Depression, Equity, and Greenspace in Parks and Residential Areas

Abstract

Humans have an innate desire to form connections with the natural world which has prompted many to consider the health implications of decreased engagement with nature due to urbanization, especially concerning mental health. Greenspaces like parks, gardens, forests, and nature preserves may be used to preserve and rekindle our relationship with nature. Depression is one of the most pressing mental health issues of our time and a growing body of research suggests that greenspace may relieve depression. Our scientific understanding of this phenomenon is still limited. Further research is needed to understand which kinds of greenspace are most salubrious and how individual, ecologic, and societal factors influence how people benefit from greenspace. The first two aims of this dissertation help deepen our understanding of how different types of greenspace in residential areas and within parks might relieve depression. For both aims, we leveraged data from a long running nationally representative cohort of older adults in the United States. In Aim 1 we quantified vegetation using satellite images. We estimated the association between residential vegetation and the prevalence of major depression. We further examined how these associations varied across climate. In Aim 2 we paired a newly curated catalog of parks in the United States with a high resolution landcover dataset to measure access to different types of greenspace within parks. We estimated the association between access to different types of park space and depressive symptoms. The goal of Aim 3 was to expand on previous research concerning equity in greenspace access by investigating how the amount and type of vegetation within parks is related to the sociodemographic characteristics of surrounding neighborhoods. For this aim, we used a high-resolution landcover dataset, publicly available park boundaries, and American Community Survey data for three of the most populous cities in the United States. In Aim 1 we found more residential vegetation is associated with a lower prevalence of major depression. These associations were modest, and it appeared that vegetation may be most beneficial in cold and tropical climates. Associations were more nuanced or non-existent in arid and temperate climates. In Aim 2 we found having access to grassy park area was associated with fewer depressive symptoms, the opposite was true for non-vegetated spaces, and there was no association with tree covered park area. In Aim 3 we confirmed parks are an important source of greenspace for urban populations, but different populations have access to varying types of vegetation in parks. Parks in neighborhoods with more Black, Hispanic/Latino, or low socioeconomic status residents had less tree canopy but more grass cover and impervious surfaces or soil. This dissertation shows that the relationship between greenspace and depression is complex and depends on many factors including climate, types of vegetation, and where that greenspace is located relative to one’s home. It also shows that the composition of greenspace within parks is related to sociodemographic characteristics of surrounding neighborhoods. These findings have implications for future research in the field in that they emphasize the importance of exposure measures that disaggregate different types of vegetation, differentiate residential exposures from exposures in parks, and consider factors like climate that bear heavily on greenspace abundance and composition. This research can also be used to inform greening interventions, park design, and initiatives to increase greenspace equity.