Tolerant greenspaces: Designing urban nature-based solutions that foster social ties and support mental health among young adults.

The voices of young adults (15−24) ring faintly in the conversation around nature-based solutions (NBS), an absence that results in a lack of both procedural and distributive justice in the provision of such solutions. NBS clearly shape young adults — including their connections with nature, engagement in pro-environmental behaviours, and social and psychological health — but the dramatic reshaping of urban areas via rapid growth, densification, and technological innovation means today's young adults have fewer opportunities to benefit from NBS. In a potentially vicious cycle, this shortfall can result in a weakened sense of connection with nature, leading to less time spent in natural environments and fewer sustainable behaviours. Achieving justice for young adults requires understanding their preferences, clarifying relationships between NBS characteristics and use, and translating research into evidence-based design. This paper fills these gaps by summarising interdisciplinary knowledge regarding the impacts of contact with nature on the development and well-being of young adults; describing case studies conducted in formal parks located in Australia's largest cities of Sydney and Melbourne to clarify connections between our existing knowledge and the real-world provision of NBS; and applying these findings to develop an appraisal framework comprising three primary attributes — order, diversity, and seclusion and retreat — that supports the design and integration of urban greenspaces that uniquely benefit young adults' social development and mental health. Finally, we explore the framework's implementation, demonstrating its utility and flexibility for urban planners, municipal policymakers, and natural-resource managers seeking to advance intergenerational equity. • Young adults are a missing middle in research on NBS and health, resulting in a lack of procedural and distributive justice. • Novel appraisal framework focuses on fostering social ties and supporting mental health among young adults via NBS. • Informed by literature review and Australian case studies, framework comprises order, diversity, and seclusion and retreat. • Framework advances collaborative planning that achieves intergenerational equity via creation and maintenance of urban NBS. [ABSTRACT FROM AUTHOR]