• Photo: flickr\René Ehrhardt
    Photo: flickr\René Ehrhardt

At a suburban house outside Toronto, armed with assorted gadgets for measuring trees, I politely ask the homeowner whether I can assess the vegetation in part of his backyard. “My tax dollars put to good use,” he says sarcastically.

I’m working on a project to evaluate the state of the urban forest throughout the Greater Toronto Area, I explain, but attempting to ease his skepticism is futile. Thankfully, as my partner and I follow aerial maps to chase down plots throughout Brampton, Ont., another team is roaming the streets of Toronto, collecting data from over 400 random samples.

This was more than two years ago, part of an effort to use a new research model in Canadian cities. Developed by the U.S. Forest Service, i-Tree Eco (originally called UFORE, for Urban FORest Effects), is a set of software tools that quantifies the benefits provided by trees in urban communities. Combining onthe- ground assessments of tree types and sizes with local weather and pollution data, i-Tree offers a snapshot of the city’s urban canopy and highlights its positive effects on air pollution, energy use in buildings and carbon emissions.

The model’s primary goal is to appeal to the wider public by speaking their language, says research forester David Nowak, one of i-Tree’s lead developers. “We have to tie results to issues such as human health and air pollution,” he says, “as these issues matter to everybody.”

At an urban forestry conference last fall in Truro, N.S., Nowak described i-Tree’s “second generation,” which will integrate GIS software and Google maps for even more accessibility. Nowak hopes to engage people beyond the urban-forester circuit, from city planners to school and community groups, to increase i-Tree’s relevance as a management tool.

Toronto Parks, Forestry and Recreation director Richard Ubbens, former director of the city’s urban forestry division, always had a “gut feeling” about the worth of his city’s forests. “The combined value of the urban forest is huge,” he says. “Urban trees convert a subdivision into a neighbourhood and a community.”

The results from Toronto’s i-Tree assessment, released in a September 2010 report called “Every Tree Counts,” confirmed what Ubbens had always known but also quantified a great deal of information he can now use to convince others. The replacement value of Toronto’s roughly 10 million trees is estimated at $7 billion, and their value in annual ecological services is $60 million. Each year, Toronto’s trees store 1.1 million tonnes of carbon (roughly the annual emissions of 733,000 cars), intercept about 1,430 tonnes of air pollution and save $10.2 million in energy costs for buildings.

But all is not rosy. Experts suggest the canopy should cover 30 to 40 percent of the city, but Toronto’s trees cover roughly 20 percent. To reach his goal of 35 percent canopy cover within 50 years, Ubbens says we must keep planting and remain proactive about protecting existing trees.

WHAT LIES BENEATH

Were Johnny Appleseed alive today, he’d probably be cursing urban design. Greening a city involves much more than tossing a seed over your shoulder. There are traditional challenges, such as drought and high winds, says Ed Gilman, an environmental horticulture professor at the University of Florida who was at last fall’s Canadian Urban Forest Conference in Nova Scotia. Then there are urban-specific obstacles: young trees are susceptible to vandalism, trees with broad crowns may need constant pruning to avoid obscuring road signs, and too much shade cast by skyscrapers can prove fatal.

Noting that “large, long-lived trees might be the logical choice” for planting because “they provide for a lasting effect,” Gilman also believes in carefully choosing and even modifying planting sites. Trees should be rooted in soil that’s not covered by sealed surfaces, which means rerouting existing sidewalks at times. Gilman also notes the potential of using alternative sub-base material, an idea that engineers at DeepRoot have developed for the densest urban settings. DeepRoot, a California-based company with an office in Vancouver, has created a product called the Silva Cell: rigid frames made from a high-strength compound of glass and polypropylene that support hard surfaces such as sidewalks and parking lots (LEFT). The units can be stacked underground, preventing soil from becoming compacted and allowing air, water and nutrients to reach trees. Silva Cells were used at Vancouver’s Olympic Village and have been installed at several sites in Toronto. Johnny Appleseed would approve.

— Tyrone Burke