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

128 Chapter 5
independent of those observations used to structure the model and to estimate its
parameters (Shugart 1984).
The FORCLIM model was developed to allow for projections of forest dynamics in a
changing climate; thus its validation should deal with its behaviour along climatological
gradients. There is a wealth of observations on past and current forests in central Europe
that potentially could be used to validate various aspects of forest gap models, such as
• Yield tables (e.g. Anonymous 1983, Schober 1987)
• Forest inventories (Zingg & Bachofen 1988, Mahrer 1988)
• Forest reserves (Leibundgut 1978, Broggi & Willi 1993)
• Tree-ring chronologies (Schweingruber et al. 1984, Briffa et al. 1990)
• Pollen records (Huntley & Birks 1983, Ammann & Tobolski 1983, Lotter
1988, Birks 1990, Huntley 1992)
• Remotely sensed data (Guyenne & Calabresi 1989, Blasco & Achard 1990,
Runkel 1990, Roughgarden et al. 1991, Hall et al. 1991, Treviño Garza 1992)
• Phytosociological descriptions of the potential near-natural forest types
(Schmid 1949, Ellenberg & Klötzli 1972, Ellenberg 1986)
The advantages and deficiencies of these data sources are summarized in Tab. 5.4. It
becomes evident that there is no “ideal” source of data for the validation of FORCLIM.
Most of the criteria in Tab. 5.4 are met by data from forest reserves and by phytosociological
descriptions. While the former are available at a few sites only and thus hardly
allow to study climatological gradients, the latter do not cover the temporal aspects of
forest dynamics. However, Rehder (1965) and Ellenberg (1986) developed an interesting
approach that was based on a large body of phytosociological data: They developed a
scheme that presents the dominating species of near-natural forests of central Europe in a
climatological space spanned by the annual mean temperature and the annual precipitation
sum (Fig. 5.1). A simulation study of these forests could provide detailed information
about the changes of the species composition along climatic gradients under current climate
and the agreement of the simulated forests with those hypothesized by the two
authors. These advantages outweigh the static nature of these descriptions; hence section
5.3 shall deal with such an analysis.
FORCLIM was constructed using an altitudinal gradient in the European Alps (chapter 4).
Thus, another transect in the same area would not be really independent of the first one.
However, a similar transect in another continent, i.e. with a set of species and climatic