Think of the tree as the Earth’s breathing apparatus, an organ that helps regulate the planet’s atmosphere by exhaling fresh oxygen and inhaling the carbon that animals, decay, and civilization spew into it. The tree, under this new description, is not merely a member of the local forest ecosystem (where we’ve known for some time that it exerts considerable influence on the local life, soil, and even climate); it’s also a vital organ in a global system more intricate and interdependent than we ever realized. The Earth may not be a spaceship but an organism, and the trees may be its lungs.