Monday, September 23

Bark beetles gobble up nutrients from trees


An insect no bigger than a peanut is partly responsible for the
destruction of trees hundreds of years old in the Lake Arrowhead
area.

The bark beetle, native to the area, has been taking advantage
of trees weakened by drought and high temperatures.

Bark beetles burrow into a host tree and sap nutrients from it.
Then they reproduce, laying eggs that will mature into adult bark
beetles and colonize other trees.

Typically, trees would defend themselves by drowning out the
beetles with their resins; however, lately trees have not received
the moisture necessary to withstand a bark beetle attack, said Hart
Walter, UCLA professor of biogeography and ecology.

In normal conditions, the beetles will prey on weakened trees or
trees that must compete for resources in areas with thick growth,
said Timothy Paine, professor of entomology at the University of
California, Riverside.

“These weakened trees die and the less weak trees have
less competition and more nutrients and water,” Paine
said.

Bark beetles also have natural predators, including woodpeckers
and other insects, he said.

“The natural enemies remove about 30 percent of the
population,” Paine said. “Under normal circumstances,
that’s enough to keep the population (of bark beetles)
relatively low.”

In addition to natural factors, humans are partly responsible
for the condition of trees in the Lake Arrowhead area.

Because the Lake Arrowhead area was heavily logged a century
ago, most of the trees in the area are roughly the same age and
size, said Philip Rundel, professor in the UCLA department of
organismic biology, ecology and evolution.

“Pristine forests with mosaics of different age classes
burn less readily,” he said.

Man-made air pollution is partly responsible for weakening
trees, Rundel said, but is relatively only a small stress
factor.

“The trees have been exposed to even worse pollution 30 to
40 years ago and there were no bark beetles,” Walter
said.

The forests also have an artificially high density of trees from
previous logging and the exclusion of fire for decades, making them
susceptible to more intense fires, Rundel said.

“It is the combination of this high density and the dead
trees that allowed for very hot crown fires rather than cooler
ground fires,” he said.

Management decisions used to control urban forests where people
live, such as Lake Arrowhead, have “implications” and
can create conditions conducive to beetle growth, Paine said.

It is uncertain how long it will take for the affected areas to
recover, though it is expected that they will recover
“relatively quickly,” Rundel said.

“There will be a variable rate of recovery in these
forests, related to many factors including the intensity of the
fire in a given area,” he said.

Though there was a bark beetle infestation 10 years ago, this
year’s bark beetle infestation is much worse, Walter
said.

“This is really a calamity,” he said.

Fires in Lake Arrowhead were within one mile of The UCLA
Conference Center on Lake Arrowhead’s north shore, but never
reached the center.

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