The advantages of urban greenspace enhance the local eco-system while providing opportunities for humans, affecting health in many positive ways. Trees and plants generate life-giving oxygen; aid in the retention of ground and rain water amd remove toxins from the surrounding air. Trees can also make enough oxygen for one person and can absorb twenty pounds of air pollution every year. Under the shade of a canopy of trees things are reducing heat retention cooling down more quickly. Marcus Hiles explains that in a community with ample canopy coverage, air-conditioning requirements are lower. When a car was placed in the shade, it stayed fifty degrees cooler than one parked in the sun. In cities, parks and recreation for spaces must be created and maintained through human intervention and assistance.