Trees, grass, or concrete? The effects of different types of environments on stress reduction

Abstract

Despite a number of studies about how natural environments can affect human health and well-being, few have examined the potentially different effects of different types of vegetation. We therefore designed and conducted a randomised controlled experiment to identify the restorative potential of different types of trees and grass in an urban virtual reality (VR) environment. We initially induced stress in participants (n = 89) by asking them to complete a 5-minute math test while listening to noise, after which they were randomly assigned each to one of three VR environments: a courtyard with grass, a courtyard with trees, or a courtyard devoid of any vegetation. Participants were immersed in the VR experience for 10 min, during which we measured skin conductance levels (SCLs). We also assessed participants’ positive and negative affect scores at baseline, before VR immersion, and after VR immersion. Repeated-measures analysis of variance with a general linear model indicated that the grassy environment had the greatest effect on positive affect. SCLs during the second half of VR immersion were significantly lower in both the grass and tree environments than in the concrete-only environment. Our results are consistent with Ulrich’s theory that unlearned factors of evolutionary origin influence affective responses to environments. Our findings provide preliminary practical evidence for landscape planning that can maximise the restorative effects of urban environments.