By Laura Zuckerman
SALMON, Idaho (Reuters) - Dogs trained to sniff out invasive plants are the latest weapon in the war against weeds that threaten to choke off vast stretches of native forests and grasslands across the West.
Each of the eight canines owned by Working Dogs for Conservation, a nonprofit company in southwestern Montana, can scent as many as five types of invasive plants, often in rugged brush-covered terrain where detection eludes the human eye.
In an arsenal that includes herbicides and teams of weed-pulling volunteers, the dogs are key new combatants in a campaign to spot exotics before they gain too much ground, targeting areas where native plants and grasses are still many and invaders few.
"The best chance we have is early detection and rapid response," said Steve Shelly, invasive species coordinator and regional botanist for the U.S. Forest Service in Montana.
The targets of conservation dogs are narrow, since aerial surveys and even casual observation reveal major weed infestations.
"If you've got a monster patch, you don't need a dog to find it," said Alice Whitelaw, co-founder of Working Dogs for Conservation.
The dogs -- from border collies to German shepherds -- are selected for intelligence, high energy and a tendency to be obsessed with toys, all traits well-suited to the company's reward-based training. But it is dogs' keen sense of smell that makes them especially valuable as weed detectors.
Studies suggest dogs in some cases are six times more likely to locate their quarry than trained scientists.
"All the data show dogs are more efficient at finding the plants than humans; we're sight-oriented, not smell-oriented," said Tim Prather, professor of weed ecology at the University of Idaho.
Experts with the Forest Service and the federal Bureau of Land Management (BLM) say weeds are among the leading threats to the nation's forest and rangeland ecosystems, with the takeover by invasive plants described as a creeping biological disaster.
More than one-quarter of the 250 million acres of mostly Western lands under BLM management have been ravaged by invasive plants, which daily claim thousands of additional acres.
The portion of national forests under assault by weeds likewise has grown from less than 5 percent in 1996 to 10 percent in some forests today, government research shows.
Scientists say everything from fish and wildlife to water resources and natural fire cycles are disrupted by the invasion, which costs $138 billion a year in damage and control efforts.
The thousands of nonnative plant species in the West range from spotted knapweed, an import from Europe, to cheatgrass, which is blamed for fueling more frequent and severe wildfires in the sage-brush steppe of Nevada, Utah, Idaho, Oregon and California.
Working Dogs' four-legged detectives are credited in Montana with uncovering previously unknown colonies of Dyer's woad, a weed of the mustard family that hitchhiked to Utah in an alfalfa shipment.
That weed also has run rampant in Idaho, Wyoming and Washington, but its reach in Montana is so far limited to just a handful of infestations.
Marilyn Marler, natural areas specialist with the University of Montana, said the conservation dogs this month nosed out unseen clusters Dyer's woad in Missoula.
"We used to pull out 500 Dyer's woad; we won't even reach 100 this year," she said.
Because invasive plants face few natural enemies and their spread is assured by seed-snagging livestock, wildlife and vehicles, they are not expected to be expunged from the landscape any time soon.
But experts say strategies like deploying dogs to scent isolated populations may preserve some areas.
"You just try to contain weeds where they are well-established; with new infestations, you try to take them out," said John Simons, BLM weed specialist in Montana.
(Editing by Steve Gorman and Ellen Wulfhorst)