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

Behaviour of FORCLIM along a transect in the European Alps 99
4.2 FORCLIM-S
The buildup of soil organic matter was evaluated at six sites along a gradient of increasing
actual evapotranspiration (Bever, north-facing slope; Davos; Sion; Bever, south-facing
slope; Bern; Locarno; cf. Tab. 4.1). It was assumed that there is no organic material at
the beginning of the simulations and that there is a constant annual input of litter into the
system (Tab. 4.4). The simulations were run until the steady state of soil organic matter
was reached.
Bever (north facing slope), ForClim-S
400
Organic matter [t/ha]
Available nitrogen [kg/ha]
300
200
100
0
0
50
100
150
200
250
300
uAvN
LOM
HOM
SOM
Simulation time [years]
Fig. 4.5: Buildup of soil organic matter content on a north-facing slope at the site Bever
as simulated by FORCLIM-S. LOM: litter organic matter; HOM: humus organic matter;
SOM: total soil organic matter, SOM = LOM + HOM; uAvN: nitrogen available for plant
growth. Litter input is from Tab. 4.4, and actual evapotranspiration is from Tab. 4.1.
Fig. 4.5 shows typical simulation results obtained from FORCLIM-S for a northern slope
at the site Bever. The steady state of belowground organic matter is reached within 200-
250 years, and Tab. 4.3 gives an overview of the steady-state results obtained at the six
sites.
As mentioned in the section on the assumptions of FORCLIM-S, both LINKAGES and
FORCLIM-S lack a carbon pool with a turnover rate in the order of 1000 years (Parton et
al. 1987, Verberne et al. 1990). Hence the steady state of belowground organic matter is
reached too fast and is slightly too low in these models (cf. Fig. 4.5). A hypothesized
“slow” compartment would be small and would react much more slowly to climatic
change than the species composition. Moreover, within the next few hundred years the