A new PNW Research Station study
explored how carbon dynamics in Washington State may be altered
by more-frequent wildfires, triggered
by a warming climate. The study looked at the effects of greater
area burned on both live biomass and nonliving biomass, such as the
dead standing trees and downed wood shown here. Photo by Tom Iraci.
PORTLAND, Ore. July 23, 2012. Forests
in the Pacific Northwest store more carbon than any other region
in the United States, but our warming climate may undermine their
A new study conducted by the U.S. Forest Service’s Pacific
Northwest Research Station and the Climate Impacts Group at the
University of Washington has found that, by 2040, parts of Washington
State could lose as much as a third of their carbon stores, as
an increasing area of the state’s forests is projected to
be burned by wildfire. The study—published in the July 2012
issue of the journal Ecological Applications—is the first
to use statistical models and publicly available Forest Inventory
and Analysis data to estimate the effects of a warming climate
on carbon storage and fluxes on Washington’s forests.
“When considering the use of forests to store carbon, it
will be critical to consider the increasing risk of wildfire,” said
Crystal Raymond, a research biologist based at the station’s
Pacific Wildland Fire Sciences Laboratory and lead author of the
study. “Especially in the West, where climate-induced changes
in fire are expected to be a key agent of change.”
Trees remove and sequester carbon from the atmosphere, in the
form of carbon dioxide, acting as important stores, or “sinks,” of
carbon that help to offset its accumulation in the atmosphere.
When trees and other woody material in the forest are burned by
fire, they release carbon back to the atmosphere, mostly as carbon
dioxide, where it may once again act as a greenhouse gas that promotes
warming. This land-atmosphere exchange of carbon is increasingly
of interest to land managers seeking ways to actively manage forests
to store carbon and help mitigate greenhouse gases.
To explore what
effect climate-driven changes in wildfire might have on the ability
of Washington’s forests to act as carbon
sinks, Raymond and station research ecologist Don McKenzie used
a novel approach. They combined published forest-inventory data,
fire-history data, and statistical models of area burned to estimate
historical and future carbon carrying capacity of three regions
in Washington—the Western Cascades, the Eastern Cascades,
and the Okanogan Highlands—based on potential forest productivity
and projections of 21st century area burned.
“Forests on both the eastern and western slopes of the Cascade
Range will lose carbon stored in live biomass because area burned
across the state is expected to increase,” Raymond said. “Even
small increases in area burned can have large consequences for
carbon stored in living and dead biomass.”
looked at live biomass, which includes living trees and vegetation,
as well as nonliving biomass in the form
of coarse woody debris, which includes dead standing trees and
downed logs. Both contribute to the carbon cycle, but in different
ways—living biomass removes carbon from the atmosphere as
vegetation grows, and coarse woody debris releases carbon over
time as the material decomposes.
Raymond and McKenzie projected
forests of the Western Cascades to be most sensitive to climate-driven
increases in fire, losing
anywhere from 24 to 37 percent of their live biomass and from
15 to 25 percent of their coarse woody debris biomass by 2040.
forests store significant carbon and typically burn with high
severity, killing many trees and consuming coarse woody debris.
the other side of the mountains, the researchers also projected
a decrease in live biomass by 2040—of anywhere between 17
and 26 percent in the Eastern Cascades and in the Okanogan Highlands—but
no change in coarse woody debris biomass, or possibly even an increase,
because coarse woody debris biomass increases as trees are killed
by fire and subsequent low-severity fires burn only a small portion
“Changes in fire regimes in a warming climate can limit
our potential to use forests in the Pacific Northwest to store
additional carbon and to reduce atmospheric carbon dioxide,” Raymond
Understanding the possible effects of more area burned by
fire can help managers decide whether forests need to be actively
for their fire potential to minimize carbon loss.
To read more
about the study, visit http://www.esajournals.org/doi/abs/10.1890/11-1851.1.
The PNW Research Station is headquartered in Portland, Oregon.
It has 11 laboratories and centers located in Alaska, Oregon,
and Washington and about 425 employees.