The Amazon might not have a ‘tipping point.’ But it’s still in trouble

The shore of a sea of nearly 400 billion trees winds through the central Brazilian state of Mato Grosso. Here, the Amazon rainforest rubs up against the Cerrado, the world’s largest savanna.

The two are distinct worlds — one a wet and verdant jungle, the other relatively dry and blanketed in wild grasses, shrubs and small trees. But no clear line demarcates the Amazon and the Cerrado. Instead, there’s a messy transition zone, a continuum of vegetation that grows taller toward the rainforest. Over thousands of years, the boundary ebbs and flows, driven by natural fluctuations in climate.

“But in this formula is a new element,” says ecologist Beatriz Marimon of Mato Grosso State University in Nova Xavantina. Humans, with their ambitions to domesticate the land, she says.

About half a century ago, throngs of people started streaming into the region along new highways, clearing forest for farmland and cattle ranches, she says. Fifty years is a blink in the life span of a forest nearly as old as the dinosaurs, but it’s plenty of time for humans to…