Tree canopy is associated with lower levels of depression, but not for everyone: Findings from a large, nationally representative sample.

Depression and other mental health conditions affect large numbers of people worldwide. Increasingly, studies examine the potential for neighborhood features to improve mental health, including residential green space. However, few studies have examined differences in green space benefits across sub-populations, and there has been no large-scale national study in the United States (US). The objective was to examine the cross-sectional relationship between residential tree canopy and depression among US adults (n = 39,301) in the National Health and Nutrition Examination Survey (NHANES) from 2005 to 2018, including whether relationships differ by subgroup and whether physical activity mediated relationships. Greater tree canopy was associated with lower depression scores. Physical activity partially mediated this relationship in the expected direction, such that higher tree canopy was associated with higher physical activity and higher physical activity was associated with lower depression. Stratified analyses revealed significant negative associations between tree canopy and depression for non-Hispanic White individuals, those without a high school degree, and metropolitan populations. No significant associations were detected in analyses stratified by employment, poverty-income ratio, or time spent outdoors, though some analyses showed consistent magnitude and direction, though non-significant. Some have discussed the potential for tree planting to address health inequities, particularly given differences in green space exposure across high and low socioeconomic areas. We found some evidence that trees provide greater benefits for more disadvantaged individuals.