The lands of the Rice Lake Plains and, indeed, most of Northumberland County, are host to a myriad selection of invasive species. The major problems, however, are caused by a few culprits, details of which follow.

At the top of the list are Dog-strangling Vine, Garlic Mustard, European Buckthorn and Scots Pine. Then, more recently, a very unpleasant plant has established itself in some areas. It is the Giant Hogweed. Some of the notable invasive species are honeysuckle, sweet white clover, spotted knapweed, Timothy’s smooth brome grass and Norway Maple.

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Dog-strangling Vine (also known as swallowwort) is a perennial plant native to eastern Europe. It has been spreading rapidly in southern Ontario and New York State. The plant has tiny brown five-petalled flowers and shiny spade-shaped leaves. As a member of the milkweed family, it has white sap, and disperses its seeds by wind. DSV can take over entire fields or the forest floors, reducing native plant diversity.

Photo by Ken Towle

Garlic Mustard was probably introduced by European settlers as a food source. When squeezed leaves smell somewhat like garlic. The plant is biennial. In the first year it forms a basal rosette of serrated kidney-shaped leaves that remain green through the winter. In the second year it grows a stem up to one metre high with tiny four-petalled white flowers. Garlic mustard spreads rapidly along forest edges and within forests, displacing native wildflowers. The plant secretes chemicals in the soil that retard the growth of other plants, preventing competition.

Photo by Ken Towle

European Buckthorn is a shrub species that was introduced as a fast-growing windbreak. It has shiny oval leaves with a distinctive pattern of veins arching toward the tip. These leaves remain green long after most trees and shrubs have shed their autumn foliage. Female plants produce thousands of black berries that attract birds, including flocks of European Starlings. Birds then spread the seeds throughout the landscape. European buckthorn can quickly take over the understory of woodlots, displacing native shrubs and wildflowers.

Photo by Ken Towle

Scots Pine: In Europe and parts of Asia, Scots pine is valued both as an important commercial species and for its ecological value. In Ontario, where it was introduced in the 1920s, it is now considered to be an exotic (non-native) tree species that has invasive tendencies and can be host to a wide range of insects and diseases. It is a prolific producer of seeds which germinate well if given the right light conditions. Thus if not removed, it will rapidly spread and completely take over abandoned fields.


Giant Hogweed is a very large plant in the parsley family. It has broad, deeply toothed leaves, a thick stem, and broad, umbrella-like white flower heads. It looks very similar to Cow Parsnip, but is much larger. Giant Hogweed is a threat to human health. If the oil from the plant gets on the skin and the skin is then exposed to sunlight it can result in severe and painful blistering. If the oils get in eyes they can cause temporary or permanent blindness. Do not touch this plant!
Ontario Invasive Plant Council ~ ~ Publications

Sweet White Clover: This has been planted as a forage crop. It can grow tall and crowd out native prairie plants.  Many prairie plants are adapted to do well in soils with low nitrogen but sweet white clover increases the nitrogen in the soil and therefore reduces any competitive advantage that the prairie plants have.

Photo by Janine Mcleod

Spotted Knapweed is native to Eurasia and was introduced to North America over 100 years ago. It does well in disturbed locations, with dry conditions and poor soil.  It can quickly invade old fields and restoration sites.   It spreads mainly by seed and each plant can produce over 1000 seeds.  It also releases chemicals in the soil that limit the growth of other plants.

Photo by Janine Mcleod

Timothy (L) and Smooth brome grass (R): These are introduced cool season grasses which come up early in the spring. Native prairie grasses are warm season grasses that come up after any chance of frost has passed.  The cool season grasses compete with the native grasses for resources such as water, soil nutrients and sunlight. 

Photos by Janine Mcleod

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