The Impacts of Invasive Plants in BC: Why are they a Problem?

Did you know that taxpayers help pay for control measures to stop the spread of invasive plants that threaten biodiversity and local economies? Or that people unknowingly transfer invasive plants to new areas in British Columbia (BC) through activities like gardening, recreation, or even on the job? Growing rapidly and spreading quickly, invasive plants are non-native to BC, and can cause significant damage to the environment, economy and human health and safety.

Invasive plants were brought to Canada and into BC both accidentally and intentionally. Many invasive plant species arrived with increased trade, immigration, and colonization in the 1800s. Popular gardening and landscaping activities have also resulted in purposeful introductions of invasive plants. Characteristics that are ideal for the garden, such as self-seeding, fast growth, and adaptability to a variety of growing conditions, are also what make invasive plants a threat to natural resources.

Commonly, invasive plants spread from gardens when people dump contents of hanging baskets and garden waste or soil into natural areas or nearby community gardens. Himalayan balsam (Impatiens glandulifera), otherwise known as ‘Policeman’s helmet,’ has jumped the garden fence on the Lower Mainland of BC and now takes over riparian areas, causing bank erosion when vegetation dies back in the fall. Other invasive plants like English ivy (Hedera hibernica), purple loosestrife (Lythrum salicaria), and Dalmatian toadflax(Linaria dalmatica) were also popular with the home gardener and now cause significant environmental and economic damage in various regions of BC.

Arriving without their natural pathogens or predators to keep populations in check, invasive species like spotted knapweed (Centaurea biebersteinii) and Scotch broom (Cytisus scoparius) become highly competitive to surrounding vegetation. This advantage allows them to spread rapidly by producing large amounts of seed, forming deep taproots, or flowering early. They form dense infestations over large areas and out-compete desired vegetation, permanently altering ecosystem functions, degrading agriculture and range values, and impacting local economies.

Agriculturally, invasive plants like spotted knapweed can have huge economic impacts by competing with desirable crops, and reducing crop yields by up to 15 percent. Since animals rarely eat these species, infestations go unchecked on rangeland and wildlife habitat. According to the BC Ministry of Agriculture and Lands, every year, BC farmers and ranchers lose an estimated $50 million in crop revenue to invasive plants, and then also pay several million dollars more for control measures, such as herbicides and cultivation. Invasive plants can also negatively impact the forestry industry by damaging newly planted seedlings. For instance, Douglas fir plantation failures in Oregon and Washington have been linked to extensive Scotch broom infestations.

Invasive plants not only threaten natural resource industries, but also alter fragile habitats and disrupt ecosystem functions. For example, the Garry Oak Ecosystem Recovery Team states that Scotch broom and gorse (Ulex europaeus) pose some of the most serious threats to Garry oak ecosystems on Vancouver Island by shading out low-growing plants and altering conditions needed by many birds, butterflies, and other species. Gorse acidifies surrounding soils, preventing native species from growing, and increases fire hazard due to volatile oils contained in the plant as well as large amounts of litter infestations produce.

Some invasive plants, such as Scotch broom and giant hogweed, pose health and safety risks to people. Scotch broom is known to cause allergy symptoms of wheezing and sneezing with the spring arrival of its yellow blooms. Giant hogweed contains a toxic sap that can cause severe burning, blistering and scarring of the skin, leading to a Toxic Plant Warning by WorkSafeBC. Found in southern BC, giant hogweed was introduced for its showy foliage, umbrella-shaped flower heads, and architectural stems. At maturity, plants can grow up to five metres in height, taking over recreational trails and limiting access.

Reducing recreational and landscape aesthetics is a social impact of invasive plants. Infestations make trails impassable, and the burrs, spines, and prickles of many species can puncture bike tires and reduce enjoyment of natural areas. Seeds and plant parts hitch a ride on hiking boots, clothing, pets, birds, and vehicles, resulting in new infestations over great distances. For example, carpet burweed (Soliva sessilis) is a nuisance to recreation enthusiasts on Vancouver Island and the Gulf Islands. Spiny seeds cause physical discomfort and sometimes infection when stepped on, resulting in reduced enjoyment of parks, beaches, sports fields, and golf courses. It also forms unsightly brown patches in summer, reducing the aesthetic value of parks and golf courses, according to the Canadian Food Inspection Agency.

While impeding recreation and reducing aesthetics of enjoyable landscapes, invasive plants also lower property values. For example, due to the explosion of leafy spurge (Euphorbia esula), Manitoba has experienced a $30 million reduction in land values. Leafy spurge infests 340,000 acres of land in Manitoba, costing taxpayers an estimated $19 million per year in protection of grazing land, public land, and right-of-ways.

Like terrestrial invasive plants, aquatic invasives also lower land values, clog waterways, and displace vegetation crucial to surrounding ecosystems, thereby reducing biodiversity. Eurasian water-milfoil (Myriophyllum spicatum), for example, clogs watercourses and lakes, making areas impassable to boaters and swimmers, and threatens aquatic ecosystems. Eurasian water-milfoil is tolerant of low water temperatures, allowing it to quickly grow to the surface, forming dense canopies that shade out surrounding aquatic vegetation. A study in the early 1990s on its establishment in Lake George, New York, found that infestations reduced native plants from 5.5 to 2.2 species per square meter in just two years. Eurasian water-milfoil has caused significant ecological damage to the Great Lakes region bordering Canada and the United States that requires expensive management in the region. Prevention practices like cleaning off boats before entering and leaving water features is key to reducing the spread of aquatic invasive plants.

Invasive plants are spreading across BC at alarming rates, making control efforts difficult and eradication especially challenging. Invasive plants reduce biodiversity, alter ecosystem functions, create management costs to natural resource industries, reduce recreational opportunities, and ultimately cost taxpayers millions of dollars each year. All citizens, regions, and industries in BC are affected; therefore, prevention and awareness is key!

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