Trees reduce runoff by breaking rainfall, thus allowing the water to flow down the trunk and into the earth below the tree. This prevents stormwater from carrying pollutants to the ocean. When mulched, trees act like sponges that filter this water naturally and use it to recharge groundwater supplies. On hillsides or stream slopes, trees slow runoff and hold soil in place. Skin cancer is the most common form of cancer in the United States. Trees reduce UV-B exposure by about 50 percent, thus providing protection to children on school campuses and playgrounds, where children spend hours outdoors. Studies have shown that patients with views of trees out their windows heal faster and with fewer complications. Children with ADHD show fewer symptoms when they have access to nature. Exposure to trees and nature aids concentration by reducing mental fatigue. An apple tree can yield up to 15–20 bushels of fruit per year and can be planted on the tiniest urban lot. Aside from providing fruit for humans, trees provide food for birds and wildlife. Excess carbon dioxide (CO2) is building up in our atmosphere, contributing to climate change. Trees absorb CO2, removing and storing the carbon while releasing oxygen back into the air. In one year, an acre of mature trees absorbs the same amount of CO2 produced when you drive your car 26,000 miles. Trees absorb odors and pollutant uses (nitrogen oxides, ammonia, sulfur dioxide and ozone) islander particulates out of the air by trapping them on their leaves and bark. In one year, an acre of mature trees can provide enough oxygen for 18 people. Average temperatures in Los Angeles have risen 6 °F in the last 50 years as tree coverage has declined and the number of heat-absorbing roads and buildings has increased. Trees cool the city by up to 10 °F, by shading our homes and streets, breaking up urban “heat islands” and releasing water vapor into the air through their leaves. Three trees placed strategically around a single-family home can cut summer air conditioning needs by up to 50 percent. By reducing the energy demand for cooling our houses, we reduce carbon dioxide and other pollution emissions from power plants.
Shade from trees slows water evaporation from thirsty lawns. Most newly planted trees need only fifteen gallons of water a week. As trees transpire, they increase atmospheric moisture. Trees reduce runoff by breaking rainfall, thus allowing the water to flow down the trunk and into the earth below the tree. This prevents stormwater from carrying pollutants to the ocean. When mulched, trees act like sponges that filter this water naturally and use it to recharge groundwater supplies. On hillsides or stream slopes, trees slow runoff and hold soil in place. Skin cancer is the most common form of cancer in the United States. Trees reduce UV-B exposure by about 50 percent, thus providing protection to children on school campuses and playgrounds, where children spend hours outdoors.
A tree’s root system is responsible for nutrient and water absorption, utilizing roots as sensors to detect water-deficit conditions and send signals to shoots above ground. Drought-tolerant native species have water-seeking roots that penetrate deep into the soil to tap into local groundwater to draw to the surface. Healthy soils are critical to the establishment of trees. Utilizing structured soils within the urban planning process allows for adequate root growth support for soil and tree health.
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