Research project examines if trees help people stay healthier

LOUISVILLE, Ky.—Imagine trees as a drug to prevent heart disease.

Aruni Bhatnagar, a medical professor at the University of Louisville, does— along with a team that unveiled a $14.5 million research project in Louisville on Thursday.

“We think (trees) might be more effective than statins,” the air pollution expert said of the widely prescribed class of drugs used to lower blood cholesterol, a risk factor for heart disease and stroke.

The Green Heart project, as it’s called, involves the University of Louisville, The Nature Conservancy, The Institute for Healthy Air, Land and Soil and other partners who will transform four South Louisville neighborhoods with as many as 8,000 trees and other plantings.

The area is roughly between Churchill Downs, Iroquois Park and Louisville International Airport. It’s home to about 22,000 Louisvillians.

The trees will need to be large enough to make a difference right away. That means some could be as tall as 30 feet.

Trees, shrubs and other plants will be placed where they can best soak up lung-damaging air pollution, like along the Watterson Expressway or other busy roads within the study area. Researchers at the university and across the country—backed by $8.5 million from The Nature Conservancy and other grants from the National Institutes of Health and other sources—will then closely track the health of as many as 700 residents, looking primarily at any cardiovascular response.

The idea that human health is related to trees extends back to the story of Genesis, where a tree of life was planted in the Garden of Eden to bring immortality. In recent decades, scientists have been exploring the connections between health and trees.

This study seeks to add more certainty to earlier research that’s associated trees with improved public health but has fallen short on definitive conclusions and details, the Green Heart partners said.

Trees breathe in their own way, taking up the heat-trapping gas carbon dioxide while creating life-sustaining oxygen. While trees produce volatile organic compounds— source of ozone pollution—they also absorb ozone and other pollutants and trap especially dangerous tiny particles.

But Bhatnagar said that “nobody has evaluated the specific health effects of planting green spaces.”

There have been no other studies like it, where people’s health is monitored before, during and after a major, neighborhood-scale tree planting, he added.

The health of people who live near the newly planted greenery will be compared to those who live elsewhere in the study area. “We are hopeful to see changes in a few years,” he said. It’s like a drug trial, with nature as the drug. “Instead of giving someone a pill, we are giving them greenness,” said Chris Chandler, director of urban conservation with The Nature Conservancy’s Kentucky chapter.

The trees, he said, will be “some of the largest that will be able to be transplanted,” he said, adding that “it (will be a) really unique urban laboratory.”

With guidance from the public, Green Heart team members will be deciding where and what to plant based on what’s best for reducing air pollution. That could include obtaining permits to plant in state and federal rights of ways, as well as permission from property owners, he said.

Trees also could be planted at homes, churches, schools, businesses and parks, along with shrubs and native grasses and other plants, he said.

“We are going to build a relationship with the community,” said Veronica Combs, executive director of philanthropist Christy Brown’s air, water and soil institute. The institute has identified 200 community leaders and begun to meet with them. “We are getting their feedback,” she said, noting trees are not everyone’s top priority. Crime is a top concern for many, she added. In addition to studying cardiovascular health, researchers also plan to see if there are any changes in crime rates, stress, economics and other social-psycho outcomes. Some studies suggest trees can help in those areas, too.

A city-sponsored study in 2015 found Louisville was losing some 54,000 trees a year due to age, disease and storms—and that was before the emerald ash borer began wiping out tens of thousands of additional trees locally.

The Louisville metro area has also long suffered from poor air quality. While it’s much improved over decades past, the region still struggles to meet ever-tightening clean-air standards for ozone and the smallest particulates.

And like in other cities, roads and freeways jammed with cars and trucks and their exhaust can create localized pollution hot spots.

The new research has its roots in a pilot project at a Louisville school. The Healthy Air, Water and Soil

Institute, of which Bhatnagar is a board member, the city of Louisville, the university and other partners, first experimented with trees and air pollution last year.

A wall of trees and shrubbery was planted in the front lawn of St. Margaret Mary school to act as a filter for the air pollution from vehicles on Shelbyville Road. The levels of the smallest particulates dropped as much as 60 percent, and there were indications that some students’ immune systems had improved, Bhatnagar said.

While tree advocates often speak of the value of trees— they also cool cities and reduce stormwater pollution and sewage overflows—their specific benefits to air quality and human health have not been “nailed down yet,” said Portland State University environmental sciences professor Linda A. George, who has researched the subject but is not involved in the Louisville study.

“There is quite a bit of variation in the literature about the role of trees (with) some studies show an effect other do not. Usually, this kind of variability means that there are other variables involved,” she said.

Still, in Portland, her research has calculated the potential annual respiratory health benefit from trees due to a reduction of just one pollutant, nitrogen dioxide. That Oregon city could thank its trees for an estimated 7,000 fewer days of missed school due to asthma in youth; 54 fewer emergency room visits of all ages; and 46 fewer hospitalizations among the elderly due to respiratory problems triggered by the pollutant, which is associated with tailpipe emissions.