Since the Pacific Northwest’s “timber wars” of the 1990s, the federal Northwest Forest Plan has managed conservation and logging interests in regional forests.

The plan was formulated by a team of scientists from several fields, tailoring their rules to mandates from Congress. The Forest Service announced earlier this year that it was looking to update those rules to meet the growing challenges of wildfire and climate change.

But Oregon environmental advocates say those rules, among many others issued by federal regulatory agencies, could now come under threat. The Supreme Court late last month overturned what’s known as the Chevron decision, a longstanding precedent that lower federal courts should defer to agencies — staffed by experts — on “reasonable” rule changes to enforce legislation.

The ruling effectively means federal regulators will have a harder time defending those rule changes in court. It could also make existing rules easier to challenge.

Industry groups and conservatives say the Chevron decision gave too much power to the executive branch. Liberal groups largely agreed with the doctrine, arguing judges should defer to topic experts on policy.

The federal government owns more than half of Oregon’s land, meaning decisions by national regulatory agencies play an outsized role in the state. But environmental groups that have pushed for some of those decisions now worry they could be reversed by courts, threatening land use policies, logging restrictions and endangered species protections.

No regulatory agencies responded to questions about how the ruling will affect their rulemaking.

But industry groups, environmental organizations and lawyers believe a wave of challenges is inevitable.

Daniel Rohlf, a professor of wildlife law at Lewis & Clark Law School, said the reversal of Chevron could be compounded by another lesser-noticed ruling last month — Corner Post Inc. v. Board of Governors of the Federal Reserve System.

He said that previously, there was a six-year statute of limitations for challenging federal regulation, beginning when the regulation was implemented. But now, the six-year clock starts when the regulation begins to affect the entity mounting the challenge.

Rohlf said this means old rules could be opened up for litigation. And he expects future challenges could throw a wrench in an already overworked legal system.

“It’s sort of a full employment act for administrative law practitioners,” he said.

The Supreme Court’s Chevron ruling also could reignite some of Oregon’s most enduring conservation battles.

The federal Bureau of Land Management administers 16 million acres of public land in Oregon and Washington used for grazing, logging and many facets of rural economies in Oregon. Many timber industry advocates say the agency has been too restrictive in its land use, while other environmentalists argue it has allowed too much logging.

Grazing rules, and fees, have proven particularly controversial. Issues over grazing rules came to a head in 2016 after a federal judge ordered Harney County ranchers Dwight Hammond Jr. and son Steven Hammond back to prison for setting fires on federal land in 2001 and 2006. An appellate court had ruled an earlier sentence was too light.

In response, a group of armed protesters took over the Malheur National Wildlife Refuge in eastern Oregon and encouraged ranchers to halt payments of grazing fees. The occupation lasted 40 days, resulting in 27 arrests and the deadly shooting of an occupation leader by police at a roadblock. President Donald Trump pardoned Dwight and Steven Hammond in 2018.

Rules interpreted from the Clean Water Act are also influential in Oregon, Rohlf said, in promoting salmon and steelhead conservation and restricting water pollutants that can contaminate or harm.

“The sort of pollutants that tribal communities are exposed to disproportionately because they consume a lot more fish,” he noted.

Irrigation in the Klamath Basin, where farm advocates said farmers aren’t getting enough water to fully irrigate their fields, has been a flashpoint that could soon lead to litigation. Farmers say restrictions by federal agencies that have the regulatory authority over endangered species of fish have caused the issue, not a lack of water.

However, many court cases over the past decades have affirmed that the government must protect tribal water rights and the needs of endangered species in the basin.

Greg Addington, executive director of the Oregon Farm Bureau, said he supported overturning Chevron. Federal agencies, he argues, won’t admit if they make a bad decision.

So deference to agency officials, he said, was “a little bit like the fox watching the henhouse.”

Associated Oregon Loggers Inc. said the Chevron reversal will require Congress to legislate more precisely, reducing ambiguity in individual regulatory agencies’ mandates.

“While small business forest professionals often support federal agencies’ expertise in public forest management projects, this change may help reduce politically driven agency overreach,” the trade association said.

Quinn Read, the Bird Alliance of Oregon’s conservation director, said she’s alarmed by a ruling that would make judges, who are usually not experts on environmental policy, the arbiters of those policies.

She said recent rules intended to address climate change are especially threatened. That’s because many are based on environmental protection statutes written more than 50 years ago, she said, when climate change was less understood and discussed, much less written into legislation.

The ruling, Read said, also could cause regulatory agencies to be overly cautious in approaching rule changes, resulting in less ambitious conservation agendas and a slower response to new science on climate change.

The Northwest Forest Plan is also a chief concern for her organization. The plan regulates land use and endangered species — such as the northern spotted owl that sparked the fire of the timber wars. But that plan could be under threat, she said in a later email, and environmentalists in the Pacific Northwest should keep a close eye on it.

“The survival of species like the northern spotted owl and marbled murrelet may depend on how the Forest Service responds to this post-Chevron world,” she said.

Though the cases that overturned Chevron were brought by industry groups that sought to reduce regulation, the decision could cut both ways.

Rohlf, the professor of wildlife law, said overturning Chevron could also create an opening for environmental groups to challenge a conservative administration’s efforts to loosen regulations it views as onerous or overreaching.

“It’s going to be kind of a wild ride,” he said.

— Andrew Miller covers business news. Reach him at amiller@oregonian.com or 971-803-2954.