By ARIADNE WILL
Sentinel Staff Writer
Sitkans noticing hemlock trees turning red shouldn’t be too concerned, says Elizabeth Graham, entomologist for the U.S. Forest Service Alaska Region office in Juneau.
“It’s a natural part of our forest,” Graham told the Sentinel.
The species responsible for the rust-colored hemlocks appearing on vast stretches of the forested landscape of Southeast Alaska — including in Sitka — is the western blackheaded budworm.
The adult western blackheaded budworms – moths that are about a half inch in size – lay their eggs on the needles of the hemlocks. The larvae then hatch around June and move into the tree’s buds.
“They start mining the buds and as the (hemlock’s) shoots elongate, they start feeding on the new needles,” Graham said.
The last major outbreak of the budworms in Southeast was from 1992 to 1995, according to the Forest Service.
Graham said that it’s only in “extreme cases” that hemlocks are unable to recover from the infestation, but the budworms can cause a tree to lose the top third or more of its foliage.
“We’ll definitely be monitoring ... how the trees recover,” she said of the current outbreak.
Factors that will determine the impact on hemlocks in the region include the weather, viruses, and funguses that usually keep the budworms in check.
“June is the time the caterpillars start to hatch and (when they) are feeding and active,” Graham said. “The warmer conditions help with their lifestyle.”
Western blackheaded budworm larvae. (Photo from USDA)
Conversely, more moisture aids a fungus that helps to control the budworm populations.
Graham says that the number of years the outbreak lasts will also make a difference.
But like all parasites, the budworm won’t be able to live large forever: if the species exausts its host, the outbreak will subside.
“For the most part, the outbreaks take care of themselves,” Graham said.
And the rest of the forest can benefit from an overabundance of budworms: the dying of upper branches of hemlocks can allow more light to reach farther down, which makes for better growing conditions nearer to the forest floor.
“It’s definitely very dramatic and it looks bad in places,” Graham said. “I don’t want to downplay the seriousness of it, but I want to put people at ease in that this is a natural part of the forest and the forest does recover.”
The Forest Service is interested in what the public is witnessing. People can submit photos of budworms or the moths – which will be hatching soon – to iNaturalist, a free program and app. Images and other media can be uploaded at inaturalist.org/projects/alaska-forest-health-observations.
