FOREST BIOME - ScholarsArchive at Oregon State University

words, this computer simulation model will be modular. Since the basic
relationships will be expressed as ordinary differential equations, much
attention will be given to the problem of time scales. Levels of resolution
developed during year 2 will still be coarse. In fact, many
relationships will be frankly empirical. Nevertheless, we expect to be
able to run computer simulations of the Thompson ecosystem during year 2.
Our objectives in developing this computer model at this stage of our
work are (1) to develop a framework on which later improved ecosystem
models can be erected; (2) to be able to inform the Biome director of
important gaps in substantive research and modeling areas; and (3) to
determine the effects of key parameters on the behavior of an ecosystem
model which incorporates several submodels.
The study of theoretical aspects of ecosystem models will be directed
toward several primary objectives. The comparison of model prediction,
from models of two levels of ecological resolution, has been examined
by Overton as a means of model validation. This investigation will
continue. A second objective is to investigate alternative model structuring
to account for temporal and spatial heterogeneity. In some cases
(e.g., population models and growth models), it is apparent that a
coarse observational resolution, leading to difference equations rather
than differential equations, may often be used to advantage. Again, the
problem of comparison of models of different resolution arises. The
third major objective is to investigate a model form for ecological
information. Existing ecosystem models emphasize the flow of quantities
(e.g., nutrients and energy) from one ecological state to another. It
is not apparent that the self-organizing, self-perpetuating properties of
ecosystems will derive from these models. Neither is it apparent that
model structures exist which will satisfactorily treat, within the
context of present models, the control aspects which we call disruptive-pathogens,
pests, physical catastrophe, and man. An attempt will be made
to model these forces as flow of a quantity, information, through a
compartment system.
Primary' Productivity
8.16
Hatheway proposes to develop a model for net assimilation in Douglas-fir in
cooperation with P. B. Walker, D. R. M. Scott, and R. Waring. Recent
models for photosynthesis in cultivated crops have emphasized the role of
leaf arrangement in the canopy of the stand in the interception of light,
but have relied on empirical formulations to describe production of
carbohydrates in leaves. The complex geometry of conifer stands may preclude
the development of a satisfactory theory of light interception at various
levels of the canopy. On the other hand, some theory of production at
the level of the leaf and branch may be within reach. Critical to its
development will be submodels for stomata] opening and closing (which will
depend in part on the general level of moisture stress in the tree), leaf
temperatures, and incident radiation. Considerable data on assimilation
in Douglas-fir have already been accumulated, and a satisfactory theory
for transpiration (Gates, 1968) is available.
Nutrient Cycling Within the Terrestrial System
York on simple nutrient cycling models which will begin in year 1 will
continue in year 2. Such models will be useful in the total ecosystem