American Forests analyzed the Delaware Valley region to provide community leaders with detailed information about the region's tree cover and its environmental and economic impacts. It documents the landscape changes that have occurred over time and identifies the impact these changes have made on the environmental services provided by the region’s urban forests. In addition, American Forests created a “green data layer” –a digital tool that local communities can use to integrate urban forest ecology into future planning.
The Urban Ecosystem Analysis of the region shows changes in the landcover over the last 15 years.
Overall, the nine-county Delaware Valley region is dominated by agricultural, grasslands, and other open space land. In 1985, this grasslands/ag. category comprised 41% of the area (1,011,525 acres). Heavy, tree canopy (50% or greater) comprised the next largest land cover with 36% (880,715 acres) followed by urban areas making up 16% (387,167 acres). The remaining land cover was comprised of medium tree canopy (20-49%) at 3%, water at 2% and light tree canopy (less than 20%) at 1%.
By 2000, urban land cover increased most dramatically by 22% to 473,067 acres; however other landcover trends did not change as much. Grasslands/ag. declined by 8% to 925,249 acres and heavy canopy declined by 1.5% to 849,444 acres. Medium and low density forest both increased by 10% (82,399 acres) and 14% (31,320 acres) respectively. However since their size is small compared to urban, grasslands/ag and heavy canopy, these increases are not as significant.
Even though the changes in landcover were modest over the last 15 years, the ecological impact of tree loss when calculated over the 2.4 million acre area is huge.
Trees slow stormwater runoff, reducing peak flows and decreasing the amount of stormwater storage needed. With the decline in tree cover, the Delaware Valley’s urban forest lost the ability to detain almost 53 million cubic feet of stormwater, a service valued at $105 million. This represents the cost to build stormwater retention ponds and other engineered systems to intercept this runoff. The region stored 2.9 billion cubic feet of stormwater in 2000, valued at $5.9 billion. Stormwater costs were calculated for a typical 2-year peak storm event and a $2.50 per cubic foot construction costs for the stormwater retention ponds.
Trees improve air quality by removing nitrogen dioxide (NO 2 ), sulfur dioxide (SO 2 ), carbon monoxide (CO), ozone (O 3 ), and particulate matter 10 microns or less (PM10) in size. The Delaware Valley’s tree canopy lost its ability to remove approximately 1.7 million pounds of air pollutants annually, at a value of $3.9 million per year. In 2000, the region’s trees removed 73 million lbs. valued at $167 million.
Trees help clean the air by storing and sequestering carbon in the wood. Total storage and the rate at which carbon is stored (sequestration) can be measured. If the regions’ trees had not declined since 1985, they would have stored an additional 633,000 tons of carbon and sequestered an additional 1,373 tons annually. In 2000, the region’s urban forest stored 26.8 million tons of carbon and sequestered 8,585 tons per year.
The local governments within the Delaware Valley should set tree cover targets for specific areas or land uses in the community and develop strategies to reach these goals.
Average tree cover for a metropolitan area in the Delaware Valley should be 40%.
The Green City Strategy in Philadelphia is an example of a specific strategy to increase the area’s tree cover.
If the Delaware Valley Region and its local communities were to reverse the tree loss trend and increase tree canopy, the environmental benefits would be significant. Setting tree canopy goals to maximize the benefits of tree cover in urban areas is a cost effective way to improve the environment.
The natural landscape should be recognized for its economic and ecological value. Tree cover is a good measure of the ecological health of the Delaware Valley.
Sprawl development has large, measurable negative environmental and economic consequences.
As rural areas outside of established cities develop, it will become even more important to increase tree cover to offset the environmental impacts of increased impervious surfaces,stormwater runoff, and air pollution.