Trees - gotta love ‘em. A walk in nature often relieves stress, but the benefits of forests go bigger than that. Photosynthesis in plants and especially trees acts to sequester the greenhouse gas carbon dioxide and produce healthful oxygen. In simplistic terms, it’s like breathing in one and out the other - while keeping the biosphere in balance. A recent study from the US Forest Service tries to quantify the health benefits of trees to humans and suggests they save us billions in healthcare costs and actually prevent about 850 deaths per year.
http://www.nrs.fs.fed.us/pubs/46102
http://www.slate.com/articles/health_and_science/science/2014/08/_trees_save_human_lives_studies_link_forest_with_upper_respiratory_illness.html