Monday, March 22, 2010

Prescribed Burns May Help Reduce U.S. Carbon Footprint

The following is courtesy of NCAR.

The use of prescribed burns to manage Western forests may help
the United States reduce its carbon footprint. A new study finds that
such burns, often used by forest managers to reduce underbrush and
protect bigger trees, release substantially less carbon dioxide
emissions than wildfires of the same size.
"It appears that prescribed burns can be an important piece of a climate
change strategy," says Christine Wiedinmyer, a scientist with the
National Center for Atmospheric Research (NCAR) and lead author of the
new study. "If we reintroduce fires into our ecosystems, we may be able
to protect larger trees and significantly reduce the amount of carbon
released into the atmosphere by major wildfires."

The study is being published this week in Environmental Science and
Technology. It was funded by the National Science Foundation, NCAR's

Drawing on satellite observations and computer models of emissions, the
researchers concluded that widespread prescribed burns can reduce fire
emissions of carbon dioxide in the West by an average of 18 to 25
percent, and by as much as 60 percent in certain forest systems.

Wildfires often destroy large trees that store significant amounts of
carbon. Prescribed fires are designed to burn underbrush and small
trees, which store less carbon. By clearing out the underbrush, these
controlled burns reduce the chances of subsequent high-severity
wildfires, thereby protecting large trees and keeping more carbon locked
up in the forest.

"When fire comes more frequently, it's less severe and causes lower tree
mortality," says Matthew Hurteau of Northern Arizona University, the
study's co-author. "Fire protects trees by clearing out the fuel that
builds up in the forest."

-----The importance of trees-----

Forests have emerged as important factors in climate change. Trees
store, or sequester, significant amounts of carbon, thereby helping
offset the large amounts of carbon dioxide emitted by factories, motor
vehicles, and other sources. When trees burn down or die, much of that
carbon is returned to the atmosphere. It can take decades for forest
regrowth to sequester the amount of carbon emitted in a single fire.

In the western United States, land managers for more than a century have
focused on suppressing fires, which has led to comparatively dense
forests that store large amounts of carbon. But these forests have
become overgrown and vulnerable to large fires. Changes in climate,
including hotter and drier weather in summer, are expected to spur
increasingly large fires in the future.

This could complicate U.S. efforts to comply with agreements on reducing
carbon emissions. Such agreements rely, in part, on forest carbon
accounting methodologies that call for trees to store carbon for long
periods of time. Large carbon releases from wildland fires over the next
several decades could influence global climate as well as agreements to
reduce emissions.

To determine whether prescribed burns would likely affect the carbon
balance, the scientists first estimated actual carbon emissions from
fires for 11 Western states from 2001 to 2008. They used satellite
observations of fires and a sophisticated computer model, developed by
Wiedinmyer, that estimates carbon dioxide emissions based on the mass of
vegetation burned.

Their next step was to estimate the extent of carbon emissions if
Western forests, during the same time period, had been subjected to a
comprehensive program of prescribed burns. The scientists used maps of
vegetation types, focusing on the forest types that are subject to
frequent natural fires and, therefore, would be top candidates for
prescribed burns. Emissions in the model were based on observations of
emissions from prescribed burns of specific types of forests.

The results showed that carbon emissions were reduced by anywhere from
37 to 63 percent for the forests that had been subject to prescribed
burns, depending on the vegetation mix and location of the forests.
Overall, carbon emissions for the 11 Western states were reduced by an
annual average of 14 million metric tons. That is the equivalent of
about 0.25 percent of annual U.S. carbon dioxide emissions, or slightly
more than the annual carbon dioxide emissions from all fossil fuel
sources in some less-populated states, such as Rhode Island or South Dakota.

The authors cautioned, however, that the actual impacts in the Western
states would likely be lower. Their study assumed that prescribed burns
could be set in all suitable forests, whereas forest managers in reality
would be hard-pressed to set so many fires, especially in remote regions
or near developments.

New Mexico had the highest average annual reduction (35 percent) because
of its forest types, followed by Montana, Arizona, California, and

The study notes that prescribed burns could lead to additional air
quality benefits. Previous research has indicated that such burns could
reduce emissions of pollutants such as fine particulate matter and
carbon monoxide.

"While it can be costly to set controlled fires, there is also a cost in
leaving forests vulnerable to larger fires," Wiedinmyer says. "More
research can help forest managers make better decisions about our
forests and climate change."

The University Corporation for Atmospheric Research manages the National
Center for Atmospheric Research under sponsorship by the National
Science Foundation. Any opinions, findings and conclusions, or
recommendations expressed in this publication are those of the author(s)
and do not necessarily reflect the views of the National Science

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