Image: Pixabay

Cannabis—for obvious reasons—has always been a lucrative crop in the U.S. As state-by-state legal landscapes have warmed to the use and production of medical and recreational cannabis, the market has mushroomed, with an upcoming seismic shift in the national market associated with California’s start of recreational sale in January 2018. But there may be a dark side to this burgeoning crop.

The outdoor cannabis industry is having a serious impact on the environment. According to a new study, cannabis agriculture is driving a potent form of deforestation and habitat loss in California’s far northern temperate rainforests, and trouble may be ahead for more ecosystems as cannabis production is set to dramatically expand.

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To measure the influence of cannabis cultivation on forests, the research team, made up of scientists from UC Berkeley and Ithaca College, targeted the U.S.’s seat of cannabis production: California’s “Emerald Triangle,” three rugged and rural counties in the far northwestern corner of the state. Ecosystem changes in Humboldt, Mendocino, and Trinity counties are only expected to grow in step with the estimated three-fold swelling of the national cannabis market by 2020.

The team took forest change data from 2000 to 2013 from sixty-two randomly-selected watersheds within or bordering Humboldt County. By differentiating between impacts of timber harvesting and other sources (like cannabis cultivation), the researchers were able to determine how cannabis production has reduced forest cover and increased habitat “patchiness” at the county scale, as well as how its impact compares with that of timber extraction.

So, what was the toll of thirteen years of cannabis production on Humboldt County’s forests?

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High. Very high. The study’s results—published this month in the journal Frontiers in Ecology and the Environment—show that cannabis grows have contributed to deforestation and fragmentation in a manner that is decidedly distinct from timber harvests, and in some important measures, even more disruptive.

Google Earth timelapse of Humboldt county, a major cannabis-growing region of CA

Between 2000 and 2013, timber harvests were responsible for the vast majority of reductions in forest cover. The Emerald Triangle’s nearly impenetrable rainforests have been timber country for more than a century, and while logging has declined in recent years, the timber industry still dwarfs cannabis in the sheer scale of its physical influence.

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But cannabis production’s comparatively small total footprint—in this study, 6.2 square kilometers of impacted area versus the 207.7 square km occupied by timber harvests—belies the unique severity of its effect upon a given area of forest.

Timber is typically extracted in large chunks, from the forest edge inward, leaving the forest looking like a half-eaten pan of brownies, with big, geometric pieces missing. But cannabis cultivation usually takes place within the isolated interiors of forests, creating holes of disturbance that have highly irregular edges, making the forest look like Swiss cheese.

Cannabis cultivation is, in other words, more effective at reducing the “core area” of forest patches, the regions that are typically most pristine. The perforation pattern of cannabis cultivation also drastically expands forest peripheries, which are more open than shaded interior forests. As forest interiors are converted to edges, certain shade-loving plants and animals will find their surroundings difficult to endure.

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Both forms of forest degradation contribute to a growing global problem, but punching holes in the forest could have an especially disruptive impact.

The study’s findings add to a growing list of concerns over the long-term impacts of outdoor cannabis cultivation on forest ecosystems. These impacts include the crop’s outsize diversion of water resources, and environmental contamination with nasty, wildlife-killing poisons, worsened by clandestine grows operating in pristine habitats.

“This analysis has done a lot of work into drawing attention—in a useful way—to how these impacts can be important on a small, local scale,” Anne Short Gianotti, an assistant professor in Boston University’s Department of Earth and Environment who was not involved with the study, told Earther.

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By identifying environmental impacts of cannabis early in the industry’s explosive growth, the hope is that we can develop strategies now to mitigate ecosystem disruption. But are deforestation and fragmentation destined to spread at a similar rate in the current “green rush”? What does the future of cannabis production look like? In a word: uncertain. Other environmental threats, like climate change-driven heat and wildfires—like those that caused this fall’s particularly brutal round of fires in Northern California and the destruction of many outdoor cannabis crops—could complicate the issue. However, the changing legal environment for cannabis may still have the most immediate impact.

The legal landscape for cannabis in California and other states has changed considerably since 2013, and the period of time addressed by the deforestation study happened to exhibit the least amount of regulation and enforcement of cultivation ever. Is it possible that future cannabis production may not be so bad for the environment?

“What you saw from 2000 to 2013 was a growing social acceptance of cultivation, and a reduction of cultivator enforcement,” Short Gianotti said.

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“What we’re seeing now is a tremendous shift in the regulatory regime,” she continued. “Starting in 2017, if you’re going to be growing for the legal market in California, you’re going to need to be licensed by the state, and to be licensed by the state, you’re going to have to adhere to all of the environmental regulations associated with cannabis cultivation that are coming out of the Department of Agriculture.”

This means that growers for California’s legal market will have to show that they’re complying with various water and stream-crossing laws, for example.

While upcoming regulations show some promise for reigning in the environmental impact of the legal cannabis market, a huge cause for uncertainty is the presence of unlicensed operations producing for the black market. The success of the black market strategy may be largely dependent on the effectiveness of the regulations, says Short Gianotti.

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“It depends on how the regulations work, how easy it is for people to comply, and it depends on what enforcement of the regulations looks like. If it’s still easy to grow for the black market, I think a lot of people will grow for the black market.”

Outside factors, like the federal government’s recent shift in tone on state legal markets and those that participate in them, may also have a chilling effect on proper registration.

“That may make people a little more wary in participating and putting their name down on California’s licensing list,” Short Gianotti noted.

In the coming years, how growers fall into certain groups, either abiding by regulations or not, or dropping out of the industry altogether, may be key to cannabis’s overall environmental impact. Short Gianotti’s big concern looking forward? Mitigation of the impact of the black market, which can be partially done through the funding of environmental remediation and restoration programs following busts of illegal grow sites.

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The new deforestation and fragmentation study provides important details on what specific kinds of ecological impacts cannabis production has the potential to inflict. The findings may even be conservative, since illegal and covert cannabis production wasn’t included in the analysis. These forests’ futures may be partly at the whim of the maddening complexities of a not-quite-all-the-way legal commodity, and the relative strengths of legal and black market economies.

Jake Buehler is a Seattle area science writer with an adoration for the Tree of Life’s weird, wild, and unsung—follow him on Twitter or at his blog.