WYOMING -- Aerial spraying of chemicals — including one banned in Europe —  to kill sagebrush and invasive plants appears to be “the most-reasonable option” for the Bighorn National Forest to meet range and habitat goals, the U.S. Environmental Protection Agency says.

The EPA made its comments on the national forest’s proposal to kill mountain big sagebrush, native larkspur and non-native weeds in a July letter to Forest Supervisor Andrew Johnson. Administrators of the 1.1-million-acre Bighorn National Forest would attack invasive Medusahead and Ventenata grasses, plus the native sagebrush and larkspur, to preserve wildlife habitat, improve domestic stock grazing and reduce the threat of fire, according to a draft environmental impact statement.

The Bighorn plan “appears to be the most-reasonable option” to achieving the national forest’s desire for up-to-date and effective “vegetation overgrowth management techniques,” wrote Philip Strobel, the EPA’s regional director for compliance with environmental law. The letter lends an imprimatur for the project from a significant federal partner tasked with overseeing toxic substances and pollution.

The EPA endorsement of the national forest plan may assuage some worries about both aerial spraying, which critics said would hit untargeted areas, and the proposed use of the herbicide tebuthiuron, which is banned in Europe.

The chemicals “have all been registered by EPA and provide more selective and effective options for controlling targeted plant species,” Strobel wrote. “Aerial applications will cover areas not easily accessible for ground application and will be more effective for treatments in large areas with fewer applications.”

Several environmental, community and bird groups have criticized the Bighorn plan. The Forest Service has not provided copies of comments, but the EPA gave its letter to WyoFile following a records request.

Despite EPA support for elements of the long-range Bighorn proposal, the environmental agency echoed others’ criticism of the draft 246-page draft environmental impact statement. The Bighorn Forest, which stretches from Montana to Tensleep, from Story to Shell, had to complete that study to authorize aerial spraying.

The Forest Service was imprecise in describing how much acreage it would treat to reduce mountain big sagebrush, the EPA said. The EIS also is vague when it comes to describing how big the overall vegetation treatment area would be, the environmental agency said.

The national forest’s descriptions of its proposed eradication and reduction program could span an area that could be more than five times as large as indicated in the EIS, depending on how one reads the document, the EPA suggested.

“[I]t is unclear in the Draft EIS that the maximum treatment of 15,000 acres of mountain big sagebrush over two years will satisfy the project’s desired conditions rapidly or whether 76,500 acres (5,100 acres per year for 15 years) is the goal,” Strobel wrote.

Similarly, the forest’s description of total treatment acreage for all types of vegetation could be interpreted widely, the EPA said. “[I]t is never clearly identified if 79,650 [acres] or 375,000 acres of treated vegetation is the goal,” the letter reads.

National Forest officials also should map where the herbicides are to be sprayed and where vegetation would be otherwise killed. “We recommend the USFS include waterbodies, wetlands and other sensitive areas on maps near treatment areas,” Strobel wrote

Finally, the Forest Service should look to changing domestic stock grazing methods as part of its strategy, the EPA said.

“[T]he Draft EIS does not discuss additional changes to livestock grazing protocols in the BNF that could be incorporated to avoid disruption or restoration of the natural vegetation regime with minimal mechanical, chemical, or biological interventions,” Strobel wrote. “We recommend that the Final EIS evaluate if there are additional modifications or best practices the BNF can adopt for livestock grazing to lessen the overall need for human interventions in the management of mountain big sagebrush over the next 15 years.”

Western Watersheds Project has criticized the project saying the Bighorn Forest has “a fictional understanding of sagebrush ecology.”

The Council for the Bighorn Range has said treating sagebrush and removing larkspur “are not beneficial to the myriad of sage-dependent birds that inhabit the sagebrush-steppe.” The Bighorn Audubon Society called the proposal to thin sagebrush “a very unreasonable plan that purposely further reduces bird and other wildlife habitat.”

WyoFile is an independent nonprofit news organization focused on Wyoming people, places and policy.