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.