Trees function as a natural recycling machine. Tree leaf surfaces take in moisture from the air (carbon dioxide) and heat from the sun to make food, a process called photosynthesis. This process, translated to a homeowner, means improved air quality around the home. Not only do trees absorb carbon dioxide and provide oxygen, but the presence of trees in your landscape is like a natural air conditioner.

Heat from hot air passing over and under leaf surfaces is partially absorbed by evaporation of surface moisture. The process cools the air that surrounds the leaves and lowers air temperatures by as much as 9 degrees Fahrenheit. The more leaf surface in an area, the cooler the surrounding air temperatures.

Planting trees on your property can also save dollars. Proper placement of trees around your home or business landscape can reduce cooling costs by 30 percent or more. Plant trees to shade west-facing walls and windows to avoid heat buildup from the afternoon sunshine. Tall trees strategically placed in the landscape eventually will shade the roof from midday heat.

Trees should be planted no closer than 15 feet from the foundation of a house to avoid damage from root systems. Home gardens located close to power lines should not grow trees or shrubs that will reach higher than 30 feet tall at maturity. You don't want your shade trees to interfere with safe, reliable electrical service.

To celebrate Arbor Day, Hawaiian Electric Co., along with its partners, gives away native and introduced trees and shrubs at various sites around the Islands. Kaua'i, O'ahu and Maui will be celebrating tomorrow. The Big Island celebrated a week earlier with more than 500 trees. Visit www.arbordayhawaii.org to find locations closest to you.

To find more information about trees from the University of Hawai'i College of Tropical Agriculture and Human Resources, visit the "Landscape" section on our free publications Web site, www.ctahr.hawaii.edu/ctahr2001/PIO/FreePubs.asp.

Happy Arbor Day, Hawai'i!

Jayme Grzebik is an urban horticulturist with the University of Hawai'i College of Tropical Agriculture and Human Resources Cooperative Extension Service. Reach her at grzebik@hawaii.edu.