Put down the apple. It’s the tree that can help keep the doctor away.
In urban areas, trees shade sidewalks, absorb air pollution, deaden traffic noise—and are simply beautiful to look at. And by removing climate-warming carbon from the atmosphere, trees are good for the planet, too.
It turns out that the health benefits of all that greenery add up.
A recent study in Portland, Oregon found that fewer people died in neighborhoods where a nonprofit planted more trees.
The paper by US Forest Service researchers adds to a burgeoning research group on the health benefits of living in the countryside. Their findings boil down to a recipe for policymakers to plant more trees.
“City trees are an essential part of public health infrastructure and should be treated as such,” said Geoffrey Donovan, the Forest Service researcher who led the study, which was published in the December issue of the journal Environment International.
For three decades, Portland’s nonprofit Friends of Trees planted nearly 50,000 oak, dogwood, and other tree species across the city, providing Donovan and his colleagues with detailed data on how the canopy has changed over time.
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using a mathematical model By controlling for factors such as race, income, age and education, the team found that for every 100 trees planted, there was about one fewer non-accidental deaths per year.
“Across the board, the benefits of trees are amazing,” said Yashar Vasef, executive director of Friends of Trees, which plant in six counties in Oregon and Washington. “And they’re less expensive than many other solutions.”
The health benefits of living under trees flourished as the trees themselves grew. As the trees got older, taller and their leafy branches broadened, the mortality rate among people nearby dropped, the study found.
Or as Donovan put it, “Bigger trees, bigger impact on mortality, which is what you’d expect.”
The findings are consistent with findings from other researchers, who suggest nature is good medicine for many diseases, including depression and high blood pressure. Another recent study published in the British medical journal The Lancet found that a third of premature deaths from a heatwave in Europe in 2015 could have been avoided with 30 per cent more trees.
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“Many other global studies have addressed similar research questions but use different study designs,” said David Rojas-Rueda, an assistant professor of epidemiology at Colorado State University, who has studied the health benefits of vegetation but was not involved in this latest article . “Most evidence supports that tree planting helps reduce premature mortality.”
There are several reasons trees may promote health, including better air quality, reduced stress, and more physical activity among people living in tree-lined neighborhoods. The link between planting trees and reducing mortality rates exists both in already leafy neighborhoods, which tend to be more affluent, and in tree-sparse neighborhoods, which tend to be poorer.
“Studies have found associations between exposure to the natural environment and improved health in a variety of different cities and countries,” Donovan said. “We certainly know that air pollution, stress and lack of exercise are bad for people, regardless of their race or socioeconomic status.”
Unfortunately, the opposite also seems to be the case. Mortality rates appear to be increasing in areas where tree cover is being lost.
In a previous study, Donovan and colleagues saw an increase in deaths related to cardiovascular disease and lower respiratory tract disease in counties from Minnesota to New York that were losing trees to a wood-burrowing pest called the emerald ash borer.
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The study outside of Portland has limitations. Donovan’s team did not have access to each person’s medical records. Instead, the team looked at overall deaths in the neighborhoods. And the researchers had no other detailed data that could shed light on other factors affecting residents’ health, such as a neighborhood’s smoking rate.
The paper came close to asserting a direct cause-and-effect relationship between trees and mortality.
Still, Donovan took this research to heart. He has lived in Portland since 2002 and has planted fig, plum and pear trees in his Oregon backyard.
“I really like fruit trees,” he said. “If you can get a sun-warmed fig in that bowl with yogurt and honey, it’s not that bad.”