Armed with new information on the benefits of its urban trees, officials plan for a greener and more ecologically based future.

By Cheryl Kollin

CPS's Margarita Regalado (left) and Jenna Terrez take tree measurements.

San Antonio successfully straddles the line between historic relic and modern city. Tourists flock by the thousands to visit the Alamo, site of the decisive 1836 battle for Texas independence, or to stroll the banks of the San Antonio River along downtown's commercially successful River Walk. The city is ringed by springs, creeks, and rivers that arise from fault lines along one of the nation's largest limestone aquifers. The lush and varied vegetation that results attracts an array of migratory birds-and nature lovers.

These natural and manmade attractions have brought the city and its surrounding area impressive population growth and urban expansion. Now the greater San Antonio area is trying to meet the clean air, clean water, and energy needs of its many residents. Looking to improve environmental quality, the Alamo Forest Partnership turned to American Forests for assistance in evaluating the area's tree canopy cover. The Alamo Forest Partnership is a consortium of governmental and environmental organizations spearheaded by the city's publicly owned energy company, City Public Service (CPS).

What's A Community To Do?

To do that, American Forests conducted an Urban Ecosystem Analysis (UEA) of the greater San Antonio area. The analysis-which encompassed 788,000 acres of Bexar County, including the city of San Antonio-reevaluated the area's assets to include the environmental benefits provided by trees. The first phase determines landscape changes over time and assesses the impact those changes have had on air and water quality and on residential energy consumption.

Using satellite and aerial imagery along with Geographic Information Systems (GIS) technology, changes in land cover were measured between 1985 and 2001. In autumn, American Forests will complete the second phase of the study: creating a "green data layer" of information about urban forest ecology that the local community can use when making planning and management decisions.

Municipalities increasingly are turning to the analysis to make the powerful point that trees are an integral and money-saving part of the urban infrastructure. "Although we have acknowledged the benefits of tree cover in reducing air conditioning costs and improving air quality for some time," says Milton B. Lee, CPS's CEO and general manager, "prior to the study, we didn't have any scientific data that measured the extent of our tree canopy or the values it provided."

Ecological Issues

Bexar County, in south-central Texas, sits at the edge of a wave of urbanization spreading north into the Hill Country and onto the Edwards Aquifer Recharge Zone. The recharge zone, home to endangered bird and aquatic species, is where rain and streamwater enter San Antonio's primary source of drinking water, and it needs protection from pollution.

The greater San Antonio area has a particularly sensitive ecosystem built upon hard limestone bedrock and thin soils.The limestone's faults and sinkholes allow rainwater to drain directly into the aquifer without the benefit of passing through soil, which naturally filters out sediment and urban runoff pollutants. In addition, because its thin soil doesn't hold water well, the region is prone to flash flooding.

These problems have been exacerbated by increased urbanization and a corresponding decrease in tree cover. San Antonio's population has risen 22 percent in 10 years, making it the ninth largest city in the U.S.

In the first phase of the analysis American Forests determined that since 1985 San Antonio has lost 39 percent of its heavy tree cover (canopy coverage greater than 50 percent). The corresponding decrease in greater San Antonio's tree cover is 22 percent. Urbanized areas (less than 20 percent canopy cover) in greater San Antonio increased from 69 percent in 1985 to 77 percent in 2001.

The trends in moderate tree density (20 to 49 percent) show that as the area is developing, tree canopy is not being conserved. The region falls short of American Forests' recommended 25 to 30 percent overall tree canopy for the semi-arid southwestern part of the U.S. The greater San Antonio area and city currently have 20 percent and 14 percent heavy tree cover, respectively. This trend needs to be reversed to tap the natural improvement benefits trees can provide.

When population increases, the pressure on the surrounding natural resources increases as well. Reduced tree cover and an increase in impervious surface area take their toll on a region's air and water quality and energy consumption. The greater San Antonio area has lost 45,000 acres of heavy tree canopy (22 percent) over the last 15 years, costing its citizens $9 million a year for air pollution abatement and $146 million for stormwater management. They also lost $17.7 million in residential summer energy savings.

The San Antonio region exceeds U.S. Environmental Protection Agency air quality standards for ozone pollution levels, which could jeopardize federal funding for transportation projects. Officials there recently signed an Early Action Compact, which allows the region to create a local plan to bring down pollution levels and make its air healthy again. Signing the agreement were the EPA, the Texas Commission on Environmental Quality, and elected officials representing the San Antonio Metropolitan Statistical Area. Leading the effort to find reasonable ozone pollution control strategies is the Alamo Area Council of Governments' Air Improvement Resources Committee.

Additional tree planting and tree preservation could be an effective part of the overall solution. Trees have proven effective in helping to counter the effects of the urban heat island, a condition in which city centers with greater impervious surfaces and less tree canopy cover generate warmer temperatures and greater air pollution compared to their rural surroundings.

In the greater San Antonio area, trees currently remove 17.6 million pounds of pollutants, a benefit valued at $42 million. Trees lost between 1985 and 2001 would have removed an additional 3.7 million pounds of pollutants annually, a savings of approximately $9 million per year.

"As nonattainment status for air quality looms over San Antonio, we know it will be necessary to do more to improve air quality," says Scott Smith, director of CPS's environmental management department. "That's why CPS formed the Alamo Forest Partnership, so that we can collectively have a greater impact on air quality in San Antonio."

The members of the Alamo Forest Partnership, which sponsored the UEA, work together to preserve and plant trees. Along with City Public Service, partners include the Texas Forest Service, city of San Antonio, University of Texas at San Antonio, Alamo Area Council of Governments, San Antonio Water System, Texas Parks and Wildlife, U.S. Department of Defense, U.S. National Park Service, local nonprofits San Antonio Forest and San Antonio Trees, Bexar Audubon, and the Neighborhood Resource Center.

Other partners include Texas Department of Transportation; Keep San Antonio Beautiful, Inc.; Texas Master Naturalist; San Antonio River Authority; Bexar County Environmental Services; and the Open Space Advisory Board.

Ripples of Change

The study findings have sent promising ripples of change across the community. The UEA results got the attention of the Bexar County Commissioners and the support of San Antonio Mayor Ed Garza and some members of City Council, especially Councilwoman Bonnie Connor. Connor saw the report as a good source of scientific data for decision making, calling it very useful in preparing an upcoming city watershed management plan. Most dramatically, the UEA revitalized the need for San Antonio to finalize and pass a revised Tree Preservation Ordinance, a controversial process that had been intensively reviewed and negotiated for three years.

The Citizens' Tree Coalition, a collection of ecological organizations and neighborhood associations, used the UEA to show the importance of a tree ordinance. The revised ordinance recognizes the value of San Antonio's urban forest and provides greater protection of its desirable trees. A key provision for the protection of tree cover offers developers an incentive to use tree stand delineation, a holistic approach to documenting trees by their canopy cover, roots, and associated growing space rather than the more narrowly defined tree stem count.

This method for documenting tree-save areas allows developers to reduce "unanticipated expenses and delay..." and to be "excused from the individual tree surveys and construction measures..." The end result is a means for developers to fast-track their projects through review.

Other new provisions clarify that protected trees will be preserved in 100-year floodplains, give clusters of trees greater value than individual trees, award variances to preserve trees in residential setbacks, and preserve any species having a trunk at least 30 inches in diameter. Setting aside their differences, both developers and environmentalists wholeheartedly supported a new provision requiring all municipal agencies to adhere to the tree ordinance. City Council is expected to pass the ordinance this spring.

Armed with this new information, community leaders are reversing the tree-loss trends. "Based on compelling business reasons cited in the study, CPS is developing a comprehensive tree planting and preservation program. This program will help improve air quality in San Antonio and save CPS customers on air conditioning costs," says Milton B. Lee, of City Public Service. Jenna Terrez is an environmental analyst for City Public Service and chair of the Alamo Forest Partnership. The analysis, she says, "will help us identify priority planting areas for CPS's new Green Shade Program." While the program is still in its formative stages, she plans to work with neighborhood associations to plant appropriate species in residential yards, placing them to maximize energy conservation.

"I plan to run an analysis of every tree-planting project, documenting the benefits of their neighborhoods with before, after, and 20-year growth projection analyses," Terrez says. "People need to see how their tree planting efforts impact the environment in real and tangible savings."

Building a Green Data Layer

With the momentum building, the greater San Antonio area is poised to create a greener plan for future development.

In the second phase of its Urban Ecosystem Analysis, American Forests will provide the tools to do just that. By turning high-resolution satellite imagery into detailed digital data, American Forests will, in essence, create a green data layer that is rich with technical information, based on scientific and engineering models. San Antonio City Council's Open Space Advisory Board has endorsed this next phase, recognizing that the digital data will be a valuable tool for local planners to have at their fingertips during daily decision-making.

"But there's still a lot of work to be done," cautions Mark Peterson, regional urban forester for the Texas Forest Service. "Changing mindsets and adopting new policies and procedures that support trees as ecological assets comes more slowly. Some people still have the notion that tree benefits are purely aesthetic."

The Texas Forest Service is committed to integrating the green data layer into local planning. Peterson envisions the city's planning department using it for long-range planning and the developmental services department using it for site plan review. This rich layer of green data will also be invaluable in identifying, purchasing, and protecting significant ecological areas within groundwater recharge zones and in determining optimal tree canopy levels during development, he says.

At City Public Service, Terrez concurs with Peterson's vision for integrating the green data layer. In fact, Terrez says, all municipal agencies must comply with the new tree ordinance's aerial image mapping requirement for capital improvement projects. "Project managers can use the green data layer to see how trees will impact their site plans for new development."

While the signs are good, integrating trees into all aspects of community development is just beginning. San Antonio's community leaders must continue to protect their precious source of drinking water while taking steps to comply with EPA's air quality standards, reduce flooding, and find ways to expand urban growth with environmental sensitivity.

The Alamo Forest Partnership must find ways to solve these complex problems while fostering a "trees as asset" mindset within all levels of decisionmaking. Fortunately, it is armed with facts on tree cover trends and ecological benefits-and soon will have a green data layer-all the tools it will need to make good planning decisions that ultimately will increase tree canopy and improve local ecology. AF

Cheryl Kollin is director of American Forests' Urban Forest Center.[TOP]