County to tackle a development side effect: invasive plants

EVERETT — In the next 100 years, native plants and habitat could vanish from urban forests like Meadowdale Beach.

That’s because Himalayan blackberry, English holly and other invasive species are slowly choking out large trees emblematic of the Pacific Northwest, according to the environmental nonprofit Forterra.

As development creeps farther into the rural reaches of Snohomish County, human disturbance is increasingly allowing invasive species to encroach on the 12,000 forested acres owned by the county.

The local government is partnering with Forterra to keep those plant invaders at bay, dedicating $130,000 last year to the Healthy Forest Project.

It kicked off in January as a 1,000-acre pilot project in 10 locations: Portage Creek, Kayak Point, Smith Island, McCollum Park, Picnic Point, Lake Stickney, the Evergreen State Fairgrounds, Lord Hill Regional Park, Meadowdale Beach and the Paradise Valley Conservation Area.

The sites are centered around woods that impact salmon-bearing streams. Large trees shade the water, keeping the temperature cool enough for young fish to thrive, Moore said. Tree bark and leaves support an array of stream insects and critters that fish eat.

Of the 1,000 acres, about 22% have a high presence of invasive species, Forterra reported. Another 46% have a medium presence.

Scott Moore manages the native plant program for Snohomish County Public Works. He said the reasons for saving these stands of trees are endless.

For one, they provide Snohomish County residents with a nearby space to get outside. Ever heard of forest bathing? It refers to the therapeutic benefits of walking in nature. Immersion in the woods lowers blood pressure and helps us relax, Moore said.

Urban forests also reduce stormwater runoff and erosion. The tree canopy can catch almost 50% of rainwater, Moore said, and it’s evaporated back into the atmosphere.

Those trees also store carbon.

The new project aims to develop a 20-year plan for keeping the county’s forests healthy, and to create a structured volunteer system to carry out that plan.

Forterra started gathering data last year on what kinds of trees are growing and the types of invasive species present.

Himalayan blackberries are the most common unwanted guest, followed by English holly and English ivy.

Forterra also found other invaders like reed canary grass, creeping buttercup and English laurel.

Some of these like Hedera helix, better known as English ivy, are a remnant of early non-native invaders of another species: homo sapiens.

“During early settlement, people brought favorite plants from Europe to remind them of home,” Moore said. “Ivy is one of them.”

The vine is particularly aggressive. It swarms the ground, choking out native underbrush and climbing up large trees, smothering them.

Then there are blackberries. Those vines creep into forests in an impenetrable mass, overwhelming younger trees and wiping out any sort of native underbrush. Larger animals like deer can no longer get into the woods.

“That disrupts the whole ecosystem and stamps out diversity,” Moore said.

Other nonnative species show up in forests when people move in nearby, Forterra program manager Elby Jones said.

“We have a lot of areas that get degraded by development or other disturbance,” she said. “Especially next to where people are, a lot of invasive species are brought in.”

People living in houses up against wooded lots often toss yard waste over the fence into open space, Moore said. Birds and other critters then pick up nonnative backyard plants and spread them around.

Forterra will prioritize certain stands of trees in the pilot project for restoration.

Aggressively removing invasive species and planting new native trees and shrubs will help return forests to a sustainable condition, where they’re better able to keep nonnative plants from establishing, according to Forterra.

But they won’t necessarily work on the worst areas first, Snohomish County Energy and Environmental Sustainability Manager Lisa Dulude said. Program managers looked for forest with the highest risk.

“We tackle healthy stands with lots of invasive cover,” she said, “so it doesn’t become unhealthy.”

Next, Forterra will look for people in the community who want to take on a project site. Those people will be responsible for organizing volunteers to carry out the Forterra projects.

Forterra will begin recruiting and training stewards in May, Jones said.

The nonprofit has done similar work in partnership with about 15 cities in the past, including Everett. This is the Forterra’s first time working with a county.

“The hope is we can try this out and demonstrate that it’s successful,” Dulude said. “We’re really actively trying to move the needle to restore the health of Puget Sound.”

Julia-Grace Sanders: 425-339-3439; jgsanders@heraldnet.com.