PE EIE[R-Rg RESEARCH ON - HJ Andrews Experimental Forest

Proceedings-Research on Coniferous Forest Ecosystems-A symposium.
Bellingham, Washington-March 23-24, 197 2
Criteria for selecting an optimal model:
terrestrial photosynthesis
Kenneth L . Ree d
College of Forest Resources
University of Washingto n
Seattle, Washington 98196
an d
Warren L . Web b
School of Forestr y
Oregon State University
Corvallis, Oregon 9733 1
A bs tract
In theory, there exists an infinite number of models of a given system. These models differ in resolution,
scope, descriptive and predictive power. Because the models described in the literature generally reflect th e
personal perspectives and goals of the researchers who developed the models, it is helpful to be able to evaluat e
the potential of a given model to provide the information needed in another research problem . Several criteria
for selection of models or modeling approach are suggested in this paper. The use of the criteria is illustrated by
discussion of several mathematical models of photosynthesis taken from the literature . The models discussed
include a linear regression model, an energy budget model, and models based on theory of enzyme kinetics and
gas exchange .
Introduction
A great many models are available that de -
scribe photosynthesis, some of which will be
discussed below . Because of the many models
now available, we had hoped that we woul d
not have to develop a new model-that w e
need only choose or modify an existing model .
Thus it was necessary to consider certain criteria
by which to judge the applicability of a
given model to the purposes of the IBP .
Several of the criteria will be discussed be -
low. This list is probably not complete, but i s
suggested as a guide to model selection, modeling
approach, or both . Because most scientists
are modelers in a broad sense, this discussion
is intended primarily for those scientists
who are least familiar with formal aspects
of modeling .
Criteria for Model Selectio n
Because plant growth and presumably community
composition are greatly influenced b y
photosynthetic capacity, that phenomeno n
has been the object of a great deal of study .
Photosynthesis is only one component of the
biochemical system resulting in plant growth .
Failure to consider other factors in growth, a s
well as the fact that photosynthesis can be
uncoupled from growth, results in the general
failure of attempts to predict growth from
photosynthesis. However, a model of photosynthesis
is an important component of a
growth model and because the process o f
photosynthesis is a physical-chemical system ,
attempts to model photosynthesis should b e
consistent with some basic tenets of systems
theory as well as physical reality .
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