Researchers at the Nanyang Technological University, Singapore (NTU Singapore) used virtual reality (VR) to examine whether vertical greenery truly had a stress buffering effect in an urban setting. They studied 111 participants as they walked down a virtual street for five minutes. Participants were randomly assigned to either a street that featured rows of planted greenery (e.g., on balconies, walls and pillars), or one with only buildings that had green painted walls in place of green plants.
While walking on the virtual street, heavy traffic sounds were played, and subjects' heart rate variability was tracked using a portable electrocardiogram (ECG) device, giving the researchers a physiological indicator of stress levels. Participants also answered a questionnaire that assessed their positive and negative emotions, and the level of anxiety they felt.
Those who viewed only the buildings with green paint experienced a significant increase in stress as recorded by one measure of heart rate variability, while those who viewed the plants did not experience any change in stress. They also reported feeling less positive when walking through the street with buildings covered by only green walls, while those able to view buildings covered by plants did not report feeling either more or less positive.
The researchers concluded that vertical greenery offers more than sustainability benefits; it has the ability to connect people closely to nature and assist in mental health. "Our findings have important practical implications for city planning and design, especially for high density urban areas that face land constraints. It provides evidence that vertical greenery systems, which make use of vertical structures above ground, may help moderate the detrimental consequences of stress," said co-lead author of the research, Sarah Chan, a PhD candidate from the Interdisciplinary Graduate Program at NTU.