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

subsystems as objects . In addition, the formal
structure effectively partitions our effort and
ensures that all . bases are covered . Boundaries
between subsystems and the appropriat e
coupling variables must be identified jointl y
by those responsible for the subsystems involved.
After boundaries and coupling variables
are agreed upon, then the activities o f
elaboration of internal structure are independent
among subsystems . This is another
expression of the earlier observation tha t
identification of the couplings effectivel y
uncouples the subsystems .
These values of the model formulation can
be expressed as explication, conceptualization,
and organization . Existing concepts are
given explicit expression, new concepts ar e
developed and research efforts are given structure
and organization, all by the formal ecosystem
model . The fact that the model structure
is arbitrary in no , way obviates thes e
values . On the contrary, the arbitrariness o f
the model structure enhances these values ,
because as we proceed with the process of
elaboration, and bring existing knowledg e
into sharper focus by the process of modeling ,
we are constantly forced into adjustments, re -
orientation, and reorganization .
Structures, like figure 3, are not meant t o
be permanent . They live and die like generations
of insects . In fact, the insect analogy is
quite appropriate for figure 3 . This structure
was conceptualized in the spring and earl y
summer of 1971, during Round One . I t
developed underground, so to speak, all during
the fall, undergoing several transitions, t o
emerge in December in the form presented .
By mid-January 1972 this form had lived ou t
its life and given birth to a new form which is
yet in the larval stages and not ready for th e
light of day .
At the next lower organizational level ,
progress has been made in elaboration of the
internal structure of the food chain subsyste m
and the I-U subsystem . The first is reported
here by Strand and Nagel, but the second i s
not represented in this symposium and I
would like to include a brief description of
that subsystem as additional illustration o f
the way in which we are using the Universe -
Coupling structure .
Figure 4 represents a model form date d
back in 1971, which form has been replace d
by a new but incompletely developed form, in
accordance with the changes being made a t
the next lower resolution (fig . 3). However ,
figure 4 serves to illustrate the concept of th e
I-U process and, again, the point is made tha t
this is developed more fully in the document s
of Round One .
The I-U subsystem is postulated on the following
statements :
1. If nutrients remain in soil solution, they
must be lost to the system by soil and
groundwater transport .
2. Nutrients must be in solution in order t o
be available to uptake .
3. Some microorganisms and some highe r
plants are "leaky ."
4. It is concluded that a successful syste m
must have a tightly coupled, highly interactive
and buffered subsystem of nutrient
interchange and uptake .
The modeling contribution here is th e
recognition (4) that the three stated feature s
of the traditional processes of nutrient inter -
change are such that a successful terrestria l
ecosystem (i .e., one which does not lose it s
nutrients downstream) must have a tightly
coupled I-U subsystem . That is, the traditional
study by individual process canno t
possibly answer the questions we want to ask ,
unless we explicitly define the couplings .
Coupling definition is difficult in a tightl y
coupled system, and appears exceedingl y
difficult in this one . The identified task is th e
conceptualization of properties and behavior
of the I-U subsystem as a whole .
It is my very strong conclusion here that
the Biome research effort should be re -
oriented to accommodate the concept of th e
I-U subsystem. Present conceptualization an d
specification of that subsystem is yet very
primitive and will receive considerable attention
in the next year .
From the model structure point of view ,
the primary productivity subsystem is th e
least well defined in our model . This is, in
part, because most of our research effort ha s
been at lower organizational levels than i s
necessary for ecosystem models . It is a giant
step from tree to community . The primary
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