FILADELFIA, Paraguay — The Chaco thorn forest, a domain with 118-degree temperatures so forbidding that Paraguayans call it their “green hell,” covers an expanse about the size of Poland. Hunter-gatherers still live in its vast mazes of quebracho trees.

But while the Chaco forest has remained hostile to most human endeavors for centuries, and jaguars, maned wolves and swarms of biting insects still inhabit its thickets, the region’s defiance may finally be coming to an end.

Huge tracts of the Chaco are being razed in a scramble into one of South America’s most remote corners by cattle ranchers from Brazil, Paraguay’s giant neighbor, and German-speaking Mennonites, descendants of colonists who arrived here nearly a century ago and work as farmers and ranchers.

Image Paraguay's Chaco forest lies in the Gran Chaco plain, which spans several nations. Credit... The New York Times

So much land is being bulldozed and so many trees are being burned that the sky sometimes turns “twilight gray” at daytime, said Lucas Bessire, an American anthropologist who works here. “One wakes with the taste of ashes and a thin film of white on the tongue,” he said.