Forest Park, Portland, Ore.
The USDA Forest Service – Northern Research Station (NRS) released a report entitled Sustaining America’s Urban Trees and Forests, offering an overview of the current status and environmental, financial and health benefits of America’s urban forests and how these forests vary in different regions of the country. The report defined urban forest as “all publicly and privately owned trees within an urban area – including individual trees along streets and in backyards, as well as stands of remnant forest.” Providing essential services to more than 220 million people (supporting 79 percent of the population), urban forests in the U.S. are estimated to contain about 3.8 billion trees and worth an estimated $2.4 trillion.
According to the report, urban forest services and benefits include (but are not limited to):
- Local climate and energy use—Trees influence thermal comfort, energy use, and air quality by providing shade, transpiring moisture, and reducing wind speeds. The establishment of 100 million mature trees around residences in the United States is said to save about $2 billion annually in reduced energy costs.
- Air quality—Trees improve air quality by lowering air temperatures, altering emissions from building energy use and other sources, and removing air pollutants through their leaves. Urban trees in the conterminous United States remove some 784,000 tons of air pollution annually, with a value of $3.8 billion.
- Climate change—Urban trees can affect climate change by directly storing carbon within their tissues and by reducing carbon emissions from power plants through lowered building energy use. Urban trees in the conterminous United States currently store 770 million tons of carbon, valued at $14.3 billion.
- Water flow and quality—Trees and soils improve water quality and reduce the need for costly storm water treatment (the removal of harmful substances washed off roads, parking lots, and roofs during rain/snow events), by intercepting and retaining or slowing the flow of precipitation reaching the ground. During an intense storm in Dayton, OH, for example, the tree canopy was estimated to reduce potential runoff by 7 percent.
- Noise abatement—Properly designed plantings of trees and shrubs can significantly reduce noise. Wide plantings (around 100 ft) of tall dense trees combined with soft ground surfaces can reduce apparent loudness by 50 percent or more (6 to 10 decibels).
- Wildlife and biodiversity—Urban forests help create and enhance animal and plant habitats and can act as “reservoirs” for endangered species. Urban forest wildlife offer enjoyment to city dwellers and can serve as indicators of local environmental health.
- Soil quality—Trees and other plants help remediate soils at landfills and other contaminated sites by absorbing, transforming, and containing a number of contaminants.
- Real estate and business—Landscaping with trees—in yards, in parks and greenways, along streets, and in shopping centers—can increase property values and commercial benefits. One study found that on average, prices for goods purchased in Seattle were 11 percent higher in landscaped areas than in areas with no trees.
- Individual well-being and public health—The presence of urban trees and forests can make the urban environment a more aesthetic, pleasant, and emotionally satisfying place in which to live, work, and spend leisure time. Urban trees also provide numerous health benefits; for example, tree shade reduces ultraviolet radiation and its associated health problems, and hospital patients with window views of trees have been shown to recover faster and with fewer complications than patients without such views.
- Community well-being—Urban forests make important contributions to the economic vitality and character of a city, neighborhood, or subdivision. Furthermore, a stronger sense of community and empowerment to improve neighborhood conditions in inner cities has been attributed to involvement in urban forestry efforts.
The specifics of how urban trees provide these benefits have been discussed at length, but this report adds value by comparing different urban forestry areas and their management, which vary by size and region across the United States.
The report determines which urban forestry areas provide the greatest relative canopy cover, as well as the areas that have the most potential for future tree coverage. Results indicate the area of tree cover in cities within naturally forested areas was nearly twice the percentage of cities in grassland regions, and more than three times the cover of cities in desert regions. Regional climate and landscape is not the only influence on urban forests, as land-use activities such as development play a large role. Overall, the regions with the greatest amount of tree cover for urban areas are the Southeast and New England states.
These findings would lead some to believe that it is the rest of the country that urban forest advocates need to focus on, however certain precautions need to be taken into account, such as fire risk, energy cost and water usage. Therefore, “maximum tree coverage may not be optimal tree coverage.”
Even though there is a widespread acknowledgment of the benefits of urban forests, the level of resources allocated to the management of these areas varies greatly by region. The report suggests a long-term comprehensive urban forest management plan for cities, though it recognizes that these plans can be complicated, especially for forested areas that cross multiple government jurisdictions.
Cities that choose to increase their urban forests face many challenges with comprehensive management, such as lack of funding, volunteer time and initiation, completion or implementation of a management plan. Most of the innovation comes in the form of software and websites, such as i-Tree and CITYgreen, a program used to calculate the monetary values of the economic and ecological benefits provided by trees in specific locations.
In this report, the USDA Forest Service shows how urban forestry decisions made today impact the future of cities and the well-being of their residents. It shows that only by collaboration between local governments and communities, as well as planners and landowners, can we hope to make urban areas more sustainable and desirable places to live.
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