Urban Tree Canopy, Asthma Prevalence, and Health Equity in Los Angeles: A Geospatial Analysis with Implications for Urban Forestry

In this cross-sectional, ecological study of Los Angeles County ZIP codes, we evaluated the association between tree canopy coverage and asthma prevalence. Urban tree canopy has been promoted as a way to improve air quality and mitigate urban heat, but its relationship with asthma is not well established. Previous studies have shown mixed results, and little is known about whether associations differ between children and adults or across communities with varying demographic compositions. This study evaluated the association between tree canopy coverage and asthma prevalence across Los Angeles County ZIP codes. Data from 75 ZIP codes with complete information on canopy cover and asthma prevalence were analyzed using correlation, t-tests, and regression models adjusting for population density and minority population composition. Greater canopy coverage was associated with lower pediatric asthma prevalence (β = −0.625, p < 0.001); pediatric rates were 12.7% in low-canopy ZIP codes compared with 10.5% in high-canopy ZIP codes (t = 6.07, p < 0.001). This inverse relationship was stronger in ZIP codes with higher minority populations (interaction β = –0.0145, p = 0.006). In contrast, canopy coverage showed a weak but statistically significant positive association with adult asthma prevalence (β = 0.33, p < 0.001). These findings suggest that urban tree canopy may play a role in reducing pediatric asthma disparities, underscoring the potential of equitable urban forestry strategies as part of public health planning.