Increasingly powerful storms threaten Ottawa's tree cover

After extensive damage to trees and forests wrought by the May derecho and 2018 tornadoes, it's unclear just how soon the City of Ottawa can reach its goal to boost tree coverage to 40 per cent.

Resilient canopy needed as climate change takes root, foresters and advocates say

Debris from a snapped tree along a street in Ottawa on May 24, 2022, days after a severe derecho windstorm swept across Ontario and western Quebec. Many thousands of trees across the National Capital Region were destroyed. (Hallie Cotnam/CBC)

The City of Ottawa wants 40 per cent of its lands covered by trees in the future, according to the new official plan — up from 31 per cent in 2017.

But after the May derecho and 2018 tornadoes destroyed many thousands of trees in the area, it's unclear just how soon that can be achieved.

As efforts to repair the canopy take shape in the coming weeks and months and as climate change conjures increasingly powerful and frequent storms, a more resilient tree canopy is needed to better stand up to them, foresters and green space advocates say.

A detailed picture of the damage hasn't yet emerged as cleanup continues after this latest storm, but it won't be too much longer before one materializes.

A major tree canopy assessment for the entire National Capital Region was done in 2017, producing a highly detailed interactive map of the canopy as it existed that year (the results were made public in 2019).

It showed that 31 per cent of Ottawa was covered in trees, compared to 45 per cent of Gatineau and 76 per cent of National Capital Commission (NCC) lands in and around both cities (NCC-controlled land is not included in the Ottawa and Gatineau figures).

It just so happens that the next detailed assessment — they're being done every five years — is scheduled to begin this month, with flights as long as the weather co-operates, according to Jason Pollard, a section manager for Ottawa's forestry department.

It'll take months to collect and process the data (a combination of aerial imagery and lidar data that reflects everything on the Earth's surface), but when it's finished it'll show us just how destructive the derecho and tornadoes were across the region, among other changes.

Windblown trees still partially block a trail off Goldfinch Drive in Kanata on June 14, 2022. (Francis Ferland/CBC)

Some neighbourhoods lost many trees

The City of Ottawa covers a vast area and an overall drop in tree canopy of even one per cent would represent "a massive number" of destroyed trees, said Paul Johanis, chair of the Greenspace Alliance of Canada's Capital. 

The organization pushes the municipality to protect and expand the city's tree cover.

But zooming in to examine hard-hit areas, Johanis said neighbourhoods that had about 50 per cent tree cover may see it reduced by as much as 20 per cent.

"I think that we will see very measurable impacts … because at a neighbourhood level, it really did have a big impact for those that were very much affected by the derecho," Johanis said.

"Clearly, this is unprecedented. I don't think we've seen anything like this before in terms of damage."

Paul Johanis, chair of the Greenspace Alliance of Canada's Capital, says the tools to improve the city's tree canopy are in place, but more money is needed to back them up and get more trees in the ground. (Francis Ferland/CBC)

Pollard called the derecho "the most significant weather-related forest disturbance in decades," with damage varying in intensity in every neighbourhood.

Some of the areas hit hardest already had little existing tree canopy, according to the 2017 canopy assessment, which allows residents to look up tree canopy percentages specific to their neighbourhoods.

Only 15 per cent of Navan and Sarsfield were covered with trees in 2017, for example, and Stittsville had a canopy of just 21 per cent.

Blossom Park, Merivale Gardens and the Greenbelt were also hit hard. They boasted some of the densest tree cover in the city at about 44, 52 and 40 per cent, respectively — and may see those figures reduced.

WATCH | Derecho damage in Blossom Park: 

What some of the derecho damage looked like from above

2 months ago
Duration 0:30
This drone video shows extensive damage in Ottawa’s Blossom Park neighbourhood after a severe thunderstorm swept through on May 21. (Video by David Johnson)

Researchers expand EF2 downburst damage zone

Meanwhile, researchers with Western University's Northern Tornadoes Project have continued assessing damage in and around Ottawa since the derecho and have found that winds consistent with an EF2 tornado caused damage along a much longer path than initially thought.

While no tornadoes touched down in the city, an EF2 downburst — with winds reaching an estimated peak of about 190 km/h — struck in the southeast along a path now believed to be about 36 kilometres long and five kilometres wide.

The entire EF2 downburst damage zone is now about 36 kilometres long and just under five kilometres wide, according to Western University's Northern Tornadoes Project. Yellow indicates intermittent EF2 damage, green indicates intermittent EF1 damage, and blue indicates intermittent EF0 damage. (Northern Tornadoes Project)

The intermittent EF2 downburst damage zone starts just east of the Ottawa airport around Blossom Park, continues east through rural Navan and Sarsfield, and ends past the community of Hammond in neighbouring Clarence-Rockland, Ont.

Damage includes paths with most trees snapped or uprooted, farm outbuildings and silos demolished and broken hydro poles.

Researchers also logged intermittent EF0 (104-137 km/h) and EF1 (138-177 km/h) damage across a much wider swath of eastern Ontario and western Quebec.

They used satellite images taken just before and after the storm (May 18 and May 25) to examine changes to tree cover.

Some dramatic differences could be seen in McCarthy Woods; the forest along the Rideau River on the west side of the Ottawa airport; a wooded area between Frank Kenny Road and Delson Drive in Navan; and along the northeast edge of Mer Bleue Bog, among other places.

Researchers created this map of tree canopy damage visible via satellite in southeast Ottawa and beyond after the derecho. Each black X marks identifiable changes to tree cover, and red indicates worse damage. (Northern Tornadoes Project)

Building resilient canopy in the face of climate change

Some patterns have begun to emerge about what came down in the derecho — lots of coniferous spruce and eastern white pine trees as well as lindens, according to Pollard, the city's forester.

Plans to replace downed trees haven't yet been made with cleanup still underway, Pollard said, but discussions will take place in the coming weeks and months.

"We may have to look at ways to increase the numbers of trees being planted," he said. "Once we get through this initial phase of removing the hazardous trees, then we'll have some time to … have staff look at areas that need some targeted planting effort in response. We're not there yet."

Jason Pollard, a City of Ottawa forestry services section manager, says forestry departments across Ontario have to build more resilient canopies to withstand the effects of climate change. (Francis Ferland/CBC)

Replanting efforts will have to focus on better handling more powerful and more frequent storms, he added.

"Looking forward, I think for any municipal forestry organization across Ontario … we all need to be thinking about how we create a resilient forest canopy in the face of climate change and more severe weather," Pollard said.

"That will include things like species diversity, but also diversity in … the age of the species and the age of the tree canopy."

It's a question of decades, really, to have the canopy recovered to what it was.- Paul Johanis, Greenspace Alliance of Canada's Capital

Johanis of the Greenspace Alliance said the city has been moving in the right direction in recent years with a strengthened tree bylaw and relatively new forest management plan, but that more money is needed to actually see those changes through and get more trees in the ground.

"It's a question of decades, really, to have the canopy recovered to what it was," Johanis said. 

"And so … maybe, seeing that this is a kind of event that looks to be occurring more frequently, there needs to be better budget reserves established to deal with replenishing the canopy more effectively,"

WATCH | Some of the post-derecho forestry thinking: 

After the derecho, a new challenge — how to make ‘more resilient’ forest canopies

2 months ago
Duration 1:28
Jason Pollard, a section manager with the City of Ottawa's forestry department, says the severe thunderstorm in late May sparked concerns about how to protect the tree canopy from future weather events.

How to replace trees

Want a free tree seedling to plant on private property, perhaps to replace one that came down in the storm? Ecology Ottawa is giving away 20,000 seedlings this year and there are three giveaway events today and this coming weekend.

After June, more giveaways are planned for the fall planting season. 

The City of Ottawa tries to plant about 100,000 trees in a normal year, according to Pollard. The spring planting season generally happens between May 1 and June 30, but what remains of it was cancelled after the storm to allow crews to focus on cleanup. 

All scheduled spring plantings have been bumped to the fall.

"Although postponing planting and cancelling events is disappointing, I want to assure members of council that we will be looking closely at how to re-establish forest cover in the community once storm cleanup efforts are complete," wrote Alain Gonthier, the city's general manager of public works, in a June 1 memo to council.

City of Ottawa arborists clear downed trees and branches at Aladdin Park in south Ottawa near the airport on June 17, 2022, nearly a month after the May 21 derecho. Crews are still focused on cleanup efforts, and will later turn their attention to replanting efforts in hard-hit areas. (Jacques Corriveau/Radio-Canada)

In parks, staff are building a list of significantly damaged trees to replace in 2023 and beyond, according to the city.

Anyone wishing to replace a city tree on their street-fronting property or to plant one where there's room can apply online to have a tree planted by the city.

It's free but there are conditions and criteria to meet, including that property owners pledge to water newly planted trees for three years.

Cleanup operations

City crews have been making special trips to collect tree and shrub debris from curbs since the storm, but will stop on June 24.

After Friday, any remaining debris will have to be properly cut up, bundled or bagged to conform to regular weekly leaf and yard waste collection standards. 

Tree removal permits are not required to remove storm-damaged trees that pose an immediate threat to health and safety, according to the city, but photos should be taken ahead of removal to prove removal was required. The same goes for trees damaged to the point that they won't survive.

This dangerously leaning white pine, seen on June 14, 2022, will have to be removed at Brian Parsons Park in south Kanata. It was damaged along with many other trees in the area during the derecho on May 21. (Francis Ferland/CBC)

Residents needing stumps removed from their property are asked to be patient as the city comes up with a plan to perform that work over the summer months.

A total of 528 city parks suffered tree damage in the derecho. As of June 9, cleanup was still needed in 272 of them, the city said.

Much remains closed due to fallen trees on NCC-controlled lands in Ottawa including McCarthy Woods, Mer Bleue, Green's Creek, Pine Grove, Southern Farm and Pinhey Forest, Stony Swamp, Conroy Pit off-leash dog park, and the dense forest in Bruce Pit off-leash dog park.

Interested in learning more about the region's tree cover?

This is Ottawa's inventory map of city-owned trees (note: the data can take some time to load). It was first published in 2018 and last updated in February 2021. At that time there were nearly 281,000 trees logged.

Residents may want to update the city about any destroyed city-owned trees on their property after the storm. The city says you can report changes to the tree inventory by calling 311.

This is the city's urban forest management plan, which is guiding tree canopy protection and expansion efforts until 2037.

And this is the report stemming from the last major canopy assessment for the National Capital Region.


Kristy Nease


CBC Ottawa reporter Kristy Nease has covered news in the capital for nearly 15 years, and previously worked at the Ottawa Citizen. Get in touch: