An urban tree advocate said the city should boost the space between elm trees, increase biodiversity, and consider not planting the tree in the future to reduce the inevitable effects of Dutch elm disease on Edmonton's urban forest.
"This might be a controversial statement, but I think that the city should stop planting elm," Dustin Bajer told Taproot.
Bajer recently co-created an urban canopy conference in Edmonton, runs the Shrubscriber community for people interested in growing, and played a central role in the city's urban farm.
"I love elm, but I think in order to protect the ones that we have, we should stop adding elm to our inventory," he said. "I really think that every elm we put in is a liability."
In August, City of Edmonton officials detected Dutch elm, a fungal disease spread by beetles that can kill the popular tree. As of Oct. 1, the city has found and removed four infected elms, Mark Beare, the director of infrastructure operations, told Taproot in an email.
Bajer said we'll never know how Dutch elm got to Edmonton, though he said a beetle may have "hitched a ride" on a train. Regardless, he said the disease's appearance in Edmonton was "inevitable," thanks to its steady spread westward across North America since it was first detected in Ohio in 1930.
Bajer said the city has already stopped planting ash trees in response to tree disease, as the trees are vulnerable to the emerald ash borer beetle. But he suggested that a similar decision with elm would be harder because it's well-suited to city life.
"I would go so far as to say that Edmonton is addicted to elm," he said. "It's a beautiful tree, and it is very tolerant of urban environments. It does well with salt; it does well with pollution. It has this sort of vase shape to it, which means that you don't have these low-down branches that are impeding any of the buildings or structures below it. And they kind of touch at the top of the canopies."
Beare said the city has already reduced elm's presence in its replacement planting programs, aiming for just 15% of required tree replacements to be elm. He added that elm is now only planted in harsh growing environments like boulevards. Taproot asked if the city has considered putting an end to planting elm. Beare did not respond.
The city wants to add two million new trees in addition to replacements for removed trees by 2030. Short of a moratorium on elm to prevent it being part of those numbers, Bajer suggested other ways to slow the spread of Dutch elm or at least preserve the city's overall canopy. One is to plant a greater diversity of trees.
Bajer said he's pleased to observe the city planting oaks, honey locusts, and lindens, and said it appears it is "playing around" with the Kentucky coffeetree. Bajer suggests experimenting with other kinds of trees that are not traditionally used as boulevard trees in Edmonton, such as conifers. The trees provide shade in summer but allow sunlight to pass when their needles drop in the winter, he said.
"I think we have more options than we think we do," Bajer said. "There's a lot of stuff we haven't tried here."
Beare said the city plants "a wide variety of different tree varieties and species with an emphasis on species native to the region," but did not specify which ones.
Elm trees like these in Old Strathcona are ubiquitous along boulevards because they are well-suited for harsh conditions in urban environments. But with Dutch elm disease now in the city, tree advocate Dustin Bajer thinks Edmonton needs to employ new thinking. (Colin Gallant)
Another of Bajer's ideas is to plant elms further apart, perhaps with other kinds of trees between them. Dutch elm disease can be transmitted by tree roots, which can touch when elms are close together, he said.
Another option, though the least helpful, would be to plant a greater diversity within the elm family. Bajer said most of Edmonton's elms are the Brandon cultivar. "Not only are we still planting elms, we're still planting essentially identical twins," Bajer said. "If one is susceptible to a pest or disease, they're all very susceptible."
As for the tree inventory, Beare said the city is doing more than just removing diseased elms. Approximately 238 non-infected elms in poor condition have been removed since the end of August. An additional 81 are set for removal in October, Beare said. The city has also enhanced its monitoring, testing, and treatment of trees, changed its disposal options for elm wood, added beetle traps, and conducted surveys about the situation.
Additionally, Beare said the city used TreeAzin Systemic Insecticide on trees in the immediate area of the four diseased elms it discovered. This helps elms fight both the beetle and Dutch elm fungus. The city has also acquired the preventative Arbotect 20-S fungicide to apply as needed. Beare said both are safe for humans and animals.
Bajer said that while chemicals are useful to stave off the spread of Dutch elm, they're best used as an opportunity to buy time to slowly make replacements to the canopy.
"If (insecticide) slows it down while you can continue to diversify the canopy and remove old, infected trees, and start interplanting, maybe you can slow it down long enough that you can transition from an old canopy to a (different) old canopy," he said. "It's a 100-year transition to go from 100-year-old trees to 100-year-old trees. I think what we want to avoid is having to replace all those trees all at once."
Asked why Dutch elm didn't arrive in Edmonton until 94 years after it was found in North America, Bajer said it's mostly due to the city's western location. He said work by Stop Dutch Elm Disease (called STOPDED for short) and others likely helped, too. The province also mandates (based on direction from the Canadian Food Inspection Agency) that elms not be trimmed between April 1 and Sept. 30.
Bajer doesn't want his outlook to be misunderstood: He said he chooses to be "cautiously optimistic," and thinks it's possible the four trees found by the city are the sum of the infected population.
But that optimism is more about how we live with Dutch elm disease rather than its eradication, he said. "Even if we are successful this time, it's still (just) a matter of time before it shows up again. We've seen it coming for decades, but we really like this tree, so we keep planting it."
The city encourages anyone who suspects a tree is infected with Dutch elm disease, on public or private property, to call 311. The provincial Agricultural Pests Act dictates property owners are responsible for preventing, controlling, or destroying any pest on their property. Beare said the act gives the city permission to enter a property to conduct tests, and that property owners must dispose of infected trees if the city issues them a notice.