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

Introduction 3
1.2 Methods for the analysis of forest ecosystems
The term “forest dynamics” spans huge ranges both in time and space: The enzymatic reactions
of photosynthesis operate within fractions of a second; foliage development takes
a few weeks, while tree growth lasts decades to centuries, and the dynamics of soil organic
matter span millennia. On the other hand, the germination of a seed takes place on a
few square centimetres, a sunfleck moving over the forest floor covers a few square meters;
a dominant tree in the canopy occupies 0.01-0.1 ha, and the quasi-equilibrium of a
forest landscape may be reached on the scale of several hectares only (Shugart & Urban
1989). Levin (1992) hypothesized that the central problem in ecology is that of pattern
and scale, and that the various temporal, spatial, and organizational scales should be interfaced
in order to understand the dynamics of ecosystems.
Due to the size of trees, even the measurement of simple indices of forest ecosystems,
such as allometric relationships or total biomass, requires much personnel, time, and
money (Burger 1945-1953, King 1991, Woods et al. 1991, Smith et al. 1991, Wang et
al. 1991). On the other hand, the longevity of the dominant organisms makes measurements
on a temporal scale appropriate for the whole ecosystem practically impossible
(Botkin 1981, Shugart 1990). Not surprisingly, empirical studies of forests typically
cover a few years and a few ares at most. For example, many investigations on the direct
effects of carbon dioxide on vegetation (Eamus & Jarvis 1989) dealt with the short-term
increase of photosynthesis (Oechel & Strain 1985), growth rates of tree seedlings
(Bazzaz & Williams 1991), or competition in model ecosystems (Miao et al. 1992,
Körner & Arnone 1992). The effects on natural forest ecosystems can not be estimated
simply by extrapolating these findings across scales (O'Neill et al. 1986), and their incompatibility
makes it difficult to deal with several scales simultaneously on an empirical
basis (Shugart & Urban 1989). Thus, other methods are required to investigate the couplings
and feedbacks between scales in ecosystems. The present study is based on the assumption
that ecological models provide an opportunity to do so.
Unfortunately, ecologists continue to be substantially separated into those who build and
use quantitative models, and those who don't (Botkin 1981). In fact, ecological models
can be neither built nor tested without a sound empirical basis. The “empirical” (fieldoriented)
and the “theoretical” (model-oriented) approaches have complementary functions
and depend on each other (Fischlin 1982): Field data serve as a basis for developing
and testing an ecological model; on the other hand, sensitivity analyses conducted with
the model can be used to test our understanding of the system and to identify research