When the temperature heads into the triple digits here in the Sacramento Valley, people walk on the shady side of the street and park their cars under trees whenever possible. They know trees make life more comfortable, but do they know trees help make them healthier?
Research connecting trees and human health was almost nonexistent before 2000 and has increased dramatically since – and the findings are remarkable.
At the Sacramento Tree Foundation, we have gathered a growing body of evidence on how trees significantly impact our health and well-being. Trees provide such a complex symphony of health benefits that it is sometimes hard to isolate the various ways they help make us healthier. All this is in addition to providing the oxygen necessary for life on this planet – which we take for granted with every breath.
Here are just four ways that trees are making our lives better beyond providing cooling shade:
• Trees directly affect our health by reducing blood pressure and stress levels.
“If you have chronic stress, you are at risk of getting sick more often, for staying sick longer, and for dying sooner than your colleague who doesn’t have as much stress as you do,” Bill Sullivan, a University of Illinois professor, said at a Sacramento Tree Foundation conference on health and trees this year.
Taking a different tack to reach the same conclusion, research by Geoff Donovan of the U.S. Forest Service reveals a significant increase in cardiovascular disease in communities that lost large tracts of urban forest due to climate change and emerald ash borer infestation.
• Trees filter and capture air pollution from cars.
Evergreen, needle-leaf trees are most effective as natural air filters near high-traffic roadways. Several studies have shown that ultrafine particulate matter is especially dangerous for our health as these particles are so small that they penetrate human tissues.
• Trees increase the walkability of neighborhoods.
Living in a neighborhood with more trees has been tied to higher physical activity levels. Regular walking and biking have many health benefits such as reduced obesity, diabetes and cardiovascular disease.
• Trees and green spaces bring people together to chat and play, leading to stronger social ties.
Trees have long been associated with gathering spaces as they provide outdoor “architecture” as well as shade, natural air conditioning and aesthetic appeal. Stronger social ties are also linked to reduced stress, increased well-being and longer life.
Some of these findings were recently echoed in a study launched by the Sacramento Tree Foundation. The goal of our Green Prescription study was to see if there are correlations between neighborhood tree canopy cover and a variety of health outcomes for urban residents in our region. The study used health data provided by UCLA’s California Health Interview Survey, the largest state health survey in the nation, reaching 50,000 Californians every two years.
Using regression models, the preliminary results of the study show that there are positive relationships between trees and physical and mental health. Specifically, the greater the tree canopy, the more physical activity, better social cohesion and less adult obesity and asthma in a community.
A fascinating part of the Green Prescription study used statistical modeling to extrapolate the expected health outcomes of adults in two hypothetical neighborhoods with differing amounts of trees.
One neighborhood had a tree canopy of 18 percent and the other 28 percent. Income, education, home ownership, race and other socioeconomic factors were statistically controlled in order to provide a comparison of identical populations.
The results are quite compelling – in fact, they will inspire you to grab your shovel and start planting trees.
In the community with 28 percent canopy cover, we would expect to find 18 percent less obesity and 20 percent less Type 2 diabetes, as well as 11 percent more vigorous physical activity. Obesity is a major factor in many of the chronic diseases becoming so prevalent in the U.S., which means any reduction in obesity – even 5 percent – has incredibly important health implications.
Another, more controversial finding of the predictive modeling is 10 percent less asthma in the neighborhood with higher tree canopy, when high traffic roadways are factored into the analysis.
This is especially notable because asthma has a complicated relationship with trees. Trees significantly impact respiratory health by capturing large amounts of air pollution and by cooling the air, yet certain tree species also exacerbate asthma due to the allergens they produce.
At the Tree Foundation, the evidence from these recent studies on the health benefits of trees has led us to redouble our efforts to carefully plan, plant and nurture more trees – preferably large trees – in all of our urban and suburban communities.
Cindy Blain is research and innovation director for the Sacramento Tree Foundation.