The measurable benefits of urban trees

A tree grows on RoncesvallesLocal resident and Roncesvalles Renewed member Jane Humphreys forwarded an interesting article from a recent issue of Planning, the magazine of the American Planning Association. It’s called “Branching Out” and is written by James Schwab. You can read the PDF here or view it in HTML format here. The article condenses the findings of a new APA study called Planning the Urban Forest (this link has further links to other tree/urban planning resources, including a podcast from an Oct. 2008 APA symposium on the urban forest).

Much of the information will be familiar to readers of this blog, where the BIA has repeatedly urged the creation of a Living Sidewalk along Roncesvalles. This project would integrate Roncesvalles’ stormwater sewer with an innovative new tree planting system that would finally allow urban trees to grow to maturity, instead of dying within 5-10 years of age. With healthy trees, sidewalks would become massive absorption pads, sucking up huge amounts of water and reducing the frequency of raw sewage overflows into our lake. In addition, mature urban trees will provide shade, cool the street and absorb 15 times as much carbon dioxide as the same tree in a rural setting

But turns out, there are even more benefits.

Trees absorb carbon dioxide, obviously, but they also improve air quality by removing five key pollutants: sulfur dioxide, nitrogen dioxide, ozone, particulate matter, and carbon monoxide. And the tree’s effect on air quality is enhanced further as it cools the street, since heat is a big factor in the production of ozone and smog (in 2005, there were 48 High Health Risk smog days in Toronto).

Scientists are also now seriously studying a developing concept known as “environmental justice.” For example, it is now understood that urban communities with access to natural settings tend to have better health, such as lower asthma rates. Trees also tend to make neighborhoods safer (see “Green Streets, not Mean Streets” a condensed summary of a 2001 study by the University of Illinois, which shattered a long-standing myth that trees provided criminals with places to hide, prompting many property owners to cut them down). In jurisdictions such as Connecticut, trees and parks are forming part of their social policy.

Once again, we are learning that trees are not simply decorative frills, but also have enormous environmental, health and social benefits that can be measured and valued. Trees are an important long-term investment whose worth must not be underestimated.

The Living Sidewalk is not yet adequately funded, and time is running out to get the project included in the 2009-10 reconstruction of Roncesvalles. If you would like to offer support to the Living Sidewalk project, you can email Councillor Gord Perks at