Three years ago, beavers returned to an Aspen-area testing ground for regenerative agriculture. What’s happened since has been nothing short of transformative, according to Eden Vardy, who started The Farm Collaborative in 2008 with the ambitious goal of finding solutions to climate change. “Everything has transformed,” Vardy said. “There’s been just so much new growth in the riparian area. We’re starting to see predatory birds explore; I’ve se…