Emerald ash borer poses a concern for vital wetlands tree

By Nicole Montesano

Smoke Signals staff writer

The trees are a familiar sight along creekbanks, leaning over the water, shielding it from the worst of summer’s heat. The Backyard Habitat Certification Program calls Oregon Ash a “wetland supertree” for its ability to stabilize soil, filter pollutants and provide food and habitat for a wide range of species including birds, numerous butterfly species, various other insects, crustaceans, waterfowl, and both land and aquatic mammals.

In part, it’s because Oregon Ash is one of the few trees that can withstand the seasonal high water tables in wetter parts of the state, that “can exclude nearly all other tree species,” according to the Oregon Department of Forestry. “In dense stands of Oregon Ash, understory vegetation is often sparse, consisting primarily of sedges (grass-like plants).”

In addition to their significant ecological value, the trees have a long history of use by Tribes across the state, including Grand Ronde.

Tribal Natural Resources Specialist Anna Ramthun noted that the trees are favored for making traditional canoe paddles.

According to the Oregon Readiness and Response Plan, “Ethnobotanical records report medicinal and ceremonial uses of ash (leaves, bark, twigs and roots) in addition to the use of ash trees as fuel. Records and artifacts also show that ash wood was used in the construction of tools, such as poles, canes and pipes. The Cowlitz used Oregon ash to make canoe paddles and digging sticks. The Karuk used the root fibers of ash trees to weave baskets. Traditional Costanoan Tribal wisdom suggested Oregon ash sticks and leaves would repel venomous snakes.”

The Tribe still makes canoe paddles from ash wood. Cultural Education Coordinator Jordan Mercier said that in addition, buckets and trays were, and are, made from ash bark collected from young trees in the spring.

The young trees are typically cut down in order to harvest all of the bark and the wood is used to make handles for knives and other implements. The bark is carefully peeled off and either used immediately to make a gathering bucket, or rolled and stored for winter, when there’s time to sit and work on projects.

“We use them now for berries and stuff, because it’s pretty easy to gather the bark and make one in an hour or so,” he said.

After folding and rolling the soft, malleable bark into a bucket shape, he said, holes are pierced in the edges and stitched together with fine lengths of spruce root or sinew.

In the winter, the bark is soaked to soften it and formed into trays or canoe bailers, Mercier said. Historically, the trays were filled with hot coals and used to parch tarweed seeds.

The Cultural Resources Department spends the spring and summer gathering materials such as bark from ash, maple and cedar, he said, and stores them in its workshop for Tribal members to use later.

However, ash trees are under threat from an invasive species; the emerald ash borer, a brilliant metallic green type of jewel beetle, whose larvae feeds on tissues found under the bark.

The beetle is originally from eastern Asia, and in its home territory, “Trees have to be fairly stressed out to be killed by it, because other species keep it in check,” Ramthun said.  

But trees in the United States, which did not evolve with the insect, have no such defenses and without effective natural controls, the borer kills both healthy and stressed trees, according to the state’s readiness plan. 

The borer was first found in the Midwest but has been moving west over the past two decades, and although it’s been known to be in Oregon since 2022, originating in Forest Grove, it has now been found in Yamhill County.

According to the Oregon Department of Forestry, Yamhill, Washington, Marion and Clackamas counties are under a permanent ash material quarantine.

The state Forestry Department’s readiness and response plan sounds a significant alarm, calling the borer “possibly the most destructive forest pest in North America.”

 Its establishment, “could devastate whole habitat types, such as ash swales and sensitive riparian zones, as well as reduce urban forest cover,” the plan warns. “EAB has the potential to cause the local extinction of Oregon’s native ash species. The loss of these trees could result in wide-reaching economic impacts, endanger important cultural resources, damage water quality and create direct human health impacts.”

“It’s been very destructive in the Midwest,” Ramthun said. “I think it was first detected in Michigan about 20 years ago…It was causing about a 95% death rate in their ash trees. So that does understandably have folks fairly concerned about its progress as it spreads out from there.”

The borer has been particularly destructive to ash and olive trees, Ramthun said, and is now known to have spread to about 24.6 square miles of the state.

“Around 10.4 (acres) are around the original site (and) includes the recent detection in Yamhill County,” Ramthun said. “Oregon Forestry Department has released three biological controls; a little wasp that feeds on the larvae which could slow the spread, not present in other states when it was introduced there,” Ramthun said.

Four wasp species have been approved for use in the United States, to try to control the borers.

“In wetter parts of the Willamette Valley, ash is the predominant tree species and the loss of ash trees will likely result in significant changes,” the Forestry Department stated. “Since ash trees often do not show symptoms during the first years of an infestation, EAB can go unnoticed for several years after it is introduced.”

Typically, the department added, it is in the fourth year that “larval densities build high enough to cause rapid mortality of ash trees. Previous studies have suggested that ash populations in forested sites can go from health to nearly 100% mortality of mature trees within 6 years of an infestation.”

The borer is often spread when infested firewood is moved long-distances by members of the public.

The state plan encourages cities and land managers to establish biodiverse tree species mixes, rather than relying heavily on single species such as Oregon ash, and to collect and store native ash seed to preserve its genetic diversity. The state also will have to decide whether to remove infested trees or commit to an expensive plan of potentially permanent insecticide treatment in order to save healthy trees.