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

successful .
Thus we can see modeling as the impositio n
of structure on existing knowledge . As such ,
it is a joint activity between those familia r
with forms and structures and those familiar
with a body of knowledge . In time, the structure
imposed becomes integrated into th e
scientific paradigm of the object, providin g
new insight and a base for extending concepts
. In this view, modeling is an integra l
part of the theoretical advance of a subject
science, not an external, nor peripheral ,
activity engaged in by mathematicians o r
other specialists .
Now I don 't think that I am the only on e
with this view, but there are sufficiently man y
opposing views among modelers and sufficiently
many misconceptions among subjec t
specialists that verbalization of this perspective
is essential in an introduction of th e
present topic . I view our efforts to develop a
total ecosystem model as a contribution to
the scientific paradigm of ecosystems . Ou r
primary activity as modelers is the conceptualization
of theoretical ecosystem structure s
and behavior. The present paper deals wit h
the structural aspects of a developing family
of models for the forest ecosystem at a date
late in 1971, and with the strategy we have
adopted to pursue our objectives .
Approaches to System
Theory and Definition
Klir (1969, 1972) discusses in some detail a
variety of definition forms and approaches t o
developing a general theory of systems . This
seems a productive direction and the following
section is my own interpretation and
elaboration of these passages in Klir . There
may be inadvertent deviations from Klir 's
intent .
The State Variable (or State Space) approach
seems to describe the model structur e
currently most popular in several fields, including
ecology . The essence of this approac h
is that the system is defined as a set of variables,
the state variables, and a set of variable s
representing the environment, in a particular
temporal resolution . A popular version de -
fines compartments, with the state variable s
describing the contents of the compartments .
The definition is completed by specificatio n
of algorithms for change of the state variables
in time .
Klir has proposed a general systems theory
which, although not distinct from the stat e
variable approach, has certain features whic h
apply nicely to study of ecosystems . Specifically,
he identifies five ways in which a
system may be defined :
1. By the set of external quantities and th e
resolution level
2. By the given activit y
3. By the permanent behavio r
4. By the Universe-Coupling structure
5. By the State-Transition structure
The models of the system follow definitio n
forms 3, 4 and 5 . Definition form 1 is used in
the planning stages of a modeling or data
collection activity, and a collection of data i s
a realization of definition form 2. It follows
that definition form 1 is implied by form 2
and by forms 3, 4, and 5. When applied to th e
same system, the forms must be mutually
consistent . In the Coniferous Biome, we hav e
adopted a particular combination of the thre e
model forms for our model of the forest ecosystem.
We view each system (or subsystem )
as modeled at two levels :
1. Holistically, according to its Behavior (o r
State-Transition structure) .
2. Mechanistically, according to its Universe-Coupling
structure .
That is, we view Klir ' s Behavior and S-T
structure as useful forms for characterizing
the holistic behavior of a system "as a n
object," and consider that such holistic characterization
is necessary for each define d
system or subsystem . Further, we consider
that in most cases we will also wish to model
the system according to the U-C Structure ,
that is, as a collection of subsystems, eac h
modeled according to its Behavior and with
the collection coupled in a manner appropriate
to the behavioral forms used .
Some further elaboration of these term s
seems necessary, but a formal definition (as i n
Klir 1969 and Orchard 1972) is inappropriate .
An attempt to informally define some of th e
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