Ashes To Ashes: The Impending Death Of Millions Of Critical Riparian Trees

By Andy Walgamott

We’ve got a back 40 full of Oregon ash trees. Nice big old tall ones my wife can barely wrap her arms all the way around; robust saplings waiting in the wings; a kajillion sproutlings.

They’ve all recently been handed a “death sentence,” as has nearly every other ash tree in the entire Willamette Valley (and the rest of the Northwest). That’s going to be bad news for the valley’s suddenly robust coho population – which has posted record returns the past two years, markedly expanding a salmon fishery that has consumed no small portion of my free time in recent Septembers and Octobers – as well as its spring Chinook and winter steelhead, two other favorite pastimes of mine.

Oregon ash is the dominant tree in the Willamette Valley’s bottoms. It’s been dubbed “wetland supertree” – which should also tell you all you need to know about our backyard and its rainy-season streams and swamp. With their unique tolerance for the valley’s thick clay soils and moisture, ashes line waterways such as rivers, creeks and sloughs, and they tower over seasonally flooded areas, ponds and whatnot, helping to keep the water cool enough for young salmon and steelhead, trout and other species. 

Their bane will be the emerald ash borer, an invasive insect that’s wreaked havoc on Midwest ashes since turning up there around the turn of this century. Illinois and Michigan report mortality rates greater than 99 percent for trees attacked by the half-inch-long, metallic-green bug originally from eastern Asia.

“At this point,” the U.S. Geological Survey has stated, “all ash trees in North America are threatened and [emerald ash borers] could ecologically eliminate them from North American forests.”

Here on the West Coast, emerald ash borers were first discovered in Oregon in Forest Grove west of Portland in 2022, but they may have been here longer than that. Last summer, a large infestation was found in the Pudding River and Butte Creek bottoms, on the east side of the Willamette River between Portland and Salem, and given how much canopy loss there was, EABs may have actually landed there first.

Observable dieback occurs several years after larvae begin chewing through a tree’s cambium layer, breaking the up and down transport of water and nutrients. Adult bugs leave a distinctive D-shaped exit hole (the “D” can face down, up or any direction) in the trunk when they emerge in late spring to feed on ash leaves, then mate and lay eggs in the nooks and crannies of other ashes.

Ultimately, 999 out of every 1,000 EAB-stricken ash trees will die, typically in four to five years, and here in the valley they’re likely to eventually be replaced by much shorter plants with less shading and cooling power – Himalayan blackberries, reed canary grass, for starters. Essentially, one invasive species is paving the way for the further expansion of two others, and likely many more, to the further detriment of fish and other riparian species, some of which are listed under the federal Endangered Species Act.

And looking at the big picture, tiny EABs will eventually remake the Willamette Valley landscape on a scale not unlike far larger forces have in the past – the repeated Missoula Floods at the end of the last ice age that left deep, rich soils behind; eons of seasonal burning by local tribes that made the valley floor and foothills much more productive hunting and foraging grounds for them; and Oregon Trail pioneers’ plows beginning two centuries back, along with the towns, roads, dams, tackle shacks and more we’ve sown here since then.

I LEARNED ALL about emerald ash borers this past spring after I decided to hang a trap for them up in our backyard. I didn’t think we had any in our woods (which are at least 100 years old if not older), though in summer, some of the ashes do get kind of sketchy canopies, which can also be caused by drought, heat and other non-bug issues. But I wanted to help with monitoring efforts here in our new home.

To be honest, until moving from Pugetropolis to Oregon City, all I knew about ashes was that my grandmother loved the mountain ones, they of the red-orange berries that were good for throwing handfuls of at my sisters, the neighbor kids and other satisfying targets. But as we’ve settled in here, we’ve dedicated the wild half of our property to native species like ash.

The Portland-based Backyard Habitat Certification Program posted this about Fraxinus latifolia: “The ash of the Pacific Northwest, Oregon ash is a wetland supertree. It stabilizes wetland soils and filters out pollutants. It provides food and habitat for all the usual suspects, bees and birds and small mammals, as well as aquatic insects, crustaceans, waterfowl and aquatic mammals. In addition, Oregon ash supports dozens of species of butterflies and moths. Easy to grow, strong and sturdy, and a magnet for wildlife, Oregon ash is the tree your soggy soil has been waiting for.” 

My interest in ashes and sense of alarm only grew after I attended a late April presentation on how the coho population has grown spectacularly in the Pudding River, illustrative of the productivity of even small streams that flow primarily on the floor of the hot Willamette Valley. It also helped to explain in part how the Willamette River’s overall coho run, which struggled to push more than 3,000 fish over the falls as recently as 10 years ago, has blossomed into one that saw 29,654 come back in 2023 and a staggering 53,423 in 2024. Most returned to lower-elevation streams in the north end of the valley.

“Interestingly, last year the bulk of the run stayed lower in the system (Molalla, Tualatin, Yamhill) and did not venture as far upstream as the previous year (and more like years prior). There weren’t as many fish observed in the McKenzie or Santiams,” noted Oregon Department of Fish and Wildlife biologist Ben Walczak last month.

He added that while the Willamette Valley’s heavy private land ownership and general lack of spawning surveys make it hard to observe where the salmon do end up, anecdotal reports from farmers and others indicated coho weren’t showing a preference for the Cascade or Coast Range side of the valley and were instead running up streams left and right of the mainstem Willamette River after fall rains last year.

ONE AREA THAT has seen semi-regular fish surveys is the aforementioned Pudding River – ground zero of Oregon’s largest EAB outbreak so far at 25 square miles as of last month. Rapid biological assessments conducted for the Pudding River Watershed Council have shown that coho are the most abundant salmonid in the squiggly little lowland system. In 2014, total estimated juvenile coho pool abundance was 19,303; in 2023, there were 44,806.

A run reconstruction shows that those two year-classes were spawned the fall before by 182 and 422 adult fish, respectively. Breaking it down even further, Pudding River coho represented .8 percent and 2.35 percent of all the adult coho that swam past Willamette Falls in 2013 and 2022, according to the assessment.

On the flip side, steelhead counts in the Pudding system in 2023 were half that of 2014. While there has been concern about young coho outcompeting juvenile winter steelhead (and spring Chinook), the decline here was “likely due to water temperature increases” in Butte Creek in recent years.

Still, despite too-warm water in Butte and especially in Silver Creek (of beautiful Silver Falls State Park fame) below Silverton Reservoir, the assessment found coho, steelhead, Chinook and cutthroat trout abundance was “substantially below what the streams could sustain, meaning there is a lot of opportunity for habitat improvement.”

The watershed council has a big list of projects to help fish productivity, including adding channel complexity, removing fish passage barriers and improving coldwater inputs, as well as a pie-in-the-sky goal of getting the city of Silverton to discharge cool water from deeper in its reservoir instead of the warm stuff straight off the top.

While all that work can still be done, the observed and looming massive loss of ashes along the Pudding River and its tributaries adds a new wrinkle – and urgency – to it. 

BACK TO THAT sticky purple trap hanging up in our backyard. This past spring, the Clackamas Soil and Water Conservation District announced it was looking for volunteers to help monitor for EABs. I was among the two dozen or so who signed up and attended an orientation session one May Saturday morning.

There, the district’s Drew Donahue shared a page out of the state’s Emerald Ash Borer Readiness and Response Plan for Oregon that classed the potential impact from the widespread loss of ash trees due to EABs on Willamette Valley coho, spring Chinook and winter steelhead as “high.”

Afterwards, Donahue set each of us up with a large, triangular trap, packets of EAB attractant that we needed to replace halfway through the summer, nitrile gloves for handling the scent packets, some rope and a weight to get the trap well up in an ash tree, and a bunch of paperwork on how to tell emerald ash borers from native lookalikes and other bugs. Then she turned us loose to monitor for the invaders.

The deal was to check the trap around midmonth each month through September and report back to the district whether we’d found anything or not. When I lowered my trap in June, there was nothing suspicious stuck to it, just various bugs and some leaves. By July, there was an even wider selection of insects and forest canopy litter. There was also a vaguely EAB-colored and -sized bug. I zoomed in with my phone, took a photo and attached the image to my monthly report with a note saying that it was probably just a click beetle but I was submitting it anyway because I’m not exactly an entomologist.

A few days later, Donahue got back to me to confirm my bug was indeed not an ash borer. But soon after, she emailed to say that an EAB had been caught in a fellow volunteer’s trap hung near Redland, between Oregon City and Estacada and 20-plus miles from the other two major infestations in the greater Portland area.

IT WAS DISHEARTENING, depressing news, and it had my wife Amy and I fast-tracking our plans to begin treating a few of our ashes against EABs. Inoculating them with the insecticide emamectin benzoate via trunk injection in spring is considered to be the most effective treatment, but it’s also a spendy antidote and it has to be repeated every two to three years in perpetuity, which makes it ineffective at the scale needed to save the Willamette Valley’s ashes. It can also only be applied by somebody with a pesticide handler’s license.

There are other insecticide options, including a trunk spray and what’s known as a soil drench, both of which you can do by yourself, but their big drawback is the moderate to high impact on nontarget species. The bugs and worms and whatnot are important to the woods too.

On a wider scale, the only hope is to slow the spread of EABs. Tools include selectively girdling and treating ash trees with insecticides so as to create an inviting albeit deadly trap for the bugs; releasing parasitoid wasps from eastern Asia as biocontrol agents; and continuing to raise public awareness about EABs and the dangers of moving ash wood around, which has been banned in a four-county quarantine area. 

Officials are also collecting Oregon ash seeds in hopes of finding that 1-in-1,000 tree immune to EABs and eventually restocking the region with its seeds. While there’s no perfect clay-tolerant replacement tree match for riparian zones, piper willow, white alder, ponderosa pine, even long-lived, but slow-growing Oregon white oaks can handle different portions of the super wet to seasonally dry soil moisture spectrum that Oregon ashes occupy.

(This is not to say that the valley’s streams are solely forested with ashes. Cottonwoods line many waters where soils are coarser and/or better drained thanks to robust fluvial processes.)

In the end, Amy and I will have to play god and choose which of our ashes to treat. The estimate we just received is $1,000 to inject four of them next April, $850 for three. Frankly, that’s a ton of money, so we may only be able to afford one or two. (Over the fence, our neighbor and I mulled getting our applicator’s licenses and treating trees as a side gig.) Wherever we land, we’ll be strategic to help out our long-lived oaks. Amy does love her trees and I long ago concluded the bumper sticker is true: Habitat is the key.

Ultimately, the only beneficiaries in all of this are going to be insecticide applicators, woodpeckers and tree service companies, like the one our neighbor’s son operates and whom I’m sure we’ll be calling in the future.

TO BE CLEAR, no coho swim in our backyard creeks, which rise after midfall’s rains return and eventually fade back into the muck come midspring’s beginning of the dry season. At times, it certainly feels like there’s enough water to support spawning salmon and their fry, but downstream, the runoff flows through several culverts before dumping over Canemah Bluff and becoming one with an old Missoula Flood landslide deposit.

And to a degree, coho and EABs share a certain kinship. These salmon are technically invasive in the middle and upper Willamette Valley. Before the installation of the locks and fish ladders around Willamette Falls, it’s believed that only spring Chinook, winter steelhead and lamprey were able to get any further upriver than Oregon City. Water conditions in summer and autumn are just too low for coho, fall Chinook and summer steelhead to leap the barrier. But I guess it’s also theoretically possible that flooding from fall atmospheric rivers in past millennia occasionally overlapped coho runs to nearby streams and some of those fish could have strayed over the falls.

Regardless, through much of the latter 20th century, the Oregon Department of Fish and Wildlife released millions of coho from hatcheries above the falls, and while those programs ended in the 1990s, some fish were also spawning in the wild or began to do so. The 2009 return of 25,298 adult coho and 2010’s 20,021 opened eyes to the possibilities. Then came a sharp downturn, a two-year bump into the high teens and then another crash. But since 2020, no run has come in less than 11,000 adults, and the five-year average is 25,500. 

Last year’s record run appeared to have been boosted by “good production” on the spawning grounds and in Willamette Valley rearing streams and which “lined up with good ocean survival,” ODFW’s Beth Quillian told me. It’s unclear how much larger the Willamette coho run might become, but as Walczak, the agency biologist, told me in 2023, “there’s thousands of miles of stream habitat that have different levels of access and suitability.”

The proof is in, er, the Pudding. That watershed assessment found zero young coho in Rock Creek, the river’s lowest major trib, in 2023, or Silver, that overwarm creek. But located between them, Butte Creek, where the biggest EAB infestation is, 2,418 coho were counted in 2014, while 3,360 were in 2023. And in neighboring Abiqua Creek, there were an estimated 39,070 two years ago, nearly four times as many as in 2014, a rise that “represents a piece of the success story of coho in the Willamette Basin,” the watershed council stated.

Indeed, the overall rise of the coho run is a wonder to celebrate in a region where salmon narratives usually run the opposite way. Around the Northwest, there are only a few places where returns are growing. Baker sockeye, which set a record of around 92,000 this year. Okanogan/Wenatchee sockeye, which hit a new high mark of three-quarters of a million back to the Columbia last year. Snake fall Chinook, which grew from just 337 at Lower Granite Dam in 1981 to 60,687 in 2014. Those runs have been helped in large part by people, but Willamette coho are basically adaptive self-starters.

YET THE TRAJECTORY of their moonshot is going to be intercepted by EABs in the coming years. I asked Walczak if ODFW had any sense for how significant the outbreak will be for the fish, how concerned the agency is and whether there will be time for coho to adapt or for habitat work to be done to get ahead of the problem.

“Those are all good questions. We have not/are not directly studying impacts that EABs could have on coho. Generally, when riparian areas are negatively impacted, fish are negatively impacted,” he said.

These bugs are just the latest of many headaches fish, wildlife and managers face, one so new they’ve hardly had a chance to reach for an aspirin. But it is not good news for growing coho populations in streams on the valley floor, like Butte, Abiqua and the Pudding, which contribute a portion of the new harvest. It begs the question, how high would the run and catch go if EABs hadn’t come? What other benefits would accrue?

Dominic Maze, the man who by chance discovered the first EABs at his kids’ grade school and who is a biologist with Portland’s Environmental Services Bureau, delivered what now feels like a eulogy earlier this year to Oregon Public Broadcasting.

“When we lose that Oregon ash, we lose that shade, we lose that habitat, and that shade is critical for keeping water cool,” Maze told reporter Cassandra Profiitta. “And who likes cold water? All of our salmon species that pass through the city of Portland or rear their young here.”

He termed the arrival of EABs a “death sentence” for Willamette Valley ash trees.

Sometimes, even superheroes die, and in the coming decades, a surging coho run as well as their cousins in the salmonid world will face a future without one of their greatest protectors because of a ravenous tiny little green bug.

Editor’s note: This article appeared as The Big Pic in the September 2025 issue of Northwest Sportsman magazine.