By Erica N. Spotswood, Myla Aronson , Micaela Bazo, Erin Beller, JD Brown, Iryna Dronova, Cesar O. Estien, Howard Frumkin, Joseph Galarraga, Robin Grossinger, Kim Hachadoorian, Brandon Herman, Thomas Jennings, Viniece Jennings, Ming Kuo, Robert I. McDonald, Daphne Miller, Alessandro Rigolon, Jennifer Symonds, Karen Weinbaum.

Image Caption/Credit: A green street in New Orleans protects large trees in the public right-of-way. Large trees can provide better shade, UV reduction, and temperature reduction compared to smaller trees, and have been associated with lower sales of mood disorder and cardiovascular medication. Image credit: Robin Grossinger

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Cities around the world are increasingly turning to urban greening projects to boost biodiversity. Efforts such as planting trees, restoring parks, and creating green corridors offer a range of benefits. However, researchers haven’t clearly summarized the specific health impacts of biodiversity-focused greening projects until now.

We conducted a systematic review of 1,550 studies examining how different biodiversity-supporting features in cities—such as large parks, greenways, blue spaces (like lakes and rivers), private gardens, mature trees, and overall urban greenness relate to human health. The evidence shows a wide variety of positive health outcomes. These include better physical and mental health, more physical activity, healthier childhood development, stronger social connections, and reduced exposure to harmful factors like extreme heat, air and noise pollution, and UV radiation.

Most studies reported positive health outcomes, but we also found that the majority of studies correlational—meaning they showed associations, not cause-and-effect. We need more experimental and long-term studies to strengthen our understanding of how human health is impacted by exposure to green features.

We also found that supporting biodiversity in cities can sometimes lead to tradeoffs. For example, maintaining sports fields and trails can benefit human health but may harm local wildlife. Biodiversity-friendly spaces can also pose risks, such as increased exposure to allergens, disease-carrying insects, and potential conflicts with wildlife. In some cases, they may even contribute to green gentrification, which can displace vulnerable communities.

Overall, our review highlights significant opportunities to improve public health through actions that support urban biodiversity. With careful planning and attention to possible tradeoffs, cities can design greener spaces that benefit both people and nature.