This creature has killed thousands of Idaho trees. Here’s what will happen to them

Salvage logging of moth-killed Douglas fir and grand fir trees followed by replanting with a mix of species will improve the overall health and increase profitability of a western Idaho forest, state officials say.

State Forester David Groeschl of the Idaho Department of Lands said logging practices last century removed ponderosa pine and other desired species, leaving Douglas fir and grand fir as the dominant species now being killed by tussock moths.

“We will replant it and get forest recovery going as quickly as possible,” Groeschl said July 30. “We tend to plant a mix because we believe that gives us some diversity and resilience.”

Groeschl said the strategy offers the best chance at maximizing profit on the land over the long run, the constitutional mandate of the five-member Idaho Land Board, which includes Gov. Brad Little, and which directs the Lands Department.

State lands — about 2.4 million acres (987,000 hectares) — produce money mainly for public schools and mostly through timber harvests.

The two timber sales on state land to salvage Douglas fir or grand fir that have been killed or damaged by the moths represent a remnant of past forest practices on state lands that the Lands Department has moved away from in the last 15 to 20 years, Groeschl said.

The timber up for sale is on about 3 square miles (8 square kilometers) near the communities of Smiths Ferry, Banks and Crouch in the Packer John State Forest. The Lands Department released drone video showing hundreds of dead or dying trees in the salvage area.

Packer John Salvage Sales Map from Idaho Department of Lands 7-31-19-page-0.jpg
Two auctions this summer will lead to the removal of dead and dying trees damaged by tussock moths from nearly 2,000 acres of Idaho’s Packer John State Forest north of Banks. Idaho Department of Lands

The area used to have significant stands of ponderosa pine. The dead or dying Douglas fir and grand fir trees that now dominate the area are thought to be from 75 to 100 years old, said Tom Eckberg, forest health program manager with the Department of Lands.

The trees are a fire danger, the department says.

“It is not unusual to have a tussock moth outbreak every 10 years or so, and often times trees can recover,” the department says on its website. “However, this infestation combined with several years of western spruce budworm defoliation and drought conditions in 2018, has resulted in extensive mortality. Making matters worse, bark beetles, ambrosia beetles and fir engravers are moving in to further attack weakened trees.”

Eckberg said signs of a tussock moth problem were found in the form of egg masses in 2016 and 2017. The moths in larval stages eat pine needles and defoliate trees. Trees can survive such attacks, but drought and heat can weaken their defenses.

“I think the reason we’re seeing the widespread mortality in that area is that last summer the temperatures were quite high and we got very little precipitation from June to September,” Eckberg said.

Eckberg said another moth invasion is expected in northern Idaho within three years.

Trees damaged by tussock moths in Packer John State Forest north of Banks.
Trees damaged by tussock moths in Packer John State Forest north of Banks. From an Idaho Department of Lands drone video published July 3, 2019. Idaho Department of Lands

State officials say the two timber sales in west-central Idaho will have a combined appraised value of nearly $3 million. One will be auctioned on Wednesday and another in August at a date to be named. The trees in the salvage areas are also being attacked by bark beetles and other insects, potentially making lumber from the trees less valuable if they aren’t soon harvested, officials say.

After logging, the area will be replanted with ponderosa pine, lodgepole pine, Englemann spruce and western larch, species less susceptible to tussock moth attacks. Having a mix of trees, Groeschl said, is akin to having a diversified portfolio less likely to be completely wiped out.

Douglas-fir are among the most common trees in Idaho forests, comprising nearly 30%. The tree is prized for building materials but doesn’t do well in drought conditions that can result in diseases and insect infestations.

Statesman Business Editor David Staats contributed.

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