Stephen Hamway
The Bulletin

Many more trees than previously thought — about 2,100 — are slated for removal near U.S. Highway 20, in a scenic area where an improperly applied weedkiller wreaked havoc on the forest.

On Monday, the U.S. Forest Service released a formal decision memo on the effort to knock down dead and dying trees to prevent them from falling onto the highway. The trees in the area, almost all ponderosa pines, were killed by the herbicide Perspective, which was sprayed alongside a 12.5-mile stretch of highway to kill flammable roadside weeds.

Forest Service officials first noticed dying trees in 2014 and said they continued to die after the spraying ended in 2015.

“We’ve known it was an issue, and we’ve known that these trees were starting to fade over time,” said Ian Reid, Sisters district manager for the Deschutes National Forest.

Still, environmentalists lamented the loss of the trees, particularly old-growth ponderosa, that helped distinguish the stretch of highway northwest of Sisters.

“It’s heartbreaking that the old-growth along one of Oregon’s most scenic drives is going to be logged,” said Erik Fernandez, wilderness program manager for the conservation group Oregon Wild.

In 2012, contractors selected by the Oregon Department of Transportation chose Perspective, then a relatively new herbicide, over concerns raised by a Forest Service employee at the time. The active ingredient — aminocyclopyrachlor, also known as ACP — had been linked to tree deaths in other states, and sales of a separate herbicide containing the compound were suspended by the Environmental Protection Agency prior to its use on the project. The EPA’s product label advised users not to use it near “desirable trees.”

After Forest Service employees began to notice browning pine needles and other signs of declining health among trees in the area in 2014, testing later showed that ACP was present in the trees, with hundreds of trees potentially impacted.

The problem is even more widespread than was originally believed, according to the decision memo. While the majority of affected trees are near the road, Reid said some of them were more than 75 feet from the edge of the road, which may be a sign that the herbicide has the ability to travel through the root structures of trees.

“Certainly, ponderosa pine root systems can go on for quite a ways,” Reid said.

All but 73 of the trees slated for removal are ponderosa pines, Reid said. About 30 percent of the affected ponderosa pines were at least 24 inches in diameter, a sign that they were older, mature trees, he said.

While ODOT removed a handful of trees that posed an immediate threat to drivers on Highway 20 in the fall, the transportation agency and the Forest Service have been planning a larger project to remove all dead and dying trees with the potential to fall on the roadway.

The Forest Service’s decision calls for certain trees within 75 feet of the road, including those with dead or nearly dead tree canopies, to be cut down, cleared and used as forest products. No downed trees or slash piles will be left within 30 feet of the road, according to the decision.

Trees that are farther from the road but still pose an imminent danger will be felled or topped, though many will be left in place to provide wildlife habitat. Reid emphasized that the focus of the project was making the roadway and surrounding area safer. He said additional trees could be felled if their health continues to deteriorate.

“Our No. 1 priority here is not about selling timber — it’s about getting those hazards down and on the ground,” he said.

Separately, the Oregon Department of Agriculture is developing a statewide rule that would limit the use of ACP. The proposal, released earlier in February, would prevent trees and other material exposed to ACP from being milled or composted. Reid said he was aware of the rule, and said the Forest Service would comply with any rule that the state agriculture department ends up with.

The loss of mature ponderosa pines has prompted criticism from environmentalists throughout the process. Fernandez said many of the same trees were saved a decade prior, after an attempt to widen Highway 20 to four lanes was rejected. He said the ponderosa pines in the area, particularly older trees where the bark takes on an orange hue, help make that stretch of road special.

“As you come back down from Santiam Pass, that’s how you know you’re in Central Oregon,” Fernandez said.

While some details of the project still need to be finalized, including potential road closures, Reid said he was hopeful that the project could kick off between April 15 and May 1.

“We definitely want to hit that spring window, before the summer recreation season really begins,” Reid said.

—Reporter: 541-617-7818,