First comprehensive review of the health impacts of urban trees published

Thanks to the efforts of researchers over the past few decades, we have a solid understanding of the ecological benefits of urban forests, such as reduced greenhouse gases, decreased stormwater runoff, and lessening of the urban heat island effect. In contrast, knowledge of the human health benefits of urban forests is still developing. Existing reviews of health benefits have focused more broadly on nature, green space, and greenness rather than concentrating specifically on urban trees.

To address this gap, a team of scientists reviewed the existing quantitative research on the relationships between urban trees and human health. Their findings were published last month in the International Journal of Environmental Research and Public Health in the article Urban Trees and Human Health: A Scoping Review.  

The team began by compiling 3358 peer-reviewed articles. After screening these articles and assessing their quality, 201 studies remained. The remaining studies were sorted into three categories: Reducing Harm, Restoring Capacities, and Building Capacities. Reducing Harm includes topics such as air pollution, ultraviolet radiation, heat exposure, pollen, and crime. Restoring Capacities includes attention restoration, mental health, stress reduction, and clinical outcomes. Building Capacities includes topics such as birth outcomes, active living, immune system, cardiovascular function, weight status, and social cohesion.

Taken as a whole, this review “demonstrates why urban forest planning and management should strategically promote trees as a social determinant of public health” and “will help inform future research and practice.”

The “Results-Health Outcomes” section of the article cites the findings of numerous studies. You may want to take a look. Here are a few examples:

  • “increased vegetative cover was found to help offset projected increases in heat-related mortality for heat wave conditions in 2050 by 40 to 99% across three U.S. metropolitan regions”
  • “Extensive tree mortality within neighborhoods, due to the EAB, was associated with increases in some types of crime in Cincinnati, U.S.”
  • “MRI scans of adult city dwellers living close to a forest displayed an amygdala [brain] structure associated with better capacity to cope with stress”
  • “Using state health survey data, Beyer et al. found that a 25% increase in neighborhood tree canopy was associated with a 1-point decrease on the 5-point Depression Anxiety and Stress Scales (DASS) instrument”
  • “in all prefectures of Japan, the percentage of forest coverage was significantly inversely associated with the standardized mortality ratios for lung, breast, and uterine cancers in females, and prostate, kidney, and colon cancers in males after adjusting for smoking and socio-economic status”
  • “Within cross-sectional studies, objectively measured neighborhood tree cover was associated with higher levels of: commuting-related walking and cycling among adolescents; self-reported recreational walking in adults; levels of play among children; and total free-time physical activity among students in grades 6 to 8”

You may also want to watch the webinar Health Benefits of City Trees: Research Evidence & Economic Values in which the article’s lead author, Dr. Kathleen Wolf, discusses the team’s work.

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