When Mike Wagner took Northern Arizona
University students to the site where he was trapping bark beetles
near Flagstaff, he expected to show them a simple lesson: Once
freed from a funnel-trap, the insects would find a juniper tree and
burrow into it. But as the entomologist tipped the trap, thousands
of beetles poured out, making it impossible for the students not to
swallow a few.
“The air was just thick with beetles,” he
recalls. “Everyone had beetles on their clothes. It’s the worst
infestation I’ve ever seen.”
As foresters assess the
damage from the tiny beetles with the deadly bite, reports indicate
that this year’s bugs are taking second place in the contest over
which generation can kill the most trees. Last year, the deadliest
year, more than a half-million acres of trees were affected by bark
beetles in Arizona alone. In places like Mars Hill near Flagstaff,
it’s visibly clear that something is terribly wrong.
The
hill, home to historic Lowell Observatory where Pluto was
discovered, is in the heart of the worlds’ largest contiguous
ponderosa pine forest. But a great many of these trees have
reddish-brown needles instead of green, an indication that, even
though they are standing, they are dead. In the Prescott area, more
than 80 percent of entire stands are wiped out.
Ordinarily, bark beetles infest about 5,000 acres in Arizona during
the spring and summer, says Tom DeGomez, a forest-health
specialist. “But last year and this year, the conditions have been
extraordinary to accommodate and nurture a thriving beetle
population.”
Elsewhere, in places like Southern
California and British Columbia, the bark beetle attack is also
unprecedented. “Throughout the Rocky Mountains, it’s the worst in
history,” says Wagner.
For researchers like Wagner,
DeGomez and Wally Covington, director of the Ecological Restoration
Institute at Northern Arizona University, the beetle plague was
predictable — just another chapter in the story about a forest
ecosystem on the brink of collapse.
Ordinarily, bark
beetles are as common as butterflies in a healthy forest. Pines and
junipers have evolved with a defense mechanism against harmful
insects. They are able to push the bugs out with the pitch they
produce.
One walk through the forest and it’s easy to see
how the trees have been struggling. Tall pines resemble used candle
sticks. All along the trunk, the sap dots the bark like globules of
melted wax dripping down the side of the tree. But there are simply
too many beetles for the trees to fight.
A closer look
reveals piles of sawdust-like granules, called frass, clinging to
the bark and piling up at the base of the tree. This is the stuff
the beetle pushes out as it burrows into the phloem, clogs the flow
of nutrients and starves the tree. Covington says these trees have
been weakened by overcrowded conditions in the forest and years of
drought, and they can’t withstand the army of insects chewing away
at them.
Before European settlers came to the West, the
forests looked and acted differently from how they do today.
Ponderosa pine ecosystems were very open with grassy meadows taking
up some 70 percent of the forest and perhaps only 20 to 30 trees
per acre. The trees grew in clumps and were big with distinctive
yellow bark, as many of them were hundreds of years old.
Most of us wouldn’t recognize that earlier forest as the ponderosa
pine forest we’ve come to know. Currently, hundreds, even
thousands, of small pines fight for survival on a single acre —
choking each other in the battle for sunlight, water, nutrients and
survival. The woods have grown dark. Grasses, wildflowers and
shrubs have become scarce.
Fire, like the bark beetle,
was once an important part of a healthy forest. Both now act as
predators. Whereas the bark beetle would break down dead wood and
help put nutrients back into the soil, fire would keep dead and
dying debris from building up on the forest floor. Its heat was
also a necessary signal to some plants to sprout.
Today,
we are witnessing how both fire and the bark beetle have the power
to destroy hundreds of thousands of acres, the result of more than
a hundred years of human-caused changes to the forest including
overgrazing of the grasses and fire suppression.
Covington says to save the forests we must start large,
landscape-scale restoration which involves thinning out the small
trees and allowing fire to burn the way it was intended, along the
forest floor, not in the tops of the trees.
“In Arizona,
we risk having every acre of ponderosa pine forest degraded by
fire, insects or weeds in about 20 years, he says. “We are out of
time.”
Bonnie Stevens is a contributor to
Writers on the Range in Paonia, Colorado (hcn.org). She is an
ecologist at Northern Arizona University in Flagstaff,
Arizona.
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