Conversations about the effects of legalizing cannabis frequently focus on a few key issues: economic opportunity, social justice, the potential for new medical treatments, and other health benefits. What’s less talked about, however, is how cannabis legalization impacts the environment. Researchers have long documented the ways unchecked outdoor cannabis cultivation can strain resources and negatively impact the environment. And data from the U.S. Department of Justice shows that a significant amount of illegally produced cannabis is grown on federal lands— especially, national forests.

But what if legalization was making a difference? That’s exactly the question a new, first-of-its-kind study set out to answer. Do cannabis-related policies have any effect on illicit grow operations in U.S. national forests? The answer appears to be that yes, legalization does impact illegal grows. In fact, it reduces them significantly.

Expanding Legalization Reduces Illicit Grows in National Forests by a Fifth or More, Study Concludes

As the legal cannabis industry in the United States expands, demand for cannabis products is growing with it. But in the U.S. market, supply and demand have yet to find their equilibrium. So despite the major changes in the production and consumption of legal cannabis over the past decade, the unregulated, illicit market still dominates. As recently as 2018, experts estimated that legal sales accounted for over $10 billion of the $50 billion in total cannabis sales that year. Put simply, the illicit marijuana market isn’t going anywhere, at least in the short term.

Of course, supplying that market requires a significant number of illicit grow operations. And based on data about law enforcement seizures of outdoor-grown plants, national forests appear to be prime real estate for unlicensed cultivators. Illicit grows in Oregon, Colorado and California feed the bulk of the illegal market’s supply. National forests cover 24 percent of land in Oregon and 21 percent in Colorado. California has more national forests, 20, than any other state. Not coincidentally, illicit grows are highly prevalent in national forests in those states (and other legal cannabis states) despite their shifts toward regulated commercial production.

Even in an economic environment that continues to incentivize illicit cultivation, however, legalization is cutting down on the number of grows in national forests. “Recreational cannabis legalization is associated with decreased reports of illegal grow operations on national forests,” according to “Cannabis legalization by states reduces illegal growing on US national forests,” a study just published in Ecological Economics. And that’s good news, not just for the legal industry, but for the flora and fauna of America’s forests.

Two Ways to Reduce Illicit Grows in National Forests: Legalization or Incarceration

There’s lots of data out there documenting the scale and scope of illicit cannabis grown in U.S. national forests. But there has been no published empirical research on how cannabis policy changes and law enforcement efforts are affecting illicit cultivation.

To address that gap, USDA Forest Service researchers gathered data on the number of reported grow sites in 111 national forests between 2004 and 2016. Then, they analyzed that data alongside changes in state cannabis laws. Researchers also used their dataset to run simulations allowing them test how different policy scenarios would impact grows in national forests. So in addition to testing how recreational legalization impacted reported grows, researchers also simulated changes to cannabis tax codes and even changes to law enforcement. Here’s what they found.

In the first place, recreational legalization significantly lowered the number of illicit grows reported on national forests.

Likewise, in a simulated elimination of legalization in all states, the study estimated illicit grows would increase by double digit percentages. Conversely, simulated expansion of legalization would reduce growing on national forests by a fifth or more, researchers found. Moreover, most of that reduction would happen in California. Going further and simulating a nationwide legalization of cannabis, the study estimated that illicit national forest grows could be cut in half and eventually eliminated.

But researches also ran tests from the opposite direction. Instead of legalization, they simulated increases to law enforcement presence. And while they found that increasing law enforcement would also reduce reported illicit grows, the gains were significantly less compared to legalization. For example, if law enforcement budgets and officer counts doubled from their current numbers, illicit national forest grows would decrease by 10 percent, at most.

Cannabis Taxes Contribute to Illicit Grows in National Forests

Based on their statistical analysis, the authors of the study show that legalization would have a much more positive effect on reducing illicit grows than a massive uptick in law enforcement expenditures. “Arguably, our models hint that outright, national recreational cannabis legalization would be one means by which illegal grows on national forests could be made to disappear.”

But separate from policy changes and better-calibrated supply and demand, researchers also tested how cannabis taxes are impacting illicit grows in national forests. And they found that taxes are actually contributing to those grows. “The imposition of taxes on legal cannabis sales […] appears to make illegal cannabis growing somewhat more frequent on national forests,” the study found. In other words, as long as the after-tax price for legal cannabis is higher than illicit products, taxing cannabis will encourage illicit cultivation.

Cannabis Legalization Can Protect National Forests

The study’s findings are significant for a number of reasons. But legalization’s potential to protect national forests is a key one. The unregulated use of pesticides and fertilizers, clearcutting, terracing and the poaching of wildlife by grow site workers create real and lasting environmental damage. So reducing illicit forest grows is a win not only for the environment. It’s also a win for everyone who visits and manages and ultimately enjoys the forests.