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

Discussion 175
comparably small improvements, such as adding an additional light tolerance class for
saplings, could strongly increase the realism of the results obtained so far. However, similar
to the findings from the (T,P) space, FORCLIM encounters major difficulties along
drought gradients, i.e. in the southeastern U.S.; yet other models like FORENA (Solomon
1986) and LINKAGES (W.M. Post, pers. comm.) are faced with the same problem.
Hence it appears that current forest gap models generally are not apt for simulating forest
dynamics along drought gradients.
Both the simulation study in the (T,P) space and along a latitudinal gradient in eastern
North America suggest that the simplification of a complex model like FORECE does not
have to hamper the realism with which it is capable of simulating forest succession. On
the contrary, the improvements introduced when developing the FORCLIM model appear
to have increased its realism. Moreover, the parameter space of the model could be reduced
drastically, from more than 1300 (FORECE) to 540 parameters (FORCLIM). However,
additional validation studies should be conducted to analyse further deficiencies of
FORCLIM, e.g. using proxy data like pollen records or spatial data obtained by remote
sensing techniques.
7.5 Possible effects of climatic change on forests in the Alps
The investigation of the behaviour of the FORCLIM-E/P model under three different climate
scenarios suggests that forests close to the current alpine (Bever, Davos) or dry timberline
(Sion) are especially sensitive to the climatic changes expressed in the various scenarios.
Given that the sensitivity of FORCLIM is representative of real forests, there are
two important implications of these findings: First, the forests currently growing at these
sites may be affected drastically by the expected changes of temperature and precipitation.
Second, given that one wanted to predict the potential future forest composition at specific
locations, the forecasts of future climate would have to be more precise than this appears
to be currently possible (e.g. Santer et al. 1990, Giorgi & Mearns 1991).
On the other hand, near-natural forests at mid altitudes, e.g. at the sites Airolo and Bern,
appear to be least sensitive to climatic change (cf. Bugmann & Fischlin 1994). They
show small and uniform changes of their species composition across different climate
scenarios. If this small sensitivity is real, this implies that mid altitude forests are likely to
undergo minor changes only. However, the sensitivity tests performed in this study have
a time horizon of 100 years only, although climatic change is likely to continue after the