For too long, they have suffered from the ravages of the urban environment. Now some municipalities are taking a kinder approach to caring for our street trees

By Lorraine Johnson

Money Trees

In the arsenal of arguments that justify municipal funding for street trees, the Town of Oakville has recently added some compelling economic muscle. A 2006 report (the first of its kind in Ontario), Oakville’s Urban Forest: Our Solution to Our Pollution, found that Oakville’s urban forest provides $2.1 million in ecological services annually. The town’s 1.9 million trees sequestered 22,000 tonnes of carbon dioxide in 2005 and filtered all of the town’s industrial and commercial emissions of coarse particulate matter. The report also calculated the replacement value of Oakville’s urban forest – $878 million – and the amount of annual savings in residents’ and businesses’ energy bills due to trees – $840,000.

“I don’t have any political genes,” says Marg Drummond, a retired teacher who lives in the town of Mitchell, near Stratford in southern Ontario. “I just have the tree-planting gene.” For four years, Drummond and a small team of volunteers canvassed the town, counting, measuring, assessing and identifying its trees. Ask her how many trees grow in Mitchell and she answers quickly and precisely: “13,758.” The information the volunteers gathered will help the town develop a comprehensive plan for the urban forest. Drummond’s favourite species, white birch, grows in Mitchell, as do silver maples, black walnuts, spruce and cedar hedges. But Drummond recalls with indignity a sad row of crabapples: “Those poor things were planted between the boulevard and the road, right underneath wires, so they get trimmed back to destruction every year!”

Life is tough for urban street trees. It’s no wonder that city trees – imprisoned in concrete planter boxes or sidewalk cut-outs, neglected after planting, assaulted by salt and sometimes people, blasted by exhaust fumes and the reflected heat off asphalt – often succumb to urban ravages after just a few years. (There’s a whiff of defeat in the name of Oakville’s tree department: Forestry and Cemetery Services.) For too long, our municipal planting practices have guaranteed streettree mortality. Statistics from the United States paint a bleak picture: the average life of a downtown, urban street tree is about seven years. But there is hope. Municipalities are reconsidering not only the kind of trees they plant, but also where and in what type of soil they plant them and how well they’re maintained.

“Urban forestry used to be a kind of orphan,” says Michael Rosen, vice-president of Tree Canada. “The ‘real’ forest was considered to be elsewhere, in the bush, not in major urban centres. But awareness of the value of street trees, and urban forests in general, is increasing.”

People often think that all we have to do is plant trees,” says David Schmitt, environmental and urban forest project manager for the City of Kitchener. “But there’s a lot more to it than that.” Schmitt, like many urban foresters, sees a pressing need for more long-term planning focused on what street trees need below the ground: “If we’re going to achieve healthy, tree-lined streets, then we need to create better soil habitat and root habitat.” Says John McNeil, manager of Forestry and Cemetery Services for the Town of Oakville, “You can’t plant an oak tree in a thimble and expect it to become a large shade tree.”

A number of municipalities are now engaged in proactive projects to improve the prospects for street trees. One of the most promising innovations involves “structural soil.” Structural soil is a mix of gel-coated gravel and soil. The gravel provides structural support to support the sidewalk without compacting the soil, thus allowing tree roots to grow and develop. The gel enhances the ability of roots to absorb nutrients.

Other innovations include the design of street-tree planting pits instead of small sidewalk cut-outs. Toronto’s new tree pit design provides eight to 15 cubic metres of shared rooting space for trees, as opposed to 1.2 to 2.5 cubic metres of soil per tree in the old design. Toronto is also experimenting with removable panels on trenches so that when underground utilities need servicing, the panels can simply be lifted off without tree roots being harmed.

While planting designs can improve the chances that street trees will survive, choices about what species to plant are also important. “There is no miracle street-tree species,” says Stephen Smith of the Toronto company Urban Forest Associates. “Instead, it’s always a question of what is the right tree for any particular site.”

Determining “rightness” can be complicated. “We used to plant a lot of white ash and green ash,” says Bill Roesel, manager of forestry and horticulture for Windsor’s Parks and Recreation department, “because they are so tolerant of poor soil.” But as emerald ash borer, an invasive, tree-destroying pest, swept through Essex County, Windsor paid the price for depending so heavily on just one tree genus, losing 6,500 ash trees – or 10 percent of the city’s street tree population. “We try to plant as many native Carolinian species as we can,” says Roesel, “and we’ve had good success with Kentucky coffee tree, hackberry and tulip-tree.”

Keeping street trees alive and healthy is often a matter of getting back to the basics of maintenance. “Sidewalk trees were largely neglected through the 1990s,” says Richard Ubbens, director of urban forestry for the City of Toronto. But maintenance crews now water and fertilize Toronto’s sidewalk trees and in the past year have been experimenting with compost tea, which, according to Ubbens, gives “a nice little microbial boost to the soil.” The Town of Oakville also has a watering program and a mulching program.

For more information

More information about urban street trees is available from these organizations:

Ontario Urban Forest Council [www.oufc.org]

Green Streets Canada A program of the Tree Canada Foundation [www.treecanada.ca]

For information about the Canadian Urban Forest Network, contact the Tree Canada Foundation at 613-567-5545 or tcf@treecanada.ca.

In other places, volunteers are enlisted for maintenance duty. In Windsor, a notice is left on adjacent homeowners’ doors asking them to water young street trees. Likewise, Toronto’s urban forestry department asks storeowners in some areas to water street trees during a drought. This approach has risks, however. “Sidewalk trees can die from drowning,” says Ubbens. A professional city work crew, checking conditions with soil probes, is often better equipped than well-intentioned citizens to evaluate trees’ need for water.

Ultimately, though, the will and involvement of the public will influence the resources a city devotes to its street trees. Andy Kenney, senior lecturer of urban and community forestry at the University of Toronto and a leading light in Canada’s urban forestry movement, says, “It all starts with public education because citizens of the city own the urban forest. They have to be the champions.” One Ontario municipality that has taken this to heart is Thunder Bay, where the volunteer group Trees Thunder Bay finds a sponsor to pay one-third of the cost of planting a street tree. (The city and adjacent homeowner share the other two-thirds.) In communities like this, citizens are taking the lead to protect and enhance what is, after all, a public resource, with benefits for all.

“Growing a tree is like raising a child,” says Gérald Lajeunesse, chief landscape architect for the National Capital Commission in Ottawa. “You need to keep an eye on it and take care of it, or there’s going to be trouble.”

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Lorraine Johnson is the editor of a collection of essays on the Carolinian zone, to be published this year.