Thousands of square miles of tropical forest have been chopped down to grow coca plants, whose leaves supply the world with cocaine. But the drug's environmental impact doesn't stop there.
Areas that surround coca plantations suffer particularly high levels of deforestation, too, found the first study to quantify how coca is reshaping landscapes in Colombia.
But there may be a bright side. In some parts of the country, national parks seemed to establish a buffer zone that reduced forest felling.
The relationships between coca plantations and deforestation are complex, and simply creating parks probably won't stop new coca fields from popping up. But the findings might offer insights into ways to intervene that would target both issues.
"I like the positive message of feeling like protected areas are really working at some level," said Liliana Davalos, a conservation biologist at SUNY Stony Brook. "But we can't just say that we're going to put parks all around and suddenly people are not going to plant coca."
"There are 60,000 families that grow coca in Colombia, and this is a family enterprise," she added. "If we had an easy fix for this, we would have fixed it."
Davalos started studying the connection between coca and deforestation in Colombia more than a decade ago. Along with Peru and Bolivia, Colombia is one of just three countries that produce coca leaves for the world's cocaine market. And it out-produces the other two.
At first, scientists thought that coca might actually help reduce or stabilize clear-cutting because it is such an efficient crop. Compared to a root like cassava, which requires a lot of space and effort to harvest but brings in a relatively small amount of money, coca is valuable for its dense leaf cover, and it fetches high prices. That means that coca farmers can pack a lot of value into a little space.
By the 1990s, though, studies started to suggest that, instead of slowing deforestation, coca was actually speeding it up. According to some estimates, up to four hectares of forest were cut down for every hectare of coca planted. Davalos heard those numbers, but she could not track down their source.
So for the new study, she and colleagues analyzed satellite images of Colombia that allowed them to distinguish between coca plantations and other types of land cover. They also studied aerial photographs taken during routine censuses of illegal crops by the United Nations Office on Drugs and Crime. The images covered a five-year period, from 2002 to 2007.
Over that time, the researchers reported in the journal Environmental Science & Technology, forest cover dropped from 56 percent to 46 percent in the Central region of Colombia, and from 82 percent to 78 percent in the South. The North lost nearly 5 percent of its forests each year.
Coca accounts for just a small percentage of total deforestation rates, Davalos said, but the crop threatens trees beyond the plantations themselves. Areas that are closest to coca plantations, the study found, suffer disproportionate rates of deforestation, even after taking into account the location of roads, cities, rivers, mountains and other factors that affect how accessible those areas are.
"The closer you are to coca, the more deforestation you have," Davalos said. "Our working hypothesis is that there is all this economic activity when new coca cultivation happens, and this economic activity leads to more deforestation."
The hopeful news was that deforestation rates were lower within established national parks than in comparable areas that were not officially protected. Davalos hopes that surveys and conversations with coca-growers might help explain why.
"A lot of people and scientists believe that parks really don't make much of a difference, especially when they are big and unmanned, like many of these are," she said.
"Our results were so surprising, we had one reviewer write to us and say those parks have this effect just because they're remote," she added. "We wrote back and said we took that into account."
Still, parks are probably not a panacea, said Luis Solórzano, an ecologist at the Gordon and Betty Moore Foundation in San Francisco. Often, he said, farmers who grow illegal drugs flock to parks because they seem like safe havens, offering protection against fumigation and other measures that are meant to destroy their fields.
Beyond the landscape factors considered in this study, he added, there are all sorts of socioeconomic and political issues that influence the growth and spread of coca plantations.
Nevertheless, the new work is a solid step toward finding ways to understand and combat both deforestation and illegal drug crops. Knowing how the two are related might help experts develop better law-enforcement strategies or new incentives for other types of land use.
"People usually walk away from these kinds of analyses because they are politically charged, and it's difficult to be objective," Solórzano said. By turning data into analysis, he said, the findings now have a chance to inform policy decisions.