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

The forest model FORCLIM 45
carbon balance of the whole forest ecosystem, which is important for the biospheric
feedback to the climate system (Trabalka & Reichle 1986, Post et al. 1990, Tans et al.
1990).
E G M L H
Plants
Soil
B
W
Environment
Fig. 3.1: Structure of the FORCLIM model. Dotted lines denote the dependencies within
the three submodels. The symbols are explained in the text.
3.2 Model assumptions
3.2.1 Plant submodel: Tree population dynamics
A basic paradigm of population ecology states that there are four key processes determining
the abundance of a population (e.g. Fischlin 1982, Begon et al. 1990): natality, mortality,
immigration, and emigration. Since trees are sessile and the dispersal of most tree
species is comparably slow, migration phenomena are not considered explicitly in
FORCLIM. The basic processes therefore are the establishment and the mortality of trees
(Fig. 3.2). However, we are interested not only in the abundance, but also in the structure
of the population. Moreover, tree mortality rates are influenced to a large extent by
competition; thus tree growth has to be modelled as well (Fig. 3.2).