Beetles threaten drought-weakened forests | SierraSun.com
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Beetles threaten drought-weakened forests

Ryan Salm/Sierra Sun file photoDrought has sapped the strength of the Sierra's conifers, leading to an infestation of bark beetles.
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If dry conditions persist in the Sierra, tree mortality caused by bark beetle infestation is expected to spread, raising the risk of wildfire near mountain neighborhoods, according to a Tahoe National Forest worker.

For now, at least, the Tahoe forest is fairing better than other western forests, but the risk remains.

“It can be a real problem. Your fire risk goes up dramatically in the urban interface when you throw in a bunch of dying trees,” said Mark Brown, a silviculturist for the Tahoe National Forest. (Silviculture refers to the care of trees).



From 2002 to 2003, forests in the West saw the largest recorded increase of bark beetle-caused tree death, more than doubling from 4 million to 10 million acres, according to a report released in March by the Council of Western State Foresters.

A huge insect mortality in red and white firs occurred on the Tahoe National Forest between 1988 and 1990, Brown said.



The USDA Forest Service estimates that during the next 15 years, 22 million additional acres of forests could experience significant tree mortality from bark beetles.

Brown surveyed the Tahoe National Forest from the air last week and noticed hundreds of pockets of dead trees, tell-tale signs of bark beetles.

“They stick out like a sore thumb from the rest of the forest,” Brown said of the brown, yellow and red trees. Ponderosa Pines were the most predominant species noted in Brown’s aerial survey.

Bark beetles are a natural component of forests and some beetle-caused tree mortality is desired for proper ecosystem function.

Beetles become a problem during periods of severe drought. Trees exposed to fire are also more susceptible to insect infestation.

The bark beetle penetrates the bark and creates insect galleries or nests. When the larvae hatch, they girdle the tree by eating the cambium layer, which prevents water and nutrients from traveling up the trunk.

Several thinning projects in the Yuba and American River districts and near the town of Truckee are underway to prevent beetle outbreaks in years to come. If the trees are bigger than six to eight inches, they can be harvested for timber to offset costs of the operation, Brown said.

“We just don’t sit around and wait for something bad to happen,” Brown said.


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