Trees and greenery are an important community priority, for both aesthetic and environmental reasons. Urban trees provide shade, cool the air and actually consume 15 times as much carbon dioxide as the same trees in a rural setting. For these reasons, the City wants to double the urban tree canopy from the current 17 percent to 30 percent.
To achieve this, the City must abandon the much-hated concrete planters (right) that imprison most Roncesvalles trees. But it is not enough to dig a hole and stick the tree in the ground, either. Trees need water, air and non-compressed soil. Without them, Toronto’s trees will continue to die within 5-10 years of life, and Toronto’s tree canopy will continue to shrink. In fact, the successful trees we do have on Roncesvalles are currently thriving thanks only to the broken sidewalks, but when they are fixed in 2009 the trees will likely suffer if we simply seal them over with new sidewalk concrete.
According to forestry guru James Urban, successful urban trees also require special planting systems to allow air and water to reach the roots and to keep the soil from compressing. In his keynote address at the City’s 2004 Tree Symposium, Urban recommended “soil cells” (left), simple structures that would support the sidewalk while preventing compression of the soil beneath. The cells would then be covered over by “unit-pavers,” in such a way as to allow water and air to reach the tree roots. Unit-pavers also allow utility companies to have easier access to their underground services, since the paver can be lifted up and then replaced, instead of the current practice where the sidewalk is jackhammered, given a temporary asphalt patch, and then permanently repaired by the City months or years later.
The City has built similar systems using a continuous soil trench that supports a concrete lid. But when more concrete is poured over top, the trees will often die for lack of water and air. The City is still exploring its options, but it is clear that a successful urban tree planting system will cost much more than the status quo. But what is the cost of replacing dead trees every 5-10 years, without ever getting a proper canopy?
Other cities in North America are moving ahead with creative urban street greening plans. A project in Portland, Oregon recently won a national award for its innovative “Green Street.” And Seattle’s Street Edge Alternatives Project (right) reduced the amount of stormwater leaving the street by 99 percent, and allowed for lush landscaping on sidewalk bumpouts.
What are your ideas for greening Roncesvalles? Please email us at firstname.lastname@example.org, or leave a comment below.
Ahead of the Storm – Toronto’s new action plan for climate change, which includes $24 million for tree planting, in addition to the $40 million yearly budget for the Forestry Unit.
Moving towards High-Performance Infrastructure, by Mary Vogel – an image-rich summary of some innovative sidewalk designs that combine stormwater management, greenery and urban spaces.