Once the planet was full of trees. They were tens and hundreds forests were lungs Earth, but the evolution of the industry and technological development of man has required more space, more wood for furniture, paper and fuel. Man cut with machines acres of forest, but not plant anything. Nature could not cope and failed, leaving the people with no good air. Oxygen concentration decreased more and more, and the man had to return to the technology that have destroyed the air. He built areas of life where we live to have under control the concentration of oxygen, nitrogen and carbon dioxide.
Brassy leaves fall from the trees while you do stunts on your bike.