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

20 Chapter 2
5000
Davos, 7500-7600
Bern, 7500-7570
Total tree number (#/ha)
4000
3000
2000
1000
7600
7500
7550
7500
7570
7535
0
6
7
8 9 10
LAI (m2/m2)
11
12
6
7
8 9 10
LAI (m2/m2)
11
12
Fig. 2.3: Phase diagram of total tree number vs. double-sided leaf area index (LAI) at
Davos (left) and Bern (right). Numbers in the graphs denote simulation years.
1 Davos
1 Bern
CCF
0
CCF
0
-1
-200
-100
Lag
0
(years)
100
200
-1
-200
-100
Lag
0
(years)
100
200
Fig. 2.4: Cross-correlation functions (CCF) of total tree numbers vs. leaf area index at
Davos (left) and Bern (right) for the simulation years 1'005-12'000. The dotted lines indicate
the 95% confidence limits for CCF = 0.
To elaborate the pattern underlying the simulated time series of biomass and tree numbers,
the total number of trees was plotted against leaf area index (LAI), which is closely
correlated with total aboveground biomass (Fig. 2.3): There is a cyclical behaviour of
these variables because low LAI causes enhanced sapling establishment, which in turn increases
LAI until light availability drops to a point where establishment is reduced again.
Finally, LAI decreases strongly when a canopy dominant dies, and the cycle repeats.
However, the examples in Fig. 2.3 represent ideal rather than typical cases. In the
model, the cycles may be interrupted earlier because a large tree dies prematurely, or they
often last longer because a suppressed subdominant tree comes to dominate after the