Lining city streets with trees reduces physiological symptoms of stress in humans. The thicker the tree cover, the lower the stress levels, study finds.
We all know that a walk in nature can help slow the maddening pace of modern life and bring us back into the moment, but a recent study tells us just how many trees are necessary to keep us calm.
Researchers put people in stressful situations and then showed them 3-D videos of various “city”scapes, each with different densities of tree cover.
The thicker the tree-cover, the lower the subjects’ stress levels dropped.
The researchers, from the University of Illinois and the University of Hong Kong, subjected 160 participants to various stressful scenarios, including having them prepare to deliver a speech, or perform a math test, in front of judges and cameras.
Once the participants were fully stressed out, they viewed one of 10 six-minute videos of city streets that changed only in the amount of tree coverage, ranging from 0 to 70 percent.
Which image makes you feel more relaxed?
What they found was the higher the density of trees, the lower the levels of stress the subjects reported. Inversely, the lower the density of trees, the less helpful the video was in helping the subject recover from stress.
While this study, published in Environment and Behavior, was based on self-reported questionnaires, an earlier 2016 study, published in the International Journal of Environmental Research and Public Health, measured reduced physiological markers of stress in subjects simply looking at images of nature.
“The findings suggest that keeping a few snapshots of greenery around your work desk might not be a bad idea. When participants viewed the natural images in the experiment, their stress levels lowered, thanks to the activation of their parasympathetic nervous system – which controls certain rest functions,” Science Alert reports.
While the sympathetic nervous system regulates the fight-or-flight response — increased heart rate, myocardial contractility, and sweat production — the parasympathetic system causes slowing of the heart, increased heart-rate variability, stimulation of salivary glands, and other responses that induce relaxation and help compensate for periods of high stress.
“High levels of parasympathetic activity have been associated with numerous benefits including more adaptive emotion regulation strategies and decreased risk of cardiovascular disease,” the researchers write.
The moral of the story? Spend as much time as you can in the presence of trees. The forest is our natural habitat.