A stand of bear-clawed aspen trees on the San Francisco Peaks is the jumping off point for this month’s Canyon Commentary by Scott Thybony. It was the base camp of naturalist C. Hart Merriam in the late 1800’s. He was working on a groundbreaking project: studying the distribution patterns of plants and animals from the bottom of the Grand Canyon to the top of Humphrey’s Peak. Merriam called them ‘Life Zones’, the boundaries which reflect climate and ecological variation in mountains, deserts, rivers and canyons. They are still used today to assess how ecosystems respond to a changing climate.