Using a complex network of chemical signals, trees talk to each other and form alliances with fellow trees, even other species. In fact, whole forests exist as a kind of superorganism. And some trees are incredibly old. Did you know a single bristlecone pine can live up to 6,000 years? And the root mass of aspens might live 100,000 years? We explore the science and history of trees and talk with Richard Powers about his epic novel "The Overstory."