Eight thousand years ago, when humans played only bit parts in the world ecosystem, trees covered two-fifths of the land. Since then, humans have grown in number while thinning and shaving the forests to cook, keep warm, grow crops, plank ships, frame houses, and make paper. Fires, saws, and axes have cleared about half of the original forestland, and some analysts warn that within decades, the remaining natural forests will disappear altogether. But forests matter. A good deal of the planet's biological diversity lives in forests (mostly in the tropics), and this diversity diminishes as trees fall. Healthy forests protect watersheds and generate clean drinking water; they remove carbon dioxide (a greenhouse gas that traps heat in the atmosphere) from the air and thus help maintain the climate. Forests count?not just for their ecological and industrial services but also for the sake of order and beauty. Fortunately, the twentieth century witnessed the start of a "Great Restoration" of the world's forests. Efficient farmers and foresters are learning to spare forestland by growing more food and fiber in ever-smaller areas. Meanwhile, increased use of metals, plastics, and electricity has eased the need for timber. And recycling has cut the amount of virgin wood pulped into paper. Although the size and wealth of the human population has shot up, the area of farm and forestland