TREES AND GLOBAL WARMING
ugene’s trees are more than just a pretty
face; logging the urban forest is also an
environmental issue. “Urban trees have so
many benefits,” says Snyder. Beyond creating
community and a more livable neighborhood,
he says, they “improve safety, spur economic
development” and improve mental health by
reducing “stress and noise levels.” And impor-
tantly, he added, trees respond to global cli-
mate change by reducing greenhouse
gases.
Human fossil fuel consumption in the form
of coal, gas and oil combustion is one of the
largest sources of greenhouse emissions on the
planet, accounting for approximately 90 per-
cent, according to the U.S. Environmental
Protection Agency. The EPA identifies agricul-
ture, industry, transportation and electricity
generation, in order from least to greatest, as
the primary sources of U.S. greenhouse emis-
sions.
Since 1990, total greenhouse gas emissions
have risen 16 percent with carbon dioxide rep-
resenting the dominant gas produced. Other
atmospheric pollutants released through the
burning of fossil fuels that contribute to the
greenhouse effect or ozone depletion are
nitrous oxide, methane and fluoridated com-
pounds.
We use fossil fuels to sustain our current
way of life. But do urban trees represent a real-
istic way to reduce fossil fuel consumption
and lower carbon dioxide emissions?
Trees help control the excessive amounts
of greenhouse gases in the air “by absorbing
carbon, but that doesn’t add up to much,” says
Michael Kuhns, extension forestry specialist
and professor of Forest Resources at Utah
KATHRYN SCHUESSLER
E
‘Tree planting is one tangible thing people can do
to immediately help the environment.’
— Paul Ries, state of Oregon urban forester.
State University. Kuhns spent his sabbatical at
OSU and has presented his research on trees
and global climate change at various locations
around Oregon.
Through the natural process of photosyn-
thesis, trees remove carbon dioxide and other
greenhouse gases from the air and store them
in the roots, trunk and branches.
However, as Kuhns’ research indicates,
“we should not be planting trees in U.S. cities
and towns thinking that we are absorbing great
amounts of carbon dioxide and reducing glob-
al warming.” In his opinion, “landscape tree
planting or even rural tree planting in the U.S.
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can not make a significant dent in absorbing
the carbon dioxide we release.”
Nevertheless, Kuhns finds that “trees can
play an important part” in reducing green-
house gas emissions by lowering our con-
sumption of fossil fuels.
“Tree planting is one tangible thing people
can do to immediately help the environment,”
says Paul Ries, state of Oregon urban forester.
“You can view a tree as an oxygen enhancing
device” and “as a natural air conditioner,” he
says.
“The real benefit of trees is in all the things
they do to reduce energy use,” says Kuhns.
“The most direct way trees save energy is
in shading property,” Kuhns says. Trees
“counter the urban heat island effect” or the
warming of cities compared to their rural sur-
roundings, he says. Dark surfaces such as
pavement and commercial and residential
rooftops cause air temperatures to rise, there-
by increasing the demand for electric power in
the form of air conditioning. Kuhns’s research
indicates that “trees planted to properly shade
a building reduce energy use for air condition-
ing by up to 70 percent.”
Moreover, his work reveals that “well-
placed trees that slow the wind can reduce
energy use for heating by 30 percent.”
Urban trees also clean the air by absorbing
fine particulates, Kuhns says. Breathing fine
particulates has been linked to many serious
lung and heart diseases such as lung cancer
and cardiovascular diseases. Fine particulates
(also known as PM 2.5) are created by field
burning, fire-based home heating and diesel
and gas exhaust.
City trees also help with erosion and
stormwater control by slowing rainwater, Ries
says.
But small, young trees require decades to
grow to full size, and a larger tree removes 60
to 70 times the pollution a small tree does,
according a June 2007 article on urban forests
in Time magazine. And it’s the leafy crown of
older, bigger trees that intercepts rainwater
and helps with stormwater control.
But energy conservation is the most impor-
tant thing people can do for global warming,
Kuhns says. “I worry that people will have
extremely consumptive lifestyles and will
think that planting a tree compensates,” he
says.
ew