Green space and biodiversity in relation to health: assessing the impact on the Belgian population

Abstract

Evidence before this study: Systematic reviews have shown that natural environments and urban green space provide ecosystem services or ‘nature-based solutions’ that have the potential to enhance public health and well-being. There is relatively strong evidence for positive associations between exposure to green space and cardiovascular health, respiratory health, immune system regulation, and self-reported mental health. Most of this evidence has been obtained from models that estimate the association between human health outcomes and NDVI (a measure of residential greenness) or relatively coarse land cover data. Other frequently used green space exposure indicators are presence, accessibility, and proximity of green spaces. The roles of different types of green space, the precise quantity of green space, the biodiversity within green spaces, or projected changes in green space properties remain relatively underexplored. In addition, very few evidence is available for the specific Belgian context, which is complex because there are overlapping gradients of green space and socio-economic and environmental confounding variables. Added value of this study: Results from a cohort of 88 pollen allergy patients, from three longitudinal ecological register-based studies comprising up to 11575 census tracts, and from an empirical modelling study of 18 urban parks and 5940 trees are reported. Generalized log-linear models, complemented with a variety of supporting statistical techniques, were used to investigate associations between self-reported mental health (GHQ-12), prescribed reimbursed medication sales for specific morbidities (cardiovascular disease, childhood asthma, and mood disorders), and exposure to residential green space, adjusting for potential socio-economic confounders. In addition to the commonly used Corine Land Cover data, very high-resolution maps of high green (> 3m), low green, and land cover (forest, low green, grasslands, and gardens) were used to accurately determine the quantity and typology of residential green space at the level of the individual and at the level of official census tracts. We found moderate to very strong evidence for protective associations between several residential green space types (in particular forests and grasslands) and different health endpoints but also for a number of risks. In the panel of tree pollen allergy patients, self-reported mental health was associated with the amount of high green and low green within a buffer of 1km but the perceived presence of allergenic tree species near the residence was associated with higher levels of seasonal distress. Area-level relative cover of forest, grassland, and all green were typically associated with lower medication sales for cardiovascular disease or mood disorders in adults, although the magnitude and sometimes the direction of the associations varied among the three administrative regions of Belgium, and between urban and rural areas. No association was found between forest cover and childhood asthma medication sales; instead, the relative area-level covers of grassland and gardens emerged as risk factors. In all models, socio-economic background variables, such as level of education, employment status, or housing quality had considerable impacts on the associations between health and green space. Finally, the analysis of present and projected tree species composition and traits in urban parks in Brussels indicated that the allergy risk is very low, but that the risk may double due to increased allergenic potential and pollen season duration induced by climate change. Implications of all the available evidence: Exposure to green space near the place where people live in Belgium is associated with beneficial health effects, although there may be regional differences and specific risks in vulnerable populations such as children or pollen allergy patients. The evidence indicates that size more than green space type is important for health. Taken together, these results seem to suggest that health effects of exposure to green space are mainly effects of reduced exposure to stress-inducing grey space, although specific green space types such as forests and grasslands may generate additional benefits through impacts on physical activity, social interactions, or connection to nature. The main implication for urban planning and public health is that available green spaces should be maximally conserved, not only in rural areas but also within cities, where the majority of the population lives, and this not only for biodiversity but also for human health.