OHIO-Kendra McSweeney knew that something was off. When the geographer at The Ohio State University in Columbus traveled to Honduras’s La Mosquitia region in 2011 to study its indigenous communities, she saw changes to the once lushly forested landscape that shocked her: huge, indiscriminate clearings in the middle of nowhere.

When she asked locals what was going on, they insisted on a sole culprit. “Los narcos.” Drug smugglers who had moved into the region in the mid-2000s—right around the time Mexico’s war on drugs intensified, and almost a decade after McSweeney herself had lived in eastern Honduras. Traffickers in the region had to figure out a way to funnel their money into the legal economy, and land clearing—in the form of cattle ranching, agro-industrial plantations, and timber extraction—was the preferred way to do it. McSweeney wanted to know more. So she and her colleagues decided to see whether they could match deforestation in six countries—Guatemala, El Salvador, Honduras, Nicaragua, Costa Rica, and Panama—to increases in drug trafficking from 2001 to 2013.

Connecting the dots was no easy task. It took them years to get access to databases on drug flows from the office of the U.S. “drug czar.” Forest loss data came from the University of Maryland’s Global Forest Change website. In the end, they found links in just three countries: Guatemala, Honduras, and Nicaragua.

Then, the researchers had to figure out just how much forest was being lost to trafficking. They knew that other factors fueled forest loss—in particular, land cleared by local farmers. But those losses were small, and they often occurred near main roads or in heavily populated areas. In contrast, the team anticipated that land lost to drug traffickers would be characterized by unusually large, remote, and rapid forest clearing. “[Narcos] want to move large sums of money, so you’re going to see big things happen: larger areas of deforestation, faster rates, and patches in zones that are isolated,” says Steven Sesnie, a spatial ecologist from the U.S. Fish and Wildlife Service in Albuquerque, New Mexico, who wrote a paper based on the data.

The team used 15 metrics, including the size and speed of the deforestation, to build a model that could distinguish patches of narco-deforestation from other types of forest loss. Their findings suggest that cocaine trafficking accounts for between 15% and 30% of annual forest loss in Honduras, Guatemala, and Nicaragua over the past decade, they report in Environmental Research Letters.

“We’re seeing areas with clandestine airstrips where a hundred hectares were cut in a year—it’s not some campesino out there with a hatchet,” Sesnie says. “To do that kind of clearing, you need gas, you need chainsaws, you need people. This is not subsistence deforestation.”

Those losses are bad news for indigenous communities, which are being displaced from their lands and losing the forests they’ve depended on for generations. Land cover changes driven by drug trafficking could also jeopardize international programs aimed at mitigating the effects of climate change, and they put almost 7% of the world’s biodiversity at risk.

That’s a particular problem, because much of the cleared land is inside natural protected areas, like the Río Plátano Biosphere Reserve in Honduras. But Marco Espinoza, regional manager of the reserve at the Honduran Institute of Forests Conservation (ICF) in Tegucigalpa, denies that the activity is related to smugglers. “We’ve found no [on-the-ground] data to say that we’re losing our forests to drug trafficking.” Yet ICF does have records showing a recent increase in cattle ranching inside the park.

Liliana Dávalos, an ecologist and evolutionary biologist at the State University of New York in Stony Brook, praises the work. “If drug trafficking is destroying forests, they should at least find a correlation, which they do.” But she also cautions that the researchers haven’t definitively linked the large forest losses to drug trafficking. They could also be coming from subsistence activities or from legal agriculture. To show causation, she says, the researchers would need to have land records, ownership transfer records, and other documents “that [are] very difficult to obtain,” especially if that activity is illegal.

Whether her team turns out to be right or wrong, McSweeney says the local drug trade—which accounts for some 90% of cocaine in the United States—is ravaging the region. “No one I know in Central America, including some drug traffickers, ever asked for the cocaine to be rerouted through them,” she says. “And yet everyday they pay the price for policies that are supposed to deal with that and fail to.”