Can urban forests survive the housing boom?

Alongside the usual suspects at a construction site — trailers, temporary fencing and construction workers in high-visibility vests — there’s something less usual: a mature maple tucked in amongst the structure and an oak at the back.

Brightside, the non-profit housing organization that redeveloped two seniors’ housing units into a larger building in Vancouver, made it a priority to save the two stately trees. The maple was particularly challenging, said Adam James, a principal architect with Ryder Architecture who designed the building. They had to change the prescribed design to accommodate it.  An arborist determined the space needed to protect the tree's roots, and during construction they built a protective boardwalk platform over top, as well as installed irrigation to ensure the trees had enough water.

“The tree told us how to design the building,” James said. However, to almost triple the number of seniors’ housing units, 15 trees — some in the middle of the site — had to be sacrificed. While they planted 29 more to replace them, it will likely take decades before the young trees provide the same benefits as a mature one.

Canada needs an additional 3.5 million housing units by 2030 to address its housing shortage. Various governments are trying to increase supply, from cities adopting “missing middle” policies, B.C. legislating municipalities to increase density, or the federal government slating public lands for affordable housing. Trees, meanwhile, help cool the air, manage stormwater, sequester carbon, decrease air pollution, provide wildlife habitat and promote people’s mental and physical health. And when they grow in the same places people are trying to build that much-needed housing, sometimes a choice has to be made: keep the trees, or cut them down?

This balance is something that municipalities across the country are grappling with as they try to address Canada’s housing and climate crises simultaneously. 

'A finite amount of space'

Todd Irvine, an arborist who runs a company called City Forest in Toronto, recognizes there aren’t always easy solutions that allow for densification while keeping trees.

“Unquestionably, there’s a finite amount of space, and so every place where there’s another building is a spot there will never be a tree. And that’s just the reality,” he said.

Still, he says densification is needed, not only because of housing affordability but because it is also less damaging than the other alternative: urban sprawl. New suburbs and single family homes are the biggest contributor to urban tree loss in Canada. To build new neighbourhoods, agricultural land, forest and wetlands are cleared away.

“I would much rather lose two trees in downtown Toronto to build a building that’s going to house 100 people, then have those 100 people spread out over multiple acres in [what is] presently farmland or Greenbelt or remnant forest,” Irvine said.

He also understands that maintaining and growing an urban forest within existing neighbourhoods is needed, but that there has to be compromise.

“There needs to be sacrifices somewhere. And that sacrifice might be the big backyard, stone patio,” he said. “That sacrifice may be the two-car driveway in front of your house.”

Cars are also competing for much-needed space. A 2021 report estimated that Canada has 3.2 to 4.4 parking spaces for every car on the road — amounting to up to 97 million parking spaces. 

Put together, that’s an area twice the size of Calgary that we reserve for cars, and cars alone.

“If we really wanted to provide more room for trees, one of the biggest ways to do that would be to have less cars in the city. So I would rather get rid of cars before I get rid of homes,” Irvine said.

But how those new homes are built can make a big difference to how many trees can be retained. Stephen Sheppard, a University of British Columbia professor of urban forestry, admits that it’s difficult for developers to design and construct new housing units and keep trees, but that it is “a cost of doing business.”

“If you’re a developer, it’s going to be way easier to take all the vegetation out, do whatever you need to do — grading, digging, et cetera, et cetera,” he said. “It’s much more complicated when you are trying to protect, preserve, limit the impact on the natural infrastructure.”

There are opportunities to build housing with smaller footprints. Helical piers, for example, screw into the ground and can replace a foundation that would otherwise disturb tree roots.

While protecting trees during construction might have a higher price tag, he said it will lower future costs that come from flooding, heat waves, air pollution or even the mental health impacts from living in a “concrete jungle.” Sheppard said municipalities need to enforce guardrails to protect trees and thus mitigate these costs.

 The planning problem

Urban forest experts say a city should have around a 40 per cent tree canopy cover to garner its benefits. Vancouver, Toronto and Victoria are some of the country’s leafiest cities, with about 25 per cent,  28 per cent and 29 per cent tree cover, respectively, while Calgary lags far behind with just eight per cent of its sprawling area shaded by trees.

No city exceeds Ottawa-Gatineau, however, which claims a 46 per cent cover. 

Tree canopy may be unequally spread between cities, but it’s also spread inequitably within cities. Low-income and racialized neighborhoods tend to have lower tree canopy — and fewer benefits — than others.  

Danijela Puric-Mladenovic, a professor of urban forestry at the University of Toronto, says the distribution and lack of trees overall is the result of how Canadian cities are planned via various zoning regulations. Planners rarely look at the city’s tree cover as a whole.  

“We are stuck in times when the land was abundant,” she said. “We need to grow, but we aren’t doing it in a clever way.”

Cities need to increase green space as their populations increase, Puric-Mladenovic said. While many have tree protection policies and bylaws or have developed urban forest strategies, she said that development is often the first priority.

Alex Boston, a climate consultant, says cities have an underutilized opportunity to create more green space: municipal land, which accounts for about 25 per cent of a city. Roads, back alleys and parking lots offer ample space for more trees.

“That’s the area where municipalities have the greatest degree of control. And that’s where they should start,” Boston said.

“This isn’t a zero-sum game where density necessarily drives the loss of urban tree canopy.”