New Study Shows Tree Deficit in the Philadelphia Area

American Forests
Thursday, 27 March 2003

Nonprofit to announce findings, offer decision makers new tools for regreening

According to a new study by conservation organization AMERICAN FORESTS, Delaware Valley's urban forest is experiencing a tree deficit. The area does not have adequate tree cover to compensate the changes made to the landscape, making it difficult to maintain stormwater and air quality at healthy levels.

AMERICAN FORESTS conducted an Urban Ecosystem Analysis study to provide community leaders with detailed information about the region's tree cover and its environmental and economic impacts. The study covered a 2.4 million-acre area, including nine counties in southeastern Pennsylvania and four counties in southern New Jersey. In addition, four urban watersheds are also detailed to assist local communities in the development of their watershed management plans.

According to the report, the nine-county Delaware Valley region currently has a 38 percent grassland and agricultural land cover and a 35 percent heavy tree canopy cover—a decline of 3 and 1 percent respectively over the last 15 years. Even though these changes in landcover were modest when considering the entire 2.4 million-acre area. The ecological impact of tree loss is significant in specific land use areas. With this decline in tree cover, the Delaware Valley's urban forest can no longer detain almost 53 million cubic feet of stormwater—a service valued at $105 million in stormwater containment construction.

American Forests recommends a minimum canopy coverage of 40 percent in urban areas. At 35 percent, the Delaware Valley has a tree deficit, and the challenge to reverse this trend it twofold. In urban areas like Philadelphia re-greening becomes complicated because natural conditions like good soil no longer exist. At the same time, the pressure for future development has shifted from established cities to suburbs. The greatest challenge in rapidly growing counties will be to retain existing tree cover and add more in areas where agricultural land has been replaced by urban land use, offsetting the effects of increased stormwater runoff and air pollution. Local agencies have recognized these challenges and have embraced the information and tools provided by AMERICAN FORESTS to improve the environment for the future. "The recommendations from this study will enable local governments to establish tree cover goals, and focus on results," says USDA Forest Service Northeastern Area Director Kathryn Maloney.

Department of Conservation and Natural Resources Secretary Michael DiBerardinis noted it has been just slightly over a year since DCNR joined the U.S. Department of Agriculture (USDA) Forest Service and City of Philadelphia in announcing a partnership to protect and enhance the city's open space and natural resources. "At each site our foresters documented every tree or shrub that could reach at least 15 feet in height at maturity," Secretary DiBerardinis said. "They undertook this effort with a commitment that reflects the value Delaware Valley residents place on their green canopy, and a pressing importance that recognizes the threats."

Over the next 25 years, Chester, Bucks, and Gloucester counties are expected to grow 27 percent, 25 percent, and 27 percent, respectively, according to the Delaware Valley Regional Planning Commission's 2025 Plan. When projected to the year 2025, future development in these three counties will produce distinct changes in agricultural, tree cover, and urban areas. In Chester and Gloucester counties, heavy tree cover will decline as
urban areas increase. In Bucks and Gloucester Counties, however, grasslands/ag land is projected to decline dramatically as urban area increases. Unlike the other counties, tree cover in Bucks County is projected to increase over time thanks to landscaping around new developments in areas previously used as farmland.

With the population expected to grow in outlying counties in coming years, the associated tree loss will result in costly and unhealthy environmental consequences. To this end, the report makes a number of recommendations for the area's decision-makers, including some for older communities focused on revitalization and growing communities attempting to stem urban sprawl.

The study suggests communities establish goals and create a system to maintain these goals. Second, the community should develop specific management strategies to achieve tree cover goals, such as planting trees to meet stormwater management goals and requiring trees as part of redevelopment and new development projects. Third, the community should use the green data layer to document the environmental benefits of these strategies and incorporate this information into land use, development and watershed planning. Lastly, the report recommends that the community should encourage local greening partners like the Pennsylvania Horticultural Society to use the green data layer and document environmental benefits of their work.

"The study shows that the Delaware Valley's trees are a very important community asset," said Gary Moll, vice president of AMERICAN FORESTS' Urban Forest Center. "The real strength of this project is in the data it provides to regional and local communities who can use it for future planning and local analyses of tree canopy. The Delaware Valley's communities have now taken the first step and are poised to take full advantage of the project."

AMERICAN FORESTS' study highlights the important role trees play in retaining stormwater in urban areas. Trees help reduce stormwater runoff by intercepting rainwater on their leaves, branches, and trunks, where it evaporates or slowly soaks into the ground, reducing peak flow after a storm. Trees also reduce the volume of runoff. Municipalities must spend millions of dollars for flood control systems and sewer infrastructure to handle stormwater runoff. Without trees in the Philadelphia Metropolitan Area, the cost of building water storage units would be very expensive. The recent tree loss has contributed to a loss of nearly $105 million dollars in containment facilities.

Besides reducing stormwater runoff, the Delaware Valley's tree canopy provides other benefits including the removal of 1.7 million pounds of air pollutants each year—a value estimated at $3.9 million annually. The area's urban forest currently stores an estimated 26.8 million tons of carbon and sequesters nearly 8,585 tons of carbon each year.

The Urban Ecosystem Analysis technique conducted in the Delaware Valley used satellite and aerial imagery, Geographic Information System technology, and scientific research to calculate the benefits trees provide to the urban environment. The analysis also serves as an introduction for local leaders to learn about ways to use tree cover as an asset—building a green data layer for future city management decisions.

The study was made possible by AMERICAN FORESTS in partnership with the USDA Forest Service; Northeastern Area; Pennsylvania Bureau of Forestry District 17 Valley Forge; Pennsylvania Department of Conservation and Natural Resources; Bureau of Forestry; Philadelphia Water Department; Delaware Valley Regional Planning Commission; and Pennsylvania Urban and Community Forestry Council.

Images from the study are available on an online server. Please call Rachel Brittin at (202) 955-4500 x234 for the address. For a copy of the Delaware Valley Urban Ecosystem Analysis Report visit AMERICAN FORESTS online at www.americanforests.org/resources/rea/.

For more information, or to contact American Forests, see their website at: www.americanforests.org