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cityscape

The City’s Trees Were Hit Hard by the Ice Storm

But a Toronto arborist explains that post-storm cleanup and long-term tree care will require far more than picking up branches and wielding chainsaws.

Photo by Flickr user Ron Bulovs.

The recent ice storm knocked the power out for 300,000 customers, and also knocked down a great many trees and branches—just how many, it’s hard to say. Although City staff initially estimated that 20 per cent of Toronto’s tree canopy had been lost, Jason Doyle, director of forestry, says that it’s just too soon to tell and that a firmer number won’t be available until the damage can be thoroughly surveyed.

What’s clear, though, is that Toronto’s trees went through a traumatic weather event, and a lot of time, effort, and money will have to go into cleanup, dealing with the trees that can’t be saved, and restoring those that can be to full health.

Cleaning up after the recent ice storm and helping trees recover will not simply be a question of walking the streets collecting fallen branches and taking chainsaws to the trees that seem obviously beyond hope.

Todd Irvine, arborist with Bruce Tree Expert Company, gave us a sense of the complexities involved in caring for trees properly in the best of times, and assessing and meeting their needs in the worst.

Storm cleanup is, on its own, a complicated and multi-stage process. It’s necessary to pick up any brush and remove branches that have broken off, or are only partially attached to the tree. Some branches will have to be pruned off, and cut back to the union where they meet a larger branch or the trunk itself. And the most hazardous trees, those that have suffered catastrophic damage, must be taken down.

Photo by Flickr user mark.watmough.

Irvine stresses that restorative pruning is critical: when a big tree, which for years has been integrated into a larger canopy, loses branches, the wind will now hit it in different ways, from different angles—putting stress on branches once largely protected. A sense of the new structure and system of the tree, and how it is likely to develop over time, will guide decisions about how and whether, say, to reduce the length of remaining branches.

Then there are tricky things called “epicormic shoots,” which further complicate the approach that must be taken to each individual tree. A tree that loses a large branch has also lost part of its ability to produce energy through photosynthesis, and responds to this threat by producing new shoots. These new shoots, Irvine notes, are “not structurally ideal, not really genetically made to be new healthy branches,” because their purpose is “just to grab as much as energy as they can.” They can be weakly attached, and often the ones that look most like branches will have to be removed before they grow too large—but, Irvine cautions, “you have to leave just enough.” The tree needs some of that compensatory energy: one can’t just identify epicormic shoots and prune them all away.

The trees will need these calculated assessments and interventions for some time to come. It might take the evidence of multiple springs, and repeated prunings, to determine how a tree has responded to the effects of this storm.

Photo by Flickr user Darren Cheng.

It’s impossible to fully militate against the consequences of another massive ice storm, but there are, Irvine says, some steps we can take to reduce them. We can plant a greater diversity of species, including ones that are hardier and more ice storm–resistant, like conifers. We can prune more often, visiting trees at least every three to five years to keep an eye on their growth and development. We can also plant more thoughtfully: “Yes, plant trees on main thoroughfares,” says Irvine. “But let’s plant more heavily where there’s room for trees—backyards, industrial areas, parking lots, commercial developments.” Places, for example, where there might not also be power lines.

While it’s important that new trees be planted, Irvine emphasizes that “planting is not enough: don’t plant a tree if you don’t intend to maintain it.” Trees need watering, mulching, and frequent pruning if they are to thrive.

And we need our trees to thrive, because a significant reduction in Toronto’s tree canopy would have serious consequences. Heat, for one. And hotness. And also extreme and uncomfortable warmth. “Trees are like a canopy of cool water over our heads,” Irvine explains. “Our engineers could never devise a better system to keep us cool.” Each tree constantly pumps water out of the cooler ground and up into its leaves, where the moisture evaporates. So trees both provide shade and cool the air; without them, we’d face hotter summers and require more energy to cool buildings. They also work to purify the air, prevent soil erosion, reduce the speed at which rain hits the ground, divert water from our sewer systems, and provide a habitat for animals and insects—making them pretty effective, city-helping multitaskers.

The ice storm did not decimate our tree canopy, and the city will still benefit from the many abilities and activities of its trees, but Irvine says that on a street-by-street level, Toronto will likely be warmer.

Photo by Flickr user Andrea Williams.

The City has announced that it will be spending $75 million on ice-storm cleanup: $25 million of that will to go to clearing branches, and $50 million to repairing and restoring the tree canopy. But according to the Ontario Urban Forest Council, 60 per cent of Toronto trees are growing on private property—which means that many homeowners will also have some decisions to make about tree care. “Amateur pruning is not recommended,” says Irvine. Removing and pruning trees are activities that require knowledge of both trees and safety practices: arboriculture can be a very dangerous business.

The effects of this ice storm will be felt for years to come. “It’s going to leave scars on the landscape,” Irvine says. “It’s going to be tough.” But trees are resilient, he adds. And with judicious and skillful tending, many of those that came to harm this past December will eventually make a full recovery.

CORRECTION: January 6, 2013, 10:50 AM This post originally stated that 300,000 people lost power during the storm when it was, in fact, 300,000 customers.

Comments

  • TorontoistCopyEditors

    You’re right—Toronto Hydro CEO Anthony Haines has indicated that one Hydro customer is roughly equivalent to two and a half people. So the fact that 300,000 customers were out of power would mean that something like 750,000 people were actually affected. We’ve made the change!

  • https://paul.kishimoto.name/ Paul Kishimoto

    This was really interesting—the idea that surviving branches would be vulnerable to wind stress that they were formerly sheltered from is something I’d never thought of before, but makes a lot of sense.

    “Decimated” is often misused—e.g. military units are sometimes said to be “decimated” when they’ve taken an unusually high number of casualties. But if 20% (or anything more than 10%) of the canopy was lost it was, literally, decimated.

    “We can plant a greater diversity of species, including ones that are hardier and more ice storm–resistant, like conifers. We can prune more often, visiting trees at least every 3-5 years to keep an eye on their growth and development.” — provided we are willing to pay for it. The myopic will quickly forget and eagerly support cutting budgets for urban forestry.

    • tomwest

      Meanings of words change. Now it means “reduced *to* 10%”, not “reduced *by* 10%”.

  • tyrannosaurus_rek

    Last summer’s storm took out three very mature trees on my street and at least one in the alley – so many branches were lost the city had to cut them down. Between storm damage, disease, and the preference for ornamental and non-canopy-forming replacements, my street probably won’t have a canopy in 10 years.

  • dsmithhfx

    But they shed it and bear the weight more easily, because their branches are mostly downward-sloping (except for brittle white pines). Another consideration is that they don’t make the best shade trees.

    • tyrannosaurus_rek

      I noticed the other day that the few evergreens in my neighbourhood all survived unscathed because they folded like umbrellas under the weight of the ice and snow.