January 17, 2013
River and forest landscape in Gooseberry State Park, Minnesota. Photo by: Jeremy Hance.
"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 with 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 looked at 1,296 counties in 15 states across 18 years to discover that the absence of trees may actually increase mortality rates from certain diseases. Comparing communities that had lost their trees to emerald ash borer—a beetle that has killed over 100 million trees in the U.S.—with other communities that still had tree-lined streets, the study found that communities without trees suffered an addition 15,000 deaths from cardiovascular disease and 6,000 deaths from lower respiratory disease.
While the researchers did not investigate a cause for this, they mentioned several hypotheses for future research, such as trees "improving air quality, reducing stress, increasing physical activity, moderating temperature, and buffering stressful life events."
There has been a flood of recent studies that have pointed to the health and mental benefits of nature. Research has shown that exercising in green space rather than an urban area provided extra mental health benefits. Another study found that spending 20 minutes in nature mitigated ADHD symptoms in children; in some cases the time in nature was even better than medication. Research has even found that patients recover better after surgery—and required less medication—when they had access to a natural scene versus a brick wall.
The emerald ash borer has been present in the U.S. since 2002, and targets all 22 species of North American ash.
CITATION: Geoffrey H. Donovan, PhD, David T. Butry, PhD, Yvonne L. Michael, ScD, Jeffrey P. Prestemon, PhD, Andrew M. Liebhold, PhD, Demetrios Gatziolis, PhD, Megan Y. Mao. The Relationship Between Trees and Human Health: Evidence from the Spread of the Emerald Ash Borer. American Journal of Preventive Medicine. 2013. 44(2):139–145.
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