A dose of nature: Tree cover, stress reduction, and gender differences

•We describe the dose–response curve for the impact of tree cover density on stress reduction.•We employed 6-min, 3-D videos of community street scenes as the nature treatment.•We measured skin conductance and salivary cortisol levels as measures of participants’ stress.•For men, the dose–response curve was an inverted-U shape.•For women, we found no relationship between tree cover density and stress reduction. Although it is well established that exposure to nearby nature can help reduce stress in individuals, the shape of the dose–response curve is entirely unclear. To establish this dose–response curve, we recruited 160 individuals for a laboratory experiment. Participants engaged in the Trier Social Stress Test (TSST) to induce psychological stress, and were then randomly assigned to view one of ten, 6-min, 3-D videos of neighborhood streets. The density of tree cover in the videos varied from 1.7% to 62.0%. We measured their stress reactions by assessing salivary cortisol and skin conductance levels. Results show a clear disparity between women and men. For women, we found no relationship between varying densities of tree cover and stress recovery. For men, the dose–response curve was an inverted-U shape: as tree cover density increased from 1.7% to 24%, stress recovery increased. Tree density between 24% to 34% resulted in no change in stress recovery. Tree densities above 34% were associated with slower recovery times. A quadratic regression using tree cover density as the independent variable and a summary stress index as the dependent variable substantiated these results [R2=.22, F (2, 68)=9.70, p