Image: Jackson Bottom Wetlands is a lush floodplain forest

The emerald ash borer, a prolific invasive pest, will soon dramatically change Hillsboro’s natural areas and urban treescape, including the 635-acre Jackson Bottom Wetlands Preserve. Forever.

The beetle, first detected near Detroit, Michigan in 2002, has already devastated hundreds of millions of ash trees in the eastern U.S. and Canada, causing an estimated $2 billion in damages. Twenty years later, the pest was spotted in nearby Forest Grove, probably arriving as a stowaway among infested firewood. 

Emerald ash borers (EAB) are incredibly destructive to native ash trees which grow along Oregon's rivers and wetlands. Adults of the little green bug species do little harm. It's their larvae, however, that feed on the tree’s inner bark, disrupting the tree's ability to transport nutrients and water. Once infested, trees can die in as little as three to five years. 

City of Hillsboro Restoration Biologist Laura Trunk and partners at Oregon Department of Forestry, Clean Water Services, and Tualatin Soil and Water Conservation District are working to slow the beetles’ progress in Washington county while devising a strategy to protect natural areas ahead of the destruction.

At Jackson Bottom Wetlands Preserve, where a whopping 95% of the mature trees are Oregon ash, preventative restoration work is now underway. 

“The complete loss of our ash trees will have devastating long-term impacts on our wildlife, native plant community, and the water quality of our rivers and wetlands,” says Trunk. "But through the work we are doing, we will be able to preserve as many trees as possible and pivot to new, more resilient species." 

Image: Oregon ash trees are currently a dominant species at Jackson Bottom Wetlands Preserve

Reshaping Jackson Bottom Wetlands Preserve

Preserving Jackson Bottom Wetlands for wildlife, nature education, and recreation will be a complicated, multi-year process. It started over a year ago with staff identifying and measuring every mature Oregon ash in the Preserve, taking special note of its health and condition. Trunk then carefully combed through the inventory to pinpoint the most valuable ash trees to save. These specimens were treated to protect them from the invasive beetle.

In the end only about 15% of Jackson Bottom’s total stock of Oregon ash will be treated. These trees were chosen because of their benefits to wildlife, the trail system, or education opportunities. But if an effective treatment exists, why not treat all the trees in the Preserve?

“The treatment only lasts two to three years. Applying and re-applying takes a lot of time and labor,” answers Trunk. “It’s about using our limited resources responsibly and saving the most valuable trees.”    

Without intervention, the remaining trees will eventually become infested by the beetles, die, and fall. Trunk and a certified arborist identified trees that pose the greatest risk to people enjoying nature trails or infrastructure throughout the Preserve. These trees are being cut down or snagged before they do any harm. (Snagging is when a skilled arborist climbs a tree to remove the tree’s leafy canopy and leaves the trunk standing). But the wood from felling and snagging ash trees will not go to waste! 

“As a formerly degraded site, Jackson Bottom never had a lot of large woody debris that you would typically see in healthy mature forests, so this is a great opportunity to repurpose these trees to improve wildlife habitat,” explains Trunk. Watch a video about the restoration history of Jackson Bottom Wetlands Preserve.

As the snagged tree dies, the standing trunk provides valuable habitat for cavity-nesting birds like western screech-owl, wood ducks, and downy woodpeckers. The downed logs on the forest floor will provide cover and feeding areas for many reptiles, amphibians, small mammals, and invertebrates. Eventually, these logs will decay, replenishing the nutrients in the soil and keeping the forest healthy and growing.
Along with providing homes for cavity-nesting birds, snagging trees also allow more light to reach the forest floor. This sunshine infusion will help with the next phase of the plan: replanting. Trunk will begin a massive replanting program to restore and protect the forest at Jackson Bottom. 

“Choosing the right species of trees to replace Oregon ash at Jackson Bottom will be very difficult because it is specially adapted to thrive in the harsh environmental conditions that exist on the Preserve,” explains Trunk. “Parts of Jackson Bottom flood in the winter, with 15 to 20 feet of water for weeks. But the whole Preserve is bone dry in the summer. These are challenging conditions to get any tree to grow and flourish.” 

With no single species to replace it, Trunk will restore the Jackson Bottom by planting a variety of native trees and shrubs. Across the Preserve, she will plant Oregon white oak, black cottonwood, big leaf maples, valley ponderosa pine, western crabapple, Scouler’s willow, and native cherries. The newly planted trees will grow into a healthy, diverse forest that will support native wildlife, improve air and water quality, capture carbon, and allow the site to recover from future disturbances, such as invasive species.

This sounds like a lot of effort, and it is. But if staff did not intervene, Jackson Bottom would quickly revert from a restored forested wetland filled with native plants and animals to a degraded site. “It would once again be choked with invasive plants like reed canary grass and Himalayan blackberry,” Trunk says.   

Partnerships and Individuals Help the Effort

Trunk has applied for and won more than $1.4 million in grant funding through the U.S. Forest Service, Tualatin Soil and Water Conservation District, Metro, and Oregon Watershed Enhancement Board to accomplish this critical work.

The Oregon Department of Forestry, the Oregon Department of Agriculture, Clean Water Services, and the Tualatin Soil and Water Conservation District are all working to slow the beetle’s spread. Unfortunately, slowing the destruction is the best outcome. There is no way to stop this invasive pest, and it will negatively impact all of our local natural areas. Expect to see changes along rivers, creeks, and wetlands. Sadly, these changes will adversely affect our native wildlife as well. 

However, there are steps individuals can take to help. Start by identifying all the ash trees on your property. The emerald ash borer will attack and kill many ornamental varieties of ash trees, not just native Oregon ash. 

If you do have ash trees, you will need to make a tough choice: Remove the tree or treat it with insecticide every three years. A certified arborist can help with this decision, as ash trees can be hard to identify, and a trained professional will need to apply the chemicals. 

The best way to slow the spread of emerald ash borers is to burn firewood where it is harvested. Transporting infested firewood is one of the easiest ways for the emerald ash borer and other invasive pests to move from place to place.

So, buy or harvest where you burn or buy certified, heat-treated firewood. In Washington County, the Oregon Department of Agriculture has put a permanent firewood quarantine in effect to stop the transport of infested tree material and slow the spread of the emerald ash borer.

Find out about safe firewood practices here.

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