Building an urban forest from scratch.

A military base becomes a living lab for a study of the cooling, humanizing power of trees.

THE TEMPERATURE was 107 degrees. Bob Skiera and his two companions mopped their faces as they trudged the shadeless sidewalks of a military base in the Arizona desert, passing row after row of cookie-cutter duplexes. Skiera noticed that the backyards were full of swing sets and Big Wheels, but not a single child was in sight, even though it was a Saturday.

"Zero kids. Zip," recalls Skiera. "I guess they were inside with the air conditioners cranked on high."

The Skiera coterie was an advance team from AMERICAN FORESTS preparing for a mass planting of 279 trees, each 10 feet tall, in a nearly treeless section of Davis-Monthan Air Force Base in Tucson. Twenty acres of the spartan military base were about to be transformed by construction of an urban forest. In a few years, the shade from those trees will lure children outdoors--even on the hottest Saturdays--to ride their Big Wheels.

For now, those trees are the stars in a large-scale research project by Cool Communities, a multi-player program coordinated by AMERICAN FORESTS to study the cooling power of trees.

The Tucson air base is the laboratory for this research project. The base will also serve as a real-life model for demonstrating that planting trees and converting building surfaces to light colors to reflect heat can greatly reduce air-conditioning bills.

The planting at the Davis-Monthan base is the largest of seven pilot projects that are setting the stage for a nationwide expansion of the program. The Clinton Administration has selected the two-year-old Cool Communities program for rollout to 250 cities and 100 federal facilities, including military bases, by the year 2005.

At Davis-Monthan and the other pilot projects--in Florida, Maryland, Texas, Georgia, Illinois, and Oklahoma--the research will build on previous studies conducted by the Environmental Protection Agency and Lawrence Berkeley Laboratory. These studies suggest that increasing tree cover and lightening wall and roof surfaces can reduce energy needs by as much as 50 percent.

A broad perception exists, however, that such estimates of environmental benefits are overstated. Surveys indicate that the public is skeptical when government agencies or utility companies make claims about potential savings. But the public is ready to be more trusting when nonprofit conservation groups take an active role in the research.

Awareness of this public attitude led to adoption of a cooperative approach coordinated by AMERICAN FORESTS in partnership with the U.S. Department of Energy, Environmental Protection Agency, Department of Defense, and Forest Service as federal players; National Association of State Foresters, representing state government; and Edison Electric Institute and American Association of Nurserymen, among others, as private partners.

EPA-sponsored studies and a guidebook have shown that a tree will cool the residence it shades and thus reduce energy consumption. What we don't know, however, is the impact of the tree's powers of shading and evapotranspiration on the house next door and the ones beyond. What are the collective benefits, how far do they reach, and what is the combined impact of a neighborhood full of trees?

The Davis-Monthan project is thus unique in that this will be the first time research will go beyond direct effects to measure the indirect impact on ambient temperatures and humidity, i.e., overall cooling by an urban forest canopy. These indirect effects will be measured in a real community where researchers can study energy usage in real-life situations--where kids leave doors and windows open and dogs tear in and out.

Selecting a community for testing energy savings is a challenge because controlling experimental variables is difficult in most neighborhoods. The houses often differ in size, style, age, or heat absorption, depending on whether surface colors are light or dark. Most importantly, the houses probably vary in energy demand, given that some owners will have beefed up their insulation and others will not.

But a military base does not suffer from the vagaries of a civilian community. The houses in Palo Verde, the 20-acre section selected for the study, are all three-bedroom duplexes (1,200 square feet) or four-bedroom duplexes (1,224 square feet). They were all built the same year and have the same amount of insulation. The roof shingles are all similar in color, and the walls are all pastel shades. Even the air-conditioner condensers were all replaced the same year and are the same model.

The similarities are more than just cosmetic. Residents have identical work schedules, so they spend a similar amount of time at home and hence have comparable energy needs.

Davis-Monthan thus comes as close as a neighborhood can come to being a laboratory. Baseline data collected there will be compared with measurements of the same variables taken five years from now.

The first step in gathering baseline information was to obtain aerial photos, which were then fed into a computer and digitized so that high-tech computer software could be used to calculate the existing tree canopy (less than 5 percent). The photos give researchers a "frozen frame" from which to evaluate the ecological baseline.

A follow-up set of aerial photographs will be taken in five years to determine changes in the community, including the increase in canopy. The computer program will help AMERICAN FORESTS staff evaluate the data to calculate the tree canopy now and at various times in the future. AMERICAN FORESTS estimates that the mature canopy at the Davis-Monthan test area will range from 25-30 percent.

Baseline data on local climate and energy use was compiled using an eight-page questionnaire, created by an advisory group. In five years, an identical questionnaire will track changes in this data as well.

In addition, scientists from the Forest Service and University of Arizona have installed weather stations for measuring temperature, humidity, and wind speeds. In three years, the trees will have grown enough to provide preliminary results.

A third set of baseline data is sociological. AMERICAN FORESTS commissioned surveys in six of the pilot communities to determine citizen attitudes toward trees and energy savings. Follow-up surveys in five years will determine whether the Cool Communities program has reduced the public's skepticism and changed behavior.

After collecting baseline information, AMERICAN FORESTS developed a tree-by-tree planting plan for Davis-Monthan indicating the best sites and the best species for each site.

Early on, a decision was made to install drip irrigation because it's the best way to establish a desert tree. The automatically operated system will ensure that, despite the turnover among residents that is typical of military bases, each tree will be able to establish a root system and grow on its own.

Irrigation will not only ensure proper establishment, it will also enable water usage to be monitored. Keeping tabs is an advantage in a desert city where humans sometimes view trees as water hogs, even though, once established, properly selected trees survive without irrigation and therefore use less water.

Irrigation will also permit controlled growth. The trees can be watered so that they grow fast enough to yield data within the experiment's timeframe. At the same time, overwatering can be avoided so that the crowns do not outpace root development. Maximizing longevity is as important as encouraging fast growth.

A critical task was selecting the species to plant. Bob Skiera, former city forester for Milwaukee, took on the challenging job of brokering agreement among local tree experts on a list of acceptable species.

"I did my homework," says Skiera. He started by collating six existing lists. One had been developed for a xeriscaping guidebook by Air Force landscape architect Bill Bushman. The second was a list of low-water-usage trees published by Trees for Tucson, a Global ReLeaf partner; the third, an inventory of native trees developed by the City of Tucson. The fourth list was published by the Arizona Native Plant Society, and the fifth compiled by the University of Arizona. The last one was a planting guide from Tucson Electric Power.

Skiera started with the objective of selecting a diversity of species to produce a hardy urban forest. That goal led to a preliminary selection of 13 species culled from the existing lists.

To evaluate his choices, Skiera gathered a panel of local authorities. They included a tree expert from the University of Arizona, the author of a book on local trees, a nursery owner, the city forester, a Forest Service scientist, a landscape architect, and a staffer from Trees for Tucson.

Skiera had used five criteria to develop his preliminary list. First, it was essential that a few species be deciduous (a rarity in the desert). Deciduous trees--those that grow and drop leaves--provide shade for windows in summer but permit solar heat gain in the winter.

The trees also had to be resistant to drought and diseases such as Texas root rot. Also, most desert species are armored, and the thorns--which can run three inches long--would be a hazard if planted where children play. Thornless species would be needed for high-use areas.

Finally, the trees should grow tall enough to shade the houses but not dominate the landscape. Skiera had come to realize that Tucson residents want their trees to fit in and not block views of the nearby mountains.

"The trees had to be not only environmentally compatible," he points out, "but also sociologically compatible."

The experts whittled the list down to eight species. Once the species were selected, the planting plan was finalized.

The next step was marking the actual sites, which takes us back to that hot Saturday when Skiera and his companions--AMERICAN FORESTS' Gary Moll and Rick Henkel, past president of the American Association of Nurserymen--trudged around ringing doorbells.

"I talked with maybe 65 families, and they all thought that what we were doing was a great idea even though they might not be at the base long enough to take advantage of the trees," recalls Skiera. "Most of them wanted us to give them an extra tree or two."

The plantings were completed in the fall of 1993. In some cases, Skiera found that the preferred planting sites were already occupied--by swing sets placed near the kitchen window where the mother could keep an eye on the kids.

"When we started planting, people would come out and ask what we were doing," Skiera recalls. "We would tell them that we wanted to put a tree where it could shade their window, but their swing set was in the way. They would say, 'Oh, no problem. We can move it.'"

The residents' eagerness to help might have been motivated by a desire to decrease the Air Force's energy bills. Or to take part in a nationally significant study of energy conservation.

They might have been motivated by an awareness that the trees will beautify a barren environment and humanize it by dividing the yards into defined living spaces. Some may have been thinking about attracting birds and wildlife.

But my guess is that they moved those swing sets because they saw that the trees are already tall enough to shade a barbecue--or lure their young couch potatoes outdoors to ride their Big Wheels.

TREES FOR A HOT PLACE

The eight species of trees planted at Davis-Monthan include:

Chilean mesquite Glandulosa mesquite Heritage oak Aleppo pine African sumac Chinese pastach Sweet acacia Blue palo verde.

TURNING BACK THE SUN

Planting trees to shade air conditioners and windows on the sunny side of houses is one way to save energy and make our communities more environmentally friendly. An additional step is to convert to the use of light colors on driveways, sidewalks, roads, and building surfaces--roofs and walls--to reflect heat-generating solar radiation.

Dark surfaces combined with a lack of shade create urban "heat islands." Unshaded blacktop pavement and dark roofs absorb the sun's heat during the day and then radiate it at night when urban areas should be cooling down. Turning back the sun--by increasing shade and heat-reflecting surfaces--could save the United States up to 50 billion kilowatt-hours of electricity annually, or enough to meet the energy needs of 500,000 people.

In the case of new construction, white or a pastel color can be selected for walls and roofing shingles. For existing buildings, however, it is logical and cost-effective to wait until the house needs repainting or the roof needs replacement.

With driveways and sidewalks, the opportunity exists--either during initial construction or when resurfacing--to use concrete or lighten asphalt by incorporating some kind of light-colored seal.

In many cases, the most practical surface to change is the roof. Personal aesthetic preferences tend to be a less intense factor with roofing materials than with house colors. In any case, changing either a roof or the house color is a voluntary way for the individual to make a difference in the environment. Education is the only way to encourage behavior change. To this end, an important component of Cool Communities is a regional program of workshops to increase public awareness.

Norah Davis, former managing editor of American Forests, writes on natural-resource issues from her home in Washington, DC.