Trees conserve energy. 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.
The relationship between trees and air pollution is a complicated one. Particulate matter suspended in polluted air tends to settle onto leaves, and certain gases including nitrous dioxide (NO2) are absorbed by leaves’ stomata, filtering the air and reducing pollution levels slightly. But trees and other vegetation also restrict airflow in their immediate vicinity, preventing pollution from being diluted by currents of cleaner air. In particular, tall trees with thick canopies planted alongside busy roads can act like a roof, trapping pockets of polluted air at ground level. To reliably improve air quality, city planners need to give careful consideration to how trees are placed.
- Save energy and money. Energy savings come from shading buildings, lowering ambient air temperatures, and reducing wind speed. Trees and other vegetation can lower air temperatures 5 °F compared with outside the tree-covered area. One well-placed large tree provides average savings of $31 in home heating costs each year.
- Increase property values. Research comparing sales prices of residential properties suggests that people are willing to pay 3 to 7 percent more for properties with many trees versus properties with few or no trees.
- Reduce storm water runoff. Leaves and branches temporarily hold rain on their surfaces. This reduces runoff volumes and slows soil erosion. Tree roots help rain soak into the soil and increase total amount of rain that the soil can absorb.
- Improve air quality. Leaves intercept and hold small particles on their surfaces–like dust, ash, pollen, and smoke—and absorb gaseous air pollution. Ground-level ozone formation is reduced because air temperatures in tree-filled areas are cooler.
- Reduce atmospheric CO2. Trees directly sequester CO2 in their stems and leaves while they grow. Trees near buildings can reduce the demand for heating and air conditioning, thereby reducing emissions associated with power production.
- Healthier communities. Tree-filled neighborhoods report lower levels of domestic violence, are safer and more sociable, reduce stress of body and mind, decrease need for medication, and speed recovery times.