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Invasive Plants BC

Invasive Plants

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  Canada thistle (Cirsium arvense) is a root-creeping perennial. Considered noxious under the BC Weed Control Act, this thistle is commonly found on roadsides, cultivated fields, pastures, logged forests, riverbanks, and other disturbed areas. It is a major concern in the Peace River, Omineca and Skeena areas, and is a widespread throughout the province. Canada thistle has purple or white flowers, with stalkless, spiny, dark-green leaves, growing to 0.3-2 metres in height at maturity. Canada thistle spreads rapidly through horizontal roots that give rise to large infestation patches nearby and out-competing native plants. Canada thistle develops seeds sparingly and may produce 1,000 to 1,500 seeds per flowering shoot. Best adapted to rich, heavy loam, clay loam, and sandy loam, it grows poorly in shaded conditions, can tolerate saline, wet, or dry soils, but does not tolerate waterlogged or poorly aerated
  (Tanacetum vulgare) Common tansy (Tanacetum vulgare) is a perennial and considered regionally noxious under the BC Weed Control Act. Common tansy is currently distributed in the following areas: Bulkley-Nechako, Central Kootenay, Columbia-Shuswap, East Kootenay, and North Okanagan Regional Districts, and within Greater Vancouver, Fraser Valley, southeast coast of Vancouver Island, Gulf Islands, Sunshine Coast, and Squamish/Pemberton.Common tansy has yellow disc flowers that resemble buttons in a flat-topped cluster at the top of the plant. With fern-like leaves, common tansy can grow 0.4–1.5 metres in height at maturity.Spread mainly through seeds and roots, common tansy can be transported by birds, animals, and on vehicles that have been in infested areas. Seeds can remain viable for up to 25 years; therefore, stopping seed spread is a main concern. Common tansy prefers sunny areas with well-drained soil, and often infests stream
  (Heracleum mantegazzianum) Giant hogweed (Heracleum mantegazzianum), also known as “Giant Cow Parsnip,” is a perennial and currently distributed in the Lower Mainland, Fraser Valley, Gulf Islands, and central to southern Vancouver Island.Giant hogweed has numerous small white flowers clusters in an umbrella-shaped head, with stout, hollow green stems covered in purple spots. Dark green leaves are coarsely toothed in 3 large segments with stiff underside hairs, and lower leaves can exceed 2.5 metres in length. Giant hogweed can grow up to 5 metres in height at maturity.Giant hogweed is a highly competitive plant due to vigorous early-season growth, tolerance of full shade and seasonal flooding, as well as its ability to co-exist with other aggressive invasive plant species. Each plant can produce up to 100,000 winged seeds (typically 50,000) that remain viable in the soil for up to
  (Ulex europaeus) Gorse (Ulex europaeus) is a spiny, perennial evergreen shrub, considered noxious under the BC Weed Control Act, and thrives on sunny clearings with dry, infertile soil such as sandy or rocky areas, roadsides, fields and pastures, bluffs, cutblocks, and cutbanks. It is currently distributed in Vancouver Island, West Vancouver, some of the Gulf Islands, and Skidegate on the Queen Charlotte Islands. Gorse is a dense evergreen shrub with a single upright stem, spine-like leaves, and fragrant yellow, pea-like flowers. Seedpods are hairy and black. Gorse can grow 1-3 metres in height at maturity.Growing rapidly for the first 15 years, gorse can live up to 45 years. Maturing seedpods explode and disperse up to 18,000 seeds per mature plant. Gorse seeds are easily distributed by ants, animals, birds, and machinery. Since gorse grows mainly by the ocean,
  (Hieracium spp.) Hawkweeds (Hieracium spp.) are perennial plants with 14 non-native species recorded in BC, and are difficult to identify among the 8 native hawkweed species. One of the 14 non-native species, orange hawkweed (Hieracium aurantiacum) is currently the only hawkweed considered regionally noxious under the Weed Control Act. Most hawkweeds have yellow flowers. Invasive hawkweeds are found throughout most forest regions and regional districts in British Columbia. The regional districts east of the Rocky Mountains, Northern Rockies, and Peace River Regional Districts only have a few known invasive hawkweed sites and efforts to prevent further establishment and spread are actively underway. Orange hawkweed is regionally noxious in the East Kootenay, Central Kootenay, Columbia-Shuswap, Thompson-Nicola, Bulkley Nechako, and Cariboo Regional Districts. Hawkweeds have bright orange, orange-red, or yellow ray flowers with several flower heads in clusters at the
Himalayan blackberry (Rubus discolor) is mostly a biennial plant, growing on disturbed sites, along roadsides and rights-of-ways, in pastures, along river and stream banks, fresh-water wetlands, riparian areas, forest edges, and wooded ravines. They are currently distributed on the Lower Mainland, Sunshine Coast, Fraser Valley, Gulf Islands, central to southern Vancouver Island, Queen Charlotte Islands, the Okanagan, and the West Kootenay areas. Himalayan blackberry has petite, white or faint pink flowers with 5 petals, arranged in clusters of 5-20. Flower stalks are prickly, with robust stems (canes) that support large, flattened and hooked or straight prickles. Canes grow up to 3 metres in height and 12 metres in length at maturity. Evergreen leaves are predominantly large, rounded or oblong, and generally grouped in fives on first-year canes and threes on second year, flowering canes. Fruits are up to 2 cm
  (Berteroa incana) Hoary alyssum (Berteroa incana) is an annual to short-lived perennial. Considered regionally noxious under the BC Weed Control Act, hoary alyssum is most common on sandy or gravelly soils and establishes on roadsides, railway embankments, and heavily grazed pastures. It is currently found in south-central and southeastern BC including the Okanagan, Cariboo, Boundary, Thompson, and Kootenay areas.Hoary alyssum has small white flowers with deeply notched petals that are supported on slender stalks. The whole plant is covered in star-shaped hairs that are rough to touch, with grey leaves that clasp closely to the stem. Oval seedpods are chambered and held close to the stem with each chamber containing 5-7 black seeds. Hoary alyssum can grow up to 0.7 metres in height at maturity.Hoary alyssum spreads rapidly through a long season of seed production. Each plant flowers
  (Cynoglossum officinale) Hound’s-tongue (Cynoglossum officinale) is a biennial to short-lived perennial, and is considered noxious under the BC Weed Control Act. Hound’s-tongue is found on dry pasture, roadsides, and logged forestland. Found primarily in the southern interior of BC, it is a major concern in the Kootenay, Okanagan, Thompson, and Cariboo areas.Mature hound’s tongue plants have a woody taproot, with rough, hairy, wide leaves and dull reddish-purple, five-petal flowers. Each flower produces four rounded-triangular seeds covered with hooked prickles. Growing 0.5-1.2 metres tall, stems leaves are short and stalkless. First year plants form a rosette with leaves hanging down to resemble the shape of a dog’s tongue.Each plant produces 2,000-4,000 barbed seeds a year that cling easily clothing, livestock and wildlife, resulting in new infestations spread over great distances. Hound’s-tongue decreases forage production on rangeland and pastures. Barbed
  (Polygonum spp.) Knotweeds (Polygonum spp.) are invasive perennials, with four species found in British Columbia: Japanese knotweed (Fallopia japonica); Bohemian knotweed (Fallopia x bohemica); Giant knotweed (Fallopia sachalenensis); and Himalayan knotweed (Polygonum polystachyum). Knotweeds thrive in roadside ditches, low-lying areas, irrigation canals, and other water drainage systems. They are also found in riparian areas, along stream banks, and in other areas with high soil moisture. Knotweeds occur in the southwest coastal region, the Shuswap, Kitimat, Stikine, Skeena, Columbia, Okanagan, and Kootenay areas, as well as the Queen Charlotte Islands. Additional plants may exist in many gardens in communities across BC.Knotweeds have small white-green flowers that grow in showy, plume-like, branched clusters along the stem and leaf joints. Hollow stems stand upright and are bamboo-like with reddish-brown speckles and thin, papery sheaths. Leaves are heart or triangular-shaped on all

Other Invasive Organisms

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Common Carp. Text.
Didymo (Didymosphenia geminate) or “Rock Snot” is a fresh water diatom most commonly found in high elevation streams and rivers throughout northern Europe and North America. It has long been considered a ‘cold-water’ algae, but has since spread to warmer lower elevation streams and rivers. It can form massive blooms causing significant negative impact to freshwater fish, plants and invertebrates through habitat and food web alteration.   Its most distinguishing feature is a slimy brown layer or ‘ blooms’ that smothers rocks, aquatic plants or any other structures in the water.  The blooms resemble thick slimy looking mats and are distinguished from other forms of algae by its brown, beige or white color.  Didymo is never green in colour.   Although Didymo looks slimy in appearance, it is spongy and scratchy to the touch and has a texture similar to
The Eastern grey squirrel (Sciurus carolinensis) may be cute and fuzzy to on-lookers, especially in the popular tourist areas of Stanley Park in Vancouver, but it is an invasive mammal in British Columbia that is ranked by the Invasive Species Specialist Group (ISSG) as one of the Top 100 Invasive Species in the world. This small mammal has some big ecological impacts—it has depleted populations of the European red squirrel through out-competition and disease (parapoxvirus), and displaces native birds of their nesting habitat, eating the birds’ eggs and nestlings. It also competes with native mice and voles. Economically, Eastern grey squirrels cost homeowners repairs due to digging up of lawns and gardens, chewing through electrical wires, eaves and shingles, and nesting in roofs, attics, and chimneys. Fruit and nut trees and vines may not produce as well due to the
Largemouth Bass  
The New Zealand mud snail is a very tiny aquatic snail (often smaller than your baby fingernail) and is native to fresh waterbodies in New Zealand. The New Zealand mudsnail is typically light to dark brown in colour but may look black when wet. The shell of adult mud snails usually have 5 – 6 whorls that lean to the right, are less than 5 mm in size and can easily be confused with other fresh water and native snails. It is thought that the New Zealand mudsnail was transported to North America in the ballast water of transport ships originating from Europe and Asia. It was first recorded in North America in the late 1980’s in Idaho’s Snake River and is now widespread in many states including Washington, Oregon, and California. The New Zealand mudsnail can live in a
Appropriately named for its ‘fire’ like sting, the European fire ant (Myrmica rubra) will attack aggressively if disrupted. When this ant attacks, it pinches down with its mandible then swings around and stings multiple times. In a few cases it has produced severe allergic reactions including anaphylactic shock. The European fire ant is a small red to brownish red ant that can be identified by its two waist segments, our native ant only has one, and the two backward pointing spines and stinger (visible with a magnifying glass).  This invasive insect was introduced from its native Eurasia to eastern North America. It was first sighted along the eastern seaboard of the United States in the early 1900s and has since spread across several Canadian provinces including Nova Scotia, New Brunswick, Quebec, Ontario, and into British Columbia. European fire ant nests

Feature Article: Impacts


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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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