Planting Shade Trees: Landscaping to Save Energy
Here's a thought: according to the U.S. Forest Service, fifty million shade trees planted in strategic, energy-saving locations could eliminate the need for seven 100-megawatt power plants.
That's a lot of megawatts. And a lot of trees. And while you are not likely planning to plant fifty million, planting as few as three trees, properly positioned, can save the average household from 15% to 35% annually in energy costs - that’s thousands of dollars you’ll save on air conditioning costs as the trees grow to provide abundant shade.
And summer is just around the corner.
How Trees Cool Your Home, Business, and Community
Trees have been used for hundreds of years to give us shade and cool our homes and businesses. With their two important cooling effects, trees help increase energy efficiency of homes and buildings and reduce energy costs.
- Trees cool the air by absorbing water through their roots and evaporating it through leaf pores. This process - called evapotranspiration - can result in reducing peak summer temperatures by 2° to 9°F.
- Trees provide shade that reduces the solar radiation that heats up our homes and businesses. Shaded walls may be 9° to 36°F cooler than unshaded surfaces. Cooler walls also decrease the amount of heat that permeates buildings, lowering the need for air conditioning. And cooler surface temperatures also reduce the amount of heat in the surrounding air, and, as a result, decrease the heat island effect.
What is the Heat-Island Effect?
Heat islands form in urban and suburban areas, which become warmer than the surrounding countryside, as natural land cover is replaced with roads, buildings, and parking lots. Reducing trees and vegetation also reduces their natural cooling effects, while tall buildings and narrow streets heat the air between them and reduce air flow. Heat from vehicles, factories, and air conditioners increases the effect.
Urban areas without adequate tree cover can become "heat islands," with significantly higher temperatures than the surrounding suburban and residential areas that have more abundant trees. Heat islands are typically 2° to 10°F warmer than nearby rural areas. These elevated temperatures can significantly impact communities by increasing peak energy demand, air conditioning costs, air pollution levels, and heat-related illness.
What to Plant, Where to Plant
Planting the right tree in the right place is the most important step in landscaping for energy conservation. Selecting trees that will effectively shade your home or business requires consideration of the size, shape, and density of the trees, and the location of the moving shadows that the trees will cast. Careful selection of trees will create the right amount of shade in the right areas to effectively help lower energy use.
Here are some important guidelines for planting trees to help conserve energy:
- To block solar heat in the summer, plant deciduous trees on the east and west sides of the building. In the winter, their bare branches allow sunshine to warm the house and windows.
- Plant shade trees over patios and driveways.
- Air conditioning units operating in the shade use 10% less energy. Plant shade trees or shrubs to shade your unit, but do not block the airflow.
- Plant deciduous trees with high, spreading crowns (like oak, linden, and walnut) to provide maximum summertime roof shading.
- Select species with lower crowns to provide shade from lower afternoon sun angles.
- Consider planting some slow-growing varieties. Although slow-growing trees may require many years of growth before they will shade your roof, they often have deeper roots and stronger branches, which can make them more drought resistant and less prone to breakage.
- Also plant shrubs, hedges, and climbing vines to help shade patios, driveways, and sidewalks.
The Benefits of Trees
Planting trees is a simple thing that everyone can do - today - and an effective way to reduce energy use and costs. According to the U.S. Department of Energy, a 6-foot to 8-foot deciduous tree planted near your home will begin shading your windows in the first year. Depending on the species and the home, you can expect the tree to shade your roof in 5-10 years.
And while you are enjoying a nice, cool home and lower energy bills during the summer, you can also enjoy the many other benefits trees provide.
- Trees add beauty and enjoyment to our physical surroundings. They create a positive psychological impact on peoples’ moods and emotions.
- Trees create a calming effect. In laboratory research, visual exposure to settings with trees produced significant recovery from stress within five minutes. Studies also show that hospital patients recover more quickly in rooms that offer a view of trees.
- Trees give off oxygen. One large tree can provide a day’s oxygen for up to four people.
- Trees clean our air. Trees absorb carbon dioxide and remove other common pollutants from the air, including nitrogen oxides, sulfur oxides, particulate matter, and ground-level ozone.
- Trees attract birds and other wildlife. Increased tree cover brings these natural elements into urban communities, enhancing the quality of life for residents.
- Trees improve water quality. Trees reduce storm water runoff and erosion, and they remove harmful chemicals from the soil to prevent them from running into streams and rivers.
- Trees increase property values. The sale price of a landscaped home is, on average, between five and 20 percent higher than a home without landscaping.
- Trees help reduce global warming. Trees absorb carbon dioxide, a leading greenhouse gas, from the atmosphere.
- Trees control noise pollution. Strategically placed belts of trees can help reduce traffic or airport noise.
- Trees build stronger neighborhoods and reduce crime. Trees increase relaxation, reduce aggression, and bring neighbors outdoors, creating additional interaction and less crime activity.
Older trees in cities and towns throughout America are already providing energy-saving benefits, thanks to the investment our community leaders made 10, 20, and 50 years ago. By planting the right trees in the right places, you can do more than reduce your energy costs each summer: properly planting trees around your home will help conserve energy - both for your family as well as the community. Neighborhood tree-planting and tree-care projects are an investment in the future.
For more information, check out arborday.org.
By Shari Aldrich, the Arbor Day Foundation
Arbor Day Foundation
Iowa State University Extension
U.S. Environmental Protection Agency
U.S. Department of Energy: Energy Efficiency and Renewable Energy
USDA Forest Service Center for Urban Forest Research.