Breathe easier

Is it really a coincidence that the shape of human lungs mimics the shape of tree roots and branches? This similarity is yet another reminder of our dependence on the lungs of the earth -- trees, of course.
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Does urban living plague our respiratory health?

Studies show that yes, there are several ways that pollution created in cities can be harmful to air quality, and thus, our breathing. One significant air pollutant found in cities is particulate matter, which comes in many shapes and sizes. Particulate matter can be made up of hundreds of different chemicals directly emitted from sources such as construction sites, unpaved roads, or factory smokestacks. Another form of air pollution is nitrogen dioxide, which can be found in high concentrations near power plants, factories, and busy roadways. (Read more here.)

City trees mitigate air pollutants that cause asthma and other respiratory conditions.

According to researchers from the U.S Forest Service’s Northern Research Station, “while trees’ pollution removal equated to an average air quality improvement of less than one percent, the impacts of that improvement are substantial.”

One study from Portland State University analyzed pollutants found around busy, trafficked roads. After setting up pollution sensors in a variety of neighborhoods with heavy traffic, they found compelling statistics on the significant impact trees have on air quality and respiratory health: 

  • Tree cover decreased local levels of nitrogen dioxide by 15%. 
  • Children ages 4-12 avoided missing 7,380 school days due to asthma attacks.
  • Residents in all age ranges avoided 54 asthma-related emergency room visits. 
  • People older than 65 experienced 46 fewer hospital stays due to respiratory illness caused by nitrogen dioxide pollution. 
  • Altogether, all health benefits from reduced nitrogen dioxide through the existing tree canopy was about $7 million (2013) in annual savings. 

More trees means fewer asthma attacks, which creates safer and healthier neighborhoods, and also lowers healthcare costs.

A study by the University of Exeter medical school found that in polluted metropolitan areas, a resident is far less likely to be admitted to the hospital for asthma cases when there are more neighborhood trees. This collaborative research project looked at over 650,000 serious asthma attacks over 15 years across thousands of urban neighborhoods in England. They found that in the most highly polluted areas, the presence of 300 extra trees per square kilometer was associated with 50 fewer emergency asthma cases than areas without said trees. The study showed that greenspace in general was helpful in reducing asthma in low-polluted areas. However, they emphasized that highly polluted areas are where trees have the greatest impact in decreasing asthma emergency rates. 

This study has huge implications for planning and health policy, especially in Nashville where the Metropolitan Planning Organization (MPO) expects the population to grow by another million by 2035. 

What does it all mean?

The most up-to-date information on urban forestry shows unbeatable evidence: trees can prevent and aid symptoms of asthma and respiratory illnesses caused by air pollution. The Root Nashville campaign uses this data to focus plantings in areas with the highest rates of hospitalization due to respiratory illness. 

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