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How to prove the tree-huggers hunch? Study a deadly beetle

If you live in the Evergreen State, chances are, you like trees. Cities around the Pacific Northwest do a lot to protect them. 

But, do they really make us healthier? An economist with the US forest service in Portlandis working on that question.

Geoffrey Donovan  loves trees. He’s already shownthey make home prices go up, energy use go down and they tend to keep crime rates down as well. So what about public health?

Since we know they’re good to have around, Donovan wanted to see, can we quantify their effect on heart and lung disease?

“If trees do in fact clean our air, if they do reduce our stress levels, if they do encourage us to exercise, which past studies suggest they do, then we should be able to identify an effect on public health,” Donovan says.

To do this study, he took advantage of a sad situation: the incidence of theemerald ash borer. It’s an invasive species that came to the Midwest from China a decade ago, an insect that looks like a shiny version of a grasshopper. It has not been detected in Washington or Oregon. But it attacks all 22 species of ash trees. And if left unchecked, it will kill them in just a few years. Communities in 15 states have seen thousands of street trees wiped out by the emerald ash borer.

“This is tragic, but absolutely fantastic for me,” Donovan says. “because it just gives you this really unique opportunity. You see a major change in the natural environment, happening in a relatively short time.”

The insects themselves are harmless to humans. But Donovan found, using data from county health departments, that communities that lost their trees saw higher death rates due to heart and lung disease.

“And, although this study didn’t have any direct insight into the mechanism, those are the plausible things: air quality, exercise, stress,” he says.

Now that he has this finding, which is published in the American Journal of Preventive Medicine, Donovan says he can continue to investigate the cause. His next study will look specifically at women’s health and trees, using data sets covering 120,000 women all over the country.

Bellamy Pailthorp covers the environment for KNKX with an emphasis on climate justice, human health and food sovereignty. She enjoys reporting about how we will power our future while maintaining healthy cultures and livable cities. Story tips can be sent to