Green enough? A dose-response curve of the impact of street greenery levels and types on perceived happiness

Although research shows that individuals report higher levels of happiness when viewing green environments, the dose curve describing the impact of greenery on happiness remains undefined. Current literature only presents dose curves representing the associations between stress recovery and tree coverage, and does not explore how this fluctuates for different types of green infrastructure. Using an image-based randomised control trial with 401 participants, this study assesses the impact of levels and types of street greenery on people's perceptions of happiness. Participants were randomly assigned to rate one of six images representing proportional increments of street greenery coverage (from 0% to 45%) across three greenery configurations – ground level, between buildings, and vertical (on building façades). The results suggest that the highest levels of perceived happiness are obtained from green coverage of between 35% and 45%, at which point the effect levels off. Vertical greenery coverage has a larger impact on perceived happiness than the other two tested configurations, and has a positive linear rather than concave relationship. The study indicates that viewing greater amounts of greenery significantly enhances communities’ perceived happiness, and shows that the relationship is dependent on the type of green infrastructure configuration used.