Debra Burke grew up in the middle of a 500-acre forest in Hardin County, Kentucky. 

With no electricity or running water, she drank milk that wasn’t pasteurized, cooked with water from a nearby spring and ate vegetables caked with dirt.  

So when she moved an hour north to Louisville, Kentucky, 23 years ago, it was a bit of a culture shock, she told NationSwell.

She scoured the urban landscape for a forested pocket to meet her tree needs. “I kept looking for a community that reminded me of home,” she said.

After living in the city for about six months, she finally found it near Iroquois Park, a 725-acre expanse filled with a few of Burke’s favorites: red maples and white oaks. 

A few months ago, Burke was on her daily walk there when a yard sign caught her attention. It talked about the Green Heart project, a scientific study assessing how health is impacted by tree canopy, the percentage of a city shaded by trees.

Burke, a 59-year-old barber, is familiar with the power of trees — not just how they beautify cities, but how they transform the lives around them — so she wanted to get involved. Now she’s one of over 800 residents participating in a health assessment to track how trees and vegetation affect their cardiovascular health. 

Her neighborhood is one of the four neighborhoods in south Louisville that has embarked on a $15 million, five-year study that will once and for all answer if health is tied to an area’s tree canopy. The study launched in 2018 when researchers collected baseline information about the neighborhood’s air pollution and resident’s heart health. Over the next three years, they’ll plant trees and monitor those same residents. In 2022, they’ll observe any changes. 

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The Green Heart project will be the first controlled scientific study assessing the impact of tree canopy on heart health.

As early as 1984, researchers were beginning to understand the role greenery plays in health. Roger Ulrich watched as patients with tree-facing windows had shorter hospital stays compared to their counterparts who looked at brick walls. The links between health and vegetation have continued for decades. Scientists saw the benefits of trees in everything from absorbing auto emissions to cooling sidewalks. They studied how greenery correlates to decreases in stress levels, heart rates, muscle tension, asthma and blood pressure.  

There’s a well-known link between health and greenness. But an important component was missing from the story: a controlled scientific study. 

The Green Heart project will be the first-ever experiment to see if increasing an area’s tree canopy will improve residents’ health.

Ted Smith, the director of the Center for Healthy Air, Water and Soil at the University of Louisville’s Envirome Institute, compared it to a drug trial “except the drug is trees and bushes,” he told NationSwell. Researchers will use a control group and a test group to see if the “drug” is effective or not. 

In this study, a control group of two neighborhoods will not receive any changes to their environment, but the test group will. Test neighborhoods will have 8,000 trees and plants added to their lawns, backyards and public spaces. Green Heart’s team surveyed public and private land in search of gaps in greenery, and the greening team went door to door asking residents if they’d like trees to be planted in their yards for free. These trees will raise the community’s tree canopy by 10% — an amount that’s “consistent with the literature of seeing a clinical benefit,” Smith said.

After about a year and a half, researchers will look at whether health improved, worsened or stayed the same between the groups. 

While it’s a study that can apply to almost every urban environment, Louisville is a compelling place to start. The city’s average tree canopy is only 28% — 16% lower than the recommended percentage, Smith said. That means a little over a quarter of the city is shaded by trees, whereas a healthy city should have a canopy of 44%. Instead of increasing, Lousiville’s tree canopy has continued to decline. About 54,000 trees are lost in Louisville each year to factors like development, age and invasive species. 

In the four neighborhoods researchers are studying, the numbers are even lower. Their tree canopy averages out at just 22%. But it wasn’t just their low tree canopy area that made these neighborhoods strong candidates: They each have high owner occupancy, which means they’re less likely to be gentrified as a result of the greening; they’re decent sizes (about 40,000 residents cumulatively); and they’re ethnically and socioeconomically diverse.

“If we can provide some evidence that there is an important effect of greenness on human health, in particular, the risk of heart disease, then that will send a case in trying to preserve the tree canopy,” Aruni Bhatnagar, the director of the Center for Diabetes and Obesity Research at the University of Louisville and lead researcher for the study, told NationSwell. 

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Aruni Bhatnagar speaks at Green Heart’s tree planting.

The $15 million study is funded by the National Institutes of Health, which supports the medical testing, and The Nature Conservancy, which is funding the vegetation. Collaborators include the University of Louisville, Louisville’s metro government, Washington University in St. Louis, U.S. Forest Service, Cornell University and Hyphae Design Lab.

“You don’t see projects come together like this very often, and we’re really trying to make sure this isn’t the only time unusual funders get together to get things done that aren’t just being done,” Smith said. 

Before planting began, the Green Heart team found more than 800 residents to complete a health assessment. Hair samples, nail clippings, urine, blood and questionnaires were all collected to assess each individual’s health. In about two years, after all the planting is done, their health will be reassessed. 

Bhatnagar and other scientists will be looking for changes in their health. For heart health, they’ll look at arterial stiffness, where increased stiffness is associated with an increased risk for heart events.

Kentucky is part of the Coronary Valley, a region of the U.S. that has the highest coronary heart disease mortality rates. While this area has higher concentrations of heart deaths, it’s a risk that everyone faces, said Bhatnagar, who has spent his career at the intersection of heart health and nature.

“We can treat it with lots of different things, stents and statins and whatever, but it’s very hard to prevent,” he said. “So prevention approach is severely and sorely needed.”

Bhatnagar hopes this study could create a blueprint for other urban cities to follow.

“If we can provide some evidence that there is an important effect of greenness on human health, in particular, the risk of heart disease, then that will send a case in trying to preserve the tree canopy. ” Bhatnagar said. “Not just in Louisville, but I think globally.”

Beyond heart health, scientists are looking at other connections between trees and people. 

Smith, who is leading the ancillary studies, said the team is conducting additional research to look at variables like sleep, noise, asthma, depression, social cohesion and biodiversity. 

Overall the study has been well-received. 

The Green Heart team is present at town halls, neighborhood meetings and community events. They’re there to spread awareness about the study but also show that they’re not just planning on extracting data from the community — they’re there for the long haul.

Nicole George, one of the two council representatives in the study’s neighborhoods, said Green Heart’s presence has helped shaped community attitudes towards the study.

“Their commitment is not just planting the tree, collecting a little health survey data and leaving,” she told NationSwell. “Their commitment is to the community.”

So whether it was Green Heart members helping a resident clean debris after a tree fell on her home or sending a birthday card to a resident, this is more than just a study.

“We’re not here to fix your neighborhood or clean up your neighborhood,” Smith said. “We’re here to figure out how to have a healthier neighborhood.”

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