Invasive Species along the Niagara Escarpment

A number of invasive species have made their way to the Niagara Escarpment. These species threaten the health of our escarpment ecosystems and can have detrimental impacts on native species.

An invasive species is a non-native species whose introduction does or is likely to cause economic or environmental harm or harm to human health. Invasive species are one of the top threats to biodiversity because they have few natural predators, reproduce quickly, thrive in disturbed systems, and can out compete native species for food and habitat.

Below we discuss common invasive species found along the Bruce Trail, explain how you can identify them, and discuss their impacts.

Garlic Mustard

Garlic Mustard
Alliaria petiolata

Native to Europe and introduced by early settlers as an edible herb, this invasive can be found on roadsides, waste places, woodlands, forests, trail edges. Garlic Mustard is shade tolerant and produces thousands of seeds per plant. These seeds may be viable in the soil for up to 5 years.

Identifying Garlic Mustard

Garlic Mustard looks different depending on its life stage. In the first year, it can be identified by its kidney-shaped leaves with scalloped edges. In the second year, it can be identified by its triangular sharply toothed leaves and white flowers with 4 petals clustered at the top of each stem. Garlic Mustard can grow up to 1 m tall in this stage with seed pods that reach upwards and contain up to 16 seeds. New leaves emit a garlic smell when crushed that fades as the plant matures.

Impacts of Garlic Mustard

Garlic Mustard displaces native woodland understory plants. It also produces chemicals that may affect the health of nearby native plants. Its roots contain sinigrin which interferes with the function of the beneficial relationship between native soil fungi and many native plants.

Dog-strangling Vine
Cynanchum rossicum

A member of the milkweed family, Dog-strangling Vine (DSV) was introduced to Canada from Eastern Europe in the late 1800s. This invasive is a perennial vine that can grow 1-2m in height by twining its way up trees and plants. DSV can invade prairies, alvars, shorelines, conifer plantations, meadows and forests.

Identifying Dog-strangling Vine

DSV can be identified by its vine that can grow up to 2 metres in length. The leaves grow opposite of each other on the vine and have rounded bases with smooth edges tapering to sharp point. Clusters of small star-shaped pink to red-brown 5 petaled flowers grow at the stem tips. Thin pointy seed pods develop in late summer before drying and revealing fluffy white seeds.

Impacts of Dog-strangling Vine

DSV forms dense colonies and out-competes native vegetation. This reduces habitat for wildlife. Native insects that rely on milkweeds, like the Monarch butterfly, can get confused and land on DSV. DSV also prevents forest regeneration.

European Buckthorn
Rhamnus cathartica

European Buckthorn is a small tree native to Europe and Asia. It was introduced to Canada in the late 1800s, to be used as a windbreak along farm fields. It is a rapidly growing, aggressive plant that invades both dry and moist habitats as well as fields, fencerows, clearings, forests, and slopes

Identifying European Buckthorn

European Buckthorn can be identified by its finely toothed, often glossy, “Egg-shaped” leaves with abrupt point at the tip and 3-5 leaf veins curving towards tip. They also have a short thorn in-between buds at branch tips. The European Buckthorn has clusters of small 4-petaled green flowers in the springtime that become purple-black berries in fall.

Impacts of European Buckthorn

Buckthorn is very shade tolerant and can colonize the understory to the exclusion of other plants. The leaves create a dense shade that blocks out sunlight for other species. The seeds have a laxative effect on wildlife which helps them spread widely. This can also increase nitrogen in the soil and prevent other species from growing.

Giant Hogweed
Heracleum mantegazzianum

Introduced from southwest Asia, Giant Hogweed was originally planted as a horticultural species in the early 1900’s. Giant Hogweed is in the Carrot/Parsley family and is closely related to native Cow Parsnip. It can now be found along roadsides, streambanks, fields, and waste areas.

Identifying Giant Hogweed

Living up to its name, Giant Hogweed can grow up to 5 metres in height and up to 1.5 metres wide. Its leaves are large with coarse teeth. The stem is bristly with distinct purple spots on a hollow green trunk. Umbrella-shaped clusters of small white flowers grow at the top.

Impacts of Giant Hogweed

Reproduces by seed, a single plant can produce up to 100,000 seeds. The hair on the stems and leaves contain a watery sap with toxins called flourocoumarins. Contact with this sap can increase the skin’s sensitivity to sunlight and may result in severe burns and blisters and temporary or permanent blindness if it touches the eyes.

Note: Never try to remove Giant Hogweed. Always contact a professional.


There are several species of invasive honeysuckle introduced from Europe and Asia. These were introduced as ornamental plants starting in the 1800s. They now can be found in forests and thickets along the escarpment.

Identifying Honeysuckle

Honeysuckles are multi-stemmed shrubs with light brown bark. The leaves grow in pairs with smooth edges. In the spring they bloom with showy white or pink flowers followed by bright red/orange berries in multiples of two. The invasive species have hollow stems.

Impacts of Honeysuckle

Honeysuckle forms dense thickets that shade out native plants, reducing plant diversity. The berries on honeysuckles are less nutrient dense for birds, reducing the nesting success.

Vinca minor

Periwinkle or Vinca Minor is a popular ground cover originally from Europe that has found its way to the gardens and lawns of Southern Ontario.

Identifying Periwinkle

Periwinkle can grow up to 40 cm high and can be identified by its small, dark, glossy leaves and light purple flowers. The flowers are about 3-5 cm wide and usually purple.

Impacts of Periwinkle

Periwinkle grows densely along the forest floor, shading out native plants, reducing plant diversity.

Spongy Moth
Lymantria dispar dispar

Previously known as “Gypsy Moth” or LDD, the Spongy Moth gets its name from the spongy egg masses it lays on trees. This moth is native to Europe, Asia and North Africa and feeds primarily on oaks, hardwoods and sometimes spruce.

Identifying Spongy Moth

Adults males are light brown with a wingspan of 2.5 cm while females white in colour with a wingspan of 5 mm. The eggs of the Spongy Moth are orange in colour, 2-8 cm long, and have a spongy, felt like appearance. The caterpillars are 6-7 cm long and yellow, grey or black in colour, with long wispy hairs. They have five pairs of blue spots then six pairs of red spots after the head.

Impacts of Spongy Moth

Spongy Moth larvae climb trees and feed on canopy leaves. This can result in the defoliation of an entire tree or tree canopies in an area. Defoliation can result in the dieback of twigs and branches and can make trees more vulnerable to other pests and diseases. Repeated defoliation can stress the tree and lead to mortality.

Other invasive species and diseases

Emerald Ash Borer

The Emerald Ash Borer arrived in Canada from Asia in 2002. Since then, it has killed millions of native Ash trees after rapidly expanding into Ontario with no known natural enemies. In some areas, this invasive species has reduced tree canopy by 25%, creating opportunities for other invasives such as Buckthorn to take over. True to its name, the Emerald Ash borer is bright green in colour.

Dutch Elm Disease

Dutch Elm Disease is a a highly infectious fungus that was first detected in Canada in the 1940s. The introduction of this fungus led to the widespread death of Elm trees in the 1970s and 1980s. Only 5% of the Elm population survives in North America today.

Butternut Canker

Butternut Canker is an invasive fungus that can infect and kill Butternut trees. First detected in the 1960s, this invasive has had detrimental effects on Butternut populations as most trees in Ontario have already been infected. Though some trees have shown some resistance, the canker can kill the tree in a matter of years. This has led to a decrease in forest diversity and food sources for wildlife. Infected trees may have sooty black wounds on the tree and often have peeling back and oozing black fluid.

Emerging Invasive Species

Three new invasive species have recently been recorded in Ontario: the Spotted Lanternfly, the Hemlock Woolly Adelgid and Japanese Stiltgrass. These new invasives could pose a threat to biodiversity on the Niagara Escarpment.

What the Bruce Trail Conservancy is doing

The Bruce Trail Conservancy is working to remove and prevent the spread of invasive species along the Bruce Trail. We are doing so by:

  • Implementing an invasive species strategy that outlines priority areas and species.
  • Doing invasive species mapping to identify where invasive species are and address how they can be controlled.
  • Installing boot brush stations.
  • Raising awareness through public education.
  • Organizing invasive species volunteer ‘pull parties’.
  • Completing larger restoration projects including invasive species removal and native species planting.

How you can help

  • Report sightings on the Bruce Trail Project on iNaturalist.
  • Monitor the invasive species’ preferred plant hosts for signs.
  • Stay on the Trail.
  • Use boot brush stations when available.
  • Buy local firewood and do not move firewood.
  • Do not plant invasive species such as vinca minor (periwinkle).
  • Properly dispose of all plant material when gardening; do not pick or transport invasive species without prior authorization
  • Learn to identify these species at their various life stages. Visit for more information.
  • Report your sightings (see links at top of this post).

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