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

116 Chapter 4
three sites along a gradient of altitude and species diversity (Bern, Airolo, Davos;
Fig. 4.12), and the distributions of the PS coefficients calculated from 200 pairs of independent
steady states were analysed statistically.
4.4.2 Results & discussion
SIMILARITY TO THE “TRUE” STEADY STATE SPECIES COMPOSITION
Fig. 4.14 shows the averages and standard deviations of the 20 PS coefficients as a
function of n and ∆t. There is a strong increase of the PS up to n ≈ 200; with higher
values of n, the increase of precision becomes comparably small. It is interesting to note
that about the same increase of precision is achieved when ∆t is increased by 50% (from
100 to 150 years) as when n is doubled, i.e. increasing ∆t is more efficient. However,
100
Average of PS coefficients
PS (%)
90
∆t = 150
80
0
200
400
n
600
∆t = 100
800 1000
SD (%)
6
4
2
Standard deviations of PS
∆t = 150
∆t = 100
0
0
200
400
n
600
800
1000
Fig. 4.14: Convergence of the percentage similarity coefficient between estimated
equilibrium states and a conjectured “true” equilibrium state at the site Bern in function of
the number of points (n) and the point-to-point distance (∆t) used.