Peak budworm infestation eats its way through Southeast forest

Look around Southeast and you will see a lot of evergreen trees that aren't so green.

Southeast Alaska's hemlock and spruce trees are fending off an assault by a number of pests and diseases, most notably a caterpillar that causes the conifers to turn reddish-brown.

The main culprit is the western blackheaded budworm, a moth caterpillar that feeds on hemlock and spruce needles, according to U.S. Forest Service Alaska Region entomologist Elizabeth Graham in Juneau.

Graham said Southeast trees are experiencing a peak budworm infestation, a cyclical event that occurs every 30 or 40 years. While the widespread browning looks alarming, she said it's not a big concern for general forest health.

"It's actually endemic to the forest here. It's not an invasive species or an exotic pest we haven't dealt with before," Graham said. "It may look really bad at first, but it's part of the dynamic forest and how it's changing."

Budworms tend to feed on new growth, leaving older parts of the tree intact. As they devour needles, they create gaps in the tree cover, providing new habitat for wildlife and letting more light shine on the understory, Graham said.

She added that budworm poop, called frass, is also beneficial for the forest, infusing the soil with nutrients when it falls to the ground.

Graham will be in Wrangell for BearFest next week, and said she is scheduled to give a presentation and talk about the budworm on July 28.

"The nice thing is it's not the spruce beetle," she said of the bug that has infested an estimated 1.6 million acres of Southcentral forests from the Kenai Peninsula to the Matanuska-Susitna Borough. That's equal to about 10% of the Tongass National Forest.

Southeast forest managers first noticed the budworm outbreak in 2020. Infestations can last a few years, building up until the population crashes, Graham said. The last time there was a major outbreak was 1992 to 1995.

The caterpillars prefer hemlock but this year they are feeding more on spruce, Graham said, likely because their population grew and more moths laid eggs on spruce trees last fall.

"In coming weeks, the western blackheaded budworm will continue to feed and the damage will become even more apparent," the Forest Service warned in a July 5 announcement. "While most trees survive the damage caused by the budworms - and some trees may even benefit in the long term - heavy concentrations of activity can lead to the death of some trees."

Some areas in Southeast have been hit particularly hard, Graham said, especially where a different insect called the hemlock sawfly also is active.

"Prior to this, though, in 2018 and 2019, we had an outbreak of the hemlock sawflies, which is another defoliating insect that occurs here and is endemic to the forest here," she said. "That (sawfly outbreak) ended in 2020, really dropped off ... but then the budworm activity started to increase."

Hemlock trees - particularly around Angoon and Petersburg - have been hardest hit in the current budworm outbreak, she said.

Graham and a colleague will conduct aerial surveys across Southeast in the coming weeks and will gain more information about the extent of the budworm outbreak. She said they fly over about 15% of the Tongass National Forest and other lands in Southeast each year. "Insects and disease don't recognize the borders."

She encourages Alaskans to engage with a citizen science program called iNaturalist, which collects data on a wide range of species, not only budworms. People can post photos and look at postings from others. The program can be found at https://www.inaturalist.org/projects/alaska-forest-health-observations.

"What iNaturalist is meant to do is just to record all the organisms out there and it's just an awesome resource for people who can help identify them," Graham said. "This isn't just limited to western blackheaded budworms or hemlock sawflies, but really any kind of cool critters you're finding in the forest or things like a fungus or cool plants and stuff like that."

Outbreaks of more serious insect threats to the forests have been linked to climate change, but more research is needed before it's shown to cause budworm outbreaks, Graham said.

"We're actually working with some researchers to look at any climate factors that may help trigger the outbreak or build the population. We know that there are some things that can be an indirect factor. And the question now, though, is with changing climates, will the frequency increase? Is it possible that instead of it being 30 to 40 years (between budworm outbreaks), will it go more 20 to 30 years? These are questions that we're all wondering," she said.