1. Trees improve air quality.
Trees are sometimes called the lungs of the Earth because they absorb pollutants through their leaves, trapping (or “sequestering”), and filtering contaminants in the air. Like all green plants, trees also produce oxygen through photosynthesis.
2. Trees improve water quality, and reduce flooding and erosion.
A tree’s leafy canopy catches precipitation before it reaches the ground, allowing some of it to gently drip and the rest to evaporate. Tree roots hold soil in place, reducing erosion. In these ways, trees lessen the force of storms and reduce the amount of runoff into sewers, streams, and rivers, improving water quality. One hundred mature trees can intercept about 100,000 gallons of rainfall per year.
3. Trees temper climate.
Trees lower air temperatures and humidity; they can also influence wind speed. Evaporation of water from trees, or transpiration, has a cooling effect. Cities develop “heat islands” because dark roofs and pavement absorb solar energy and radiate it back. Trees in parking lots have been shown to reduce asphalt temperatures by 36 degrees Fahrenheit and car interiors by up to 47 degrees Fahrenheit.
4. Trees conserve energy.
Three or more large trees strategically placed on sunny sides of a house shade it from the hot summer sun, reducing air-conditioning costs by as much as 30 percent. Deciduous trees are best for this use because they lose their leaves in winter, exposing the house to the warming winter sun, which lowers the energy needed to heat the house. Coniferous trees, because they retain their needles year-round, serve to reduce wind when placed on the north and northwest sides of a building, resulting in significantly lower winter heating costs.
