Trees help conserve energy in several ways
August 26, 2011
One-quarter of the forest canopy in the United States is found in urban counties. The trees planted within our communities are known as our “community forest” or “urban forest.” These trees provide many benefits to us: They absorb and slow down stormwater, provide habitat, reduce air pollution, extend the life of pavement, modify the local climate, reduce noise pollution and provide aesthetic beauty, to name just a few.
One of the more measurable benefits trees provide is energy conservation. On a community-wide scale, shade trees help reduce the “heat-island” effect caused in urban centers by buildings and pavement, which absorb light energy and reflect it as heat.
Trees save energy in several ways. Tree leaves absorb light energy, thereby reducing reflected heat. They also absorb water through their roots and release moisture through the leaf surfaces by a process called evapotranspiration, which cools the air in much the same way our skin cools us through the process of sweating. Trees can reduce the surrounding air temperature by 9 degrees F and the temperature directly under the tree as much as 25 degrees F. It only takes a hot summer day in Nebraska to send us looking for the shade of a tree and its cooling benefits!
Trees can be strategically planted to take advantage of their energy-saving benefits. Properly placed trees can effectively reduce the solar heat absorbed by buildings and reduce cooling costs by 30 percent. Large-growing deciduous trees are the best choice for shading and cooling. During summer, their leaves block the sun and provide shade, yet during winter months the sun passes through the leafless canopy. Placing trees on the south and west sides of your house can take advantage of the shade they provide, especially if they are planted to shade the building during the hottest part of the day or early evening. Trees with a broad canopy will provide the greatest shading benefits. A combination of large and smaller trees can be used on the west side of a building to reduce the late afternoon heat and glare when the sun is at a lower angle.
Shading other impervious surfaces such as driveways, sidewalks, streets and parking lots also can significantly improve the microclimate around your home by reducing glare and reflected heat. And if your air conditioner is not located in a shaded area, consider planting a small tree or large shrub nearby to shade the unit. Shading an air conditioning unit can increase its efficiency by 10 percent.
For winter savings, consider planting evergreens and large shrubs on the north and northwest side of your property to slow winter winds and reduce heating costs. Remember to plant diversely, using more than one species in evergreen plantings. Adding large shrubs and even small and medium deciduous trees can improve diversity, interest and habitat.