Trash accumulated by growers at a marijuana grow site raided by the U.S. Forest Service and other agency law-enforcement officers. Remediation and clean-up of sites such as these can cost thousands of dollars an acre, officials say.

Marijuana smokers might praise their drug of choice as "natural," but pot growers in national forests all over the country have caused "severe" damage to these natural treasures, according to testimony by the U.S. Forest Service's director of law enforcement.

"The illegal cultivation of marijuana on our National Forest System is a clear and present danger to the public and the environment," said David Ferrell, when he testified before the Senate Caucus on International Narcotics Control Wednesday (Dec. 7).

The U.S. Forest Service is calling for increased cooperation between government agencies to prevent further forest damage, while some experts believe changing drug laws — including the legalization of marijuana — might reduce the need to grow marijuana in parks.

A 'growing' problem

"The attributes that make the lands of the National Forest System excellent producers of wildlife habitat and clean water are also prized by illegal marijuana growers," Ferrell said in his testimony. "The lands are remote with few people, the forest vegetation is dense, there is an extensive system of roads and trails (both open and closed), soils are fertile, and water for irrigation is available for the diverting."

California National Guardsmen and volunteers prepare some of the 300 miles of irrigation line removed from marijuana-growing gardens to be airlifted out. (Image credit: U.S. Forest Service)

The forestry service has seen serious pot-growing operations sprout in 67 national forests in 20 states, a steadily rising number due to increased acceptance of marijuana use, Ferrell said. People probably first started growing marijuana in parks sometime in the mid-1960s, forestry officials believe, but large plots weren't detected on national lands until 1995, in California.

"The Mexican cartels and other growers began to think to themselves that they could make more money and run less risk if they were to grow it stateside," Warren Eth, a lawyer who wrote a review of marijuana cultivation in national forests, told LiveScience. Increasing security at national borders could have played a role in U.S. marijuana cultivation as well, he said.

"There've always been people who use the parks to do bad things, be it moonshiners or marijuana growers," Eth said. "National parks and forests are vast lands that are sparsely policed. In some areas there is one park ranger for every 100,000 acres. No one can possibly police or patrol that area."

Ecological disaster

The growers clear plots to plant, destroying natural vegetation in the area and disrupting wildlife. They transport water from lakes and streams (an average plot of 1,000 plants requires 5,000 gallons, or about 19,000 liters, of water daily). Some growers also liberally apply toxic chemicals to keep their plots clear of weeds, bugs and rodents, according to Eth.

Old tires are used to surround young marijuana plants. After harvesting the plants the tires are left to deteriorate and contaminate groundwater supplies. (Image credit: Photo courtesy National Geographic)

"The most disgusting aspect of it is the pollution," Eth said. "They just pour chemicals like nobody's business… and they get washed into streams that flow through national parks."

Specifically, increasing concentrations of the rat poison warfarin have been detected in a sensitive, and nearing endangered status, mammal called the fisher (Martes Pennanti) in California, Ferrell said. This poison could be contributing to the fisher's declining population.

The pot growers that live by the crops also poach wildlife (some endangered) from the area, leaving a carpet of animal carcasses behind, Eth told LiveScience.

Dangers to citizens

These illegal marijuana-growing operations aren't only endangering native plants and animals in the forests, but park-goers as well. [Photos: One-of-a-Kind Places on Earth]

"Many marijuana sites found on national forests are under cultivation by drug-trafficking organizations that are sophisticated and include armed guards, counter-surveillance methods, logistics support and state-of-the-art growing practices," Ferrell said in his testimony.

"Drug-trafficking organizations present a serious risk to national forest visitors and employees, as individuals are often armed with semiautomatic rifles and handguns," Ferrell said. The crops are also protected by "improvised antipersonnel devices," a technical term for homemade landmines.

Protecting our forests

In 2010, the cleanup of 335 California national forest sites removed more than 130 tons of trash, 300 pounds of pesticides, five tons of fertilizer and nearly 260 miles of irrigation piping from marijuana growing operation sites discovered on national lands. Cleanup and restoration costs between $10,000 and $15,000 per acre, the Forestry Service said.

U.S. Forest Service and Santa Barbara Sheriff's Department eradicate a large marijuana operation. Thirty law-enforcement personnel were involved in the joint operation as well as helicopters assigned to the sheriff’s department and the aviation support unit. (Image credit: Santa Barbara Sheriff's Department)

These large sites range from 10 to 20 acres (4 to 8 hectares), leading to hundreds of thousands of federal dollars spent cleaning up each site, according to the Ferrell's testimony. Since 2005, the U.S. Forest Service has torn down 3,900 sites on national lands.

The forest service can't protect and eradicate these areas all on their own, Ferrell said, and asked the caucus for help, calling for increased partnership between multiple government agencies.

Large vs. small scale

Other experts have their own ideas of how to decrease marijuana growing in national parks. [10 Most Visited National Parks ]

Eth is calling for marijuana legalization, and the associated regulation and taxing that comes with it. "The strategy they are developing is one that one would have assumed should have been there since the beginning," Eth said. "If the country could sit down and look at the damage and the untold billions of dollars that are spent to combat it, perhaps we can come to a conclusion that we don't want this in our parks, that we don't want to spend billions upon billions of dollars on something that can be regulated and taxed."

Ralph Weisheit, a criminal justice researcher at Illinois State University, has a more middle-of-the-road perspective, saying that different types of growers should be dealt with in different ways. (Ferrell's testimony specifically covered large-scale cultivations, run by drug-trafficking organizations.)

"Some on both sides of the debate about legalizing marijuana see it as an all-or-none issue — either complete legalization or complete prohibition," Weisheit told LiveScience in an email. "We don't take such extreme positions with alcohol or tobacco, and I'm not sure why it's helpful to take such positions with marijuana."

He suggests specifically that law enforcement shouldn't waste their time regulating small scale operations: "These very large unregulated operations as described in the testimony are a concern and should be responded to by law enforcement," he said. "Of course, it is important to distinguish these very large operations from small ones on a variety of dimensions, including impact on the environment and potential for violence."

You can follow LiveScience staff writer Jennifer Welsh on Twitter @microbelover. Follow LiveScience for the latest in science news and discoveries on Twitter @livescience and on Facebook.