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

The forest model FORCLIM 83
microclimatic differences, which may be especially important in the subalpine zone where
direct radiation is considerably higher than at lower altitudes.
Finally, drought stress (uDrStr) is calculated in FORCLIM-E according to Eq. 3.75; the
calculation of uAET y,l and PET y,l were described in detail by Fischlin et al. (1994).
uDrStr = 1 – uAET y,l
PET y,l
(3.75)
3.4 Parameter estimation
3.4.1 FORCLIM-P
The 30 tree species present in the model under European conditions were chosen based
on Hess et al. (1980) and Kienast (1987). The derivation of the species-specific parameter
values for these species required a major effort, which is documented in Appendix
II. The values finally obtained are given in Tab. 3.11, while the other parameter
values are listed in Tab. 3.12 & 3.13. Some of the species-specific parameters in
FORCLIM-P were simplified by defining species groups: A new species-specific parameter
called sType (species type) was introduced (Tab. 3.10). It serves the following
purposes:
• First, it separates evergreen (coniferous) from deciduous species. This distinction
is possible because all the species of a type behave similar in various respects:
(1) the foliage area per unit foliage weight (parameter kC 2,s , Tab. 3.3),
(2) the dry to wet weight ratio of foliage (kC 1,s , Tab. 3.3), and (3) the average
retention time of foliage (kFRT s ; Tab. 3.5).
• The second information contained in the sType parameter is the type of relationship
between diameter at breast height and foliage weight, thus replacing the
parameters kA i,s (Tab. 3.3). Five species types were derived from an extensive
analysis of the data by Burger (1945-1953).
The rationale for the grouping of the species and the estimation procedure for these parameters
are described in Appendix II.