Trees improve health — but not for everyone

Being around trees is proven to enhance health, from lowering stress to increasing longevity. However, a new national study led by Michigan State University researcher Amber Pearson reveals a surprise: The biological benefits of nature are not experienced equally across all populations.

“The prevailing thought among urban planners and health professionals has been that if we plant trees, everyone’s health will get better,” said Pearson, professor at the Charles Stewart Mott Department of Public Health in the MSU College of Human Medicine. “Our study found that the benefits of trees aren’t equally experienced.”

Published in the Lancet Regional Health – Americas, the study examined the relationship between residential tree canopy and allostatic load — the cumulative “wear and tear” on the body caused by chronic stress. Using Centers for Disease Control and Prevention data related to 40,307 adults matched with satellite maps of tree cover, Pearson’s team analyzed data for every census block in the country. And they found that while higher tree canopy is generally associated with lower allostatic load, that was not the case for the most vulnerable groups.

“Surprisingly, there is an association between trees and better health for those who have a higher income and education and are employed, but there is no association for less-advantaged people,” Pearson said. “The findings were consistent for non-Hispanic white and Hispanic subpopulations, but not for non-Hispanic Black participants.”

The study noted that 24% of non-Hispanic Black participants lived in high-canopy neighborhoods, yet they did not show the same reduction in allostatic load seen in white and Hispanic groups. Pearson suggests for some minority groups, other environmental or social stressors — like discrimination — may override the calming effects of nature.

“There are other things that may be more stressful in disadvantaged groups like unfair treatment, lack of good job opportunities, or poor neighborhood conditions that tree canopy is not going to overcome,” Pearson explained.

The findings suggest that while urban greening is a vital public health tool, it must be paired with efforts to address the root causes of social and economic inequality for the most vulnerable groups to reap its benefits.