AMNA NAWAZ: The Trump administration this week proposed to open nearly 45 million acres of national forestland to roads and logging, part of its broader push to boost timber production.

The announcement comes as a yearlong investigation reveals how California forests are already being managed to grow more timber using a controversial herbicide being sprayed at record levels by timber companies and the U.S.

Forest Service.

The Center for Investigative Reporting's Nathan Halverson has that story.

NATE HALVERSON: Every year, Joe Van Meter welcomes thousands of tourists into the Lassen National Forest in California, where he and his wife run the Mill Creek Resort.

JOE VAN METER, Owner, Mill Creek Resort: Yes, thank you, guys.

Have a great day.

NATE HALVERSON: They moved here in 2017 to escape the city and raise a family in what they call a slice of heaven.

JOE VAN METER: Yes, it's a beautiful piece of property.

We have about 12 acres here.

NATE HALVERSON: But since purchasing the nearly 100-year-old resort, Van Meter told us he's had to evacuate guests and staff twice to escape massive forest fires.

And how close from right here did the fires get?

JOE VAN METER: Right there, really to the edge of our property.

It's a devastating thing to live through, and it's traumatic.

NATE HALVERSON: And destructive.

So, when Van Meter learned the U.S.

Forest Service planned to replant trees in the burned-out areas around his home, he was thrilled.

Then he heard the agency's plans involved glyphosate.

JOE VAN METER: My initial reaction was, what is that?

NATE HALVERSON: He quickly discovered glyphosate is the key ingredient in Roundup, which has been at the center of lawsuits resulting in more than $12 billion in monetary judgments and settlements to thousands of people who claimed it made them sick.

The World Health Organization's cancer agency has made it clear it thinks glyphosate is a health risk.

Back in 2015, it determined the herbicide was -- quote -- "probably carcinogenic to humans."

Last month, Bayer, which bought glyphosate manufacturer Monsanto in 2018, created a new company called Ruveon to focus solely on its glyphosate-based business.

In a statement to the "News Hour," Ruveon said it stands behind the safety of its glyphosate-based products, "which have been tested extensively, approved by regulators, and used around the globe for 50 years."

The Forest Service considers it a valuable tool and has plans to spray glyphosate on about 10,000 acres in Lassen National Forest near Van Meter's home.

It claims it will help accelerate reforestation efforts.

What was your reaction when you saw that they were planning on using herbicides across the land right around your community?

JOE VAN METER: That it seems like it's poison that they're putting into the woods.

There's some real health concerns for children, for babies, right?

I have a 2-month-old.

This is our backyard.

This is where my children play.

NATE HALVERSON: Lassen National Forest is hardly alone in turning to glyphosate.

According to our analysis of more than five million pesticide reports, Roundup and glyphosate products are being sprayed in record amounts across California's forests, quadrupling in the last two decades.

The usage is especially widespread on private timber company land.

And the evidence, we discovered, is plain to see.

To my right, it's perfectly demarcated.

You see where the herbicides have been sprayed.

To my left, they haven't recently sprayed herbicides, So the bushes, the life is coming back among the pines.

To justify its continuing use of glyphosate, the Forest Service commissioned an in-depth study 15 years ago.

That study examined reports from around the world and concluded that the chemical was safe for the environment and people.

But our investigation found that the Forest Service's assessment relied heavily on studies that were manipulated by Monsanto to quietly shape the scientific record, according to company e-mails and depositions made public in litigation.

DR.

WILLIAM HEYDENS, Former Monsanto Toxicologist: I have been at Monsanto approximately 33 years.

NATE HALVERSON: Dr.

William Heydens was Monsanto's toxicologist and helped orchestrate a public campaign to promote glyphosate as safe.

At this deposition in 2017, he was asked to read an old e-mail he wrote.

DR.

WILLIAM HEYDENS: "The focus of this is, what is the carcinogenic potential of glyphosate?"

NATE HALVERSON: Monsanto e-mails revealed that Heydens and others searched for outside scientists they could pay to -- quote -- "get up and shout glyphosate is nontoxic" and write seemingly independent studies that would be -- quote -- "referenced and used to counterbalance the negative stuff."

MAN: And you knew that it would be more powerful if it was -- looked like it had been written by outside authors?

DR.

WILLIAM HEYDENS: No, that's not correct.

MAN: Let's see what it says here.

You say it was noted this would be more powerful if authored by non-Monsanto scientists.

DR.

WILLIAM HEYDENS: Oh, yes, I see that.

So I sort of misunderstood your question.

NATE HALVERSON: In another company e-mail, Heydens wrote that his team would -- quote -- "ghostwrite a study," by which he meant Monsanto would do "the writing, and scientists would just edit and sign their names, so to speak," the same way he added they handled a study called Williams, Kroes, and Munro in 2000, which turned out to be one of the most influential pro-glyphosate reports at the time.

It concluded -- quote -- "There is no potential for Roundup herbicide to pose a health risk to humans."

That study was cited 28 times in that 15-year-old Forest Service assessment on the safety of glyphosate.

And the agency continues to point to it, even though the journal that originally published the paper on glyphosate retracted it last year due to -- quote -- "serious ethical concerns" and -- quote -- "the failure to disclose the involvement of Monsanto."

RUSSELL NICKERSON, U.S Forest Service: Hey, how are you?

NATE HALVERSON: Good.

How are you doing?

We reached out to the Forest Service and asked to learn more about their use of herbicides and met up with District Ranger Russell Nickerson.

RUSSELL NICKERSON: So I'm the decision-maker for the district.

NATE HALVERSON: He oversees the management of 500,000 acres of the Lassen National Forest, including the plan to spray glyphosate across 10,000 acres near Van Meter's home.

Why use herbicides like glyphosate?

RUSSELL NICKERSON: So reforestation efforts, brush really outcompetes small trees.

It grows faster, gets taller than them and starts to shade them out.

NATE HALVERSON: Nickerson told us denser forests means the Forest Service will one day have more timber to sell.

And is it safe to use?

RUSSELL NICKERSON: I mean, really, if you want to talk more herbicide details, it's probably our Washington office that you would talk to on that.

NATE HALVERSON: We showed him that our investigation had found that five of the top seven peer-reviewed studies cited in the Forest Service's 15-year-old report about glyphosate had been orchestrated by Monsanto.

So, when this is what you're basing your decision off of, does that information give you pause?

RUSSELL NICKERSON: That's something you would have to talk about with our national office.

NATE HALVERSON: We reached out to the chief of the Forest Service in Washington, D.C., but he declined our request for an interview.

Meanwhile, the spraying of glyphosate continues.

Some of the heaviest spraying in California has taken place near Yosemite Valley, Lassen Volcanic National Park, and the Lake Tahoe area, including here in the 75,000 acres affected by the 2021 Caldor Fire.

So here I am in the Caldor Fire scar.

You can see that life is beginning to return.

Even down here, you will see that right next to each other two baby conifers are coming back.

But it didn't take long to find where glyphosate has already been deployed.

All this behind me, this has been sprayed.

This is what it looks like when they have sprayed herbicides, glyphosate.

It's killed all of the living bushes from last year.

Nearby Tahoe residents, including three time Olympian Hannah Teter, says she and her neighbors were given little say on the use of glyphosate in their backyards.

HANNAH TETER, Tahoe Resident: There's no way we would ever approve this, especially because, like, as you can see, this is some of the cleanest water in the world that flows all the way down to other communities, who drink it.

NATE HALVERSON: Yes.

These residents told us they feel like they're being exposed to a harmful chemical, and it's being forced on them by the Forest Service.

HANNAH TETER: Yes, they're taking away the choice of being surrounded by a toxic chemical that's going to be here for years.

It's going to be on the ground where we hike, where we bike, where we camp.

NATE HALVERSON: That's the same kind of concern that motivates Joe Van Meter.

As the spring goes on near his family home, he's determined to keep raising awareness to help his community push back.

JOE VAN METER: We need work to be done.

And so I want to see that work done, but I want to see it done without the use of toxic chemicals.

NATE HALVERSON: For the "PBS News Hour" and the Center for Investigative Reporting, I'm Nate Halverson in Mill Creek, California.