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

Introduction 11
The main advantage of FORECE was its capability to produce species compositions according
to phytosociological descriptions of the forests under study (Ellenberg & Klötzli
1972). Important disadvantages were that it was one of the more complex models at that
time, and that it did not include soil carbon dynamics, which would be important for calculating
the carbon balance of forest ecosystems (Pastor & Post 1985). In the meantime,
two more models have been developed for European conditions: SIMA (Kellomäki et al.
1992), a slightly modified version of the LINKAGES model (Pastor & Post 1985), and
FORSUM (Kräuchi & Kienast 1993, Kräuchi 1994), a successor to FORECE including detailed
submodels of soil water dynamics, deer browsing, and management.
1.5 Objectives of this study
Based on the research conducted with forest gap models by many authors during the last
25 years and the apparent success of these models for simulating realistic species composition,
this thesis shall address the following questions:
First, do complex forest gap models like FORECE produce plausible simulation results for
the right reasons? Do the factors that are most important for simulating forest dynamics
correspond to our ecological knowledge on those dynamics, or do these complex models
simply represent empirical parametrizations assembled during decades of model development
without evident relationships to ecological theory?
Second, what is the minimum number of assumptions, i.e. ecological factors, that must
be incorporated in such a model to simulate realistic dynamics of mountainous forests? Is
it possible to simplify some of the remaining equations, and can the parameter space of
the models be reduced further by skilful grouping?
Third, do forest models like FORECE contain implicit assumptions about climate, so that
their validity is restricted to simulating forest dynamics at specific sites and under current
climate only? If this is true, can these assumptions be replaced by explicit formulations of
climatic influences, so that the models are applicable along climate gradients and under a
changing climate as well?
Finally, how sensitive is the simulated species composition of near-natural forests in the
European Alps to the climatic change anticipated for the next 100 years as compared to
the climatic changes that have occurred in the last 500 years?