BANFF, Alta. – Weeds are pursuing a manifest destiny as they creep northward from Mexico to the Yukon, choking out native plants on the millions of acres in their path.
The costly and time-consuming challenge of identifying, cataloguing and controlling pests introduced from Europe and Asia more than a century ago was discussed during a weed experts conference held in Banff May 28-30.
Much of the groundwork falls on the shoulders of volunteers who spot the weeds, report them and pull them out.
British Columbia spends $6 million a year on invasive plant management and relies on a network of 1,000 volunteers through an invasive plants council to deal with weeds in 14 ecosystems.
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In the United States, volunteers detect and remove weeds, especially on protected wildlife areas.
“More eyes on the landscape can be really great at discovering invasives and valuable species,” said Jenny Ericson of the U.S. Department of the Interior’s fish and wildlife division.
The United States’ wildlife refuge system protects 96.2 million acres, and about 20 percent of them are infested with weeds. Canada thistle is a particular problem for land managers.
As well, federal weed control budgets are declining, which means many projects are not funded.
In 2007, $11.3 million was spent controlling invasive weeds on 14 percent of the landscape. More than 2,750 volunteers spent 40,000 hours controlling weeds on 21,000 acres.
In Canada, weed councils share information on-line about recent sightings, areas of infestation and control methods.
B.C.’s 10-year-old invasive plants council links volunteers, resource industries and government so they can stay ahead of invaders on 950,000 sq. kilometres of mostly public lands, said Val Miller of the provincial forest ministry’s range branch.
Alberta’s Scott Miller said other provinces watch B.C.’s activity because troublesome weeds that are found in that province are likely to jump borders and plague other jurisdictions.
Climate change, which increases levels of carbon dioxide in the atmosphere, is exacerbating the spread of invaders, said Lew Ziska of the
U. S. Department of Agriculture.
Many introduced species die at – 28 C, but troublesome pests are beginning to survive in new areas, such as southern Canada, as winters warm.
Increased carbon dioxide also favours yellow star thistle, Canada thistle, spotted knapweed and sow thistles.
Kudzu and cheat grass are even more productive with increased carbon dioxide, although the increased growth makes them less palatable to grazing animals. They have taken over more than 80 million acres in the western U.S.
Cheat grass, also known as downy brome, is a prolific seed producer that edges out native grasses. It provides flammable material and allows fire to spread among native perennials in dry regions.
“As fire spreads, the overall result is you have an elimination of perennials because they can’t stand a fire every five years, whereas cheat grass can,” Ziska said.
In the Yukon, five consecutive weeks of – 40 C temperatures were once commonplace, which killed off most persistent pests. Bruce Bennet, a biologist with the territory’s environment department, said that has changed.
Yukon, Northwest Territories and Alaska are reporting more downy brome, leafy spurge, sweet clover, lucerne and hawkweed. These weeds encroach roadsides and are highly flammable.
Many of the 144 reported invaders arrived with the construction of the Alaska Highway, other road work and oil and gas activity as seeds arrived on unwashed machinery.
Weed-contaminated grain was fed to horses used on this road work, and their seeds were spread from manure and spilled feed.
The 100,000 tourists that visit the Yukon annually are not the problem, said Bennett. Instead, weed surveys suggest most weeds come from road crew maintenance.
“All these things seem to be associated with maintenance and agronomics,” Bennet said.
Introduced weeds also clog North American waterways, said Al Cofranscesco of the U.S. Army Corps of Engineers, which is responsible for removing weeds from rivers, lakes and canals.
The U.S. spends about $74 million a year on weed management to keep locks and dams operating. Weeds build up around bridges and make flood control difficult. They also harm hydraulic systems and plug turbines.
