An adult emerald ash borer. (Image: Washington Invasive Species Council)

It feels as if there are always threats to forests, including our urban canopy on the Hill.

Impacts span from widespread disease to wildfires to inadequate regulation that allows for poor management. Introduced species like insects are often high on the list of worrisome threats. Writing here, I regularly come up against the reality that many of the introduced species on the Hill aren’t going anywhere, but that doesn’t mean we should open the door to more.

So, what happens when we can see a devastating insect fast approaching?

On June 30, 2022, the first report of emerald ash borer (Agrilus planipennis) was confirmed in Forest Grove, Oregon, a town west of Portland. Invasive species experts, foresters, and land managers had all been poised for this moment, or at least were ready for what seemed inevitable somewhere on the west coast. Every year the beetles were moving closer, it wasn’t if, it was when. This tiny jewel of a beetle arrived only two decades after it was first found in Michigan.

Riding out a pandemic, it shouldn’t surprise any of us that a tiny beetle, typically a half an inch long, could be devastating to large trees. The problem lies in the fact that emerald ash borers (EAB) are not from the US, but native to NE Asia; nearly 99% of the native and ornamental ashes here have no resistance to EAB and there are no substantial biological controls yet known. These buprestid beetles (a group also known as jewel beetles), likely arrived in unseasoned wooden packing material as larvae that later hatched and went off to find a place to lay their eggs (ash is a common tree used for crates and pallets because it is easily split and is very durable). The result has been the death of hundreds of millions of trees across much of eastern North America.

Here’s how it works: a gravid beetle goes off on her way, finds a suitable tree, and lays 60 to 100 eggs in the bark of an ash tree. Those eggs hatch and the grubs tunnel their way into the cambium layer of the trees all the while munching at the tasty nutrient bearing layer, creating galleries they inhabit until they are ready to hatch. This burrowing either weakens or outright kills the trees by depriving them of nutrients. A tree might not show signs immediately, but if 100 beetles hatch and go off to breed, it’s easy to see how they can quickly multiply.

EAB larvae (Image: Washington Invasive Species Council)

Every effort to contain the beetle’s spread has failed. Every state, all efforts by the USDA, nothing has stopped EAB from moving from ash to ash across the country. No quarantine or chemical campaign has done a lick of good, (except to keep existing trees alive using biennial injections, which only work if caught early and continue for the life of the tree).

Now is the moment when we step back to note something lost in all the media coverage: wood boring beetles are not evil, and where they are native are normal parts of balanced ecosystems. They are food for woodpeckers and other species while contributing to the structural diversity within a forest. Just as with the Asian giant hornet, I worry that this threat will send the general public into a froth every time they notice a similar insect to EAB, of which there are many. So don’t just go killing every shiny green insect you see, but also keep an eye out using the image below as a guide. Still, better safe than sorry: report potential sightings to the Washington State Invasive Species Council just in case.

Forest Health Watch, an initiative focused on urban trees with a variety of community science projects across the state has some novel work in hand to keep watch too. While EAB could show up via green logs, woodchips, or other wood material being moved around, it’s very likely they could arrive at a port after being unknowingly transported. Forest Health Watch in partnership with Washington State University has planted a bunch of trees at the Port of Tacoma (with plans for expansion) as sentinels to watch for a first wave of invasion. Theoretically closely monitored trees could tip off EAB presence before they spread far and wide. Ashes are in the olive family and a few of their relatives have been found to host EAB too and thus are worth watching.

We only have one native species of ash tree in the Pacific Northwest — the Oregon ash (Fraxinus latifolia). If you want to see some, go poke around the wet areas near the arboretum or down in Madison Park. Admittedly we don’t know how EAB will impact our native ash, but how things have gone with other species across the US doesn’t bode well. Nor does it look good for the ornamental ashes that line our streets. In a not too distant future we could be seeing the beautiful flame ashes that line Broadway disappear if not treated. Treatment or removal is costly.

Oregon ashes are not a very common tree in much of Seattle (likely because the wet places they like have been filled in or cleared – I don’t know for sure but I would guess all of what is now SODO would have been filled with them), but if you head to the right place they can become a dominant species. River bottoms, lakeshores, riparian corridors: they like wet feet. Drive from Olympia south to Portland and a good number of the deciduous trees you pass along the way are ash. Ashes are integral to many wetland ecosystems across Western Washington. afterall 40% of all known species on the planet rely on wetlands in some way and removing a major part of those ecosystems would clearly have deep impacts.

Oregon ash at the Union Bay Natural Area. (Image: Brendan McGarry)

This is not the first time the US has experienced the trauma of the loss of an important forest species but it’s the one in recent memory for my generation.

Landscape level change is coming quickly with EAB and has happened already across the midwest and northeast. That’s terrifying. (As mentioned before, there are treatments to keep EAB at bay, but those are not large scale solutions for forests, they are solutions for a few trees on a street or a cherished shade tree in your yard.)

Despite personal feelings of despair and hopelessness about this subject, I’m glad there are people out there paying close attention, like the Washington Invasive Species Council and many other groups. There are many lessons to be learned even if things deteriorate, and there’s hope that biological controls like parasitic wasps could help manage EAB after they arrive. With the climate catastrophe in hand, it’s entirely likely we’ll have to weather more and different newcomers that will require just as much vigilance.

The hard part is that people just can’t control everything, which of course has been the problem all along. My recommendation, besides going to war on EAB? Go sit in the shade of an ash tree, play baseball with an ash bat, sit in a handmade chair of ash, learn to make a basket from pounded ash, and consider all the gifts of plants. It’s not a solution for the issue at hand, but it will bring us closer, and that’s very important for the future of people and place.

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