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

Behaviour of FORCLIM along a transect in the European Alps 117
this would not be true for much larger ∆t where autocorrelation becomes negligible. The
choice of n = 200 and ∆t = 150 seems to provide a good compromise between the simulation
time needed and the accuracy of the estimation; moreover, these data conform to the
considerations in the sections 2.2.1 (autocorrelation) and 2.2.2 (sample size).
SIMILARITY OF INDEPENDENT ESTIMATES OF THE SAME STEADY STATE
The histograms of the distribution of the 200 PS coefficients obtained from 400 simulation
runs at the three sites conform to the hypothesis formulated above (Fig. 4.15,
Tab. 4.6): In the species-poor Larici-Piceetum at Davos (Ellenberg & Klötzli 1972), the
PS coefficients are considerably higher than in the diverse forests of Airolo and Bern.
The reason for the decreasing PS coefficients with increasing species diversity can be explained
by considering the averages of the estimated species-specific biomasses and their
coefficients of variation (CV, Zar 1984) from the 400 steady states estimated at each site.
Frequency
Bern
40
35
30
25
20
15
10
5
0
.8 .825 .85 .875 .9 .925 .95 .975 1
PS
Airolo
40
35
30
25
20
15
10
5
0
.8 .825 .85 .875 .9 .925 .95 .975 1
PS
Frequency
Davos
40
35
30
25
20
15
10
5
0
.8 .825 .85 .875 .9 .925 .95 .975 1
PS
Fig. 4.15: Frequency distribution of the percentage similarity coefficients (PS) from 200
pairs of equilibrium states estimated at the sites Bern, Airolo, and Davos, using n=200 and
∆t=150 years. The distributions at the sites Bern and Airolo are not significantly different
from each other (p = 0.12, Kolmogorov-Smirnov test, Zar 1984).