From pines to
prairie? Arizona’s
forests susceptible to fire, beetles
Posted: Thursday, January 6, 2011 5:00 am
| Updated: 3:50 pm, Wed Jan 5, 2011.
Grant Martin - Cronkite News
FLAGSTAFF - Drivers headed northwest along U.S. Route 180 from
Flagstaff to the Grand Canyon travel through an eerie landscape
amidst the otherwise lush and verdant Coconino National Forest.
Charred trunks protrude from a grassy savannah, thin skeletons of
the towering ponderosa pines that had dominated these hillsides.
Blackened tree limbs are scattered among them. There are barely any
patches of green here, and there are no sounds of wildlife.
It resembles nothing so much as a graveyard.
Arizona forestry experts fear such landscapes might be increasingly
common over the next century, as warmer temperatures and drier weather
create virtually ideal conditions for wildfires. Such fires have already
ravaged hundreds of thousands of acres of Arizona's forests in the past
few decades.
"We're already seeing fires of increased frequency and intensity,"
said Tom Kolb, a professor at Northern Arizona University's School of
Forestry in Flagstaff. "Conditions here are definitely more hot and dry
than they were a hundred years ago, and that's contributing to the fires
that have become almost an annual occurrence around here."
This summer, a blaze swept through over 15,000 acres of the Coconino
National Forest, threatening homes and destroying wildlife habitat. The
damage is just a fraction of that caused by 2002's catastrophic
Rodeo-Chediski Fire, which consumed over 468,000 acres in the White
Mountains, forcing the evacuations of Show Low and other nearby
communities.
Recent though the devastation along Route 180 may appear, it's
actually evidence of a wildfire that occurred in 1996. There has been
scarcely any regeneration of the vegetation that had thrived here prior
to that fire, and experts believe it may take several decades - if ever
- before any significant new growth restores natural beauty to these
hills.
"Ponderosa pines reproduce only by seeds," explains Pete Fule, an
ecological restoration expert who also teaches at NAU. "These seeds can
only carry a certain distance away from parent trees, so when you have a
large disturbance event that kills trees over a pretty big area, it's
difficult for them to regenerate back into that site."
As wildfires continue to eliminate the ponderosa pine and other
native trees from their habitat in Arizona, they create an opportunity
for invasive species such as bromus tectorum, commonly called
"cheatgrass," to take their place. Cheatgrass has supplanted the native
vegetation in many wildfire sites throughout northern Arizona,
essentially transforming forests into prairies.
Because cheatgrass is itself very flammable, these resulting
savannahs are veritable tinderboxes for the surrounding forests,
providing fuel that will only add to the intensity of future fires.
At least one recent study suggests that the proliferation of grassy
plains in areas previously occupied by forest vegetation - such as the
transformation evident along Route 180 - is to be expected.
Fule explained that a third of large wildfire sites throughout the
Southwest in the past half century never returned to their original
conditions.
Fire is hardly the only agent of change affecting Arizona's forests
as temperatures climb over the next 90 years.
Pine bark beetles, already responsible for the deaths of millions of
pinyon and ponderosa pines in the state, reproduce at a faster rate in
warmer weather. U.S. Interior Secretary Ken Salazar has referred to
these beetles as "the Katrina of the West," and their devastation might
just be beginning. Healthy pines are able to defend themselves against
infestation by pushing the beetles out with sap, but droughts weaken
trees, rendering them more vulnerable to attacks.
Such droughts would also threaten Arizona's spruces, firs and aspens,
which rely on moisture more than pines. Such species thrive today in
moderately moist habitats such as the temperate hardwood forests around
the White Mountains.
Also, as Arizona's forests become increasingly warm, existing
vegetation may relocate, especially at higher elevations, to areas more
favorable to their growth. For instance, junipers and pinyon pines - two
trees typically found in Arizona's low-lying woodlands, could
conceivably adapt to climate change by moving upwards in elevation to
more moderate conditions, supplanting ponderosa pines in the process.
Fule, quipping that "plants aren't really good at walking," doubts
whether the native vegetation can relocate quickly enough to adapt to
the changing climate. If this proves to be the case, the vegetation in
low-lying areas might simply die off.
"The key point about modern climate change," Fule said, "is that it's
happening very quickly. It seems unlikely that modern ecosystems, just
acting through natural processes of regeneration, would be able to keep
up. In fact, people have done modeling studies to look at how fast
plants would have to move, and it's pretty darn fast. It's something
that exceeds, by orders of magnitude, the fastest movement of plants
that we've ever seen in the fossil record."
Kolb's office looks out over a nearby hill resplendent with healthy
ponderosa pines. Asked what he would expect to see were he to look out
his window in 100 years, Kolb conjectured that the hillside would have
fewer ponderosas and more junipers and pinyons, species that would have
crept up in elevation to adapt to the rising temperatures.
Then he turned away from the window and shrugged.
"If it doesn't look like that," Kolb said, "then it might just be an
ugly, burned landscape out there."
Explore this project
Introduction: As climate warms, Arizona's deserts, forests, cities
face uncertain futures
Part One: The desert
Arizona without saguaros? Drought, plant invaders pose threats
Part Two: The forest
From pines to prairie: Arizona's forests susceptible to fire, beetles
Part Three: The people
Rising temperatures threaten cities' air quality along with water
supply
Multimedia
An interactive graphic allows you to explore the projected effects of
climate change on Arizona
© Copyright 2011, White
Mountain Independent, Show Low, AZ
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