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

The forest model FORCLIM 77
NITROGEN AVAILABILITY FOR PLANT GROWTH
The amount of nitrogen available for plant growth (uAvN, Eq. 3.62) is calculated as an
output variable of the FORCLIM-S model from the net nitrogen immobilization of all the
nLC litter cohorts (Eq. 3.61) and the nitrogen mineralization rate (Eq. 3.57). uAvN is
not a state variable because it is assumed that the available nitrogen not used by the plants
in a given year leaves the system either by streamflow or as volatile nitrogen compounds.
Eq. 3.62 also includes the atmospheric deposition of soluble N compounds (kNAtm).
gLImmob =
nLC
∑
c = 1
gNetImmob c
(3.61)
uAvN = MAX ∆HN
∆t
– gLImmob, 0 + kNAtm (3.62)
3.3.3 FORCLIM-E: A model of the abiotic environment
All the equations used in the submodel FORCLIM-E were described previously in our
analysis of the sensitivity of forest gap models to climate parametrization schemes
(Fischlin et al. 1994). Thus, only the modifications made to these equations are presented
and discussed here, using the same notational conventions as in Fischlin et al. (1994).
GENERATION OF WEATHER DATA
Cross-correlated variates of monthly mean temperature (T) and monthly precipitation sum
(P) are generated using the following method: First, we note that the long-term means (µ)
and standard deviations (σ) of these variables may be written as vectors (Eq. 3.63), and
their cross-correlations (r) as a matrix (Eq. 3.64):
µ m,l =
µ T,m,l
µ P,m,l
σ m,l =
σ T,m,l
σ P,m,l
(3.63)
R m,l =
r TT,m,l
r TP,m,l
r PT,m,l r PP,m,l
=
1 r TP,m,l
r PT,m,l 1
(3.64)
where the subscript m stands for a given month, and l for a location. The covariance
matrix of the two variables is given in Eq. 3.65 (Flury & Riedwyl 1983):