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

The forest model FORCLIM 59
Light availability
If available light at the forest floor (gAL 0 , calculated according to Eq. 3.18) drops below
a species-specific threshold (kThres s ) defined as a fraction of full sunlight, sapling
establishment is prevented according to Eq. 3.2 & 3.3:
gLFlag s =
0 gAL 0 < kThres s
1 else
(3.2)
where the species-specific threshold kThres s is calculated according to Ellenberg (1986,
Fig. 3.5 left) based on the parameter kL y,s , which denotes the light requirements of
saplings (“young trees”) on a nominal scale in the range [1..9]:
kThres s =
0.025·(kL y,s –1) kL y,s < 5
0.1·kL y,s - 0.4 else
(3.3)
Browsing pressure
The constant browsing intensity simulated in the FORECE model (Kienast 1987) was
modified in a simple way which allows to explore the possible effects of varying browsing
intensities on sapling establishment rates (Fig. 3.5 right):
0.50
1.0
kThres s
0.25
s
gBrP
0.8
0.6
0.4
0.2
kBrow s = 3
0.00
1
3
5
kLys
7
9
0.0
-0.2
0
kBrow s = 1
5
10
kBrPr
Fig. 3.5: Factors influencing sapling establishment. Left: The threshold parameter kThres s
(% of full sunlight) is a function of the species parameter kL y,s (Eq. 3.3). Right: The
probability that establishment is prevented (gBrP s ) depends on browsing pressure (kBrPr)
and the susceptibility to browsing of the tree species (kBrow s ).