Fire has been a major issue in natural resource
management, especially in Latin America and the
Caribbean.

Science News has a major article with multiple
collateral links on the subject at

http://www.sciencen ews.org/view/ feature/id/ 44800/title/ Fire

----

Plain text version of the article, but the web page has additional resources

Home / July 4th, 2009; Vol.176 #1 / Feature

FIRE

Ecology, climate and human activities conspire to set the world on fire

By Solmaz Barazesh

July 4th, 2009; Vol.176 #1 (p. 26)
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FIRE IN ACTION

View Larger Version | Top: The Terra satellite
imaged smoke from fires in southern California
last November. Bottom: Fires (shown in red)
detected between May 31 and June 9 by the Terra
and Aqua satellites. Yellow areas how the largest
numbers of fires.

Top: MODIS Rapid Response System; Bottom: Fire
maps created by Jacques Descloitres, MODIS Rapid
Response System at NASA's Goddard Space Flight
Center, fire detection algorithm developed by
Louis Giglio

Earth is a fire planet. Ever since the first
plants appeared - and provided fuel - more than
420 million years ago, fire has flourished in
Earth's oxygenated atmosphere. Some scientists
even think that long before humans, fire carved
out entire landscapes, clearing dense forests to
make way for grasslands.

In recent years, the fingers of flame have
extended their reach over more of the Earth's
surface. Wildfires are occurring more often and
becoming more severe, a perplexing change in fire
patterns that threatens to transform ecosystems,
reduce biodiversity and even alter climate. To
stamp out the flames, researchers have to
understand why fire is spreading and figure out
how to fight fire with science.

Fire has many faces. It helps some ecosystems
thrive but destroys others. It helps people clear
land but can also destroy homes and take lives.
Sometimes useful, sometimes destructive, fire is
always unpredictable - and that makes it a
difficult subject. "Understanding fire is a
science, and until now, the science of fire
hasn't been properly recognized," says ecologist
David Bowman of the University of Tasmania in
Hobart, Australia.

But now, researchers from different disciplines
are beginning to investigate the science of fire.
Some ecologists monitor forest fires burning
today, using satellite images to discern how much
forest is aflame and how severe the fires are.
Other scientists track how forests regenerate
after fires. And geologists reach into the past,
using remnants of long-cooled forest fires for
clues about how fire shaped the ancient Earth.

"Everyone in their respective fields had some
knowledge about fire. But now we've got to come
together to map out the role of fire in the Earth
system," Bowman says.

The "Earth system" is the sum of the planet's
physical, chemical, biological and social parts,
processes and interactions. Fire can shape
landscapes, shift climate and even change
processes such as the carbon cycle - blazes have
impacted the planet for eons. But now, people
could be shifting the balance in a new direction.

Bowman and other fire experts reviewed recent
fire research in the April 24 Science. The latest
work illuminates the complicated role that fire
plays on Earth and highlights the interactions
among climate, fire and humans.

People are playing more of a role in fire than
ever before, the research reveals. In the
tropics, fires are routinely started to clear
forestland for agriculture or pastureland. And as
more homes are built farther into the wilderness,
on land where fire used to roam free, the natural
patterns of fire are being suppressed.

"There's an emerging need to look at fire at the
intersection between biology, ecology and
society," Bowman said at a teleconference
coinciding with the paper's online release.

New research suggests that, while fires may burn
locally, their consequences spread globally. When
forests blaze, carbon stored in vegetation
escapes into the atmosphere as carbon dioxide, a
greenhouse gas. Added up, the fires that burn all
over the world could be a significant source of
atmospheric carbon, even contributing to climate
change.

At the same time, changes in climate could make
landscapes more prone to burning. Droughts can
set the stage for fires to burn in places where
they never used to. And when the natural patterns
of fire change, ecosystems change. Fire may kill
but not completely destroy trees. "That means
there's more fuel waiting for the next fire,"
says Eric Kasischke of the University of Maryland
in College Park, an ecologist who studies fire
and climate in boreal forest ecosystems.

Scientists don't have a complete understanding of
fire in the Earth system yet. But as researchers
pull together the threads of fire science,
integrating different areas of research, a new
appreciation of fire's global impacts is emerging.

Fire watch

Some ecosystems thrive on fire, such as arid
savannas that burst into flame easily, burn
often, but soon regenerate. For other ecosystems,
fire is a rare and serious event. Ancient forests
take thousands of years to grow to maturity and
can be destroyed by fire in a matter of hours.
The challenge is figuring out the role of fire in
each ecosystem, Kasischke says.

Using satellite data, Kasischke and his team
monitor fires in boreal forests in Alaska and
Canada, figuring out how much forest has burned
and tracking the forests as they recover.

Enlarge

FIRE FEEDBACK
View Larger Version | Studies in the Amazon
region highlight how human activities spur a
self-feeding fire cycle

All images from J. Balch

In the past, fire visited these forests
infrequently. But in recent years, fire has
picked up the pace. "Between 1959 and 1983 we saw
three big fires - that's about once a decade,"
Kasischke says. "In the last 25 years, the
frequency of these big fires has doubled."

Increasing fire frequency is disastrous for
slow-growing forests. Black spruce trees can take
30 years to mature and produce seeds. If the
forest burns before the trees mature, there won't
be any black spruce seedlings to regrow the
forest. This opens the door to more quickly
maturing species, which can soon dominate the
ecosystem, Kasischke says.

Putting out small fires can worsen the problem.
That's because small fires - which are low-lying
and burn around the mature trees without harming
them - clear brush and leaf litter, potential
fuel for bigger fires, from the forest floor.

Unfortunately, when homes and people lie in the
fire's path, letting even a small fire run its
course could be dangerous. So humans suppress the
small fires, and brush builds up, providing extra
fuel that could turn the next fire into a really
big, devastating one, Kasischke says.

Setting controlled fires to mimic natural ones is
a strategy already used in some places. Yet even
these controlled fires can sometimes get out of
hand. "There are lots of factors that turn a
small fire into a big one, and we don't
understand all of them yet," Kasischke says.

No one puts out the fires in the remote boreal
forests that Kasischke and his team monitor, and
people rarely start them. Along with the
increasing number of fires in these forests,
fires in recent years are more likely to have
been severe. "2004 and 2005 were our biggest fire
years ever," says Kasischke, noting that 2004 was
particularly warm and dry.

Conflagration climates

Fire is linked to changing weather patterns, he
and other researchers say. Warmer weather dries
out the forest, turning it into a tinder box. In
summer of 2004, a high pressure weather system
sat over the region that Kasischke monitors for
weeks -weather that lengthened the fire season,
he says.

A 2006 paper in Science investigated the
consequences of an extended fire season. Anthony
Westerling of the University of California,
Merced and his colleagues compiled a database of
wildfires in the western United States since 1970
and compared the fire records with climate data.
Since the mid-1980s, increased temperatures meant
that less snow fell and that snow melted earlier.
Those changes correlated with increases in
wildfires, which burn large swaths and last for
long times. Unusually warm springs and longer
summers dried out vegetation and provoked more
frequent fires of all sizes, the researchers
report.

"We're interested in understanding what controls
fire frequency and severity, and learning what
makes some ecosystems more resilient to fire,"
says Jennifer Balch of the National Center for
Ecological Analysis and Synthesis in Santa
Barbara, Calif. She and her colleagues
investigate fire in the Amazon's tropical forests.

Big forest fires used to rage through the
rainforest about every two centuries. Now, it's
more like every two decades, Balch says. A major
reason is that fire is a quick, easy and cheap
way to clear forest for agriculture and
livestock, and is a method widely used in the
Amazon, she says. But fire is a fickle friend. It
can easily get out of control and end up
destroying more forest than intended.

To investigate the effects of fire, Balch and her
team, with permission from farmers, deliberately
burn blocks of Amazonian forest. As the forest
burns, the scientists watch to see which types of
vegetation burn and which don't, and measure how
such factors as temperature, humidity and amount
of leaf litter affect fire intensity?-? its
temperature and duration. After the fire, the
researchers track which types of vegetation
bounce back most quickly.

"Repeated fires alter the composition of the
forest by favoring species with specific traits
that help them regenerate after a fire," Balch
says. Often, the species that take over the
ecosystem are also easy burners, such as grasses
that sprout once the trees have been cleared.
When fire has raged through a forest once, it's
more likely to return, the researchers say.

The team also calculates the amount of carbon
dioxide the burning releases into the atmosphere.
In the past, scientists have assumed that any
carbon released from forest fires would be
balanced by vegetation taking in carbon as the
forest regenerates. But as more forest burns and
less forest regenerates, changes in vegetation
could alter ecosystems and biogeochemical cycles
on a global scale.

"Our calculations show that forest fires could
account for one-fifth of the greenhouse gases
produced by humans," Balch says.
Besides releasing heat-trapping carbon dioxide,
fire contributes to climate change by releasing
aerosols, or black soot. Soot can warm the
atmosphere by absorbing solar radiation.

Fire is such a large source of carbon that it
should be incorporated into predictions of
climate change, researchers note. "The
Intergovernmental Panel on Climate Change should
take fire into account," Balch says.

The most recent IPCC report, released in 2007,
does acknowledge fire as a source of atmospheric
carbon, says Chris Field, an ecologist at the
Carnegie Institution for Science at Stanford
University, who contributed to the report.

"Fire has not been ignored. But we just don't
have good models to incorporate fire into climate
change," Field says. "The IPCC is working hard on
coming up with better models right now."

Ancient burns

Today's climate changes are not the first Earth
has endured, and some researchers think fire may
be connected with past climate change, too.
Jennifer Marlon of the University of Oregon in
Eugene and her colleagues use charcoal deposits
as records of ancient wildfires, finding that
fire has fluctuated with climate for thousands of
years. Studying changes in fire regimes over long
time periods puts recent increases in the number,
frequency and severity of fires in context.

Over many years, charcoal, which is burned
vegetation, washed into lakes, settled and was
eventually incorporated into layers of sediment.
Marlon and her colleagues take cores of the
sediment and analyze the charcoal content layer
by layer, getting a snapshot of forest fires at
different times.

In a 2008 paper in Nature Geoscience, Marlon and
her colleagues analyzed lake-bottom sediment
cores from around the world to reconstruct fire's
history over the past 2,000 years. The data show
a strong link between fire and climate, with
reduced fire in cold intervals and increased fire
in warm intervals, regardless of whether humans
were present.

From A.D. 1 to 1750, wildfires decreased in
number, the researchers reported. "Earth went
through a cooling period at that time, and fires
declined along with the temperatures, " Marlon
says.

Between 1750 and 1870, fires increased. Settlers
in the Americas and Australia slashed and burned
to clear forest quickly and make land available
for agriculture or animal grazing, Marlon says.

After 1870, fire activity hit a lull. "At that
time, enough land was cleared that the
slash-and-burn methodology slowed down," Marlon
says. And as people built homes on previously
uninhabited land, wildfires were no longer
allowed to rage as they once did. But in remote
areas, the number of wildfires remained high and
increased as climate warmed, she says.

More information on the patterns of ancient fires
comes from the trees themselves. When low-lying
understory fires rage through a forest, some
trees get damaged, picking up telltale fire
scars, says Thomas Swetnam of the University of
Arizona in Tucson. By looking at the location of
the scars in relation to tree rings, researchers
can figure out when fires have occurred.

"We sample living and dead trees that were
injured by fire," Swetnam says. "Using fire
scars, we can determine the year and the season
of the fire."

By scaling up the analysis from trees in single
forests to whole regions and even continents, the
researchers can get a global record of fires over
time.

Swetnam and his colleagues report that fire is
intimately connected with climate, with
particularly bad fire seasons in drought years.
"This is when we see many fires burning at one
time," Swetnam says. Tree-scar records show that
fire can also be impacted by El Niño and La Niña.
These oscillations in ocean temperature trigger
changes in atmospheric conditions that shift
weather patterns in different parts of the world.

La Niña brings drought to some parts of the
United States, contributing to a spike in fire
frequency, especially in the western states. El
Niño brings wet weather and flooding - but that
doesn't mean the forests are safe. "That reduces
fire activity and gives fuel a chance to build
up, meaning that the next year of fires will be
even worse," Swetnam explains. "Weather patterns
swing between El Niño and La Niña every two to
seven years. We see the frequency of severe fires
fluctuate on a similar range."

Beginning in the 20th century, though, "we're
seeing a major shift in the fire regime," Swetnam
says. "Fire is increasing, and now it's feeding
back into climate." But by collecting information
about how fire patterns have varied through
history, the researchers hope to gain a clearer
understanding of the relationship between changes
in climate and changes in fire regimes.

Fire patterns are still not well understood, but
the latest research is showing that they follow a
cycle that human activity is changing. Fully
elucidating the role of fire in the Earth system
will require figuring out how fire affects
different ecosystems and how these impacts add up.

"There's no basic ecology textbook that describes
how fire changes ecosystems or climate," Balch
says. "But we're accumulating more information -
and we're getting closer."

Solmaz Barazesh is a science writer based in Baltimore.

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