Grist: Over a decade ago, Gary Paul Nabhan moved to the plateau above the Grand Canyon to raise sheep. His timing was terrible: the beginning of one of the worst droughts on record. Some 80 percent of the pine trees around his new home, stressed by lack of water, succumbed to bark beetles. Every time he planted pastures, seedlings would push out of the earth and then wither. He was buying hay year-round, and paying dearly for it: Most of the springs that farmers relied on had gone dry, which meant that...