The easiest way to understand the value of trees is to consider a landscape without them. Life would be hotter, drier and noisier, Hawai'i's tropical views bleaker and browner, and the air you breathe more polluted.

Without trees, the Islands would erode, the trade winds blowing surface soil into the sea. Kaulunani, the state's urban and community forestry program, says trees are vital because they "literally hold our island state together."

"Trees have a lot of benefits," says Jackie Ralya, a certified arborist who serves as technical/volunteer coordinator for Kaulunani. "They clean the atmosphere. They sequester carbon. They provide shade."

To help promote urban forests, Kaulunani, public utilities, nurseries and conservation groups are joining forces on Arbor Day to give away 6,700 trees across the state. A variety will be available at various locations Nov. 7: flowering trees, fruit trees, shade trees, native plants, even patio plants.

Certified arborists will be on hand to help people decide what type of tree is best for their home and offer advice on how to grow it.

Arbor Day has been in the Islands since 1905 when the governor urged children to plant trees and shrubs on the grounds of public schools. Most states on the Mainland celebrate it in April, but in Hawai'i, Arbor Day is always in November.

Hawaiian Electric Co. has supported tree giveaways on O'ahu since 1993 because well-placed trees are not only better for the environment but they help the consumer, too, said HECO spokeswoman Janet Crawford.

"Strategic placement of trees and shrubs along the sunny sides of a house will help cool the home, thereby reducing the use of electricity for air conditioning," she says. "A well-planned landscape can reduce an unshaded home's summer air conditioning costs by 15 percent to 50 percent."

That shade may be one of a tree's most potent effects — and not just at home, Ralya says.

"Trees, when they shade a parking lot, especially if it is asphalt, reduce the noxious fumes that come out of it," she says. "There are fumes that come out of it we don't even see or smell."

And of course, a shaded parking lot is valuable real estate.

"If you go to a shopping mall somewhere, where is everyone looking for a parking space?" she says. "Under the tree."

The reasons people come to the Arbor Day giveaways are as varied as the trees they take home. Each tree has a worth often measured with personal emotion or family nostalgia.

"People who are raised with them feel like a fish out of water when they are not around," Ralya says. "Some people come because they had one when they were growing up. Some want a tree for a special occasion, to commemorate a birth or a death."