California's most valuable cash crop, marijuana, is taking a heavy toll on some of the state's most sensitive ecosystems, with the effects ranging from erosion, contamination, threats to wildlife, and heavy water use at a time of severe drought.
The situation is prompting ecologists and wildlife managers to urge greater focus on bringing marijuana plots under tighter environmental scrutiny.
It's a tall order, notes a research team calling for the added focus via an article in the August issue of the journal BioScience. Among the challenges: Money to beef up enforcement and to cover cleanup is scarce. And where some level of regulation exists, enforcement can be stymied by a disconnect between federal and state laws regarding the possession, sale, and use of marijuana.
The environmental concerns are not limited to California, notes the team, led by Jennifer Carah, an ecologist with The Nature Conservancy's office in San Francisco. Twenty-three states and at least three countries are testing the marijuana-liberalization waters to varying degrees.
Where environmental concerns have been raised, they often have centered on energy and water consumption, or carbon footprints for commercial-scale, indoor pot farms. The situation in northern California highlights the need to pay attention to the broader environmental effects of widespread cultivation as well, the team holds.
People have been concerned about the environmental effects of large growing sites for marijuana for years, Ms. Carah acknowledges. But over the last decade, and particularly within the past five years, these concerns have increased significantly, paralleling an increase in marijuana cultivation and California's worsening drought.
By some estimates, the Golden State produces 60 to 70 percent of the marijuana consumed in the United States. Estimates of the crop's value range from $11 billion to nearly $17 billion a year. California's next most-valuable commodity: milk and cheese, at $6.9 billion.
The epicenter for this activity falls within a tricounty area in northwestern California known as the Emerald Triangle. Well over 10,000 growing sites dot the region. The area also is home to two biodiversity jewels: Northern California Coastal Forests Terrestrial Ecoregion and the Pacific Mid-Coastal Freshwater Ecoregion.
Using satellite images, Scott Bauer has been analyzing cultivation activity in four study areas within the Emerald Triangle since 2009.
"In our study of watersheds, from 2009 to 2012 marijuana cultivation increased by 55 to 104 percent," says Mr. Bauer, a senior environmental scientist with California's Department of Fish and Wildlife, who gathers evidence of environmental crimes associated with marijuana cultivation.
So far this summer, he has visited 40 growing sites. "Every one of those is either new or bigger," he says, indicating that activity is still increasing.
"People call it the green rush," Carah adds. "The kinds of damage we see now are really similar to the kinds of damage associated with unregulated timber harvesting in the early to mid 1900s."
Bulldozed dirt roads connect patches of forest or oak woodlands that have been clear-cut to make way for marijuana plants – with the erosion that attends both changes to the landscape. Silt fouls streams and, in some cases, blocks them. The growing areas and the web-like networks of roads that connect them fragment habitats. Pesticides, herbicides, fertilizer, even diesel fuel contaminate some of the soil and water in areas where pot grows or grew.
A study published in 2014 revealed that 80 percent of dead Pacific fishers – weasel-like animals that live in the forests – found in northern California and the southern Sierra Nevada had been exposed to poisons typically used to kill wood rats in black-market marijuana fields.
When seen in satellite photos, individual growing areas in the Emerald Triangle, which embraces Humboldt, Trinity, and Mendocino counties, seem small. But they often are concentrated along mountain slopes whose streams are part of larger watersheds. These watersheds feed rivers and creeks that are home to salmon and trout species on state and federal "threatened" lists, as well as to other fresh-water creatures identified as "species of special concern."
Indeed, the impact of unregulated pot growing on water availability and quality is a key concern, says Bauer, a coauthor on the BioScience commentary. The growing season runs from June to October, when rain generally is scarce. During this time, surface water in streams and wetlands are the easiest sources of water to tap. Marijuana plants grown outdoors require twice the water during the growing season than do wine grapes, the Emerald Triangle's other major draw on irrigation water.
That's why the impact of unregulated pot growing on water availability and quality is such a key concern, Bauer says. Remote plantations, which include greenhouses, tend to draw water from fragile wetlands, in some cases draining them. They also could drain streams during the June-to-October growing season, when rain is scarce.
In an analysis Bauer and colleagues from the Department of Fish and Wildlife published in March in the journal PLOS One, the team reported that water needed to supply marijuana plantations at the height of the growing season exceeded the flow rate of streams the plantations used in three of the four watersheds the team studied.
As if to underscore the problem, a visit Wednesday to a growing site in northern Humboldt County, host to several thousand plants, revealed that streams flowing freely this past spring had been drained dry, Bauer says.
"The one place where they were diverting water, they were taking all of it," he says. "Basically they were taking the last of the water on the mountain."
Regulating marijuana plantations in ways designed to reducing environmental damage is complicated, notes Anne Short Gianotti, an assistant professor at Boston University whose research focuses on environmental governance.
One of the biggest impediments, she says, is the semi-legal nature of the activity – legal to varying extents in some states but a violation of federal law.
Some growers want to comply with existing regulations or take part in voluntary efforts, she continues. But many are reluctant to do so. Once they apply for permits to build roads or divert water, they put themselves on the regulatory map. This opens them to visits not only from state regulators with whom they are trying to cooperate but also from federal agents, who could use information from state permits to track them down.
Moreover, the line between marijuana grown for legal purposes at the state level and marijuana grown for the black market is less like a sharp boundary and more like a smudge, researchers have noted.
A voluntary certification program exists to support environmentally responsible marijuana cultivation, known as Clean Green Certified. But little demand exists for marijuana carrying that label.
"There isn't as much economic incentive to participate in this program as there is in organics," says Dr. Short Gianotti, another coauthor on the BioSciences commentary.
Last year, California Gov. Jerry Brown (D) earmarked $3.3 million to pay for regulation and enforcement of environmental laws related to growing marijuana, notes The Nature Conservancy's Carah. This year, several bills have been introduced in the state legislature that deal with the issue.
But more is needed, she says. A comprehensive effort to tighten regulations, beef up enforcement, and in particular to restore damaged landscapes would cost an estimated $120 million per year over the next five years.
"Three million dollars a year is a step in the right direction," she says. "But we still have a long way to go."
[Correction: This story has been updated to correct the estimated cost to fix damaged landscapes over the next five years.]