You may not live in a forest, but you need trees in order to live. People and animals depend on trees and plants for oxygen. As you breathe in, your body uses oxygen. As you breathe out, it gives off carbon dioxide. Trees do just the opposite.
Trees also help cool the Earth.
Trees give off moisture. More moisture in the air means more rain and all living things need water. Trees cool the air by shading and through water evaporation. They act like huge pumps to cycle water up from the soil back into the air. The 200,000 leaves on a healthy 100 foot tree can take 11,000 gallons of water from the soil and breathe it into the air in a single growing season.