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Environment

Colorado plans to abandon its battle against the emerald ash borer

The devastating pests detected in Broomfield and Westminster last month signal it’s time to lift the Boulder County quarantine and start planting a new urban forest

Colorado State Forest Service foresters confirmed on Sept. 11, 2019, that emerald ash borer had been found in the urban canopy in Westminster, the second confirmation in a month outside of the federal quarantine zone that includes Boulder County. The first confirmation was in Broomfield. (Photo provided by the City of Westminster)
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Mike Swanson stands under a thinning canopy of the wounded-but-still-standing, bluntly assessing the enemy.

Here on Evergreen Hill, in the heights of Washington Park, acting Denver forester Swanson is surrounded by the ghosts of soldiers cut down in their relative youth. They gave their all for the mission of bringing shade to a high-desert metropolis.

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Swanson and his forestry comrades have fought off many threats — Dutch Elm, fire blight, pine beetle, thousand cankers disease and the vicious dwarf mistletoe. But as Swanson makes a thousand-yard stare across the pond to the south, his forestry troop is offering surrender.

The dreaded emerald ash borer is no longer a distant threat confined and quarantined to Boulder County. It’s here, say Swanson and other top forestry officials across the state. We can assume it’s everywhere. The latest invasion of the boreal snatchers is as good as complete. 

“Once you find it,” Swanson intones ominously, “It’s already been in your forest for two to three years.” 

So hopeless is the fight that state agriculture officials plan to cancel Colorado’s six-year ash borer quarantine by late fall, removing restrictions on transporting infected firewood and other wood supplies across county borders. 

The discovery of an adult ash borer on a sidewalk in Broomfield, miles outside the Boulder quarantine and within a few bug hops of Adams County, was the final trigger for state forestry experts.

Mike Swanson, Denver’s acting city forester, stands next to Kentucky coffee tree in Denver’s Washington Park. The species is one of the trees suggested as a city-hardy replacement for green ashes. (Jeremy Sparig, Special to The Colorado Sun).

And as if to confirm the futility of the battle, the Colorado State Forest Service said Wednesday the pests had been confirmed in Westminster’s urban canopy, the second outside of the federal quarantine area in a month.

“We knew we couldn’t stop it completely. Six years later, we feel like we’ve done the best we can,” said Laura Pottorff, Plant Health and Certification Section Chief for the Colorado Department of Agriculture. 

The message for owners of beloved ash trees up and down the Front Range is now clear: Hug ‘em if you got ‘em, and spend $300 for a vaccination. 

But if your ash shows any sign of decline, it’s slash and burn, and time to love you some saplings of Texas red oak or Kentucky coffee.

“Mother Nature is not nice,” Pottorff said.

MORE: Read more environmental coverage from The Colorado Sun.

Heartbreaking realities 

The hardboiled forestry approach can be heartbreaking for homeowners, neighbors and whole communities. 

Jim Klett, a Colorado State University professor of Landscape Horticulture, Ornamentals, and Nursery Management and a member of Colorado’s ash borer task force, said foresters are taking down seemingly healthy trees up to 8 inches in diameter as part of a carefully crafted strategy.

“On our Arbor Day planting this year, they took out a whole row of green ash in a narrow area between the sidewalk and a parking lot,” Klett said. “We put in columnar goldenrain trees and columnar hackberries.” 

(Internet reviews say goldenrains are perfect for such “hellstrip” places.)

“We’re trying to promote the right tree for the right place,” Klett said. 

Plant quarantines, which are coordinated by the USDA, are usually meant to eradicate a pest, Pottorff noted. The ash borer quarantine in Colorado was different from the start. As far back as 2013 state officials knew by how it had spread from Eastern states that the bug couldn’t be eliminated. You couldn’t stop it, you couldn’t even hope to contain it. Just slow the march a bit and use the extra time on the clock to plant healthier trees. 

Colorado State Forest Service foresters confirmed on Sept. 11, 2019, that emerald ash borer had been found in the urban canopy in Westminster, the second confirmation in a month outside of the federal quarantine zone that includes Boulder County. The first confirmation was in Broomfield. (Provided by the City of Westminster)

The quarantine meant any ash wood from Boulder County stayed in the county, with a few exceptions: ash meant for mulch had to be ground twice so that larvae wouldn’t survive the chipper; wood for lumber had to be stripped of bark and properly milled. Firewood couldn’t leave at all. 

Lifting the quarantine means recyclers and landfills in places like Weld County can handle the material. Colorado ag department staff is recommending the change, and will hold a public hearing Oct. 16 at the department headquarters in Broomfield. The commission would vote in November, and the quarantine would be lifted Dec. 30. 

Tree lovers up and down the Front Range should give thanks to Boulder County foresters and residents who sacrificed to abide the quarantine, Pottorff said. “We all benefited. They helped slow this pest down,” she said. 

In Denver’s Washington Park, Swanson is constantly in triage mode for his ash trees and other vulnerable species whose life aspirations are complicated by climate change as well as everyday disease.

Leaf scorch is creeping into lindens and Norway maples, and gets worse in a drought year. A more volatile climate means more summer hailstorms like the one that hit central Denver in late June this year, shredding a good percentage of full-grown leaves.

“It took leaf mass out of the trees, and that’s how they gather food and light,” Swanson. Such storms sap a tree’s “stored energy” and may not show full effect for two to three years, he said. 

Human causes assault city trees in more targeted manners, as well. As he talks, Swanson keeps one skeptical eye on a lawn mowing crew in the distance. 

“Ooof,” he winces, as a rogue machine strips some bark from a cottonwood.

“We have incident reports. We do get on the email and fire a few off once in a while,” he said. 

Mike Swanson, Denver’s acting city forester, in Washington Park. (Jeremy Sparig, Special to The Colorado Sun).

Then there was the downtown bar advertising “alcohol & axes,” using one of the city’s rugged English oaks for a hatchet target. What could possibly go wrong? 

As Swanson describes plans to limit Denver losses from the ash borer, he’s standing amid a lingering reminder of a forest disaster. Starting in 2015, Washington Park lost dozens of older-growth trees from Evergreen Hill, formerly a thickly-shaded vantage point overlooking a youth fishing pond and the local fire station. 

Neighbors who walk the area multiple times a day were in mourning, and lashed out at the city for allegedly killing many of the trees with salty recycled irrigation water. Swanson calls it a “perfect storm” of factors that included faulty irrigation, too many trees planted at exactly the same time, ill-timed storms and common diseases. 

Planters are slowly mixing in new species to re-shade the hill, including Sequoia, Arizona Cypress and Bald Cypress. “I’m just trying to get it back to what it was,” Swanson said. “In 10 to 15 years,” he said, shaking hands with an 8-foot cypress, “these will be noticeable.” 

Parks officials keep fairness issues at the forefront as they confront the ash borer and other long-term threats to city greenery, as advocacy groups pinpoint economic and racial gaps in Denver services. While the city looks for more park space in underserved areas, it’s more important than ever to take care of the trees already there. 

“I worry about the neighborhoods where people don’t have as much money to take care of the trees,” Swanson said. “So that’s where we can try to tweak things and spread out our money. We’re looking for equity throughout the whole city.” 

Mike Swanson, Denver’s acting city forester, meets with The Colorado Sun in Washington Park on September 10 2019 to discuss efforts to manage and protect park trees against threats including ash borer, fire blight, pine beetle, and invasive species. In this image Mr. Swanson describes the complexity of the Kentucky Coffee Tree compound leaf. (Jeremy Sparig, Special to The Colorado Sun).

By early September, Swanson and his team were mustering against a brand-new threat. The forestry team discovered spruce ips beetles, which make tracks inside the bark layer and cut water flow from the roots.

Swanson looked at a mature ash, 200 yards below Evergreen Hill, showing some vague branch damage 60 feet above ground. Drought? Squirrel grazing? Ash borers?

In ash or spruce, he said, it takes more than one attack for the true enemy to show itself. 

“It’s a riddle,” he said. “And by the time you’ve figured out the answer to the riddle, it’s too late.” 

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