Trees and human health are interconnected, a new study suggests.

The benefits of trees are growing. We already know they boost home value by gussying up curb appeal. They serve as beautiful water filters, too, reducing flooding and keeping runoff out of precious water supplies. But it's clear their benefits stretch much farther, though, as evidenced by a new study from the U.S. Forest Service that provides an intimate look into the apparent connection between trees and human health. The takeaway: When trees aren't doing well, neither are we.

Using the example of the emerald ash borer, an invasive beetle that is decimating North American ash trees across much of the country, researchers found that in areas where infected trees died off, people were more likely to suffer heart disease–related or lower respiratory disease–related deaths.

The scientists studied 1,296 U.S. counties in 15 states over a period of 18 years and estimated that 15,000 additional heart disease deaths and 6,000 more deaths occurred in areas where emerald ash borers had taken hold and wiped out ash trees. The findings even held true when researchers considered income, race, and education, other factors that can affect lifespan.

"There's a natural tendency to see our findings and conclude that surely the higher mortality rates are because of some confounding variable, like income or education, and not the loss of trees," says Geoffrey Donovan, PhD, research forester at the Forest Service's Pacific Northwest Research Station. "But we saw the same pattern repeated over and over in counties with very different demographic makeups."

The study appeared in the American Journal of Preventive Medicine.

Inspired to plant your own tree this spring or fall? Be sure to go native. Planting trees that have evolved to thrive in your area helps your entire ecosystem. Plus, native trees are less fussy, requiring less watering and fertilizer once they are established. Consider this: A native oak tree can support 534 species of butterflies and moths. That's biodiversity in action! To find a list of trees and flowers native to your area, visit the University of Texas at Austin's Native Plants Database.