Forest insect outbreak likely to abate in coming years, says state entomologist

Since 2018, an ongoing insect outbreak has been killing the foliage of hemlock and Stika spruce in the Tongass. The Wrangell area is among the most affected.

Though residents have expressed concern at the island's gray and red-spotted hillsides, state entomologist Elizabeth Graham shared reassuring news with the Wrangell and Petersburg communities at an online forum last Wednesday. The hemlock sawfly and western blackheaded budworm populations have likely reached their peak, and though the outbreak is widespread, many affected trees have a good chance at recovery as insect populations abate.

When people see stands of red and pink trees, Graham explained, "people's first thought is 'these trees must be dead.'" But color changes like these are not necessarily fatal. Since sawflies and budworms feed on trees' needles rather than their trunks, many affected trees can survive, as long as they retain enough needles to continue photosynthesizing.

"As long as they hold on to some of that foliage, they have a chance to recover," said Graham. "It's a little less ominous than some other types of insect outbreak." She referred to the outbreak sweeping Southeast as a "defoliation event," since the insects are killing foliage.

Though the current outbreak is severe, it is not unprecedented - the Tongass has recovered from worse. Similar outbreaks occurred in the 1920s, 1950s, 1970s and 1990s. Tree rings and historical accounts indicate that the 1950s defoliation event may have been the severest in recent history.

In a 1958 report, entomologist W.F. McCambridge recorded blackheaded budworm damage impacting "nearly every forested acre in Southeast." The massive insect population even affected the visibility of pilots flying over the Tongass. After their pupal phases, sawflies and budworms transform into flying insects.

The most recent defoliation event began in 2018 on Admiralty Island and by 2022, 81,000 acres in the Petersburg area and 124,000 acres in the Wrangell area were affected.

Both areas have a light to moderate tree mortality rate. Across Southeast, 73,000 acres of tree mortality have been recorded- 19 of those acres are in the Petersburg area and 9,000 of those acres are in the Wrangell area.

Graham suspects that the defoliation event is nearing its natural conclusion. When sawfly and budworm populations become dense, parasites and diseases can spread easily from insect to insect. The current insect population levels aren't going to be sustainable and she has already noted a decrease in moth numbers.

"It's not to say that this is over," Graham said, "but we think that it has reached its point."

Deputy Regional Forester Chad VanOrmer hoped the presentation would address "concerns expressed in the community around what they've been witnessing ... this summer" and assured area residents that the Forest Service would "continue to monitor this activity (and) collect the data."

To aid in data collection, he encouraged residents to download iNaturalist, a citizen science app that biologists, outdoor enthusiasts and community members use to share their observations about plant and animal life. If forest visitors notice insects or insect damage, they can take a picture and upload it to the app. "People can really help us improve our monitoring of the forest and be our eyes on the ground," Graham said in a Forest Service press release.


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