Keeping people healthy in cities, especially poorer areas, is hard, and a simple, effective and scientifically proven prescription for improving health is to plant more trees.
The idea of planting more trees in urban environments is so simple, affordable and effective that it’s hard to understand why we aren’t doing it more urgently, especially when there is so much evidence showing how much good trees do.
Environmental epidemiologist Mark J. Nieuwenhuysen proposed a simple way to remember just how important trees are: the “3-30-300 rule,” which suggests that for optimal health, everyone should have at least three trees visible from their home, at least 30 percent tree canopy coverage in their neighborhood, and live within 300 meters of at least one hectare of green space.
Trees and urban health
Ideally, cities should have at least 30 percent tree canopy coverage. Vancouver is currently at 23 percent. THE CANADIAN PRESS/Darryl Dyck
Trees are beautiful and certainly beneficial for the environment, but the most practical rationale for planting more trees is that they provide clear benefits to public health, both in a preventive and curative sense.
As a physician and researcher, I say this with empirical confidence, and I also have strong evidence to back up my claims.
Here are 10 ways planting trees in cities can improve people’s health:
A meta-analysis showed that increased vegetation was significantly associated with a 2-3% reduction in cardiovascular disease mortality. These studies included data from 18 countries and more than 100 million people.
By improving health, trees reduce healthcare costs, allowing an overburdened system to care for more people.
Trees help reduce ground-level concentrations of urban air pollution and improve air quality, especially in areas with high levels of pollution.
Trees provide shade and cool hot urban environments, including buildings without air conditioning. Less heat in summer means fewer premature deaths.
Trees promote healing. A study at a Pennsylvania hospital compared the post-operative outcomes of gallbladder patients who recovered in a room with a view of trees to those who recovered in a room facing a brick wall. Patients who recovered in rooms with a view of trees had shorter hospital stays and required less pain medication overall.
Trees improve mental health. Published studies have shown that people who walk in nature for 90 minutes experience less rumination, the repetitive negative thoughts that undermine mental health. Spending time in natural environments has also been shown to help reduce symptoms of post-traumatic stress disorder, anxiety, depression, and anger disorders.
Trees are an important component of outdoor environments that support physical activity.
People who live surrounded by trees and greenery tend to sleep longer, which has a direct positive impact on their physical and mental health.
Regular play in green spaces has been linked to reduced symptoms of ADHD in children.
Adding more trees is strongly associated with less crime, and cutting down trees is strongly associated with more crime.
Delivering trees to hospital patients
My clinical work involves treating vulnerable patients through the Shelter Health Network and Chronic Disease Specialist Hospital in downtown Hamilton, Ontario. At the former, I see mostly men struggling with homelessness, addiction and mental health issues, typically severe depression, post-traumatic stress disorder and anxiety.
At St. Peter’s Hospital, I work with frail elderly patients and those who cannot receive continuing medical care in residential facilities.
When patients arrive at the facility and see the tree-filled courtyard and nearby woodland of the Niagara Escarpment, they often say they already feel better.
But just a few blocks away, it’s easy to find sun-baked sidewalks and stark, mostly treeless landscapes where people live, work and go to school.
McMaster University medical students plant a fast-growing “mini forest” in Hamilton in 2022. (M. Sargent), provided by the author (not to be reused)
In 2012, biologist Lorraine Ironside and I founded Trees for Hamilton. Our charity continues to advocate and support tree planting on the grounds of healthcare facilities, including a long-term project to plant 70 trees on the inner-city grounds of Hamilton General Hospital.
When patients don’t have access to trees, the idea is to bring the trees to them by planting what we call “healthcare forests.”
To date, the group has co-hosted 80 events and engaged over 500 volunteers to plant 5,000 trees. Group members have given presentations to community and academic organizations about the benefits of trees and how they can organize similar projects.
Using the knowledge and experience we gained there, we launched a related national initiative called Canadian Healthcare Forests, partnering with health care professionals and tree-planting charities across the country to plant more trees on the grounds of hospitals and clinics.
These organizations partner with several groups that advocate for tree planting and raise funds for tree planting or plant the trees directly.
Canadian city trees
Finding places to plant trees in urban areas isn’t always easy. For example, we’ve found that a surprising number of homeowners aren’t interested in planting trees in their yards because they drop leaves, twigs, pine cones, bud covers and other things that have to be cleaned up. We try to show them that planting a tree is worth more than the hassle.
Downtown parks and green spaces could do with more trees, but some neighborhoods don’t want them because they worry they’ll provide hiding places for crime. Deciduous trees don’t significantly block views, as shrubs and evergreens might.
Even after you plant a tree in an urban area, it can be difficult to protect it. Especially on public lands, “weeding” is an obvious threat to tender young trunks, as is lack of watering. But these problems are easily solved compared to the human problems that a healthy tree canopy solves.
Hamilton has about 20 percent tree coverage citywide, but only half that in its most problematic areas, and with the help of free trees from city and nonprofit programs, it aims to reach 40 percent by 2050. Getting there would require planting about one million new trees.
Other Canadian cities have varying coverage rates, including 20 per cent in Montreal, 28 per cent in Toronto, 23 per cent in Vancouver and eight per cent in Calgary, according to Nature Canada’s September 2022 report, “Canopy for All.”
Increasing these numbers to 30 or 40 percent will be difficult, but such goals are by no means impossible to achieve.
If people in every city could make planting more trees a priority, the benefits for everyone would be lasting and tangible, and would far outweigh the costs.
