Standing dead trees (often called snags) are common in our forests, and it’s hard to overstate just how vital a role they play in a healthy ecosystem. These gray ghosts provide food and shelter for a whole heap of forest critters; a total of 43 species of birds and mammals are specially adapted to nesting or denning inside tree cavities. But before a dead tree becomes a high-rise condo for a long list of species, it first undergoes a remarkable transformation. In fact, snags undergo a series of