Following growing evidence that exposure to nature makes people feel and think better, a study using 3-D videos of residential streets with varying amounts of tree canopy has demonstrated a dose-response curve.
The study involved 80 men and 78 women, who were stressed by having to deliver five-minute impromptu speeches before two interviewers and a video camera, before then having to solve several subtraction problems out loud, without using computing devices, paper or pencil. Afterwards, they watched one of 10 panoramic 3-D videos showing similar neighborhood streets on which the density of tree cover ranged from 2 to 62%.
The men displayed a bell-shaped dose-response curve, with their stress biomarkers (salivary cortisol and skin conductance levels) improving steadily as the tree canopy increased from 2 to 24%. The greatest benefits came from tree canopy in the 24-34% range, and stress recovery declined for tree cover over 34%.
Women did not show the same physiological response, although their self-reports suggested that they also experienced stress reduction benefits that increased proportionally with the percentage of tree canopy viewed.
While 41% of male and female participants who watched videos with minimal tree canopy described calming effects, more than 90% reported feeling calm or relaxed when the tree canopy was at 36%. All reported well-being when the tree cover was at 62%.
Jiang, B., Li, D., Larsen, L., & Sullivan, W. C. (2016). A Dose-Response Curve Describing the Relationship Between Urban Tree Cover Density and Self-Reported Stress Recovery. Environment and Behavior, 48(4), 607–629. http://doi.org/10.1177/0013916514552321