Western Producer Calgary reporter Barbara Duckworth attended an invasive plants conference in Calgary and filed these reports.
Since the Europeans colonized North America, about 50,000 plants and animals of various species and hybrids have been introduced here.
Many were beneficial or harmless, but a small percentage escaped and became threats to crop production and ecosystems.
Those causing trouble are referred to as invasive species. These cost the United States $13.8 billion in crop losses and control expenses last year, said Randy Westbrooks, an American invasive plant specialist.
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This is biological pollution and it does not receive nearly as much attention as it deserves, Westbrooks told an invasive plants conference in Calgary Oct. 2-3.
“Exotic species are terrific in a lot of ways but we have to control them,” he said.
Many species were introduced because immigrants wanted a reminder of a favourite plant or animal from home, never suspecting the plants could become pests in a new environment.
Others were brought in because they were attractive ornamental plants or had medicinal value.
Ten percent of exotic species will establish freely and 10 percent of that number become serious problems.
Troublesome invasive species include the Asian longhorned beetle, zebra mussel, leafy spurge, gypsy moth and chestnut blight.
People have to control these because there are no natural predators in the North American environment. These plants and insects affect agricultural land and wildlife habitat and swallow up riverbanks.
New invaders arrive in a variety of ways.
Wildflower mixes may carry noxious weed seeds. Provincial governments can order the plants removed but cannot control the movement of the seeds, which is a federal responsibility under the Canada Seeds Act.
Another route is through liberalized trade and travel where ornamentals are imported from Asia, bugs enter via wooden packing crates and seeds travel on tourists’ shoes.
Internet sales of seeds are a growing problem.
Westbrooks estimates 5,000 websites offer exotic plants and seeds for sale. The U.S. plans to monitor these sites to ensure problem plants are not imported.
Humans are almost always responsible for introducing problem species.
For example, Melaleuca trees from Australia were planted in the Florida everglades to control erosion. They have multiplied and short-circuited the hydrologic cycle because they use too much water.
In Canada, the majority of alien plants are weeds in crops, pastures and roadsides, said botanist Eric Haber.
Some introduced plants are found only in scattered groups. They become a concern when they form a dense monoculture over an area, choking out every other plant and make it impossible for wildlife or livestock to walk through.
Introduced plants often seem to have succulent roots, survive in a variety of climates and produce abundant seeds that remain viable for many years. Seeds from Scotch brome, for example, are good for 80 years.
Many of these plants are unpalatable or even poisonous. For example, leafy spurge is only palatable to goats. It also has a sap that can cause a rash on human and animal skin.
In Canada, the greatest problems are in Quebec, Ontario and British Columbia.
Ontario has 3,300 types of flora, of which about 30 percent are exotic species. Alberta has 1,900 types of flora, of which 16 percent are alien.
Nova Scotia has 1,700 species, of which 30 percent are exotic. In Nova Scotia’s case, many came in through seaports at the time of settlement. Some came in hay shipments from Europe centuries ago.
One of the most troublesome invaders is water milfoil. This is a costly weed in B.C. because it can completely cover a lake or river. It requires mechanical removal in the Okanagan lakes. The plant takes up considerable amounts of phosphorus and when it decays, it releases the mineral back into the water.
Crested wheat grass was introduced as a forage on North American rangelands. It reduces the organic content and soil nutrient levels compared to native grasses.
Another issue is hybridization, where foreign plants cross with native plants leading to the eventual extinction of some native species.
