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

4 Chapter 1
needs, which may serve as guidelines for future field work in the daunting complexity of
ecosystems.
The palaeoecological record (Delcourt & Delcourt 1987, 1991) shows that biotic responses
to past climatic changes were very complex (Davis 1990). Past changes affected each
species differently; some communities present on today's landscape have formed only
recently, such as the beech-hemlock zone in eastern North America about 6000 years ago
(Graham & Grimm 1990). Moreover, many of the communities that were present during
the Quaternary have no modern analog (Davis 1990), and the same will probably occur in
the future. Thus, the present communities will not simply shift geographically, and they
can not be expected to exhibit predictable responses and feedbacks to climate. Consequently,
assessments of the impact of climatic change on mountainous forests should be
based on models that are detailed enough to predict the species composition and the
functioning of these future no-analog ecosystems (Shugart 1990).
1.3 Spatial scales in forests and corresponding models
Many authors have classified forest models according to a wide variety of criteria (Reed
1980, Shugart & West 1980, Shugart 1984, Dale et al. 1985, Reynolds & Acock 1985,
Joyce & Kickert 1987). All these classifications concentrate on a few types of models
only; none of them covers models across many scales. Thus, the following review of
forest models will be organized according to a scheme similar to the one used by Ågren et
al. (1991): The classification criterion used here is the spatial scale of the models, ranging
from landscape models to physiological ones. Global models (e.g. Goudriaan & Ketner
1984, Emanuel et al. 1985) are excluded from the review because their large spatial scale
renders them inappropriate for a detailed study of the behaviour of mountainous forest
ecosystems. Moreover, even the most detailed global models (e.g. Prentice et al. 1992)
are not capable of predicting species composition.
Landscape models: Most landscape models view a landscape as composed of patches
of ecosystems or vegetation types, or they assume the vegetation cover to be homogenous.
Waggoner & Stephens (1970) used a Markov model (Caswell 1989) to predict
the distribution of five vegetation types on the landscape scale. Similar models were presented
by Shugart et al. (1973) and Loucks et al. (1981). A disadvantage of this approach
is that the transition probabilities are aggregate indices which implicitly parametrize many
phenomena, including competition and climatic effects. The application of these models