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Trees Keep Cities Cooler

Several trees surround homes in a neighborhood.
Trees in a city neighborhood

While riding a bicycle with a small weather station attached to it in 2016, Carly Ziter of Concordia University gathered some interesting facts about trees in city neighborhoods. She rode her bike around Madison, Wisconsin to collect a massive amount of data.


Those facts were carefully analyzed and studied by a team working with Ziter, and they came up with an interesting conclusion. They discovered that if trees cover 40 percent of a city neighborhood, those trees will provide maximum cooling benefits.


The study was published in the journal, Proceedings of the National Academy of Sciences. An article about the study written by Matt Hickman appeared in an April 1, 2019 Treehugger newsletter. Another one by Lloyd Alter appeared in the July 25, 2022 Treehugger newsletter. If you would like to know more about trees and many interesting facts about nature and gardens, go to www.treehugger.com and check out the interesting website. It's full of valuable information.


I can imagine Ziter riding around on her bicycle with a weather station as she collected all that data. She estimates she rode 400 to 500 miles around Madison, covering ten areas of the city many times during different hours of the day. That data showed that there are great economic benefits to having many areas in the city with a 40 percent tree coverage. The costs of removing pollution and the energy it takes to run air conditioners and other cooling devices are reduced. That can save many millions of dollars.


The study pointed out that planting trees just anywhere isn't always the best answer. Instead, Ziter suggested looking at areas that need a few more trees to help them reach the 40 percent coverage.


The trees promote cooling by providing shade and by a process called evapotranspiration. That process happens when the rays of the sun shine on the canopies of trees. It helps water to evaporate from leaves and cool them down. As a result, it takes less energy to warm the air.


I'm not sure what percent of tree coverage is in my city neighborhood, but I'm pretty sure it's less than 40 percent. My city is one of those that might benefit from having more trees. If trees cool the air, then people wouldn't have to use up quite so much electricity running air conditioners. If that would shave off even a few dollars from my electricity bill, it would be worth it!

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Do Trees Heal Hearts?

Trees planted in neighborhoods can help to reduce stress and improve heart health.
Neighborhood trees can promote better health

The Green Heart Project is planting thousands of trees throughout Louisville, Kentucky to learn if trees can prevent heart disease in humans. The project began in 2018.


Aruna Bhatnager, director of the Christina Lee Brown Envirome Institute at the University of Louisville, is overseeing the effort with lots of help from interested people as well as $14.5 million in donations. Major donations have come from The National Institutes of Health and the Nature Conservancy.


Through the project, about 10,000 trees were planted in many neighborhoods in Louisville during the last three years. According to a 2015 report about the city's trees, approximately 150 trees a day die in Louisville, or 54,000 trees a year. They die from bigger storms, diseases, attacks from invasive beetles, and other factors.


The city has other challenges too, including homicide, suicide, cancer, drug addiction and angry reactions to the death of Louisville resident Breonna Taylor in 2020. Heart disease has become a serious problem in the city, which has some of the highest rates of cardiovascular disease in the United States, according to an article about the project in the May 2021 Discover Magazine.


Pollution levels are high enough that the American Lung Association has consistently given Louisville a poor grade for pollution levels. Research over the past 15 years has shown a correlation between air pollution and the development of heart disease.


The Envirome Institute wants to conduct environmental research that will help to create healthier cities. A pilot project of the institute recently found that planted trees reduced pollution by 60 percent around a local school, according to the Discover article.


Bhatnager specializes in environmental cardiology. He became fascinated by information he discovered in literature that both cigarette smoke and pollution impair nitric oxide production in the body. The molecule nitric oxide plays an important role because it helps to regulate insulin in the body, and it relaxes the inner muscles of blood vessels so that blood circulation increases.


He and his staff began doing toxicology studies to find out how many different pollutants affect our cardiovascular system. Their studies showed that pollution causes many problems. Among those problems is vascular damage in humans. In a study of mice, that vascular damage suppressed stem cells, which are needed to repair damaged blood vessels.


He also learned that dozens of studies show a relationship between living near green spaces and better health outcomes, among them lower stress levels and lower rates of asthma and depression. Bhatnager is convinced the Green Heart Project can make a positive difference in many people's lives.

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