PACIFIC COUNTY — Add ravenous cloned insects with intensifying summer droughts. The result? Countless local spruce trees appearing on the verge of death.
Worried Pacific County residents have turned to the Chinook Observer and social media in the past month asking “What’s making my trees sick? What can I do about it?”
Drive down almost any street or highway in south Pacific County — and much of Clatsop County in Oregon — and it’s easy to spot spruce trees of every size and age that have turned brown. Some have lost so many needles they look skeletal, like props in a haunted-house movie.
Although it’s too soon to declare all these spruce lost causes, a University of Washington professor warns this coastal problem could be part of a larger trend that’s seriously harming other plants statewide. Everything from iconic bigleaf maples to sword ferns — and now Sitka spruce — are under threat.
Although Pacific County is still rainy by most standards — Long Beach is approaching two feet of precipitation since Jan. 1 and Naselle is around 28 inches — that’s lots less than winters and springs in the not-too-distant past. Before this week’s moderate rainfall, 60 percent of the county was considered to be in a moderate drought, with the remainder classified by federal agencies as abnormally dry. Perhaps more importantly in terms of consequences for trees, our summers and early falls have become parched — drier than Arizona during the same months.
“In some cases, we’ve seen several years of pretty bad drought and even in our rainy season we’ve seen maybe a little less rainfall than what we expect,” Patrick C. Tobin, associate professor of disturbance ecology in the University of Washington’s School of Environmental and Forest Sciences, said in a Sunday interview. “What we’re getting is more consistent summer droughts and many of our tree species and plant species in general are already being pushed to their limit.”
Regarding the problems reported in Pacific County, Tobin said, “I wouldn’t quite put it into the category of ‘this is widespread, this is a major problem,’ but certainly has that fingerprint of something that could be starting to be worse, particularly if we get some more years of [severe] summer droughts.”
Tobin and other experts agree spruce aphids, while classified as an invasive species, usually are a chronic nuisance rather than an acute risk to trees.
“Spruce aphid infestations typically occur on a three-year cycle,” Luke Colvin, a certified master arborist based in Astoria, said. “A hard frost kills them and minimum tree mortality occurs. However that has not been the case on the North Oregon and Southwestern Washington coast. Repeated years of spruce aphid infestation have left our trees stressed, and unable to properly defend against the aphids.”
Dr. Kim Patten, longtime Washington State University extension scientist in Long Beach, said, “What came first, drought or aphids? Not all affected spruce have the aphids. So they might being responding to stressed tree as they do with other plants. But once they are in high numbers, [they] affect other healthy trees.”
Tobin said aphids are “very good at smelling weakness. They sense distressed trees and they go after them.” On top of being highly opportunistic, they have the ability to explode in population size.
“Most species are what we call parthenogenetic, which means they don’t reproduce sexually,” Tobin said. “So a female can just clone herself and just pump them out left and right, so this mother aphid’s just popping out live aphids, and … they can build up into massive numbers pretty quickly. So you throw in a distressed tree, you throw in some drought, you throw in an opportunistic spruce aphid, and bam, the next thing you know the tree’s covered and the tree’s like ‘That’s it, I’ve had enough!’”
Peninsula biologist Kathleen Sayce observed “At Beards Hollow, I have seen young trees completely covered with aphids this spring. It’s quite dramatic.”
Although mostly seen here in Sitka spruce, the aphids will attack any spruce species, including the popular landscaping tree Colorado blue spruce.
Sick but maybe not dead
It’s too soon for homeowners to panic about their shade trees.
“Shocking as it looks right now, not all trees are going to die,” Sayce said. “Many will recover if we do not enter a prolonged period of long, hot dry summers.”
“This year is by far the worst we have seen in decades,” Colvin said. “We are still urging many homeowners not to cut down trees which look brown, may be losing needles, or appear dead. At this point your trees may still be preservable. We always encourage homeowners to preserve any tree which can be saved.”
As the aphids feed, a tree’s needles turn from green to yellow then to a rusty brown. Entire branches of a tree might die. The damage isn’t usually apparent until the aphids have already moved on.
According to the Oregon Department of Forestry, an infestation may cause banks of older needles to drop prematurely but aphids typically leave buds — the soft, bright green tips that signal new growth and appear on spruce trees in May and June — alone.
The best way to treat infested trees is to take action long before aphids ever show up. For now, Colvin recommends boosting the health of trees by watering them during the summer months. Soaps can be used to slough aphids off young saplings, but will not work for large trees or commercial stands.
The most effective way to inoculate trees is to use insecticides, which is not an ethical option when bees are active, Colvin said. Insecticide treatments need to wait until the fall.
It’s a difficult conundrum for people concerned about the impacts of insecticides, Colvin admitted, but there are no real effective biological means to control spruce aphids.
“So do you want to stick to your guns of no pesticides ever and let a huge percentage of the large, historic Sitka spruce die because of it? It’s kind of a toss up,” he said. “What do you do?”
People who opt to use insecticides should make sure they’re working with someone who is specifically licensed to use the product, he added.
“The problem with using biocides to control aphids is that it will also kill their natural insect predators, which are building up rapidly right now,” Sayce said. “Spot treatment of trees is less impactful than area-wide treatment. The better solution in an ecological sense is to let trees live or die on their own rather than disrupt the native predators.”
What about the future?
The battle facing Sitka and other spruce species is part of a larger story about trees and other plants starting to struggle in the Pacific Northwest.
“The last couple years, we’re seeing more reports of declining trees,” UW’s Professor Tobin said. “We’re seeing it in a lot of different plant species, both conifers and deciduous trees, as well as herbaceous plants like sword ferns, and in some cases there’s not really a ‘smoking gun’ — there’s not a single causativization.”
Spruce aphids are just one of several factors that can turn drought stress into a die-off. Aphids are something that “flare up from time to time and cause mortality. Are we seeing more of it now? Well, this could be a harbinger of things to come,” Tobin said.
“Other species like sword fern and bigleaf maple and madrone, we’re certainly seeing what we think is more die-off than what we would call the historic norm, whatever that might be,” he said. “We’re definitely seeing trends toward elevated levels and maybe the jury’s still out, but I think the situation is there where we could be facing in the future some pretty widespread mortality of a lot of different tree species.”
As trees die in greater numbers, Pacific Northwest residents will observe changes in local habitats — some for the worse.
For example, Tobin said, “Subtract bigleaf maple. Something will come back. Plants can be opportunistic. Sometimes, it’s thing we don’t want, like Himalayan blackberry.”
Residents can take control of their landscapes to some extent by selecting species more likely to survive changing climatic conditions.
“Foresters I’ve talked to recommend that if people replant, they use species that are more drought tolerant, which includes native coastal Douglas-fir, redwood, sequoia, and western red cedar,” Sayce said. “Fall is the best time to plant, by the way, after the rains start and the soils are cool and wet.”
All these changes in species are likely to have unforeseeable side effects on our ecosystems and neighborhoods.
In the case of bigleaf maples, the widespread die-off of which Tobin has studied in depth, “there are a lot of things that tree is doing. The bigleaf maple is providing seeds that provide a food resource for squirrels and other native small mammals, which in turn are a food source for predators like birds of prey. So there’s always what we call a cascading effect when something is lost and is replaced by something that isn’t providing that food and habitat for wildlife. Most importantly is what comes in afterwards, and we don’t know [answers to] those questions yet.”
— The Astorian contributed to this report