Marginalized neighbourhoods tend to have fewer and smaller street trees - and less species diversity - than wealthier areas, according to a new study from the University of Toronto Mississauga.
For the study, researchers in U of T Mississauga's department of geography, geomatics and environment analyzed publicly available municipal tree inventories from 32 cities across eight provinces, with nearly half located in Ontario.
They found inequalities in distribution of street trees in all 32 cities, with neighbourhoods bearing high-density populations found to have lower tree species diversity across the board.
Published in npj Urban Sustainability , the research provides the first cross-country snapshot of tree distribution in Canadian municipalities, and how the patterns relate to population demographics.
Lead author Alex Martin, who conducted research during his graduate studies, said street trees offer more than just aesthetic benefits - they help cool neighbourhoods, clean the air and support physical and mental well-being.
"Neighbourhoods without trees are often those that also face higher temperatures, greater air pollution and less access to nature," said Martin, a researcher in the Household-level Urban Socio-Ecology (HOUSE) Laboratory , which is led by Tenley Conway, professor and associate chair, research in the department of geography, geomatics and environment. "Planting and maintaining street trees in these areas is an important community-based approach that can help address health inequalities."
For their analysis, Martin and co-authors, who included research assistant Ashlynn Fleming, used the Gini Index - a tool often used to study income inequality - to measure how evenly trees are distributed within each city.
Then, using spatial statistics, they examined how tree coverage aligned with factors like population density, residential instability and the proportion of racialized and immigrant residents.
"[The Gini Index is used] in geography increasingly to measure the equity of things like access to hospitals, access to parks and in this case, access to street trees," said Martin, who graduated from U of T Mississauga in June and is preparing to start his doctoral studies at the University of Oxford.
"We use metrics that allow for benchmarking between cities. Urban planners and cities can see where they stand and prioritize resources accordingly."
Researchers found that in every city, street trees weren't evenly spread out, and the largest, most established trees were mostly clustered in a few neighbourhoods.
Among the factors they looked at, residential instability - a measure characterized by more renters and frequent moves - was the strongest and most consistent predictor of tree inequality.
Neighbourhoods with more racialized and immigrant residents also tended to have fewer, smaller and less varied trees.
The study also found that while tree density and size tended to increase with population density, species diversity declined, likely because fewer tree species can thrive in denser urban environments.
The researchers focused on street trees specifically because unlike trees in parks or on private property, they're publicly managed and consistently documented across cities. This allowed for more reliable data collection, said Martin, while also offering more direct pathways for urban planning and equity interventions.
Some cities stood out. Fredericton, N.B. had the most equal tree distribution, which the researchers attribute to its smaller population and long-standing planting programs. At the other end of the spectrum, Maple Ridge, B.C., had the most uneven distribution, likely due to rapid development and a focus on parks and private land over street planting.
Toronto had the highest average species diversity but still showed disparities, with racialized and immigrant neighbourhoods having smaller trees and lower diversity.
In Mississauga, some marginalized areas had relatively more trees than other parts of the city, highlighting how local context shapes distribution, the authors noted.
The findings, Martin said, contribute to ongoing conversations about environmental justice and climate resilience. Diverse street tree plantings not only help reduce air pollution and extreme heat, he noted, but are better able to withstand pests and rising temperatures.
Ensuring equitable access to healthy tree cover is key to both public health and sustainability, he said.
"To improve climate resiliency, we often need more trees and larger trees and trees that are of a species that will survive," Martin said. "We know that a more diverse urban forest is more capable of handling changes into the future projected climate scenarios."
