Invasive plant species to look out for on Vancouver Island
Learn which plants are ravaging native species—and how to stop their spread.
While English Ivy may look beautiful as it grows and crawls up old buildings, it is one of the many foreign invasive plant species in B.C. that chokes out native plant species.
English Ivy, and many other plants that aren’t native to the area, are known as invasive species and have the ability to change entire landscapes.
“With development and urbanization and things, we’ve really changed the landscape [of] what existed [on Vancouver Island] prior to colonization,” said Hunter Jarratt, also known as Invasive Species Guy. “There are a lot of evolutionary relationships that have formed over time.”
Jarratt has been sharing information about invasive species and local ecology on social media since 2021. He also recently completed his studies at Vancouver Island University in the Natural Resources Protection Program. Now, Jarratt is a full time restoration consultant at KiKi Nursery in Ladysmith, and is completing the Restoration of Natural Systems certificate program at the University of Victoria.
Jarratt said that if invasive plant species were left to take over native plants, other species — such as specialist species — would likely die out.
Specialist species are those that require a certain plant to survive. Specialist bees, for example, are bees that require a specific plant to complete their life cycle.
“So if we don’t have those plants, we lose those species,” he said. An example of this is Andrena astragali — or the death camas mineor bee — the only bee that can tolerate the toxins in death camas.
“If we don’t have death camas, we don’t have the bee,” he said. “And of course by helping insects, you help the whole food web, because then you have food for birds and butterflies and everything that eats those and so forth.”
The Discourse spoke to Jarratt about some of the more prolific invasive plant species on Vancouver Island. According to Jarratt, there are many, but a few stand out as the worst culprits when it comes to impacting local plants and habitats.
Its berries might be delicious, but this species impacts native blackberry plants, such as Pacific blackberry. The Himalayan blackberry grows in many different areas, including along pastures and roadsides, as well as the banks of streams and the edges of forests. According to the Invasive Species Council of BC, it can crowd out low-growing vegetation and its thickets can be so dense that it can limit the movement of animals. It can grow up to five metres tall, with its canes growing up to 12 metres long.
With a native geographic range of Northern Africa, Asia and Europe, Yellow flag iris — also known as water flag — is a noxious weed often found along the shorelines of lakes, ponds, streams, wetlands and ditches. Jarratt said it has a detrimental effect on the ecosystems it invades. Its seeds spread quickly, and according to the Invasive Species Council of BC, hundreds of the plants in an area may be connected to one another due to its extensive root system.
“It will go into a wetland and it will quite literally change the entire foundation of that wetland ecosystem,” Jarratt said.
This evergreen vine is described to be a “smothering invasive” by the Invasive Species Council of Metro Vancouver. It can climb up trees and make them more susceptible to wind damage by weakening them, and also shortening their lifespan. It has been successful in B.C. since it grows quickly without too much need for light or water. English ivy has star-shaped leaves that have a waxy shine to them, and it produces white to yellow-green flowers in the late summer and early fall.
In the Comox Valley, the vast areas of Scotch broom exhibit what a changed landscape can look like if invasive plants are allowed to spread and take over. Introduced from Europe, Scotch broom can live up to 25 years and produces seeds that can survive in the soil for 30 years. It grows in heights of one to three metres with woody stems and bright yellow flowers.
On Vancouver Island and the B.C. coast, an organization called Broombusters was founded in 2006 in response to various communities’ growing concerns about the spread of Scotch broom. Broombusters has volunteer opportunities all across Vancouver Island, including in the Comox Valley, Cowichan Valley and Nanaimo.
Also known as stinking willie or staggerwort, this noxious weed can grow up to 1.2 metres in height with yellow daisy-like flowers. One plant can produce 150,000 seeds which can live in soils for up to 15 years.
Tansy ragwort can cause liver damage to livestock. The alkaloids in this plant also taint honey produced by bees, causing it to be too bitter to sell.
Jarratt said that although it has Canada in its name, Canada thistle was introduced hundreds of years ago. The plant is native to sections of the eastern Mediterranean and southeastern Europe. In Biology and Management of Noxious Rangeland Weeds from Oregon State University Press, researchers speculate that it was introduced in the 1600s.
“It’s just so widespread that people think it’s from here,” Jarratt said.
Canada thistle has bright purple and sometimes white flowers that can grow up to two metres in height. The leaves have sharp edges with white hairs on the underside, but its stems are spineless. The plant’s seeds look similar to dandelions, described by the Invasive Species Council as “parachute-type seeds.”
Sometimes mistaken for Canada thistle, the main difference between the two is that Canada thistle has no spines, whereas Bull thistle flower bases do. Its seeds spread through the wind and have spiny winged and slightly woolly stems. In the summer, this plant produces purple flower heads which range from 3.8 to 7.8 cm in diameter.
Native to Europe and Asia, this plant was introduced in North America for medicinal purposes in the 1600’s. Also designated as a noxious weed, it can grow up to 1.5 metres tall with bright, round yellow flowers and green serrated leaves. According to the Invasive Species Council of BC, it is often found in disturbed areas such as roadsides or pastures. Common tansy is toxic to both livestock and humans. Common tansy is a similar colour to tansy ragwort, but the flower shape is easy to tell apart. Both plants are highly invasive.
Queen Anne’s lace (wild carrot)
Often found growing amongst common tansy and tansy ragwort, Queen Anne’s lace was also introduced from Europe as a medicinal herb. “The interesting part about [Queen Anne’s lace],” Jarratt said, “Is that we have a lot of different native carrots in North America, and often they were cultivated too.” He added that there is often a native counterpart to invasive plants. In this case, for example, the counterpart is Daucus pusillus Michx, or American wild carrot. Queen Anne’s lace flowers are usually white, shaped like an umbrella. They turn inwards into a birds-nest like shape once they go to seed.
“Knotweed is incredibly hard to get rid of,” Jarratt said. In B.C., there are four different types of knotweed that cause significant issues:
- Japanese knotweed: Native to Taiwan, Korea, China and Japan. According to the International Union for Conservation of Nature, Japanese Knotweed is among the 100 worst invasive species globally.
- Giant knotweed: Native to northern Japan and the Sakhalin Islands, this plant is the largest of the knotweed species. It was introduced in North America in the 1800s, along with Japanese knotweed, as a garden ornamental.
- Himalayan knotweed: Native to the Himalayan mountain range, this knotweed is not as abundant as the more aggressive giant knotweed and Japanese knotweed. Jarratt saidhe hasn’t seen it become a big problem on Vancouver Island, and it is usually dealt with quickly.
- Bohemian knotweed: This is a hybrid between Japanese and giant knotweed. Bohemian knotweed is very aggressive and, according to the province, has “become even more abundant and invasive than either of its parents.”
A member of the carrot family, this species resembles Queen Anne’s lace, but it can reach a height of five metres and is extremely toxic. Jarratt says this plant can cause pretty serious issues, “because of the photosensitivity of it.” Photosensitivity is an extreme sensitivity to UV rays from the sun. When it touches skin, chemicals found in giant hogweed’s sap can cause the skin to become very sensitive to sunlight. Direct skin contact with this plant can cause blisters, burns and scarring. It can grow quickly in ravines and stream banks and poses a risk to humans and ecosystems. It is also designated as a noxious weed.
Like tansy and Queen Anne’s lace, common St. John’s-Wort was introduced as a medicinal and ornamental herb to North America from Europe. It is native to Europe, Asia and North Africa. “If I’m on a hike and see St. John’s wort, I’m gonna pull it, because I know that it produces upwards of 100,000 seeds per plant,” Jarratt said. This herb can grow up to one metre in height. It has yellow flowers and dark green leaves that display small transparent dots when held up to light.
What can be done about invasive plant species?
Jarratt said there are many resources available for those who want to learn more about invasive species. A good place to start is the Invasive Species Council of BC (ISCBC). For Vancouver Island, people can turn to Coastal Invasive Species Committee, a non-profit organization working to lessen the negative effects of invasive species throughout Vancouver Island, the Gulf Islands and Sunshine Coast.
Jessica Bayley, Executive Director of the Coastal Invasive Species Committee, told The Discourse that there are a few preventative measures to take to stop the spread of invasive species.
Read some of Bayley’s tips
Play, Clean, Go: “After you play out in nature, make sure you and your furry friends are not transporting any seeds, dirt/mud or plant materials before you go.”
Clean, Drain, Dry: “Clean, drain and dry boats and equipment when moving between water bodies.”
Don’t Let it Loose: “Don’t let your pets loose and don’t dump plants, aquarium water, etc. into the natural environment.”
Buy Local, Burn Local: “Don’t move firewood.”
Be Plant Wise: “Choose non-invasive plants for your garden.”
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