On path to rebuilding our forests | TahoeDailyTribune.com

On path to rebuilding our forests

by Andy Bourelle

What: Grand Opening Ceremony of Bark Beetle Discovery Trail

When: Noon, July 31

Where: Spooner Lake State Park

An army of small beetles is responsible for killing many trees in the Lake Tahoe Basin, and officials believe educating residents may be the key to fighting the insects.

Anyone interested in learning about the bark beetle, its dangers and how to stop it from destroying the forest will have the opportunity at the Bark Beetle Discovery Trail at Spooner Lake Park.

The trail, set to open at noon on July 31, is part of a program funded by The University of Nevada Cooperative Extension and the University of Nevada Agricultural Experiment Station.

“It’s kind of a fun, easy way to learn about the bark beetle,” said Sue Donaldson of the University of Nevada Cooperative Extension. “It’s made in such a way that kids will enjoy it and learn from it as well as adults.”

The bark beetle is a major contributor to the large number of dead trees in the basin, Donaldson said. The effect is an increasing risk of wildfires in the forests.

The basin’s forests are full of 20 to 30 percent dead trees, Donaldson said, with as much as 80 percent dead trees in some places. Healthy forests have about three to five percent dead trees.

The bark beetle – a 1/8-inch-long “little, tiny insect the size of a grain of rice” – is a natural inhabitant of every forest, Donaldson said.

Normally, in healthy forests, bark beetles are present only in small numbers and kill only weakened trees. Bark beetle populations can increase, Donaldson said, when forests are “stressed” from air pollution, fungal diseases, high tree densities, ice-melting road salts and other reasons.

Lake Tahoe faced an eight-year drought from 1986 to 1994 that is believed to have stressed the basin’s forests, making trees more susceptible to the bark beetle.

Additionally, because of logging in the Comstock era and lack of periodic forest fires in the basin, forests around Lake Tahoe are thick. When trees grow too close together, they compete against each other for moisture, nutrients and sunlight, which can also weaken the trees’ health.

A bark beetle chews a hole into the bark of the basin’s Jeffrey pine trees, then feeds and reproduces in the “phloem,” or inner bark layer of the tree. They travel up and down the phloem, excavating tunnels called “galleries” in the tree. Up to 100,000 beetles can infest a single tree’s phloem, killing it.

Additionally, bark beetles also carry a fungus which infects trees, causing a bluish staining of the wood and crippling a tree’s ability to transport water and nutrients, also killing it.

A healthy tree can defend against the bark beetle by pushing sap out of the bore hole, in an attempt to “pitch” the beetle out, Donaldson said.

However, trees in a stressed forest have weakened defenses and often are unable to pitch out the insects.

Preventing bark beetle attacks, recognizing early signs of infested trees and what to do with a tree once it is infested are some of the topics the trail, and Friday’s grand opening ceremony, will address.

The best way to prevent bark beetle attacks is to reduce factors that can stress a tree. Thinning forests and watering and fertilizing trees improve their overall health, which increases their defenses against the bark beetle.

Dealing with an infested tree is also important. The outer bark can be removed to inspect the inner bark. If the phloem is full of galleries and bark beetle eggs, even though it may look alive, the tree is essentially dead.

“If the tree can’t pitch out the insects, and they’ve laid eggs, it’s too late for that tree,” Donaldson said. “There is no treatment to kill the beetles under the bark.”

Once the tree is dead and all the nutrients have been taken out of it, the bark beetles will go to another tree. Therefore, Donaldson said, it is important to remove an infested tree.

Residents should contact the U.S. Forest Service to obtain permission to remove the tree.

Once removed, the tree can be chipped into mulch or used for firewood. If residents plan to burn bark beetle-infested wood, Donaldson said, they should be careful about its storage. The wood pile should be covered in plastic and placed in a sunny location, with the edges of the plastic buried in the soil. The beetles will be unable to escape, and the heat under the plastic – which can reach 120 degrees – will kill them.

Donaldson said there are chemicals that can be placed on the bark of a tree which may repel the bark beetles. However, using them is not the answer, she said, because the chemicals can cause other environmental problems in the Tahoe Basin.

Researchers from the University of Nevada Department of Biochemistry currently are studying the bark beetle and have determined, when a bark beetle finds a suitable tree for infestation, the insect emits a pheromone which attracts more bark beetles.

When the tree is saturated with bark beetles, Donaldson said, the insects emit another pheromone which repels more beetles, telling them “this tree is full; go somewhere else.”

Researchers hope to be able to produce the repellent pheromone of the beetle, Donaldson said, to place on the outside of trees as a natural, nontoxic way of keeping bark beetles away.

For now, however, other forms of prevention are the best defenses.

Residents interested in more information about the bark beetle are encouraged to attend the grand opening ceremony Friday or to simply visit the trail after that. Also, brochures about the bark beetle are available by calling the cooperative extension at (702) 832-4150.

Tahoe Daily Tribune E-mail: tribune@tahoe.com

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