The Urban Forest and Human Health and Safety

By: Richard J. Magill, Magill & Associates, Inc.

This is the fifth in a series of six articles that will explore the various interactions and outcomes that result from human contact with our urban forests. This article will investigate the impacts of our city forests on human health and safety.

Although these subjects were touched on in a previous article (The Urban Forest and Psycho-Social Benefits), they are such important aspects of human interaction with the urban forest, further discussion of these issues is in order.

Human Health
The Urban Forest Mitigates Air Pollution

In possibly the most important study to date on the effect of urban forests on human health, recently published on-line (June 2013) by the journal Environmental Pollution, researchers with the U.S. Forest Service and the Davy Institute in Syracuse, New York estimated how much fine particulate matter is removed by trees in 10 U.S. cities; their impact on PM2.5 concentrations and associated values, and impacts on human health. Cities included in the study were Atlanta, Baltimore, Boston, Chicago, Los Angeles, Minneapolis, New York City, Philadelphia, San Francisco, and Syracuse, NY.

The entire study, “Modeled PM2.5 Removal by Trees in Ten U.S. Cities and Associated Health Effects,” is available at: https://www.nrs.fs.fed.us/pubs/43676. This is the first effort to estimate the overall impact of a city’s urban forest on concentrations of fine particulate pollution (particulate matter less than 2.5 microns, or PM2.5). Fine particulate air pollution has serious health effects, including premature mortality, pulmonary inflammation, accelerated atherosclerosis, and altered cardiac functions.

Overall, the greatest effect of trees on reducing health impacts of PM2.5 occurred in New York due to its relatively large human population and the trees’ moderately high removal rate and reduction in pollution concentration. The greatest overall removal by trees was in Atlanta due to its relatively high percent tree cover and PM2.5 concentrations.

The study found that urban trees and forests are saving an average of one life every year per city. In New York City, trees save an average of eight lives every year.

The Urban Forest Promotes Physical Activity

Kathleen Wolf at the Center for Urban Horticulture at the University of Washington has explored the idea that trees and parks can help urban dwellers to make better, more active choices about their routine activities. Ms. Wolf asserts that with an aesthetically pleasing urban forest, people are encouraged to walk in their neighborhoods during their daily activities or for recreation. This not only encourages physical activity which can help reduce obesity and weight-related diseases, but it also increases possibilities for healthy social interaction.
Urban life can be extremely demanding often resulting in stress-related health issues. It is widely accepted that urban open spaces and parks can provide welcome relief from stress, allowing us to calm and cope, and ultimately recharge and improve overall physical health.

The Urban Forest Mitigates Other Health Issues

Other heat-related health problems, such as heat-stroke, dehydration and skin cancer are mitigated by the urban forest’s ability to moderate the temperatures created by the urban heat island.

Human Safety
The Urban Forest and Road Safety

• Speed Reduction- It has been proven over many years of observation that tree-lined roadways provide “spatial definition” that makes the road appear to be narrower; therefore encouraging slower driving speeds.
• Stress Reduction- the psychological effect of trees along roads tends to reduce the occurrence of road rage and also improves the attention span of drivers.
• Physical Buffers- Vegetation can provide an effective barrier between opposing vehicular traffic, and between adjacent public spaces and pedestrian ways.
• Unwanted Obstacles- traditional road planning and design guidelines identify “clear zones” where no large objects should be allowed. Trees and other vegetation planted in these “zones” are thought of as hazards to visibility and vehicular safety. While there are certainly situations where this is absolutely true, often these guidelines are too strictly defined and applied. There are many instances where proper landscape design and plant selection would allow for trees or shrubs in or adjacent to these areas without compromising safety.

The Urban Forest Promotes Neighborhood Security

It is widely known that urban green spaces provide many opportunities for casual social interaction and are key to the development of strong social ties. Research has indicated that neighbors who have strong social ties form more effective social groups (e.g., Greenbaum 1982; Warren 1981). Further findings suggest that residents of greener buildings feel more comfortable or adjusted in their surroundings in general. If strong social ties among neighbors are key to creating more effective, safer neighborhoods, and treed spaces help promote ties among neighbors, the presence of trees in the neighborhood landscape positively affects levels of safety and security.

Next article: The Urban Forest and Urban Planning and Policy

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