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

other. The plant integrates environmenta l
stimuli. Arrows indicate the direction of flow ,
and circles are special functions regulated b y
information from the plant integrator .
We interpret environmental variables as
being external to the system and impingin g
upon it . The system, in this case the organism ,
responds only in accordance to the externa l
stimuli. Modifications in the environmen t
brought about by the organism itself are no t
distinguished from those originating throug h
other means .
The amount of material transfer from environment
to plant is determined by the kin d
and magnitude of the response ; i .e., the
amount of CO2 converted into carbohydrate
is determined by the photosynthetic rate . The
amount of carbohydrate utilized in th e
growth of foliage, stem, and roots is also
affected by the stage of plant development
and other plant responses . As long as the carbohydrate
pool does not become exhausted ,
or one of the plant responses is not death,
biomass can accumulate .
When the environment initiates a letha l
plant response, the transfer of carbohydrate s
is stopped and all of the biomass compartments
empty . Biomass loss also occur s
through respiration, consumption by animals,
the normal fall of litter, and death of roots
and twigs .
Unfortunately, we do not, at present, have
adequate knowledge for complete evaluatio n
of such an energy flow model, even for a
single species . We hope to acquire muc h
needed data through the Biome program. Still
it is safe to say that we will lack complete
data on most species to predict accurately th e
system 's response to external variables . Our
approach, therefore, is to study physiologica l
responses in relation to the environment ,
develop functional models, and from thes e
create plant response indices as a means of
interpreting environmental gradients . Further ,
we propose to correlate ecosystem propertie s
with these plant response indices . Figure 2
ENVIRONMENTA L
STIMUL I
Absolute Humidit y
Radiation
Air & Soil Temperature
Soil Wate r
Soil Fertility
Wind and Snow
PLANT RESPONSE
INDICES
ECOSYSTE M
CHARACTERISTIC S
Plant Moisture Stress
Productivity
Transpiratio n
Compositio n
PHYSIOLOGICAL
CALIBRATION
j---* Photosynthesi s _
Hydrologic Stat e
PROCESS MODELS
VALIDATION
Nutritional
Decomposition
4
PREDICTION
Temperature Growth Consumer Population s
Mechanical Stress
/
/ PHYSIOLOGICA L
/ BEHAVIO R
Stomatal Respons e
Cambial Activity
Photosynthesi s
Transpiration
Plant Moisture Stres s
Phenology
Foliar Nutritio n
Figure 2 . Physiological process models couple environmental stimuli to the physiological behavior of selecte d
conifers . From an understanding of the process models, plant response indices are derived which reflec t
major environmental gradients . These indices locate ecosystems within an environmental grid and throug h
correlation permit certain ecosystem characteristics to be predicted .
8 1