By GARLAND KENNEDY
Sentinel Staff Writer
The evergreen trees around Southeast that are turning shades of brown or even rust-red are showing the effects of an ongoing infestation of western blackheaded budworms, the U.S. Forest Service says.
While the changes are strikingly visible, the caterpillars are unlikely to cause lasting damage to individual trees or the forest as a whole, said agency entomologist Elizabeth Graham from her office in Juneau.
The outbreak has largely affected western hemlocks but can affect spruce trees as well, Graham said. Damage from the budworm infestation is in some areas compounding on defoliation caused by the 2018-19 outbreak of hemlock sawflies, she said.
A blackheaded budworm dangles from a tree. (Photo provided)
Southeast is now in the third year of the current budworm outbreak, and the bugs come and go in a “boom and bust” cycle, Graham said.
“We see all this damage and it seems like it happens almost instantly, and then just as quickly it crashes,” she said. “And so really what happens is there’s just not enough to sustain those large populations that build up. Disease will come through and knock out a bunch of the caterpillars, parasites and predators, and then ultimately starvation. They’ll just run out of their preferred food source.”
The outbreak started in 2020 and was first noted in the Petersburg area, the entomologist said.
“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,” Graham said. “And we actually see (sawflies) on the older needles of hemlock. And so fortunately, there wasn’t much activity in the Sitka area of hemlock sawfly – Sitka was actually probably the least hit.”
“That (sawfly outbreak) ended in 2020, really dropped off… but then the budworm activity started to increase and we did actually see some damage there in the Sitka area. Fortunately, your trees are in a lot better shape than some areas because they weren’t attacked by sawflies much,” Graham said.
Both insect species are endemic to the Tongass and don’t tend to kill the trees on which they feed, though they can limit growth, she said. Historical outbreaks can be visible in tree rings that reflect poor growth years, she said.
Along with obvious visible signs such as brown foliage and a proliferation of caterpillars, western blackheaded budworms also generate waste products called frass, that accumulates beneath trees. In the fall, the caterpillars enter cocoons and emerge as moths, another easily visible sign of an outbreak.
Hemlock trees – particularly around Angoon and Petersburg – have been hardest hit in the current outbreak, Graham said.
While hemlock is their preferred food source, the caterpillars are now being found on spruce, she said.
“And so hopefully that’s a sign that this is coming to an end, because there were so many adults last fall trying to lay eggs, but they probably ran out of places because they usually will lay them on the underside of the hemlock needles. But if the hemlock were hit really hard, they probably then moved over to the spruce. And so that’s what we’re seeing now with all this damage on the spruce.”
The Forest Service said the last budworm outbreak in Southeast occurred from 1992 to 1995.
Graham said in most cases infected trees are able to grow new tops and “might look bad for a little while,” but will live if they’re able to get through the initial outbreak.
“It’s amazing how well trees are able to respond,” she said.
The browning of forest “is really alarming to people and rightly so,” Graham said. “I think a lot of folks think about bark beetles and spruce beetle attacks or something like that. And are all of these trees going to die? The one thing I can say with comfort is, well, no, they’re not all going to die.”
That’s great news, she said, “because if it were spruce beetles, once (the trees) are attacked that’s the end. But this is a natural part of the forest ecosystem, and they are a disturbance agent. And so they’re basically drivers of change.”
In the long term, budworm outbreaks can allow extra light to filter through a thinner canopy and send a cascade of nutrients to feed new growth at ground level.
“And so it’s going to look ugly initially and it may not be what we’re used to seeing, but hopefully in a few years what will be seen is even more lush, and vibrant forest.”
Graham encouraged Alaskans to engage with a citizen science program called iNaturalist, which collects data on a wide range of species, not only budworms. 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. “And so 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? So these are questions that we’re all wondering,” she said.
The Forest Service will survey areas impacted by budworms later in the summer to assess damage.
“We’ll be conducting our aerial surveys in the next coming weeks to see how extensive the damage is throughout Southeast. That being said, one of the signs that we’ll look for next year will be how heavy the moth population is this fall,” Graham said.
