Long neglected as a municipal afterthought, street trees are now in the spotlight. Cities across Canada are scrambling to increase their planting and maintenance budgets, at the same time as a climate-change-savvy public is clamouring for more trees and a say as to what gets planted in front of their homes. But the reality at street level is complicated.
“The boulevard is a really hostile environment for trees,” says Shelley Vescio, city forester for Thunder Bay, Ontario. “You’ve got salt, heat from the pavement and very little organic matter.” No wonder street trees are having a hard time surviving. And now new threats are further compromising the health of urban forests throughout the country. Pests such as the emerald ash borer and the Asian long-horned beetle are attacking trees in the East, diseases such as sudden oak death are affecting those in the West, and drought—arguably connected with climate change—is having an impact across the country.
Given the stresses street trees are subjected to, municipalities must juggle a long list of competing factors in deciding what species are best to plant on boulevards in front of homes. “Cities are struggling to find the perfect specimen,” says Michael Rosen, president of Ottawa-based Tree Canada. “They’re looking for disease- and insect-resistant species that are not invasive, that don’t require much maintenance—and that homeowners will like.” It’s a tall order.
Indeed, it may be easier for municipalities to eliminate candidates from the roster of suitable street trees. Bill Roesel, manager of forestry and horticulture for Windsor, Ontario’s parks and recreation department, for example, points to the many characteristics that make certain species inappropriate choices for boulevard plantings. Brittle varieties that regularly drop branches in strong winds, such as Manitoba maple and poplars, are out. Trees with lots of thorns, such as honeylocust, may be a safety hazard on public thoroughfares. So-called messy types that drop fruit, such as crabapples, often meet with resistance from homeowners. And, finally, those with low-branching structures, such as redbud, create site-line problems near roadways, as do conifers.
In the past, when municipalities found a species that met all the appropriate criteria, they tended to plant it—a lot. Canadian cities are still feeling the effects of such monocultural street plantings, which are highly vulnerable to pests and disease. Winnipeg, for example, lost many of its grand elms to Dutch elm disease, while Windsor had 10 per cent of its street tree population succumb to the emerald ash borer.