Beware of beetles in freshly downed firewood

Although the Forest Service's tree thinning program is primarily designed to help prevent wildfires and enhance forest health there are additional benefits, as well.

One such beneficial side effect is an abundance of (almost) free firewood -- but the windfall has a catch.

The problem comes when all that freshly downed firewood also becomes a feast for the pine engraver bark beetle.

A normal population of the pest doesn't usually pose a threat to healthy trees, but a beetle population artificially boosted by a supply of downed trees can present a risk -- especially if infested trees are further concentrated when firewood gatherers bring them home.

Recent warm temperatures have sent the beetle larvae into a growth frenzy that results in the development of mature beetles capable of infesting new trees.

If the emerging beetles are concentrated so that they all head for the same live tree or trees, their numbers may overwhelm healthy trees that normally would not be at risk.

Forest Service Silviculturist Brian Tandy says that woodcutters can minimize the danger to healthy trees by following a few simple rules. The most important precaution is to dry out the freshly cut firewood as soon as possible.

He recommends putting the wood in direct sunlight and arranging it so as to expose it to air as much as possible.

It's also a good idea to get it cut up into firewood lengths right away.

"They (beetle larvae) feed on the cambium," said Tandy. "Once it's gone, they're done."

The cambium is the thin growth layer of the tree that is found between the bark and the wood.

Sometimes, certain insect larvae can be detected simply by listening. Some of the larger species can be heard munching away under the bark.

Tandy also suggests that potentially infested wood be kept as far away as possible from healthy trees and the danger can also be eliminated by removing the bark from downed wood; but that can be pretty labor intensive.

Another trick to eliminate the bark beetle pests is to cover the fresh wood with black plastic.

When exposed to the hot sun, the enclosed space under the plastic becomes hot enough to kill the bugs before they can mature.

June is a critical time in the life cycle of these destructive insects because the wintered-over larvae mature and emerge from the wood by the end of the month.

"They produce two generations a year," Tandy said.

The hatch in June sets out to colonize anew, and those beetles lay eggs that produce yet another generation before summer is over.

Most often, the early crop of insects will seek out the easy pickings in damaged, weakened or freshly downed trees.

According to Tandy, it's the summer crop of beetles that pose the greatest threat to healthy trees. This generation seeks out a convenient source of cambium and hunkers down to ride out the winter, eating away at the host trees, sometimes with fatal results.

So, if the spring hatch finds a healthy home for its offspring in your fresh firewood, fall may find that next generation checking into lodging in your favorite trees around the house.

When they do, they'll stay for a long winter of casual dining, and your favorite pine trees could become candidates for next year's firewood.

The problem, Tandy said, is that when the beetles infest a living tree, they eventually tunnel around under the bark until the tree is completely girdled.

The effect is the same as stripping the bark off the tree. The nutrient system that nourishes the tree is cut off, and the tree can no longer survive.

Tandy points out that firewood collected after the June hatch is generally free of serious infestations..

Thinning of dense stands is a long-term tool that will also contribute to healthy and insect-resistant stands of trees.

Some of the same forest health techniques now being applied by the Forest Service on a large scale can be used just as successfully by homeowners.