Portland forestry officials are bracing for a major die-off of ash trees as an invasive beetle spreads through the region.
The emerald ash borer, which is native to Asia, has killed more than 100 million trees in the United States since its discovery in Michigan in 2002, and Oregon officials have long-feared its arrival on the West Coast.
A Portland city biologist discovered evidence of the pest in June in Forest Grove.
Since then, the Portland Parks & Recreation Department has been working with Oregon’s Department of Forestry and Department of Agriculture to limit the spread.
Jenn Cairo, a city forester, said diversifying Portland’s canopy is critical for slowing down the march of the beetle.
“This is why we are actively pushing for a diversity in species when we plant and promote tree planting,” Cairo said in a statement. “So that when an invasive attacks one species it does not cause significant harm to the canopy as a whole.”
So far, the city has taken steps to map and inventory all trees across the city — home to an urban forest that consists of 220,000 street trees, 1.2 million park trees, and nearly 3 million trees on private property.
Anticipating the borer’s arrival, the city began restricting new ash plantings in 2019. The state has created a repository of ash seeds at a facility in Cottage Grove that can help with an eventual replanting.
“We know that in Portland, a love of trees is a key part of our shared identity,” Commissioner Carmen Rubio, who leads Portland Parks & Recreation, said in a statement. “PP&R’s Urban Forestry experts have anticipated the arrival of the emerald ash beetle and have taken initial steps. Once we learn more from the Department of Forestry, we’ll be able to determine additional roles and actions for Portland.”
Emerald ash borers are only ½-inch long and smaller than a dime. They leave trademark D-shaped exit holes in tree bark.
Portland’s Parks & Recreation Department officials said residents should be on the lookout for signs of the emerald ash borer and should take the following steps to limit the damage to Oregon’s tree canopy:
- Report sightings immediately.
- Avoid moving firewood from one place to another, since firewood can transport insects.
- Keep ash trees healthy, since the borer is attracted to stressed trees. That means watering trees during the summer drought.
- Avoid planting any more ash trees.
- If you are a local tree-care provider, become familiar with signs of emerald ash borer. Report sightings and dispose of wood waste properly.
For up-to-date information on Portland’s emerald ash borer response, visit www.portland.gov/trees/eab.