United States Environmental April 1993
Protection Agency
&EPA
Effects of C02 and Climate
Change on Forest Trees
EXECUTIVE
INTRODUCTION
Concentrations of carbon dioxide (C02) and other trace gases such
as methane are increasing in the atmosphere due to human activi-
ties. Evidence suggests that increased levels of these gases will
produce increases in global temperatures and associated changes
in precipitation patterns and amount, cloudiness, and other atmo-
spheric factors which are collectively known as "climate change."
The U.S. Environmental Protection Agency (EPA) has created the
Global Climate Research Program (GCRP) to provide integrated
research on all aspects of the trace gases and climate change. An
important focus of the GCRP at the EPA's Environmental Re-
search Laboratory in Corvallis, Oregon (ERL-C), is to understand
how C02 and climate change will affect vegetation in North
America. A crucial goal of this research is to provide information
to policy makers who must make decisions about forest resources.
Answers are needed for these key policy issues:
• What are the effects of elevated C02 and climate change on
the growth and productivity of forest trees?
• Will elevated C02 and climate change alter the carbon
sequestration potential of forest trees?
Environmental Research Laboratory - Corvallis
Page 1
-------
• What is the magnitude of elevated C02 and climate change
impacts on forest trees and will the impacts he widely
distributed?
Existing data are not adequate to provide defensible scientific an-
swers to the above policy issues, at either the level of an individual
tree or a forest stand. Thus, ERL-C has begun the study called
Effects of C02 and Climate Change on Forest Trees, to help de-
termine how trees are influenced by elevated C02 and climate
change. The focus will be on Douglas fir, a key Pacific Northwest
forest species, which is ecologically and economically important
and adapted to the current local climate conditions.
GENERAL To evaluate the qualitative and quantitative effects of climate
APPROACH change on forest trees, four separate but interacting research activi-
ties will be undertaken; scoping studies, experimental tasks,
modeling tasks, and integration and inference activities (Figure 1).
SCOPING C02 and Climate Analysis
STUDIES To establish experimental conditions, C02, temperature, and mois-
ture records were examined for past and present trends. It was
established that in 1990 the atmospheric concentration of CCX, was
353 ppm, or 25% higher than in pre-industrial times. At a moder-
ate rate of increase, the C02 concentration in the atmosphere may
double to about 700 ppm by the year 2059. However, other trace
gases are increasing along with C02, and will contribute to global
warming over this same period of time. Thus, realistically con-
centrations of C02 alone will be in the range of only 450-500 ppm
when global temperatures increase to a level equivalent to that
associated with a doubling of C02 concentrations.
To predict the impacts of increased C02 levels on future tempera-
tures in the Pacific Northwest, we reviewed the output of four
atmosphere/climate models. The models projected a significant
f ni'tmrrmfTtt/tt ftf search iMboratory - Corvallis
Page 2
-------
General Approach
Experimental Tusks
Shoot Carbon & Waicr Flux
Shoot Growth & Phenology
System Nutrients
System Water
Litter Layer
Root Growth & Phenology
Soil Biology
Scoping Studies
C02/C]imate Scenarios
Species Selection
Experimental Design
Modeling Tasks
Model Selection
Parameterization
Test Understanding
Integration & Inference
Conceptual Summaries of Experimental KesuUs
System Budgets (C, H20, Nutrients)
Model Application - Assess Effects of C02 and
Climate on Trees
Figure I. General research approach and relationship among the various tasks. The dotted
lines indicate information flow, and the solid lines indicate dataflow.
warming and drying of the climate in the Pacific Northwest using
a scenario which included a doubling of atmospheric C02 concen-
trations. For example, in the Willamette Valley temperatures
could increase for all months resulting in a mean from 2.3 to
5.1°C, depending on the model used. Also, growing degree-days
are projected to increase significantly by 21% to 171% from cur-
rent conditions, with greater percentage increases in
growing-degree days at higher elevations.
Environmental Research Laboratory • Cor vail is
Page 3
-------
The model-based projections for precipitation under double CO,
concentrations did not show the same consistent trend as tempera-
ture. Model outputs ranged from essentially no change to 27%
increase in annual precipitation. All models projected that the cur-
rent seasonal pattern of relatively dry summers and wet winters
will persist, but the proportion of rain vs. snow from current condi-
tions may change because of the increase in temperature.
Overall, the future climates projected from the climate models rep-
resent a significant change from present conditions. When viewed
in a south-to-north transect, the projected temperature changes
were equivalent to shifting current climates from 2()0 to 5(X) km
north, i.e., moving the climate of northern California into northern
Oregon. However, strict geographical analogues of future climate
were difficult to define since projected precipitation may remain
unchanged. Similarly, from an elevational perspective, the climate
projections suggested a 500 to 1000 m upward movement of tem-
perature regimes.
Species Selection
Douglas fir {Pseudotsuga menziesii), currently the most impor-
tant timber species in the Pacific Northwest, was selected as the
experimental plant material Douglas fir is widely distributed,
growing under a variety of climatic conditions. Seedlings were
grown from "woods run" seed lots, rather than half-sib or full-sib
seed lots, to ensure that the seedling's genetic variability reflects
that of the natural forest. Seed lots were selected from five low-
elevation seed zones (<600 m) on the western side of the Oregon
Cascade Mountains in the Willamette Valley. Seedlings were pro-
vided by the Weyerhaeuser Company as 1+1's, i.e., grown for one
year in a seed bed, then one year in a nursery bed, and then trans-
planted into terracosrns as bare-root, 2-year-old stock.
Frtvirnnmrrtfn! Research laboratory • Corvallis
Page 4
-------
EXPERIMENTAL Experimental Facilities: The study uses twelve 1.0 x 2.0 meter
DESIGN surface area and 1.2 x 1.5 meter high "terracosms" built at ERL-C
(Figure 2). Terracosms are closed systems including a sun-lit up-
per chamber where atmospheric and climate conditions are
controlled and measured, and a lower soil lysimeter where soil
water content is controlled and soil parameters are monitored. The
terracosms allow researchers to achieve control of the environ-
ment and provide a mechanistic understanding of the effects of
elevated CO,, temperature and drought on above- and
belowground uxjc and soil processes.
While the overall study will focus on the long-term effects of in-
creasing C02 and climate change on Douglas fir seedlings
growing in the terracosms, supporting experiments also will be
conducted in pots, large soil lysimeters, and at field sites. These
studies will provide additional data necessary for modeling activi-
ties and for comparison between responses of trees grown in the
terracosms and Uees growing under native conditions.
Experimental Treatments: The experimental design is a 2 x 2 fac-
torial with two C02 treatments, two temperature treatments, and
three replicate terracosms per treatment combination. The two
C02 levels are ambient and ambient plus 200 ppm (a possible C02
increase in approximately 50 years). The two temperature levels
are ambient and ambient plus 4°C (a predicted temperature over
the same period of time). The increased CO, and increased tem-
perature treatments arc added continuously to the current ambient
levels to preserve natural diurnal, seasonal and yearly variability.
Ambient conditions are based on continuous measurements from a
meteorological tower at the research site.
Soil Selection: Douglas lir is found primarily on two kinds of
soils in the Cascade Mountains of Oregon. Roughly 30% grows
in high-elevation sandy loam derived from volcanic ejecta and
glacial till. The other 70% grows in a heavy-textured soil derived
from colluvium and residuum. The sandy loam soil was chosen
Environmental Research laboratory - Corvallis
Pane 5
-------
for use in the terracosms because of the ease with which it could
be excavated and reconstituted and its resiliency to disturbance.
The soil was collected by horizon from the perimeter of a 5(X)-6()0
year-old Douglas fir stand in the Oregon Cascade Mountains and
then reconstructed by horizon in the terracosms (Figure 2). Sen-
sors, samplers and minirhizotron tubes were placed in the soil
during the reconstruction process.
Side View of Terracosm
Dew Point Hygrometer
Hot and Cold Water
Heat Exchangers
Host/Chamber COj
Sampling Ports
1.5 Meters
w
m
m
C Horizon
//i>V>
¦z
Data Acquisition/
System Control
\
TDR Probe
Multiplexer
A
Litter Layer
A Horizon
K Horizon
Root Observation
Tube*
1 Meter
Figure2. Sideviewoftermcosnichambershowingdetailsofsoilliorizons.mmirfiiwtron
mot observation tubes, data acquisition packages, dew jx)int hygrometer, and C02
tn1 Research laboratory • Corvallis
Page 6
-------
EXPERIMENTAL Seven research tasks were chosen to answer fundamental science
TASKS questions of this project (Figure 3). For each task specific objec-
tives and experimental approaches were identified. Outputs will
be in the form of data to address the science questions, and as spe-
cific inputs for a physiological process-based tree growth model.
Soil Water
Task 6
Koot (Growth and ^
Phenology J
. * ¦ *» \ i > *,«. *, >
¦: • .* ¦ .• • .* •: •V. •
•'-* •'•* •*•' •'•* *
Experimental Research Tasks
Task I
Shoot Carbon and
Water Fluxes
V J
Task 3
System Nutrients
• Plant Nutrients
Task 4
System Water
* Plant Water
Task 5
Utter Layer
Soli Nutrients
Figure 3. Research tasks for the experiment.
Task 2
Shoot Growth and
Phenology
Environmental Research iMboratory - CorvalUs
Page 7
-------
TASK 1 Science Questions:
Shoot Carbon & • Will the net carbon flux for plants change in response to
Water Fluxes elevated CO2and climate change?
• Will plant water-use efficiency (WUE) increase in response
to elevated C02 and climate change, and will this WUE
increase occur on a vegetated area basis as well as on a
single plant basis?
Objectives:
• To measure at the whole plant canopy level photosynthetic,
respiration, and transpiration rates in response to the indi-
vidual and combined effects of increased C02 and increased
temperature.
• To measure at the needle/branch level photosynthetic,
respiration and transpiration rates, and stomatal conductance
changes in response to elevated C02 and climate change.
These measurements will be made with different photosyn-
thetically active radiation (PAR) levels, temperatures, and
C02 concentrations, and will be made for different needle
age classes and leaf nitrogen levels.
• To measure at the canopy and needle/branch levels, diel and
seasonal patterns in photosynthetic, respiration, and transpi-
ration rates, and stomatal conductance in response to el-
evated CO, and climate change.
• To measure at the needle/branch and whole plant level the
influence of leaf water potential (WP), and air vapor pres-
sure deficit (VPD) on stomatal conductance and transpira-
tion. These measurements will be made with different
photosynthetically active radiation (PAR) levels, tempera-
tures, and C02 concentrations; and for different needle age
classes and leaf nitrogen levels.
• To derive photosynthesis, respiration and stomatal conduc-
tance input variables for the TREGRO model based on the
above measurements and literature values.
Research iMboratory - Corvallis
Page 8
-------
Approach: Photosynthesis will be measured at two scales: 1) total
plant canopy using the terracosm upper chamber, and 2) needle/
branch using a portable gas-exchange system. Measurements may
also be made on a whole plant level to assist in scaling from the
needle/branch to canopy levels. Canopy level measurements will
be made in the terracosms and needle/branch (and possibly whole
plant) measurements will be made primarily in supporting studies.
A limited number of needle/branch measurements will be made in
the terracosms to determine how the CO, and temperature treat-
ments affect the shoot responses characterized in the supporting
studies. Respiration rates will be measured throughout the dura-
tion of the experiment to quantify net carbon llux to characterize
metabolic rales and energy consumption. Respiration will be mea-
sured on the needle/branch and canopy scale, using a darkened
chamber during the day, and/or under natural darkness at night, as
necessary, to obtain accurate measurements. Respiration will be
partitioned, as feasible, between growth and maintenance compo-
nents. Transpiration will be measured at the following three
scales: 1) plant canopy in the terracosms, 2) whole plant in the
terracosms, and 3) needle/branch in supporting experiments. Sto-
matal conductance will be derived from transpiration and leaf
temperature measurements on both the needle/branch and whole
plant scale.
Outputs:
• Characterization of net carbon flux for Douglas fir shoots in
response to elevated C02 and climate change.
• Characterization of WUE for Douglas fir shoots in response
to elevated C02 and climate change.
• Characterization of diel and seasonal patterns of carbon and
water fluxes for Douglas lir shoots in response to elevated
CO^ and climate change.
• Characterization of relationships among photosynthesis, respiration,
tissue CZN ratios, and total nonstructural carbohydrates (TNC).
• Evaluation of potential for changes in plant canopy tempera-
ture induced by transpiration reductions.
Environmental Research laboratory - Corvatlis
Page 9
-------
TASK 2
Shoot Growth,
Morphology,
Ailometry,
Phenology, &
Carbon
Partitioning
Objectives:
• To measure, at the individual plant level, effects of elevated
CO, and climate change on shoot biomass (dry weight) by
age class of the main stem, branches, needles, and buds.
• To measure, at the individual plant level, effects of elevated
CO, and climate change on shoot allometric parameters, i.e.,
stem diameter, height, and needle elongation.
• To measure, at the individual plant level, effects of elevated
CO, and climate change on shoot morphology and allometric
relationships including numbers, rank, and weights of
branches, needles, and buds for all age classes of tissue.
Needle areas will be taken to determine specific needle
weights.
• To measure, at the individual plant level, ellects of elevated
CO, and climate change on shoot phenology. The dates of
key events, such as onset of bud break, secondary bud break,
and first frost will be carefully noted.
• To quantify the changes in the biochemical partitioning of C
between structural and nonstructural compounds in the
various shoot fractions in response to elevated C02 and
climate change.
Approach: The study will focus on the long-term effects of in-
creasing CO, and climate change on Douglas fir seedlings
growing in the terracosms. Baseline measurements will be taken
at an initial destructive harvest of 50 bare-root seedlings. Interme-
Science Questions:
• Will shoot growth change in response to elevated C02 and
climate change ?
• Will shoot morphology and allometric relationships change
in response to elevated C02and climate change?
• Will shoot phenology change in response to elevated CO 2
and climate change ?
• Will the biochemical partitioning of C in shoots change in
response to elevated C02 and climate change ?
Fnvimntn/'ntal Research laboratory - Corvallis
Page 10
-------
diate measurements will be taken to follow the course of tree
growth over time; they will be nondestructive in the terracosms
but destructive in the supporting experiments. Final destructive
measurements will be made to look at the cumulative ellects of the
treatments and experimental conditions on overall tree growth.
Outputs:
• Characterization of shoot growth of Douglas fir in response
to elevated CO, and climate change.
• Characterization of shoot morphology and allomctric rela-
tionships of Douglas fir in response to elevated C02 and
climate change.
• Characterization of shoot phenology of Douglas fir in
response to elevated CO: and climate change.
• Characterization of changes in the biochemical partitioning
of C between structural and nonstructural compounds in the
various shoot fractions in response to elevated C02 and
climate change.
• Evaluation of the performance of the CERES device tor
continuous analysis of seedling growth through stem diam-
eter measurement.
TASK 3 Science Questions:
System • w/// elevated CO, and climate change affect plant nutrient
Nutrients balance?
• Will the response of forest trees to elevated CO^and climate
change alter plant and soil nutrient pools ?
Objectives:
• To monitor changes in inorganic nutrient concentrations in
above- and belowground plant tissues, litter material, soils
and soil solutions as a function of C02 and climate change.
• To evaluate the effects of elevated C02 and climate change
on inorganic nutrient balance in Douglas fir seedlings.
Environmental Research laboratory - Corvatlis
Pni'p f t
-------
• To evaluate the physiological significance of nutrient
availability in respect to the observed responses to elevated
CO, and climate change.
• To measure C, N, S, and TNC concentrations in above- and
belowground plant tissue, litter material, soil, and soil
solutions.
Approach: Chemical analysis will be conducted on plant tissues,
litter material, soil samples, and soil solutions to 1) determine C
and nutrient concenUations, 2) quantify C and nutrient pools, and
3) monitor changes in these pools over time. Samples will be
from Tasks 2, 5, and 6 focused on above- and belowground re-
sponses, with the results of the analyses evaluated within the task
where the samples originate. Questions on the whole plant and
soil nutrient status will be addressed within this task. Analyses
will include C/H/N/S, inorganic nutrients, and TNC.
Output;
• Characterization of complete soil macro- and micronutrient
composition at the beginning and end of the experiment
both in the individual terracosms and at the field soil collec-
tion site.
• Evaluation of changes in plant nutrient concentration,
composition, and relative nutrient ratios to assess differ-
ences between experimental treatments.
• Characterization of changes in plant available soil nutrient
levels over the period of the study.
• Evaluation of the dynamic relationships between plant and soil
nutrient pools as affected by elevated C02 and climate change.
• Analysis of C/N and lignin/N ratios in plant tissues (needles
and roots), total C and N in soil, and net C and N storage.
Environmental Research luiboratory - Curvallis
Page 12
-------
TASK 4 Science Questions;
System Water • Will elevated C02 and climate change affect plant water
balance?
• Will elevated CO and climate change significantly change
the driving forces and resistances that determine water flow
in the soil-plant-atmosphere continuum?
Objectives:
• To measure the effects of elevated C02 and climate change
on the relationship between plant and soil water potential.
• To measure the effects of elevated C02 and climate change
on the overall system water balance.
• To measure and monitor volumetric water content in each
soil horizon. These data will be used to regulate irrigation
scheduling and for calculating system water budgets.
Approach: Plant water potential will be measured at the needle
level four times a year using destructive sampling and thermo-
couple psychrometry. Efforts will be made early in the
experiment to develop and apply a method for continuous and
nondestructive measurement of water status on a whole plant ba-
sis. This technique will be based on the application of the CERES
Device. Because regular collection and drying of soil samples, to
determine soil water, is not practical due to the number of samples
and time required to process them, two non-destructive technolo-
gies were selected to provide measures of soil water. The first is a
relatively new technology called time-domain reflcctometry
(TDR), and the second is the neutron moisture probe.
Outputs;
• Characterization of the independent and interactive effects of
elevated CO, and climate change on plant water balance and
soil water status.
• Characterization of relationship between short-term seedling
stem diameter changes and plant and soil water status.
Environmental Research laboratory - Corvallis
-------
• Evaluation of the potential for the continuous nondestructive
measurement of plant water status and plant water flux
through the combined use of the CERES device and stem
sap flow gauges.
• Daily characterization of volumetric soil water content by
soil horizon and rooting volume to determine seasonal
irrigation scheduling.
TASK 5 Science Questions:
Litter Layer • Will the rate of litter decomposition change in response to
elevated CO and climate change?
• Will nutrient cycling through the litter layer change in
response to elevated C02 and climate change ?
Objectives:
• To measure changes in the rale of litter decomposition with
elevated CO., and climate change.
• To determine how elevated CO^ and climate change affect
nutrient cycling in the forest floor litter layer.
• To measure changes in litter layer quality (C/N ratio, lignin/
N ratio, etc.) throughout the study.
• To determine the effects of elevated C02 and climate change
on the net storage of carbon in the forest floor litter layer.
Approach: This task focuses on the long-term effects of elevated
C02 and climate change on decomposition and nuUient cycling in
the forest floor of the terracosms. Weight loss and changes in
mineral nutrient and organic chemistry of the litter layer will be
used as integrative measures of litter processing and carbon stor-
age. Rates of litter layer decomposition and changes in chemistry
will be monitored using litter contained in inert mesh bags and
needle packs.
Environmental Research laboratory - Corvallis
Page 14
-------
Outputs;
• Characterization of litter layer decomposition rates, and
carbon and nutrient cycling of Douglas fir litter under el-
evated CO, and climate change.
• Characterization of changes in litter quality while undergo-
ing decomposition under elevated CO, and climate change.
• Characterization of net storage of carbon in the litter layer
under elevated C02 and climate change.
TASK 6
Root Growth,
Morphology,
Phenology, &
Carbon
Partitioning
Science Questions:
• Will root growth change in response to elevated C02and
climate change ?
• Will elevated C02 and climate change affect the allometric
relationships among coarse roots, fine roots, and mycor-
rhizae ?
• Will root phenology be altered by elevated C02 and climate
change?
• Will the biochemical partitioning of root C and N be affected
by elevated C02 and climate change?
Objectives:
• To quantify root growth with numbers of roots produced,
their distribution and turnover, and the total weight of the
standing stock of roots under elevated CO, and climate
change.
• To quantify dynamics of root production, development, and
mortality under elevated CO, and climate change, and to
determine the effects on root allometries, i.e., distribution of
biomass among coarse roots, nonmycorrhizal fine roots, and
mycorrhizae.
• To characterize effects of elevated CO, and climate change
on root phenology.
• To quantify biochemical partitioning of C between structural
and nonstructural compounds in the various root fractions.
Environmental Research Ixiboratory - Corvallis
-------
Approach: Roots will be assessed by two methods, one destruc-
tive (cores-to-depth) and one nondestructive (minirhizotrons).
Destructive sampling will be limited in the terracosms to avoid
destruction of the biological and physical integrity of the
belowground component, recognizing that infrequent destructive
sampling may be insufficient to characterize root biomass with a
high degree of accuracy. Two soil cores (5 cm i.d. x 95 cm) will
be collected twice a year and separated into 10-em segments by
depth. Samples will be soiled into four fractions: live coarse roots
(> 2 mm), live fine roots (< 2 mm) and mycorrhizae, dead coarse
roots, and dead fine roots and mycorrhizae. Besides diy weights, the
separated soil and root fractions will be analyzed forC fractions
and nutrients. Total C and N will be measured in the root "cellu-
lose", "extractives", and "lignin" fractions. Minirhizotrons wilJ be
used with miniature video camera system to provide a nondestruc-
tive measure of root production and dynamics.
Outputs:
• Characterization of the effects of elevated C02 and climate
change on root growth.
• Characterization of changes in root phenology caused by
elevated CO, and climate change.
• Characterization of changes in the distribution of C, nutri-
ents, "cellulose", "extraclives", and "lignin" in the
belowground standing stocks of coarse roots,
nonmycorrhizal fine roots and mycorrhizae.
• Characterization of changes in the biochemical partitioning
of C between structural and nonstructural compounds in the
various root fractions.
Environmental Research laboratory - Corvaltis
I'a^e 16
-------
TASK 7 Science Questions:
Soil Biology • Will bacterial and fungal populations, soil fauna, nematode
community structure, and the colonization of tree roots by
mycorrhizal fungi, be affected by elevated CO 2 and climate
change?
• Will soil greenhouse gas production, processing, and emis-
sions be affected by elevated CO,and climate change?
Objectives:
• To quantify the effects of elevated C02 and climate change
on total and active soil microbial populations (bacteria and
fungi), nematode community structure, and soil fauna popu-
lations.
• To characterize the carbon transformation rates of the bulk
soil microbial population under elevated C02 and climate
change as indicated by the activities of enzymes processing
organic compounds.
• To quantify the effects of elevated C02 and climate change
on the colonization of roots by mycorrhizal fungi and on the
diversity of mycorrhizal fungi colonizing roots.
• To measure trace gas production and loss within the soil
profile and the physical, chemical, and environmental factors
affecting their production and loss.
Approach: Measures of soil bacteria, fungi, mycorrhizae, nema-
todes and soil enzymes will be determined using samples from the
corcs-to-depth collected twice a year. Soil fauna populations will
be assessed using separate litter and soil samples collected at the
same biennial samplings. Bacterial and fungal total biomass esti-
mates will be performed by direct microscopy on hyphae and
bacterial cells. Bacterial and fungal active biomass will be deter-
mined by fluorescein diacelate staining followed by direct
microscopy. Soil microbial activity will be determined by mea-
suring activity of enzymes such as B-glucosidase, peroxidase,
phcnoloxidasc, phosphatase, and proteinase. Mycorrhizal fungi
colonization will be determined by microscopy. Mycorrhizal
Environmental Research Ixtboratory - Corvallis
Pftfr 17
-------
fungi diversity will be determined on a limited basis by assess-
ment of nucleic acid "fingerprints" of mycorrhizal fungi. The fate
of key soil fauna species, including earthworms, spiders, milli-
pedes, and centipedes, will be assessed by direct observation of
litter and soil samples.
Two kinds of soil gas samples will be collected and analyzed for
C02> CH4, N20, and 02. Soil gas samplers have been placed at
five depths in the terracosm soil. Headspace chambers will be
used to measure soil surface emission (litter layer-air interface).
Both kinds of samples will be analyzed using gas chromatogra-
phy.
Outputs:
• Estimates of total and active bacterial and fungal biomass,
nematode community structure, and soil faunal populations
under elevated C02 and climate change.
• Estimates of soil microbial activity as affected by elevated
C02 and climate change.
• Estimates of root colonization by mycorrhizal fungi under
elevated C02 and climate change.
• Characterization of the effects of elevated C02 and climate
change on differentiation of the mycorrhizal fungi commu-
nity on roots.
• Estimates of annual emissions of greenhouse gases from
terracosm soils.
• Characterization of greenhouse gas production and process-
ing in terracosm soils.
MODELING The primary goal of these tasks is to parameterize a process-based
TASKS tree growth model to study the responses of trees to elevated CO (
and climate change. The TREGRO model was selected because it
simulates the growth of both above- and belowground plant com-
ponents and incorporates fundamental processes likely to be
affected by elevated C02 and climate change. The model is cur-
Environmenlal Research Laboratory - Corvallis
1'age 18
-------
nently operational and provides a reasonable simulation of plant
growth. Parameterization of the TREGRO model will occur using
data from the experimental research tasks from this project, with
additional data from the initial biomass values for our population
of Douglas fir trees, published literature, and the Ozone and Forest
Response Program at ERL-C. The parameteri/ed model will be
used to lest our conceptual understanding of how Douglas fir re-
sponds to elevated C02 and climate change by comparing
experimental results to model predictions in an iterative fashion.
The output from the modeling tasks will be a parameterized and
calibrated version of TREGRO for Douglas fir, useful for studying
the effects of elevated C02 and climate change.
INTEGRATION This study will support policy objectives of the U.S. Interagency
& INFERENCE Committee on Earth and Environmental Sciences (GEES), particu-
larly in the areas of effects of global climate on ecosystems and
influences (feedbacks) of ecosystems on atmospheric C02 concen-
trations and climate change processes. The support will be in the
form of providing: 1) an integration of the experimental results
into a cohesive understanding of the effects of elevated CO, and
climate change on forest trees and soils, and 2) inference of these
effects across time and space through the application of a tree
growth model.
Environmental Research laboratory • Corvallis
Vn,.r TO
------- |