length of 20
years. To resolve these cycles, the sampling interval must not be larger than half the cycle
length. Thus the monitoring interval was set to 5 years in order to allow for an estimation
of the spectrum of the model output.
Statistical analyses of the time series data (Shumway 1988) were performed by means of
the SYSTAT V5.2.1 software (Wilkinson et al. 1992) on Apple Macintosh computers.
The first 1'000 years of each simulation were discarded in order to concentrate on model
behaviour after the transient phase.
Tab. 2.2: Additional site-specific parameters required by the FORECE model for the sites Bern and Davos
(from Kienast 1987 and Kienast, pers. comm.; cf. Kienast & Kuhn 1989a,b).
Parameter Davos Bern
Maximum aboveground biomass [t/ha] 300 540
Field capacity [cm] 27 30
Wilting point [cm] 20 20
Start of vegetation period [day number] 150 120
End of vegetation period [day number] 227 273
Frost threshold (March) [°C] 1.0 3.5
Frost threshold (April) [°C] 4.0 6.5
Frost threshold (May) [°C] 8.0 9.5
Soil moisture indicator value [–] 4 5
Seed for random number generator -12'672 -12'672
RESULTS & DISCUSSION
Davos
A typical part of the time series of species biomasses and tree numbers at the site Davos is
shown in Fig. 2.2. From the point of view of biomass (Fig. 2.2 top), Norway spruce
(Picea excelsa) is the dominating species. Swiss stone pine (Pinus cembra) becomes im-