Deep inside Northern California’s Shasta-Trinity National Forest, wildlife ecologist Mourad Gabriel is dressed in camouflage, waiting for the raid.

He’s accompanied by more than a dozen armed officers with the U.S. Forest Service, local sheriff’s office, and other agencies on a hot August afternoon. Their plan: to seize and dismantle a nearby illegal marijuana grow site, hundreds of which are discovered on California’s national forests each year.

At this site—just off Route 36, east of Redding, and down a rocky forest valley—more than 4,000 marijuana plants grow beneath sugar pine and Douglas fir. There is also a campsite with several tents, two cisterns, and hundreds of feet of irrigation pipe.

During the raid, officers arrest two alleged growers. Once the site is secured, Gabriel and his partner, Greta Wengert, move in to assess the environmental damage and clean it the best they can. For the last six years, the pair has warned about the dangerous pesticides found at many of these sites and the associated impact on local wildlife. Growers often use pesticides, some of them banned and highly toxic, to protect the marijuana plants and their camps from insects and animals.

In 2004, Gabriel and Wengert, who are married, founded the Integral Ecology Research Center, a nonprofit dedicated to the research and conservation of wildlife. They never planned to get into marijuana work, Wengert says. “But then all of our animals began to die.” (See inside a flourishing, and conflicted, weed industry.)

Animals at risk

Gabriel and Wengert first discovered the problem while working on Pacific fishers, a small, predatory mammal and threatened species in the state of California. While studying causes of mortality, disease, and decline in the population, they realized that the fishers were often dying of different types of poison. They eventually tracked the source to pesticides on illegal marijuana grow sites in remote forests, which are often in the fishers’ home range.

By 2012, Gabriel and Wengert had put numbers to the problem. In a study published in PLoS ONE, they found that 46 of 58 fisher carcasses they tested had been exposed to an anticoagulent rodenticide, or rat poison.

Before long, they realized other species were being exposed, including bears, grey foxes, bobcats, mountain lions, and the northern spotted owl, another threatened species in California. Some were exposed by accident. Others seemed to have been baited and intentionally poisoned. They’ve found pesticide-laced hot dogs on hooks in the forest. Another time, they discovered a vulture that had died while feeding on a poisoned grey fox. The carcasses were surrounded by dead flies.

“I do this work because it’s a conservation issue,” says Gabriel. “It’s not, ‘It’s an evil drug,’ that kind of attitude. I’m not talking about the plant itself.”

A growing problem

Marijuana grows have shown up on public lands for decades, though the pesticide problem is newer. The grows are especially prevalent in the Emerald Triangle, an area of Northern California so-called because of the amount of cannabis, both legal and illegal, produced there. The triangle includes Humboldt, Mendocino, and Trinity counties, where the raid site on the Shasta-Trinity National Forest is located.

U.S. Forest Service Special Agent Stephen Frick has eradicated illegal grows on public lands for 24 years. Frick says that at first the Forest Service discovered these sites only on occasion. He remembers the year 2000 as the first time Trinity County removed over 1,000 cannabis plants. By the end of the decade, there were hundreds of thousands. Last year, the agency removed over a million.

They find the sites mostly through aerial reconnaissance, but they believe many are left undetected, as just a handful of Forest Service agents patrol millions of forest acres.

In 2018, the number of new sites seemed to decrease slightly. The Forest Service cleaned more sites then it raided, which may be because of cannabis legalization in California (on January 1, 2018). But outside the state, the demand for black-market marijuana continues. And Gabriel says the pesticide problem on public lands has only gotten worse, with growers using more banned and restricted-use pesticides. (See: Organic weed?)

Highly toxic pesticides

After the August raid, one of the alleged growers told Gabriel that he didn’t use pesticides. But the next day Gabriel found several containers of over-the-counter pesticides, as well as a bottle containing a milky white substance he suspected to be carbofuran, which the Environmental Protection Agency banned in 2010. Gabriel took samples that would later be tested at the University of California Davis, where he is a faculty member.

Gabriel says carbofuran is so toxic that a quarter of a teaspoon can kill a 600-pound male African lion. Anticoagulent rodenticide, another pesticide commonly found at grow sites, causes animals to internally bleed to death.

Gabriel knows what this looks like intimately. In 2014, he and Wengert found their dog, a rescued black Labrador mix named Nyxo, writhing on the floor of their Northern California home. Nyxo died not long after. Gabriel conducted a necropsy and found that his pet’s insides were filled with blood. The dog had ingested rat poison.

“It did have us take a step back and really evaluate what we’re doing, and make sure we wanted to continue doing the work we do,” says Wengert. “We decided that was not going to stop us.”

The Integral Ecology Research Center isn’t the only organization studying and trying to fight this problem. Within the Emerald Triangle lives the Hoopa Valley Tribe. Illegal grow sites have also been found on their reservation. The tribe’s fishery and forestry departments are both worried about the environmental impacts. Tribal members fish salmon for food, and pesticides can get into the water. Their land is also habitat for fishers and northern spotted owls.

In 2012, Hoopa Valley forestry head Mark Higley located a tagged fisher near his office that had ingested anticoagulant rodenticide. The fisher staggered as it hemorrhaged and ultimately was put down. Higley has no doubt that pesticide came from illegal marijuana cultivation. “He was definitely poisoned,” he says.

Higley initially assumed that fishers on the reservation would have more exposure to the pesticides than owls, since owls are pickier eaters. But a 2018 study by Gabriel, Wengert, and others in the journal Avian Conservation and Ecology found that seven of 10 northern spotted owls tested positive for rat poison. Gabriel and Wengert said they find poisoned wildlife near grow sites on about half of their visits.

A controversial drug

Eradicating illegal marijuana grows, even in the name of science, isn’t always popular. Gabriel says he has been criticized for working with law enforcement at a time when public opinion around marijuana is shifting. The U.S. Forest Service sometimes uses aggressive tactics to nab alleged growers. At the August raid, a police dog bit one fleeing alleged grower in the abdomen, sending him to the hospital. Gabriel compared the policing to efforts by poacher hunters in Africa.

“I look at this threat in North America, particularly our Western states, as no different than the levels of chemicals and poaching that happen in Africa,” he says.

Frick says marijuana growers are sometimes armed, and that they have found links to drug trafficking organizations in Mexico, though he admits Forest Service efforts to document the money flow have proven difficult. Many growers face charges of both manufacturing a controlled substance and depredation of National Forest lands, which can result in decades in prison. After they serve time, non-citizens can be deported.

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Etan Zaitsu, a Sacramento-based federal criminal defense attorney, is representing one of the men arrested during the August raid. He has defended suspects arrested at illegal marijuana grows in the past and says they tend to be day laborers or farmworkers from Mexico or southern California who are offered enticing deals to earn more money by growing marijuana in the woods.

“The guys getting caught are not in the cartel,” he says. “They are just farmworkers. The connection is that somebody way up above is running the show and they are usually not present when the raids happen.”

Zaitsu says his client is facing a 10-year mandatory minimum sentence for his alleged role in the illegal marijuana farm in the Shasta-Trinity National Forest, which he thinks is far too harsh. He adds that recruiters don’t fully disclose the risks associated with the grows and that the growers themselves often have trouble knowing the difference between more lenient state laws and strict federal laws.

“The penalty is supposed to deter people from committing the crime but I’m not sure we’re seeing a reduction,” he says. “These guys don’t know what the penalties are and they are being lied to.”

Recently, the Forest Service got a boost for its eradication efforts. Its 2018 budget saw a $2.7 million increase to get rid of grow sites on public lands, citing both a risk to public safety and the environment. But that money doesn’t go toward cleaning and restoring grow sites.

After assessing the environmental damage, Gabriel, Wengert, and their team, with the help of the U.S. Forest Service, do what’s called a reclamation of the site, which means not only removing any pesticides they’ve found but also cleaning the often thousands of pounds of trash left behind. Resources for these efforts are slim, and sites are almost never restored to how the forests once were.