An outbreak of western blackheaded budworms that’s been damaging trees in Southeast Alaska for the past few years is tapering off in most places, but a large infestation is still occurring in Juneau because the larvae arrived here later than some other parts of the region, U.S. Forest Service officials said Thursday.
Such outbreaks have been a normal occurrence every 30 years or so for at least the past century, typically lasting two to three years, and are triggered by “certain environmental conditions,” said Elizabeth Graham, a Forest Service entomologist, during an online press conference. The budworms, which are the larval stage of budworm moths, feed on spruce, hemlock and other trees, leaving the damaged needles with a brownish appearance.
“It can make hillsides look like they’re dying,” she said. “The reality is they’re just feeding on new growth, so in most cases the trees have been able to recover.”
Widespread damage from western blackheaded budworms is seen on Admiralty Island in July of 2021. (Robin Mulvey / U.S. Forest Service)
Also, even infestations severe enough to kill some trees can be beneficial to the forest’s overall health in the long run, said Molly Simonson, a Forest Service silviculturist, during Thursday’s press conference.
“Trees do die, whether it’s clusters of them during a particular event or individually during forest development,” she said. “Having that scattered among the forest is not a bad thing.”
An update at the forest service’s website, based on data still being collected, states defoliation occurred most heavily in 2021 and 2022, with the worst damage occurring on Admiralty, Kupreanof, Mitkof, and Wrangell Islands, as well as several locations on the mainland. Aerial surveys indicate about 685,000 acres of forest suffered damage — with “mortality” damage consisting of about 73,500 acres of western hemlock in 2022.
Juneau is an outlier in the region, however, since areas ranging from downtown to Echo Cove have significant defoliation occurring, Graham said.
“Mostly it’s because Juneau is really on the fringe of the outbreak,” she said. “We really just started seeing some of the damage here last year.”
But while infestations are peaking in some areas of Juneau, Graham said she expects activity to taper off considerably by next year.
While infestation cycles every few decades have been normal, Graham said climate change may be a factor in the current outbreak.
“If we have fewer frost-free days that tends to be an association with triggering an outbreak,” she said. The outbreaks didn’t extend to British Columbia, she added, “maybe because it was too warm.
“It could be we’re in this perfect little climate window right now for outbreaks,” she said.
But Graham emphasized other variables also are involved — and after outbreaks end due to parasitism, predation, disease and starvation among the budworms “there’s also a time variable to building up that population” again.
• Contact Mark Sabbatini at mark.sabbatini@juneauempire.com or (907) 957-2306.
