A new scientific study associates tree planting with fewer deaths
At Friends of Trees, we champion the many benefits of urban trees: they clean the air and water, provide wildlife habitat, and shade our homes and streets. Trees improve our environment, but they also improve our quality of life. Dr. Geoffrey Donovan, a researcher with the United States Forest Service, wanted to investigate one step further — do trees save lives?
His new study, published in December 2022 in the journal Environmental International, found that each tree planted was associated with significant reductions in non-accidental and cardiovascular mortality. Donovan’s study used the planting data from the nearly 50,000 trees that Friends of Trees planted in Portland neighborhoods since 1990.
Looking at all 140 census tracts in Portland, Donovan showed that on average, 11.7 new trees in each neighborhood were associated with 15.6 fewer non-accidental deaths and five fewer cardiovascular deaths each year. As the trees mature, their benefit grows too. Trees planted 11-15 years ago had twice the impact of trees planted within the last five.
“It’s incredible,” says Friends of Trees Executive Director Yashar Vasef. “We know that trees can transform a community, but it’s really meaningful to see the data analysis.”
The study went on to associate the reduced death with an incredible economic benefit, based on the EPA’s statistical value of a human life. Planting one tree in each of the 140 census tracts in Portland is associated with a reduction in non-accidental death of 1.33, which has a statistical value of $14.2 million. To plant and care for those 140 trees would cost just $3,000-$13,000.
“In short, trees are cheap and human lives are valuable,” Donovan says. “The public money that went to Friends of Trees generated remarkable rates of return.”
Residents of Eugene and Springfield are very familiar with inversions. On a cold, clear winter day, pollutants get trapped in the valley, hanging low like a fog and causing notably poor air quality for people on the ground.
“On a cold, dry day, you can pretty much expect an inversion,” says Friends of Trees Eugene Director Erik Burke. “It’s not uncommon to see air quality alerts in winter.”
One thing that can help? You guessed it, more trees! Trees improve air quality by providing surface area for airborne particulates to stick to. Those particulates are then washed by rain into the soil, where microorganisms break them down into something less harmful.
“We’re trying to get trees in the ground where air quality is worst,” Erik says.
Like in plenty of other cities, the neighborhoods that are closest to polluters in Eugene are low-income neighborhoods. Air quality is one of the many benefits of trees that low-canopy neighborhoods are deprived of. Friends of Trees plantings in the Bethel neighborhood are in part to address air quality concerns there. And every year, Friends of Trees plants along the railyard and the Northwest Expressway, where idling locomotives and automobiles are releasing particulates.
Each and every tree provides so many benefits to our urban forest. This time of year, we want to shout out the year-round workhorses: evergreens. Because they don’t drop their leaves and go dormant in winter, evergreens work all year to produce oxygen and store up carbon through photosynthesis, and provide important stormwater benefits by intercepting precipitation in their dense canopies.
“Most of our rain comes in winter,” Eugene Director Erik Burke says, “so evergreens are essential. We have a lot to learn about evergreens and air quality, too.” All trees improve air quality, but evergreens are particularly useful because they keep their leaves or needles all year.
We often think of conifers when we think of evergreens, but other species like California live oaks, holm oak and California bay laurel are also evergreens that keep their leaves year-round. When you’re picking the next tree for your yard, consider going evergreen!
It’s our 34th season of planting and caring for trees – JOIN US!
Get outside this winter! We still have plenty of planting events left this season. Whether it’s in a neighborhood or natural area, we would love your help building community with trees. It’s a great way to take climate action, and as a volunteer named Caela puts it, planting trees is the “best reason in the world to wear rubber pants and play in the mud!”
Here are some upcoming volunteer events:
February 4, Salmonberry Trail plant rescue, Banks
February 4,Neighborhood planting, Parkrose, NE Portland
February 11,Natural area planting, Arrowhead Creek Park, Wilsonville
February 25,Neighborhood planting, West Vancouver, WA
Crew Leaders and Assistants—watch your inbox for Crew Leader News on the first of the month!Trained Crew Leaders sign-up for eventshere.
Show love for your tree with a Friends of Trees yard sign!
Do you have a tree from Friends of Trees in your yard or planting strip? We want to celebrate your tree and the benefits it provides with a beautiful yard sign! We want people to know how important trees are to their communities, and to see the impact that Friends of Trees and its supporters have made throughout western Oregon and southwest Washington. Visit here to learn more and get in touch.