Wolf, K. L., Lam, S. T., McKeen, J. K., Richardson, G. R. A., Bosch, M. van den, & Bardekjian, A. C. (2020). Urban trees and human health: A scoping review. In International Journal of Environmental Research and Public Health (Vol. 17, Issue 12, pp. 1–30). MDPI AG. https://doi.org/10.3390/ijerph17124371
The importance of trees in urban areas has long been studied. Scholars have researched the importance of trees in cities for their contribution to fighting climate change, promoting outdoor recreation, helping humans have healthy air to breath, and adding to the biodiversity in cities. The benefits of urban trees have more recently become an area of interest for governments, as they write plans and policies to help prepare their cities for a changing climate. The body of literature covering the importance of urban trees is vast, and unfortunately, sometimes new research can be buried in the wide array of publications. To help consolidate the large existing literature, Dr. Kathleen Wolf and her colleagues wrote a comprehensive scoping review of the literature examining the human health impacts of urban trees. Their teams’ work was the first review of its kind and helped to not only inform future urban tree research and practice but provided a foundation of evidence for why urban forest planning and management should promote urban trees as a “social determinant of public health” (Wolf et al., 2020).
Before diving into the human health benefits of urban trees, it’s important to determine a definition of urban trees and what it is we’re talking about here. Urban trees make up the urban forest, comprised of a variety of tree species and vegetation across public and private properties, streets, and waterfronts. The urban forest is typically referred to as green infrastructure because it provides a service to urban inhabitants both from a visual and functional perspective.
As with other features of infrastructure, green infrastructure and specifically urban trees for the purpose of this study, services are provided to urban inhabitants that range from providing shade on a hot summer day to capturing carbon dioxide and cleaning the air. Additionally, urban trees are able to decrease stormwater runoff, mitigate excess heat in urban centers (commonly referred to as the urban heat island effect), and provide recreational activities and a sense of natural beauty. These services, referred to as ecosystem services, give urban trees a special capacity to help promote human health and city officials are starting to recognize the importance of the health benefits of trees. The authors aim with this extensive review project was to help educate urban decision makers and planners on the importance of maximizing the public health benefits of urban trees by providing easy to digest scientific support for “better tree policy, planning, and management” (Wolf et al., 2020).
In an effort to consolidate the wide body of literature on the health effects of urban trees, the authors conducted a scoping review, searching published literature using keywords and academic search engines. Initially, the authors found nearly 3,400 peer-reviewed articles exploring the human health and urban trees! After strategic consolidation the authors were able to more clearly refine their search. They focused on publications that specifically evaluated the health outcomes of urban trees and removed any duplicate or non-relevant papers. Once they had the relevant papers they needed in hand, they conducted a quality assessment and a thematic analysis to ensure that the papers they considered had robust analyses and were thematically related to the goals of their project.
Upon completion of their analysis, the authors sorted their findings into thematic categories, or domains, that could provide a snapshot of the published literature under different domains of public health. The domains they explored were then broken down into subdomains to give even more clarity about the complexity of the relationship between urban trees and public health. Their domains included:
reduction of harm
- Air pollutant reduction and improved respiratory health
- Health impacts of tree pollen and other air pollutants (such as volatile organic compounds)
- Reduction of heat and cooling provided by trees
- Improved cognition and attention restoration
- Improved mental health, anxiety, and mood
- Reduced psychological stress
- Improvement of clinical health conditions
- Improved birth outcomes
- Healthier immune systems
- Promotion of active lifestyles
- Lower body weight
- Improved cardiovascular function
- Improved sense of community and social trust
Examining the literature and consolidating it into these more easy to manage domains allows urban planners and decision-makers to learn more about the health concerns most relevant to them and the health of their city.
The authors stress in their conclusions how broad and robust the body of work is recognizing the importance of urban trees to human health, both physical and mental. However, there are some negative health effects to emphasize, especially with allergies related to pollen. Overall, the authors found that the multiple health benefits of urban trees generally outweighed any negative health concerns and want their work to be considered as an educational tool for urban planners and elected officials looking to learn more about the importance of urban trees in their cities and towns. Many cities and towns are facing an urban forest that is decreasing and budgets are not always allocated for the improvement of urban trees so promoting the health of the urban forest is a challenge in some areas. However, addressing the vast environmental and health disparities that exist across city neighborhoods further highlights the importance of building a robust urban forest so that all urban inhabitants can enjoy the multitude of health benefits that come from urban trees.