As Amazon urbanizes, rural fires burn unchecked

Earth Institute at Columbia University: Over past decades, many areas of the forested Amazon basin have become a patchwork of farms, pastures and second-growth forest as people have moved in and cleared land--but now many are moving out, in search of economic opportunities in newly booming Amazonian cities. The resulting depopulation of rural areas, along with spreading road networks and increased drought are causing more and bigger fires to ravage vast stretches, say researchers in a new study. The study, focusing on the Peruvian Amazon, is the latest to suggest that land-use changes and other factors, including possibly climate change, are driving increasingly destructive wildfires in many parts of the earth. An interdisciplinary team at Columbia University's Earth Institute will publish the paper this week in the Proceedings of the National Academy of Sciences.

Nearly all fires in the Peruvian Amazon are set by humans seeking to burn woody vegetation off pastures, clear fallow land for planting, and release nutrients back into the soil—millennia-old methods used in many parts of the world. So-called slash-and-burn agriculture got a bad name in recent decades when fast-growing numbers of tropical ranchers and farmers deforested vast areas with fire, leading to massive soil erosion and releases of carbon. With many now abandoning land or working it only part time in favor of city jobs, some scientists started thinking this might lead to fewer fires. But the study shows the opposite: with fewer people around to control fires, and flammable small trees and grasses quickly taking over uncultivated plots, more blazes are spreading out of control and burning off bigger areas--not only forests but farms, fruit plantations, homes and villages.

"Farmers are often blamed for deforestation and environmental destruction, but they are fairly sophisticated in managing fire—they plan when, how and where to burn the land," said lead author María Uriarte, a forest ecologist in Columbia's Department of Ecology, Evolution and Environmental Biology. "However, when you have more fallow land and fewer people around to work at control, that combination generates these big fires."...

In this NASA image, intact forest is deep green, while cleared areas are tan (bare ground) or light green (crops, pasture, or occasionally, second-growth forest). The fish bone pattern of small clearings along new roads is the beginning of one of the common deforestation trajectories in the Amazon. The smoke is from slash-and-burn farming