United States
Environmental Protection
Agency
Effects of C02
and
Climate Change
on
Forest Trees

-------
~	What is Climate Change?
Life on Earth depends on a phenomena
called the "greenhouse effect." This effect is
produced by the presence of "greenhouse
gases" in the atmosphere. Like the panels
of a greenhouse, these gases trap solar heat
that would otherwise be lost into space.
The most common greenhouse gases are
water vapor and carbon dioxide. Over
thousands of years, levels of these gases
remained stable. However, since the begin-
ning of the Industrial Revolution, concen-
trations of carbon dioxide, as well as other
trace gases such as methane, nitrous oxide,
ozone and chlorofluorocarbons, have risen
in the Earth's atmosphere. As a result,
scientists expect Earth's air to warm and
precipitation, humidity and other aspects of
the world's climate to significantly change
over the next century.
To understand how a changing climate will
affect plants in North America, the United
States Environmental Protection Agency
has created the Global Change Research
Program. As part of this program, the
Corvallis lab has begun a study of Pacific
Northwest forest species.
~	Trees and Climate
Trees "breath" by absorbing carbon dioxide
for photosynthesis and releasing oxygen.
With slight increases above current levels of
carbon dioxide, photosynthesis increases

-------
TRF.GRO M«kl
and trees produce more growth. Thus, in
the near term, trees may actually store some
of the excess carbon dioxide by adding
more bulk.
But over a longer period of time, say in one
hundred years, what will happen when the
amount of carbon dioxide in the atmosphere
may double? Under these conditions,
current models project that the Earth's
atmosphere will warm considerably and
drought conditions in the Pacific Northwest
will worsen.

-------
Tree growth and structure are weakened by
prolonged dry spells. Also, the soil itself is
affected by drought. For example, decom-
position of soil organic matter increases as
soil temperatures increase and this releases
even more carbon dioxide into the atmo-
sphere. How will trees respond then?
~ The TERA Project
To help find answers to these questions and
to make predictions about the future of
forest resources, the Corvallis study is
divided into three tasks; scoping studies that
define the limits of the research; modeling
studies that extend experimental data to the
forest itself; and the TERA project, a series
of experimental studies that simulate forest
ecology in a controlled environment.
Key questions to be answered by the
Corvallis study are, how much climate
change can occur before significant changes
in forests take place? For example, as moist,
moderately cool conditions in Western
Oregon become drier and warmer, will the
coniferous species currently growing there
die out, to gradually be replaced by hard-
woods and drought-resistant conifers such
as pines?
This kind of vegetation change would have
significant impact on the economy of the
region. Currently, the Pacific Northwest
grows one of the most versatile and valu-
able timber crops in the world — Douglas

-------
		
Side View of Terracosm
Dn» Mm Hjipomttr
H)«l/Chamhcr CO]
Sampling fort*
Fir. If the climate will no longer support
the growth of this tree, vast changes could
occur in the Pacific Northwest.
The TERA Project will explore the ramifi-
cations of climate change through the use of
specially constructed miniature forest
environments called terracosms, twelve of
which have been built on the EPA lab site in
Corvallis.
The atmosphere, temperature, moisture and
soil conditions in the terracosms can be
completely controlled and closely moni-

-------
tored. To study many different scenarios at
one time, each terracosm will contain a
different habitat. For instance, one will
have an atmosphere containing a higher
level of carbon dioxide than is now present
in the earth's atmosphere. Another terra-
cosm will have an elevated temperature.
Yet another will have an elevated tempera-
ture and increased levels of atmospheric
carbon dioxide.
With the aid of video cameras and
computer-controlled remote sensors, plus
periodic sampling of plant material, EPA
scientists will monitor the growth of Doug-
las fir seedlings over a 2- to 4-year period.
These studies will yield valuable data about
tree responses under a changing climate and
increased carbon dioxide levels.
~ The Future
Finally, and crucially, people will have to
respond to a changing forest ecology. To
assist them, the EPA's TERA Project will
contribute valuable information about this
complex situation to scientists, business and
government policy makers who must make
decisions about forest resources.
USEPA Environmental Research Laboratory
200 SW 35lh Street	C<>«
July 1993
Corvaltis, OR 97333
503-754-5600

-------