’Tis the season for spring’s sneaky visitors
Experts warn Ontarians to watch out for invasive species that pose a threat to native ecosystems
As spring arrives and more people tend to their gardens, Ontarians may begin to notice more non-native creatures and plants.
“Ontario has the largest number of invasive species in Canada — more than 180 aquatic invasive species, at least 39 forest insects, 10 tree diseases, and around 500 non-native plants, with more added every year,” said Karen McDonald, the Toronto and Region Conservation Authority’s senior manager of restoration and infrastructure.
Horticulture groups and environmental clubs may take it upon themselves to rip out some common invasive plants, but others are particularly “high priority” for the government to regulate, said Colin Cassin, invasive species policy manager at the Invasive Species Centre.
“New species arrive in Ontario every year, and the early detection and rapid response of new species is critical to achieving effective control,” McDonald said.
Why are we hearing more about invasive species?
Experts agree that people are becoming more aware of invasive plants as the weather warms, but that there is generally more interest among the public.
“Reports typically increase in the spring through the summer as people start noticing plants waking up from the winter,” McDonald explained.
Plus, interest in native and nonnative plants is increasing, she said. People are learning to identify plants and realizing how many in Ontario are invasive, particularly through apps like iNaturalist.
Ontario’s Ministry of Natural Resources and Forestry, for its part, believes its recent updates to the Invasive Species Act have sparked curiosity.
“As a result of the ministry’s recent regulation of new species under the Invasive Species Act, there has been increased interest in the issue, particularly in lesser-known species such as nutria and marbled crayfish which represent a significant concern to Ontario’s natural environment.”
Why are invasive species harmful?
Invasive species pose a threat to biodiversity, McDonald and Cassin explained.
“These species are super-competitors,” said McDonald, noting invasive plants claim more space, nutrients, food and water than their native counterparts. “They largely lack natural controls and are able to flourish in our natural greenspaces, waterways and even backyards.”
Their imposition adds to the “biodiversity crisis” that already exists; they’re the second most significant threat to biodiversity after direct loss of habitat, she said.
That’s harmful to local ecosystems, Cassin said, because biodiversity is what makes them “resilient” against climate change and other challenges.
At the same time, climate change will lead to the growth of invasive plants, McDonald said.
“All of this impacts the very foundation of healthy ecosystems — the soils and native vegetation that support biodiversity, including wildlife and human populations,” she explained.
Invasive species to look out for in Ontario
Cassin noted that oak wilt and hammerhead worms are newer invasive species that authorities are paying attention to. Phragmites, though in Ontario now for decades, is another invasive species that are continuously monitored.
Oak wilt was only detected in Ontario for the first time in 2023, in Niagara Falls and Springwater, a township near Barrie, Cassin said.
It can spread from tree to tree, through roots, and kill an oak tree in just three weeks, he said.
According to the Ministry of Natural Resources and Forestry, signs of oak wilt include: wilted or discoloured leaves starting at the top of the tree; leaves dropping prematurely in mid- to late summer; a black stain in the sapwood of the tree; a white, grey or black fungal mat forming under the bark that may smell fruity; and bark cracks on the trunk and large branches.
Hammerhead worms are another invasive species newer to the province, which “gobble up” native seeds and plant material, Cassin said. It’s not regulated in Ontario, but there have been some sightings here as well as in Quebec.
The worms secrete a dangerous, paralyzing toxin that can be harmful if ingested. They have no natural predator and prey on slugs, snails and millipedes, posing a threat to ecological balance.
Phragmites is notable as well, Cassin said, although more common in Ontario and here for decades now.
The invasive species, which is regulated by the Ontario government, is a “thick and robust” grass that you might see along the highway, he said. It grows to be so impermeable that it acts more like concrete than grass, and can cause flooding, and so dense that it crowds out other species.
Invasive species in the GTA you didn’t know were invasive
The most common invasive plants in the GTA are phragmites, dogstrangling vine, the European buckthorn (a tree or shrub), and garlic mustard (an herb) and invasive honeysuckles, McDonald said.
The most common invasive animals in the area are common carp and round goby (both fish) — as well as mute swans and goldfish, which may come as a surprise, considering they’re a common sight in a store or fair.
“If you are an angler and you catch an invasive fish like round goby, never release it back into the water,” McDonald advised. “In fact, round goby is illegal to release back into the water.”
Cassin and McDonald both recommended taking a photo of a species you believe may be invasive and reporting it to EDD Maps (Early Detection and Distribution Mapping System). There, an expert will determine if it is indeed invasive.
McDonald also advised people not to buy invasive plants, many of which are unregulated and can still be purchased in garden centres and plant nurseries.