Forests of the United States have more capacity than previously estimated to sequester carbon, especially the conifer forests of the Pacific Northwest. (Photo courtesy of Oregon State University) |
A
research group has concluded that forests and other terrestrial
ecosystems in the lower 48 states can sequester up to 40 percent of the
nation’s fossil fuel carbon emissions, a larger amount than previously
estimated – unless a drought or other major disturbance occurs.
Widespread
droughts, such as those that occurred in 2002 and 2006, can cut the
amount of carbon sequestered by about 20 percent, the scientists
concluded in a recent study that was supported by the National Science
Foundation and U.S. Department of Energy.
The
research, published by scientists from 35 institutions in the journal
Agricultural and Forest Meteorology, was based on satellite measurements
and dozens of environmental observation sites in the AmeriFlux network.
Not all of this data had previously been incorporated into earlier
estimates, and the new study provides one of the most accurate
assessments to date of the nation’s carbon balance.
“With
this data it appears that our forests and other vegetation can
sequester as much as 40 percent of the carbon emissions in the lower 48
states,” said Beverly Law, a co-author of the study, professor in the
Department of Forest Ecosystems and Society at Oregon State University,
and science team chair of the AmeriFlux network.
“That’s
substantially higher than some previous estimates, which indicated
these ecosystems could take up the equivalent of only about 30 percent
of emissions or less,” Law said. “There’s still some uncertainty in
these data, but it does appear that the terrestrial carbon sink is
higher than believed in earlier studies.”
However,
the scientists cautioned that major disturbances, such as droughts,
wildfires and hurricanes, can all affect the amount of carbon
sequestered in a given year. Large droughts that happened twice in the
U.S. in the past decade reduced the carbon sink about 20 percent,
compared to a normal year.
“With
climate change, we may get more extreme or frequent weather events in
the future than we had before,” Law said. “About half of the United
States was affected by the major droughts in 2002 and 2006, which were
unusually severe in their spatial extent and severity. And we’re now
learning that this can have significant effects on the amount of carbon
sequestered in a given year.”
Carbon
dioxide, when released by the burning of fossil fuels, forest fires, or
other activities, is a major “greenhouse gas” and factor in global
warming. But vegetation, mostly in the form of growing evergreen and
deciduous forests, can play an important role in absorbing some of the
excess carbon dioxide.
Such
information is important to understand global climate issues and
develop policies, the researchers noted. This study examined the carbon
budget in the U.S. from 2001 to 2006. Also playing a key role in the
analysis was the PRISM climate database at OSU, a sophisticated system
to monitor weather on a very localized and specific basis.
The
period from 2001-06, the researchers noted, had some catastrophic and
unusual events, not the least of which was Hurricane Katrina and the
massive destruction it caused. It also factored in the 2002 Biscuit Fire
in southwest Oregon, one of the largest forest fires in modern U.S.
history.
The
research found that the temperate forests in the eastern U.S. absorbed
carbon mainly because of forest regrowth following the abandonment of
agricultural lands, while some areas of the Pacific Northwest
assimilated carbon during much of the year because of the region’s mild
climate.
Crop
lands were not considered in determining the annual magnitude of the
U.S. terrestrial carbon sink, because the carbon they absorb each year
during growth will be soon released when the crops are harvested or
their biomass burned.
“Our
results show that U.S. ecosystems play an important role in slowing
down the buildup of carbon dioxide in the atmosphere,” the researchers
wrote in their conclusion. “The dominant sources of the recent
interannual variation included extreme climate events (e.g., drought)
and disturbances (e.g., wildfires, hurricanes).”
Forests
of the United States have more capacity than previously estimated to
sequester carbon, especially the conifer forests of the Pacific
Northwest. (Photo courtesy of Oregon State University)
