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Harbourfront Centre at York Quay - Michael Van Valkenburgh Associates, Inc.



European buckthorn, Norway maple, emerald ash borer: these are the species we commonly see signs of while walking around natural sites in Ontario. Online videos of people struggling to get rid of spotted lantern flies and spongy moth caterpillars have also been going viral for the last few years. Starting my landscape architecture degree, I remember learning about how many plants were invasive in my plant identification class and wondering why they were so frequently planted. Turns out, invasive species have not been receiving due or effective regulation and management in the province, according to the 2022 Auditor General’s report.

The emerald ash borer is a wood-boring beetle native to Asia. IMAGE/ Courtesy of the Invasive Species Centre

Last November, Ontario Auditor General Bonnie Lyst came out with a series of scathing value-for-money reports on the provincial government’s spending practices and policies, among which was an alarming audit of Ontario’s invasive species management. According to the report, the Natural Resources Ministry “is not effectively monitoring the introduction and spread of harmful invasive species in Ontario.” The Ministry, which is the provincial lead in the matter, has demonstrated various inefficiencies in regulating invasive species. Examples include delays in regulation, unregulated, harmful invasive species, ineffective monitoring, and insufficient funding for regulation and collaborative partners.

Starry Stonewort is a freshwater macroalgae from Europe and Asia that displaces local plants and aquatic animals. IMAGE/ Courtesy of the Invasive Species Centre

The inefficiency in dealing with invasive species holds significant consequences for Ontarians, including those in the landscape architecture profession. Invasive species create concerns for agriculture, forestry, tourism, and fisheries, and they impact public health, infrastructure, and the environment. Climate change may also have a hand in accelerating the spread and impact of invasive species because of increasing favourable conditions for some of these species. A Global News article on the report emphasized the gross economic impact of invasive species with a striking headline: “Ontario spends $4 million fighting invasive species, a $3.6 billion problem.”

Seed pods of a dog-strangling vine, also known as European swallow-wort. IMAGE/ Courtesy of the Invasive Species Centre

Dr. Robert Corry, one of my landscape architecture professors at the University of Guelph who holds a doctorate in Natural Resources and the Environment, says that invasive species have always been a problem. Many invasive plants are not listed on municipal noxious weed lists, complicating the process to deal with them and removing the impetus for something to be done. This then allows the species to have more time to spread.

Tree-eating spotted lanternflies, native to Southeast Asia. IMAGE/ Courtesy of the Invasive Species Centre

When it comes to landscape architecture, specifically, invasive species are a huge challenge for restoration work. In ecological work, Dr. Corry says that due to the lack of budget to do broad-scale intensive revegetation of a site, “anything that has a gap in it—meaning bare soil—is the opportunity for those species to spread into these lands.” In addition, when ground is lost to invasive species, they increase, outcompete, and become harder to manage. As a result, restoration work done by conservation authorities require strict sanitary protocols for machinery.

A leaf suffering from “oak wilt,” a disease caused by fungus threatening to spread north from the U.S. IMAGE/ Courtesy of the Invasive Species Centre

Other landscapes heavily impacted by invasive species are riparian zones and highway corridors, examples Dr. Corry points out are easily invaded. “Partly it is because of the continuous network of the landscape, and partly because they’re just sort of outside of the realm of ordinary kinds of management and maintenance.” Saltwater from the road creates conditions for salt-tolerant invasive species, while the movement of water and wind across these landscapes helps spread them.

The bamboo-like Japanese knotweed outcompetes native plants. IMAGE/ Courtesy of the Invasive Species Centre

When asked about the potential consequences of inaction regarding invasive species, Dr. Corry said, “The direst consequence is we’ll actually lose loads of [native] species because they can’t compete, which could be a local thing or even more widespread.” The species loss can also have a compounding effect on entire ecosystems. Working against invasive species makes it more difficult to monitor and manage a landscape, and it makes projects more expensive.

Oak wilt-infected bark. IMAGE/ Courtesy of the Invasive Species Centre

How can we, as landscape architects and project managers, help mitigate the spread of invasive species? Many levels of a project, from planting design to maintenance, offer opportunities to introduce or prevent the spreading of invasive species. And, Dr. Corry says, the $3.6 billion-problem only refers to the base level of species; below that, invasive genes in native species are also becoming a problem. “A lot of landscape architecture practitioners, especially restoration-minded ones, are starting to become much more attentive to what the seed supply was or where the genetic material came from.”

The egg masses of the spongy moth, whose caterpillars devour foliage. IMAGE/ Courtesy of the Invasive Species Centre