Most of Kansas was once covered by an ocean of grass and wildflowers. But that diverse prairie biome is collapsing, partly because of our obsession with trees. Humans have unleashed an aggressive “Green Glacier” that’s swallowing the Great Plains, and for these ranchers, saving the environment means being a tree killer — not a tree hugger. (This episode comes to us from the new KCUR Studios podcast Up From Dust, reported by Celia Llopis-Jepsen and David Condos.)