Urban Tree Canopy and Anxiety Before and During the COVID-19 Pandemic: Evidence from Emergency Medical Service Calls

Urban tree canopy has been linked to psychological benefits through stress reduction, support for physical activity, and opportunities for social interaction. However, its relationship with acute psychological disorders such as anxiety remains underexplored, particularly during the pandemic, and tree canopy is often unevenly distributed across neighborhoods, disadvantaging low-income communities. The study examined 2,219 census blocks within 160 block groups in Marin County, California, from March 2019 to March 2021. Anxiety- and psychiatric-related emergency medical service calls served as the outcome measure. Tree canopy coverage was derived from 2018 NAIP aerial imagery, with residential population included as an exposure variable. Models adjusted for sociodemographic, economic, and built environment factors and were estimated using zero-inflated negative binomial regression. A total of 638 mental health–related EMS calls occurred before the pandemic and 662 during the pandemic, indicating no significant change in overall volume. Higher levels of tree canopy were associated with fewer anxiety-related incidents, with the strongest protective effect observed prior to COVID-19. During the pandemic, this association weakened, while household income became a stronger predictor of mental health outcomes. Moderation analyses further showed that the protective effects of tree canopy were more pronounced in higher-income neighborhoods. These findings suggest that tree canopy contributes to psychological well-being under typical urban conditions, but its buffering capacity may diminish during periods of acute stress. Persistent socioeconomic disparities highlight the importance of equitable green infrastructure investments to support urban mental health resilience.