How to save an urban tree

Talking to an arborist to find out what trees need to thrive in density

When the Sooke School District built the new Belmont Secondary School in Langford, it wanted to preserve a lot of the mature trees. It had been an elementary school with a sizable forest of stately Douglas fir trees and gnarly Arbutus trees. The new school would be significantly larger, but designers tried to retain as many of the old trees as they could.

Now, eight years after construction on the school finished, those trees are letting us know they might not survive the disturbance to their root zones.

When I look at an Arbutus, I notice the colour of its bark and its sculptural shape. Or consider a Douglas fir, I see its impressive height and strength.

But when arborist Dave Saunders regards a tree, he’s looking for signs of stress or disease. He pictures what’s happening to the roots underground, and where a branch might land if it falls.

I met Saunders after school one day to learn what signals these Belmont trees are sending. A half dozen grow on the thin slope between Glen Lake Road and the school’s side driveway that curves behind the trees on top of compressed earth.

Pointing to a Douglas fir trunk a couple of feet from the curb, Saunders tells me its roots are suffocating under the compressed soil below ground.

He can tell because the fir’s needles are chlorotic, meaning they’re not getting enough chlorophyll. The same loss of chlorophyll is what turns most deciduous trees yellow and red every fall, but in evergreens like Douglas firs and Arbutus trees it’s a sign that all’s not well.

The needles on the particular fir we’re looking at are noticeably more yellow than a healthy fir across the street, and it has a lot fewer needles. A healthy fir looks fluffy from a distance; branches on this one are spindly and sparse. It’s been spiral cut at some point, a pruning technique that reduces wind drag and helps prevent falling branches, but its thin appearance is beyond pruning.

“There’s a symbiotic relationship between everything. On a Doug fir you have the anchor roots, and at the ends of them are feeder roots. Within that organism there are mycorrhizal root zones that allow the tree to absorb the energy and nutrients,” Saunders says. The mycorrhizal fungi that live with the roots are how trees communicate with each other, sharing nutrients and even warnings.

“Certainly, [that absorption] isn't happening here because it's pretty compact. We've disturbed the system. They've tried their hardest [to retain the trees], but at the end of the day, they've jeopardized the entire system.”

On the other side of the school driveway, another copse of trees was left with more space. There’s a small garden with loose dirt and bushes. These trees’ roots weren’t compressed, and their foliage is still bushy and deep green.

For forest trees to survive in an urban environment, they need space.

A general rule of thumb repeated by arborists and reflected in several local tree bylaws, suggests that if you want to build around a tree and have it survive, you need to leave an undisturbed radius around the trunk that’s at least half as wide as its canopy stretches. Even then, there is no guarantee the tree will survive.

On top of that, building density close to trees means there’s a higher risk that they become dangerous simply because of their proximity to humans. The trees outside of Belmont Secondary wouldn’t be a problem if it weren’t such a high traffic area. But hundreds of students and staff pass by those trees every day.

“This isn't a natural occurrence, so they have to be monitored all the time, because it's not natural. They're meant to be in the forest,” Saunders says. “So this Arbutus, they've done their best to retain it, but it’s struggling to live. The top is dead, the root system has been affected to the degree that it’s dying off. Any time a root system is affected, that affects the top.”

He’s referring to a particular Arbutus tree between the parking lot and sidewalk and the west side of the school. Whole segments of its crown are dead, and at waist level a large column of its bark is dead, indicating that its main roots have not survived the changes to its environment.

It needed more space, he says, which might sound obvious, but it can easily conflict with all the requirements that come with developing new houses and buildings in an urban setting.

Last year Saunders was hired to cut down a particularly large, and beloved oak tree that grew across the street from a Saanich elementary school. Students threw small pinecones at him in protest while he worked.

What they didn’t understand—and, Saunders suggests many Greater Victorian politicians also don’t—is that Saanich’s zoning requirements on the new building edged into the space the tree needed to safely grow. After requirements for utility hook ups, a driveway, and sidewalk improvements were met, there was not enough space left for tree.

This is what Saunders wants municipalities to understand: in order for trees to be retained, adequate space they need has to be built into the zoning requirements.

Some places like Colwood already do this by combining density allowance with mandatory open space. By allowing buildings to go taller, builders can still get the square footage they want, while leaving up to half the lot open and undisturbed.

On a single family lot, that might look like a three-storey house and driveway, with an open backyard. Or a taller storey apartment building, with land donated to the city as undisturbed park space.

Langford’s new council is in the midst of developing its policy to manage trees in the city, after public outcry against a perceived lack of tree retention by the previous leadership.