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Study finds trees are linked to the reduction of psychological stress

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Natural scenery has long been accepted and utilized in mental health circles as an effective tool for the reduction of psychological stress. However, the exact nature of this relationship has yet to be thoroughly examined in academic literature.

A new study by Bin Jiang and colleagues, published in the May 2016 issue of Environment and Behavior, helps to lessen this deficit by employing a dose-response curve model to analyze the link between tree canopy coverage and stress reduction in an urban environment.

In the experiment, 158 subjects were first exposed to a mild stressor and then viewed an urban scene with varying amounts of tree coverage using a 360-degree headset. The researchers were careful to exclude potential subjects with depression and posttraumatic stress disorder (PTSD), as these conditions could have had an undesirable impact on the experiment (and vice versa).

To induce stress, each participant completed a series of stages designed to elicit stress as a natural response to specific social situations. The test required the preparation and delivery of a public speech, followed by the performance of a subtraction task in front of judges and a video camera. After being intentionally stressed, the subjects viewed one of ten six-minute 360-degree videos featuring metropolitan areas that varied only in the amount of visible tree canopy coverage (ranging from 0-70%).

The level of participants’ mental stress was measured with a self-reported questionnaire. Results were gathered at three points during the study: prior to being stressed, immediately following the last judgement task and after a short cool-down period at the very end of the experiment. Scores from these reports were used to execute a variety of analyses related to the development of a dose-response curve.

A scatterplot graph clearly shows the traits of a positive linear relationship, with tree cover density and reported stress reduction increasing together. This association type is further supported by multiple regressions. Most participant responses were also examined using a content analysis that identified the use of keywords like “relaxing”, “calming”, and “tranquil” within descriptions of stress recovery experiences.

This study adds further support for the beneficial effect of natural scenery on stress reduction, while helping us to better understand the fundamental structure of the association. The presence of a linear positive relationship has important implications because it means that tree canopy exposure benefits will be reduced as less coverage is available. As the authors succinctly state, “these findings suggest that viewing tree canopy in communities can aid stress recovery and that every tree matters.”

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