The importance of trees cannot be overstated. Sure they can be cut down and used as wood, which has been important throughout history. But it's likely that if not for trees, human life on earth would not even be possible--and that's got nothing to do with lumber! Scientists believe trees are the largest single source of breathable oxygen in the atmosphere. They're also a major source of food and medicine. Finally, trees contribute aesthetically both indoors and out and help to produce lower stress environments