Beetle invasions! Freaky freezes! Droughts! Storms! Aaugh! Saskatchewan’s urban forests face climate chaos peril

Ecology | Gregory Beatty | Feb. 10, 2022

When I first pitched this article, it was with the idea of extending a big, mushy, red-hearted Valentine’s Day wish to our urban forest (Wood U B Mine?) for all the great benefits trees give us [see sidebar]. Then I checked up on the state of Regina and Saskatoon’s forests.

Uh oh. Suddenly it seemed like a better gift shop choice might be a Get Well Soon card.1

In November, Regina released a report saying that from January 2020 to September 2021 the city lost 1,402 trees. The report blamed a multi-year drought and storm damage, which in 2020 saw Regina suffer a net loss of 356 trees with new planting outstripped by trees removed.

A further 600 trees suffered storm damage and needed repairs.

The picture in Saskatoon is similar, says Linda Moskalyk of SOS Trees Coalition.

“Last summer we had record-breaking temperatures, and that came after a winter where we’d had some of the lowest moisture levels ever. Drought is one reason we’ve been losing trees. A few years before that, we lost [over 4500] black ash and Manchurian ash trees to an insect called the cottony ash psyllid.”

Even when lost trees are replaced one for one, urban forests still suffer because it generally means a net loss of canopy cover — such as when a mature tree with a lush crown is replaced by a sapling.

So yeah, our trees definitely need some TLC.

Shallow Roots

The first thing to understand about our urban forests is that they are not natural, says Dale Hjertaas of Nature Regina.

“My understanding, and certainly it’s corroborated by early pictures, is that pretty much every tree in Regina was planted or is descended from a planted tree,” says Hjertaas. “When Regina was established, this was a treeless area.”

Outside of riparian trees along the South Saskatchewan riverbank, Saskatoon was similarly treeless, so all its trees are planted, too. Work began in earnest in the early 1900s, and it’s continued through several generations — of people, not trees, as most of them are probably still alive.

With contributions from private landowners and Wascana Centre (Regina) and Meewasin Valley (Saskatoon), both cities have over 200,000 trees.

Truly, it’s a wonderful story. But with climate change a growing threat, will it have a happy ending?

Historically, southern Saskatchewan was simply too dry to support trees. The settlement era from the 1890s on has actually been one of wetter periods in the last 2,000 years. Even as recently as the late 1850s, the region was written off by British surveyor John Palliser as semi-desert grassland where nothing could grow.

Thanks to climate change, southern Saskatchewan seems to be getting hotter summers, shorter winters with less snowpack to insulate tree roots and provide water in the spring, and the rain that does fall comes in intense (sometimes destructive) storms.

Drought is the biggest threat our trees face, says Hjertaas.

“Drought can just outright kill trees,” he says. “We had a fierce drought in the mid-1980s where that happened. But it also stresses trees and makes them more vulnerable to other stresses — and I’ve seen many over the years.

“When Regina’s cankerworm outbreak is really high, I’ve seen trees defoliated,” Hjertaas says. “They can grow new leaves and keep going, but if you combine that with drought, it makes it harder to recover the energy expended to grow the new leaves.”

Freeze/thaw cycles in winter seem to be more common too, and that has Moskalyk concerned.

“It’s similar to what Calgary experiences with chinooks,” she says. “A lot of trees there are poplar because other species don’t do well, and unfortunately we’re starting to see some of that here.”

Hjertaas points to early spring as an especially sensitive time.

“Say we get a warm spell with an early run of sap, followed by a cold snap. I think that can be hard on trees. A false spring might get trees expending energy, and then it turns cold again.”

Another big challenge for Saskatoon and Regina is forest make-up. In both cities, ash and elm dominate — accounting for 50.7% of Saskatoon’s trees, and 67.3% in Regina.

Just like nature abhors a vacuum, it doesn’t much like monocultures. And as (bad) luck would have it, both our elms and ash face threats that have caused major grief for cities further east and south of us — both in trees lost, and dollars spent trying to deal with the problem.

Dutch Elm Disease has already hit Regina and Saskatoon. The fungus spreads tree-to-tree through interconnected roots. So far, outbreaks have been contained. To limit the spread, neighbouring elms can be inoculated with a fungicide. We also have the prairie as a natural barrier against the elm bark beetle that transmits DED longer distances. Still, we need to be vigilant.

The ash family’s looming nemesis is the emerald ash borer.

“I don’t believe there have been any outbreaks in Saskatchewan but it’s definitely on the minds of urban forestry people,” says Moskalyk. “Ash was a tree that once the DED scare arose, cities switched to planting because it’s a good, hardy street tree. But now we probably have too many.

“They said the emerald ash borer would never come to the prairies because of the cold,” she adds. “But with our changing climate, that’s been proven wrong.”

Insect and disease outbreaks are a natural part of the environment, says Hjertaas. “But if you have a drought too, plus the weight of air pollution, it all adds up and collectively weakens the tree.

“A healthy tree is certainly better able to handle whatever comes at it,” he says.

Budget Boost For Trees

Regina and Saskatoon have done studies calculating the value of their urban forests. As a capital asset, Regina valued its forest at $1.4 billion. Saskatoon puts the economic value of its forest at $530 million.

It’s an investment worth protecting (and growing). But to do that, more resources will be needed.

One big recommendation in Regina’s November forest report was to increase the annual tree replacement budget from $91,000 to $125,000 in 2022, with a further increase of $25,000 per year for the next five years. Alternately, the city could boost funding to $175,000 now and accelerate the planting program.

The report also proposed an annual Arbor Day on June 1 to promote tree appreciation, and creating a tree donation program to plant on public lands.

In 2020, Saskatoon passed an Urban Forest Management Plan. It lays out a 10-year strategy for growing Saskatoon’s canopy cover and maximizing the health and diversity of its forest.

One important feature, says Moskalyk, is a tree protection bylaw.

“There are all kinds of circumstances where people damage trees or remove them illegally, but without a bylaw it’s hard to go after them,” she says. “Hopefully, once one is in place it will help. At the same time, it will [teach] people [that] if they take trees out there will be consequences.”

Saskatoon is currently working on the bylaw. A draft is expected this fall.

To address drought now and into the future, Moskalyk would like to see cities make better use of non-potable water. Two common sources are stormwater run-off and untreated fresh water from rivers and lakes.

“Species selection is another thing that will have to be considered,” she says. “We don’t really know how to predict what trees will do better as the climate warms and we have these dramatic shifts in temperature. And that may require us to experiment.”

Regina is doing that now with a test planting of two honey locust trees, normally native to the U.S. southeast, in an inner-city neighbourhood.

“We might need to do more soil testing to figure out optimum areas to plant,” says Moskalyk. “We wonder if it’s better to do more group planting because it’s much easier to mulch those areas and keep the roots cool. As well, trees just naturally grow better in groups, so that might have to be considered, along with more funding for watering and planting.”

1. It’s possible trees don’t WANT cards, however affectionate and sympathetic, because A) trees can’t read and B) what are cards made from again? Oh right.2

Sidebar

More Value Than Dollars Measure

Scientists use the term “ecological services” to describe benefits humans receive from natural processes and species.

Some services can have hard dollar value, while others are perhaps more nebulous. But they’re all important says Nature Regina’s Dale Hjertaas.

“I’m reading Mark Carney’s book Values,and he makes the point repeatedly that efforts to assign an economic value to everything and make all your decisions that way tend to fail because we are more than economic beings. If I was to list values we gain from trees, I’d mention shade and temperature regulation, biodiversity and habitat, and aesthetic value as beautiful objects.”

Because trees absorb carbon dioxide to grow, they’re also an important ally in our fight against climate change. In 2020, Regina estimated that its forest stored 63,300 tonnes of carbon from the atmosphere — equivalent to pulling 17,000 cars off the road.

Trees improve air quality too, by filtering dust and absorbing pollutants such as nitrogen dioxide, ozone, sulfur dioxide and heavy metals. And through the shade they provide, they help counter what’s known as the “urban heat island” effect.

“Trees are the city’s air-conditioning,” says Hjertaas. “I remember my running days. If it was a hot day, it was always better to run on the shady side of the street. It can be up to seven degrees cooler compared to being in the open.

“It’s the same with buildings that are in shade, you will spend a lot less on air-conditioning,” he says. “Obviously, we will be facing more extremes like the heat dome we had last summer. And areas that don’t have trees are going to be the least attractive spots of the city to be in.”

For homeowners, trees translate into higher property values. On the tax front, they can provide valuable support to civic infrastructure.

Stormwater run-off is one example, says Hjertaas.

“In recent years, cities have been creating retention ponds to slow run-off. But trees do that as well — even just water getting hung up in the canopy can slow the peak flow. And roots loosen the soil, which improves infiltration so more water gets in.”

Most of what’s mentioned above translates into hard dollar value. As for more “nebulous” ecological services, consider the social impact of trees.

“People like being under trees. They enhance the appeal of outdoor environments, which increases physical activity,” says Hjertaas. “There’s also research that shows trees improve mental well-being.”

Trees do wonders for songbirds and other wildlife too, which is good for them and us. So Happy V-Day trees: U Better Beleaf It, We’re Rootin’ 4 U!