This is a photo of the Anaktuvuk River fire burning in August 2007 on the North Slope of the Brooks Range in Alaska. University of Florida ecologist Michelle Mack and a team of scientists including fellow UF ecologist Ted Schuur found the fire released a significant amount of soil-bound carbon into the atmosphere. Photo: Alaska Fire Service |
After a 10,000-year absence, wildfires have returned to the
Arctic tundra, and a University
of Florida study shows
that their impact could extend far beyond the areas blackened by flames.
In a study published in Nature,
UF ecologist Michelle Mack and a team of scientists including fellow UF
ecologist Ted Schuur quantified the amount of soil-bound carbon released into
the atmosphere in the 2007 Anaktuvuk River fire, which covered more than 400 square miles
on the North Slope of Alaska’s Brooks Range.
The 2.1 million metric tons of carbon released in the fire—roughly twice the
amount of greenhouse gases put out by the city of Miami in a year—is
significant enough to suggest that Arctic fires could impact the global
climate, says Mack, an associate professor of ecosystem ecology in UF’s
department of biology.
“The
2007 fire was the canary in the coal mine,” Mack says. “In this wilderness,
hundreds of miles away from the nearest city or source of pollution, we’re
seeing the effects of a warming atmosphere. It’s a wakeup call that the Arctic
carbon cycle could change rapidly, and we need to know what the consequences
will be.”
Smoke
from the fire pumped greenhouse gases into the atmosphere, but that’s just one
part of a tundra fire’s potential impact. The fire also consumed up to 30% of
the insulating layer of organic matter that protects the permafrost beneath the
tundra’s shrub- and moss-covered landscape.
In
a pine forest, fire would burn up leaf litter on the ground, but not the soil
beneath. Because the Arctic tundra has a carbon-rich, peaty soil, however, the
ground itself is combustible, and when the fire recedes, some of the soil is
gone. In a double whammy, the vulnerable permafrost is not only more exposed,
but also covered by blackened ground, which absorbs more of the sun’s heat and
could accelerate thawing.
“When
the permafrost warms, microbes will begin to decompose that organic matter and
could release even more carbon that’s been stored in the permafrost for
hundreds or thousands of years into the atmosphere,” Mack says. “If that huge
stock of carbon is released, it could increase atmospheric carbon dioxide
drastically.”
The study shows how isolated fires can have a widespread
impact, says University
of Alaska biology
professor Terry Chapin. “When you think about the massive carbon stocks and
massive area of tundra throughout the world, and its increasing vulnerability
to fire as climate warms, it suggests that fire may become the dominant factor
that governs the future carbon balance of this biome,” Chapin says. “The paper
by Michelle and her colleagues raises this possibility for the first time. It
presents a very different perspective on the way in which climate change may affect
this biome in the future.”
Using
radiocarbon dating, coauthor Schuur and researchers from the University of Alaska
Fairbanks, the Alaska Fire Service, and Woods
Hole Marine Biological Laboratory, found that carbon up to 50 years old had
been burned in the 2007 fire.
Mack
also developed a new method that can now be used by other tundra researchers to
measure soil loss. By comparing the tussocks of sedge plants, which resprout
after a fire, Mack was able to quantify soil heights and densities before and
after the burn.
Mack
hopes her findings will open a dialogue about how tundra fires are managed.
Because the Anaktuvuk
River fire was in a
wilderness area, it was not suppressed or contained. With better data on the
long-term impact of tundra fire on global climate warming, Mack says, putting
out these fires might become more of a priority.
“This
fire was a big wakeup call, and it can happen again, not just in Alaska but in other parts of the Arctic, like Canada and Russia,” Mack says. “Suppressing a
fire in the wilderness is costly, but what if the fire causes the permafrost to
melt? We need to have that discussion.”
