Trees aren't just pretty to look at. They're also good for yew.
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More U.S. cities are planting trees as a way to improve public health and reduce climate threats. New data shows they might be on the right track.
In 2018, south Louisville began going green in a big way. Researchers with the University of Louisville’s Christina Lee Brown Envirome Institute planted more than 8,000 trees and shrubs in the four-square-mile neighborhood to test the hypothesis that living amid dense greenery would improve residents’ health.
Now, six years later, the initial data from the Green Heart Louisville Project is in: Living closer to lots of trees can contribute to a lower risk of inflammation, which is associated with heart disease, stroke and heart attacks, and other health benefits.
The findings offer government leaders quantifiable data to make a stronger case for the human benefits of supporting forests, said Aruni Bhatnagar, head researcher of the Green Heart Louisville Project and director of the Envirome Institute.
“The biggest lesson is that we have to be thoughtful in our planting,” Bhatnagar said.
It’s not enough to stick a tree in the ground and call it a day, he said, pointing to the importance of the types of trees used and where they are planted. Small canopy trees placed on the sides of roads, for instance, could end up trapping heat and air pollutants closer to the ground—and to residents’ lungs—because their leaves are too dense to allow much air flow, Bhatnagar said.
Project partners planted thousands of trees in residents’ yards, along major roads and at businesses between 2019 and 2022. They used trees like magnolias, spruce, yews and others because, Bhatnagar said, they have needles or thick leaves that can absorb air pollution better.
When people breathe in ultrafine particles in polluted air from car tailpipe emissions or other sources, Bhatnagar said, the particles pass through a person’s lung tissue and blood stream. They contribute to the buildup of plaque on arteries, which can lead to emergency situations like a heart attack or accelerate long-term conditions like cardiovascular disease.
“We thought it might take a few years to [see results],” Bhatnagar said, “but we saw a very large effect right away. That was surprising.”
People living closer to the new trees saw a significant decrease in proteins associated with the risk of heart disease, stroke, heart attacks and other cardiovascular conditions by the end of the study, which examined blood, urine, hair and nail samples from 745 residents ages 25-75. Among the participating residents, 50% had a household income of less than $50,000, 60% were women and 77% were non-Hispanic white.
The lower protein levels correspond to a 10% to 15% decrease in the risk of heart attacks, Bhatnagar said, which offers communities potential cost savings by preventing emergency department visits and hospitalizations.
Residents living near the trees and shrubs also had lower blood pressure and lower exposure to air pollutants, he said.
The project’s initial findings come amid a nationwide push to plant more trees in recognition of their potential to reduce the effects of extreme heat, alleviate flooding and pollution, and improve residents’ health.
The conservation organization American Forests, for instance, announced Wednesday it is awarding 36 U.S. communities and organizations $25 million to support initiatives aimed at planting and maintaining trees. The funding is part of $50 million awarded to the organization under the Biden-Harris administration’s $1.5 billion allocation for trees and green spaces announced last April, which aims to improve public health and “deliver real economic and ecological benefits” to communities nationwide.
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