How do species richness and colour diversity of plants affect public perception, preference and sense of restoration in urban green spaces?

Urban development has led to an overlap between natural and artificial environments, affecting individuals’ experiences with nature. To create high-quality urban natural environments, it is crucial to understand the residents’ perceptions, preferences and psychophysical health benefits concerning biodiversity. This study, employing various experimental designs, investigated the perceptions, preferences and restorative experiences of 695 participants concerning different levels of plant species richness and colour diversity in four typical urban green space types (lawn, forest, square and streetscape). The following discoveries were made: (i) The colour diversity carried by vegetation in lawns was an important basis for the public to identify plant diversity. Lawns with high richness achieved by different grass species (that have green colour) were not preferred by the public, and increased colour diversity that can be achieved by adding flowering plants (forbs) was preferred by people more than a single green lawn. The species richness of forests was positively correlated with public perception, preference and perceived restoration, with single green forests being preferred by the public. Additionally, people preferred vegetated environments over unvegetated squares or streetscapes. (ii) Participants’ perceptions, preferences and perceived restoration were positively correlated. Their preference for and perceived restoration from plant diversity depended more on their perception of it than on the actual species richness. (iii) Participants’ gender, expertise, physical condition, ecological knowledge, childhood living environment, frequency of use and accessibility of green spaces, natural orientation (connectedness), gardening, sense of security and well-being all influenced their perceptions, preferences and perceived restoration from plant diversity to varying extents. Significant distinctions were found between different forms of experimental design. Combining between-subject and within-subject designs could both control individual errors to some extent and avoid long-term effects on the participants compared to using either design alone. These findings provide a theoretical basis and practical approach for future biodiversity-oriented urban green space planning and management to better maximise the ecological and social service benefits of urban green spaces.