Beetle threat prompts local tree survey

Coast Fork Youth Conservation Corps members gather around what is thought to be the oldest tree within Cottage Grove city limits.

Tree surveys performed by the Coast Fork Youth Conservation Corps (CFYCC) this summer are giving youths a chance to gain real-world environmental work experience — but they’re also gathering information for an impending invasion.

“It’s something the Midwest and the East Coast have been struggling with for a number of years, since the early 2000s,” said Coast Fork Willamette Watershed Council Projects Coordinator Reilly Newman, “and now we’re understanding that it’s actually coming west and we have an opportunity to prepare for its eventual arrival.”

The emerald ash borer, an invasive insect species sweeping across North America, has prompted the City of Cottage Grove and environmental organizations to take index of their trees, a project which had been sluggish to gather momentum until this year.

With indexing having started in June, Newman said it may take “multiple years” to get a comprehensive inventory of all the trees in Cottage Grove’s city limits. Meanwhile, cities and states across the country have developed preparedness plans for the insect.

The Oregon Department of Forestry calls the emerald ash borer “the world’s costliest forest pest,” estimating the bug had done $3.5 billion in damage to U.S. forests as of 2017. Over the next 10 years, costs to municipalities could exceed $12 billion by some estimates.

The green, wood-boring beetle comes from Asia and is thought to have been introduced to North America in the 1990s by being carried over on shipping pallets and packing materials.

Since first being discovered in 2002 in Michigan, the insect has spread into Canada and at least 21 states, being reported as far west as Colorado.

If conditions are right, emerald ash borer populations can travel several miles per year. While some estimates say the insect could be in Oregon in the next 10 years, the bug has been known to hitch rides with humans, speeding up their migration.

“The major transportation of emerald ash borer is firewood,” said Newman. “It skipped about three states, like Ohio or Michigan all the way to Colorado, and that was because somebody actually transported the larva in their firewood to Colorado.”

Finding a way over the Rocky Mountains would prove difficult for the bug, but much of that depends on the human factor.

As such, forest service entities have launched campaigns encouraging campers to buy their firewood locally and burn it all before moving on.

The speed at which the wood borer travels in North America is also largely due to its lack of natural deterrent. In the insect’s native land, ash trees have co-evolved with the bug, developing a resilience which keeps insect population densities low enough to not be lethal to a healthy tree.

North American ash trees have no such resistance, enabling the insect to target and kill local ash species with ease. The beetle has killed at least tens of millions of ash trees so far and threatens to kill most of the 8.7 billion ash trees throughout North America, according to the U.S. Forest Service.

“The Willamette Valley has the highest risk of infestation of emerald ash borer, just because of the low elevation,” Newman said. “You’re going to find most ash between zero and 1,000 feet, so the valley floor is going to have a high population of ash on the coastal range.”

The death of ash trees in the region has multiple potential impacts.

Dead ash trees can become a public safety hazard, risking personal injury or property damage as branches or whole trees fall.

“Our export nursery tree [industry] is almost a $100 million a year and a lot of them grow ash trees,” said Newman. “So there’s some economic risk.”

The loss of ash trees can also alter the pH balance of soil, which increases the encroachment of other invasive plant species.

The preponderance of ash trees along river corridors also provides shady canopies for cold water fish species, which can be adversely affected by a sudden ash tree reduction.

“It does actually stand to impact some of our listed endangered species,” said Newman.

Part of preparing for this invasion is taking stock of just how many local trees are at risk.

“By doing the inventory, we’re just trying to get a handle on how many are here in town so that if it does come, we have ideas of where we could potentially put traps out,” Newman said.

For now, the CFYCC is the only group working to index the area’s trees, operating this summer with funding from a combination of the U.S. Forest Service, U.S. Army Corps of Engineers, Coast Fork Willamette Watershed Council, Cottage Grove Rotary and other private and corporate donations.

“The first step is really knowing what trees are where in the city,” said Newman. “It might be ash this time, but maybe next time it has to do with big leaf maple or something. So we’re not going around just surveying ash trees. We’re getting every tree.”

In the meantime, the Watershed Council is looking at other ways to address the threat.

Ash trees are popular as urban trees and are on both the Cottage Grove and Creswell list of approved street trees.

“Removing ash off the street tree list is something we’re looking at doing,” said Newman.

As the surveying project moves along, the public may be invited to inventory their own backyards, though future plans to recruit volunteers are not yet fully formed.

Oregon Forest Pest Detectors training, which trains volunteers in landscaping or forestry jobs who might be first detectors of pests or tree disease, is one potential program to get the public involved.

“With emerald ash borer specifically, it’s actually very difficult to detect in the first year or two of infestation because the insects themselves actually colonize the top of the tree and then work their way down the bottom,” Newman said. “And so by the time it’s at eye level, it’s far too late.”

Even so, preparedness plans are gaining momentum and cities like Cottage Grove are starting to highlight the problem.

Newman has been pleased with the city’s response this year.

“They’ve been a really great partner in this,” she said. “They’re making plans. They’re looking ahead. They’re saying, ‘Hey this is something that we need to think about.’”

More information about the emerald ash borer can be found at


Video News
More In Home