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GARDENING : Urban Forestry Is at the Root of Improving Air


Resting under the shade of a tree is surely among life's great attractions: It is to that cool space we are drawn to catch our breath, collect our thoughts, enjoy the view, eat our lunch, sneak a nap.

Trees act as nature's air conditioner, cooling and cleaning the air. It is why a community, a home, a yard shaded by trees is so inviting. It is why organizations such as the Tree Society of Orange County and ReLeaf Anaheim are actively planting trees on public property, and encouraging people to do the same at their dwellings.

Planting a tree is a way for individuals to do something positive for the overall environment and for their own home, says Genni Cross, the Irvine-based director of California ReLeaf, an organization dedicated to increasing the tree population of urban California.

"Trees cool buildings and the surrounding environment by both shading dwellings and releasing water into the atmosphere in a process called evapotranspiration," says Tom Larsen, a certified arborist who has written and implemented a shade tree program for Edison and the City of Anaheim.

Larsen is president of Integrated Urban Forestry Inc. and of the Tree Society of Orange County.

Evapotranspiration simply means that plants draw water from the ground through their roots; use what's needed for growth and moderating their own temperatures; and release the excess moisture into the air.

"The process acts like a swamp cooler. Wind blows across the trees and as the leaves release moisture, the air is cooled," Larsen said.

Research reveals that trees transpire up to 100 gallons of water in a day. In a hot dry climate like Southern California, this cooling effect is similar to five air conditioners running for 20 hours.

Urban forestry has become an important issue in the United States as well as worldwide. Last year, the Environmental Protection Agency issued a publication, "Cooling Our Communities: A Guidebook on Tree Planting And Light-Colored Surfacing," in which it emphasized the urgency of planting trees to cool a rapidly heating world.

It states that summer temperatures in urban areas are now typically 2 to 8 degrees Fahrenheit higher than in their rural surroundings, a phenomenon called "the urban heat island effect." Orange County is not exempt from this phenomenon.

"Anytime you remove vegetation and add concrete, roads, cars and buildings, you have an increase in temperature," Cross said.

One simple and very effective solution is to plant more trees. Trees do a better job of shading buildings than Venetian blinds or window coatings. Studies show that homeowners with adequately shaded houses reduce summer air conditioning costs from 15% to 35%.

There are other environmental benefits, too. As people use less air conditioning, utility companies use less fossil fuel, thereby reducing air pollution, as well as less water for generating electricity.

Additionally, said Larsen, trees act as Nature's dust mops because they filter air pollutants. "Studies show one tree can absorb 26 pounds of carbon dioxide, the amount produced by a car driven 11,000 miles in a year," he said

If you're convinced that your property will benefit from the addition of one or more trees, don't rush out and buy one without considering the factors that determine which ones are right for your situation.

"More than 1,000 species of trees can grow in Orange County landscapes," said Alden Kelley of Fullerton. Kelley is a consulting arborist and a director of the Tree Society of Orange County.

"Homeowners need to evaluate their specific climate zone, whether they want to plant trees in a lawn or garden beds, do they want fruit, what is the overhead clearance and soil type," Kelley said.

The arbor experts all agree that for trees to shade a house effectively, they should be located no farther than 20 feet from the dwelling. This means it's crucial to select trees that are deep-rooted. Otherwise, invasive roots will seek out the water pipes and also can cause serious problems to foundations or patios.

Shade trees should also be planted on western, southwestern, or eastern exposures to block the hot rays of hot summer and early fall. Deciduous trees are recommended since the leaf drop permits the cooler winter rays to enter the structure without overheating it.

Many people like ornamental trees with either flowers or colorful foliage. But you have to consider how much leaf, flower, fruit or seedpod drop you're willing to tolerate or clean.

Fruit trees can be used in landscapes, but they're high maintenance trees requiring annual pruning, feeding, insect control and crop picking.

Water needs are also a crucial factor.

Many trees require deep, infrequent irrigation and are poor candidates for planting in lawns. But there are some that are compatible with turf grass.

The daunting selection of varieties can be reduced to the ones best-suited for your needs by considering the above requirements.

Made in the Shade

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