Shared spaces and civic participation.
Parks and public space sit at the intersection of public health, civic life, and equity. The experimental evidence in this domain is thinner than in more program-focused policy areas — most parks research is observational. But the available evidence on participatory governance and urban greening is instructive about the conditions under which shared spaces serve their communities.
2
experiments
2
positive results
0
null or negative
0
replicated
Key Findings
01
Community advisory boards for parks shift spending toward underserved communities and increase maintenance quality — when they have real decision-making authority.
Los Angeles's park advisory board experiment tested whether giving communities formal governance roles in park management changed investment priorities and maintenance outcomes. Boards with meaningful budgetary influence shifted capital spending toward parks in lower-income areas that had historically received less investment. The critical condition was real authority — advisory boards without budget influence produced no measurable spending shifts. The finding echoes the Porto Alegre participatory budgeting evidence: participation works when it is genuine.
02
Urban tree planting reduces heat, improves air quality, and has measurable effects on physical and mental health — but equity of placement matters.
Urban tree equity analysis across US cities found that lower-income and higher-minority neighborhoods have systematically lower tree canopy cover — and higher heat exposure. Cities that have targeted tree planting toward lower-canopy areas produce more equitable health outcomes than those that respond to resident requests (which skew toward wealthier neighborhoods). The evidence on causal health effects of individual tree planting is harder to isolate, but the correlation between canopy and health outcomes is robust across city types.
What the Evidence Cannot Yet Tell Us
Does access to parks increase physical activity for nearby residents — or does physical activity drive park use, with limited causal effect running the other direction?
What park features (sports facilities, trails, playgrounds, natural areas) produce the strongest mental health benefits for different age groups?
How does park privatization or selective access (permit requirements, fees) affect equity of use in dense urban neighborhoods?
Can urban greening interventions — tree planting, pocket parks, parklets — produce measurable effects on crime, social cohesion, or property values in controlled studies?