The History of Invasive Plants in BC: How did they get here?

One of the greatest joys of traveling can be returning home with souvenirs for friends and family. Today’s travelers tend to purchase luxury items, while the first European settlers in British Columbia traded livestock and feed, plants, seeds, and other essentials for basic survival. This early movement of goods included the transfer of plants with beneficial characteristics into BC, but also those with invasive tendencies. Though unforeseen during early settlement, invasive plants now pose a significant threat to the environment, society, and economy.

Many of the goods imported by settlers became staples of the Canadian agriculture sector including forage crops such as corn and wheat. Unfortunately, among these beneficial exotic plant species also came invasive plants.

Invasive plants are commonly referred to as “alien,” “non-native,” or “introduced” plant species because they were brought to BC from other areas without their natural predators that would otherwise keep their populations in check. Aggressively out-competing native plants, invasive plants permanently alter fragile ecosystems, destroy wildlife habitat, harm human health and safety, and cost natural resource industries and taxpayers millions of dollars every year in management and control. So how did this problem evolve?

Records of invasive plants are limited, but indicate that since the 17th century, European settlers transported thousands of plants to North America for medicinal, agricultural, and ornamental uses.

The progression of invasive plants into BC began with the fur trade of the early 1800s. For instance, fur-trade gardens were established at Stuart Lake in 1811, Fort Langley in 1827, and Fort Thompson in 1842. These gardens may have contributed to the transfer of invasive plants and seeds to new areas of the province, either unintentionally in hay and other livestock feed products, or sold deliberately as ornamentals for flower gardens.

The highly invasive plant, Purple loosestrife (Lythrum salicaria) was introduced to BC as an ornamental, and has now spread rapidly through prolific seed production and trade among gardening enthusiasts. It has invaded wetlands, replacing diverse native vegetation with dense monocultures, thus impacting wildlife that depend on these wetland ecosystems for foraging, nesting, and breeding habitats.

As well as ornamental uses, invasive plants were introduced for medicinal benefits. For example, common burdock’s (Arctium minus) brownish-green, deep roots are used as a traditional medicinal herb and remedy for dry and scaly skin conditions such as psoriasis and eczema, and as a blood purifier clearing the bloodstream of toxins. In traditional Chinese medicine, burdock is often used with other herbs to treat sore throats and colds.

Despite some positive medicinal uses, burdock is now considered highly invasive as its burs cling to livestock and wildlife, causing irritation to eyes, throat, mouth, or the inside of the stomach. Infestations also reduce crop quality and desirable grazing vegetation, and are responsible for tainting milk products if grazed in large quantities.

In addition to ornamental and medicinal uses, invasive plants were brought to BC on overseas vessels for erosion control along early highway corridors. An example of this was described in the writings of explorer Captain Walter Grant in 1850 in which Scotch broom (Cytisus scoparius) seeds were obtained from the Sandwich Islands of Hawaii and brought to Vancouver Island. About three plants were introduced in Sooke, and infestations now colonize much of southern Vancouver Island. Consequently, these original plantings now pose serious problems for sight lines and require exhaustive maintenance to control.

Scotch broom is also a serious competitor to conifer seedlings; Douglas fir plantation failures in Oregon and Washington have been credited to dense infestations. During the spring bloom, Scotch broom causes allergy symptoms in people.

The environmental, economic and social consequences of introducing invasive plants
were not foreseeable to settlers of the 19th century, especially with the discovery of gold that drove a fever of activity and settlement in the province during the Gold Rush of 1858-1866. This dramatic increase in movement of people and resources became a key pathway for invasive plants. The Gold Rush brought approximately 30,000 people, 20,000 cattle, innumerable sheep, horses, and even camels to BC, resulting in the town of Barkerville, and marked trade routes, transportation corridors, roadhouses, farms, and ranches in the Cariboo region.

Since invasive plants quickly capitalize on disturbed, open ground, any newly formed trail, roadway, tilled farmland, and even the railway became key vectors for their introduction and establishment. One of North America’s earliest floral colonizers, Canada thistle (Cirsium Arvense), arrived in contaminated hay and grain seed. Canada thistle and knapweed (Centaureaspp.) infestations, as well as other invasive plants, are now known to cause a reduction in forage crop yields by as much as 15 percent and significant economic losses to BC farmers and ranchers, according to the Ministry of Agriculture and Lands.

As early as the 19th century, invasive plants like thistles were being recognized as problem plants. The first weed legislation in the new Province of British Columbia (1871) was the Thistle Prevention Act of 1877. This act refers to “perennial thistles” with no specific species identified, but was the first attention by government to restrict the movement of goods that were harming healthy farm and ranch production. The Noxious Weeds Act in 1888 listed eight species, with the purpose of preventing the spread of noxious weeds or invasive plants. The BC Weed Control Act has since replaced the Noxious Weeds Act and currently includes 48 noxious weeds. Recent provincial legislation that governs the management of invasive plants also includes theCommunity Charter Act, Forest and Range Practices Act, and the Integrated Pest Management Act.

Research into invasive plant identification and cultural control methods for invasive plants began in the 1920s, with the first course on weed identification at the University of British Columbia (UBC). UBC also developed a “Weed Science” course in the 1950s that was among the first of its kind in Canada.

Management practices to combat invasive plants began in the 1940s with chemical control. The BC Ministry of Highways began spraying knapweed along roadsides in 1967, and the BC Ministry of Forests began chemical control of knapweed on Crown land in the East Kootenays in 1969.

The use of biological agents evolved as an alternative control method, involving detailed screening, propagation, field release, redistribution, and monitoring of agents. The use of biological agents began in 1951, when Chrysolina beetles were successfully introduced on the invasive plant, St. John's-wort (Hypericum perforatum), near Edgewood, BC. Since then, more than 70 biocontrol agents have been released on 21 invasive plant species in BC.

As more research was conducted and management undertaken, results began to indicate an alarming trend: without management, invasive plants would exponentially increase and could cause irreversible damage to surrounding ecosystems, agricultural lands, and communities. These findings drove subsequent coordination and collaboration in the 1970s and mid-1980s to include expanded programs at UBC and other universities, innovative research by Agriculture Canada, and six new biocontrol agents for knapweed were made available by 1984 through the BC Ministry of Forests. Current collaborations involve efforts by more than a dozen regional invasive plant councils and committees, the Invasive Plant Council of British Columbia, all levels of government, private industry, the natural resource sector, non-government organizations, First Nations, and concerned individuals to minimize the impacts of invasive plants and prevent new infestations.

After more than 150 years since original introductions, increased transport, trade, travel, and tourism activities that form today’s global marketplace are bringing an unprecedented number of invasive plants to Canada and BC. As native plant communities are replaced by invasive plant infestations, biodiversity declines and habitats change. Improved collaboration among land managers, academia, industry, and government, as well as public awareness of invasive plants, will help to reduce their introduction and spread.

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