It's no secret that plants play an essential role in the health and well-being of our planet. But a new study suggests that as the trees around us become fewer, it may actually come at the expense of human lives.
Over the past decade, an estimated 100 million trees have perished across the eastern and midwestern regions United States, victims of the devastating emerald ash borer invasion. Since first entering the U.S. in 2002, the invasive beetle has gone on to attack trees in 15 states, leaving a lifeless tangle of baren branches and tree-stumps in its wake.
Although ash borers have no direct impact on anything other than ash trees, the plant deaths they cause appears to cascade into the realm of humanity.
A team from the U.S. Forest Service, led by Geoffrey Donovan, set out to see what effect the loss of all these trees was having, if any, on human health. The researchers examined mortality data from 1,296 counties where ash borers are present, comparing pre-invasion figures to those after the massive tree die-off, from 1990 to 2007.
After adjusting their findings for demographic variables, like income and education, the team discovered a startling association: fewer trees aligned with more human deaths.
From their study, published in the American Journal of Preventive Medicine:
There was an increase in mortality related to cardiovascular and lower-respiratory-tract illness in counties infested with the emerald ash borer. The magnitude of this effect was greater as infestation progressed and in counties with above-average median household income. Across the 15 states in the study area, the borer was associated with an additional 6113 deaths related to illness of the lower respiratory system, and 15,080 cardiovascular-related deaths.
In an interview with PBS News Hour, Donovan says that the speed and breadth of the ash borer invasion presented a unique 'before-and-after' scenario with which to study the link between trees and health. And considering that more and more trees are losing ground in cities across the U.S., it might be resulting in a wider health crisis, albiet harder to study.
"Maybe we want to start thinking of trees as part of our public health infrastructure," says Donovan.
"Not only do they do the things we would expect like shade our houses and make our neighborhoods more beautiful, but maybe they do something more fundamental. Maybe trees are not only essential for the natural environment but just as essential for our well-being. That's the message for public health officials."