A profound unraveling is underway in the American Southwest, happening across a thousand-mile arc from Santa Fe, New Mexico, to the central Sierra. In an unprecedented calamity, the most widely distributed, most iconic tree of the region—the beautiful ponderosa pine—is disappearing. So significant is this loss, both visually and ecologically, that it’s reasonably fair to say it may be triggering the first post-climate-change landscape in America.