If the phrase "war on weeds" seems over the top, consider this: Noxious weeds infest more than 100 million acres of North America—an area roughly the size of Montana. Like it or not, we're engaged in a battle to win back the Western landscape.
Weeds now conquer more than three million acres each year, invading an estimated six square miles of U.S. Forest Service and Bureau of Land Management lands every day. They've already claimed seven million acres of our national parks. Aggressive exotics like cheatgrass, leafy spurge, spotted knapweed and Dalmatian toadflax have infested millions of acres of wildlife habitat and ranchlands, undermining plant diversity and leaving the cupboard bare for large herbivores such as deer, elk and pronghorn.
Some of these noxious weeds—the legal term that state and federal agencies use to denote plants that pose serious threats to agriculture and wildlife—came to America by accident. They arrived in North America as stowaways, their seeds inadvertently lodged in shipments of grain. Others were deliberately imported and brought over by well-meaning folks—some of them at federal agencies—to enhance gardens or help control streambed erosion.
Once they've arrived, many plants and their seeds hitch rides across the country aboard magpies, mule deer, wool pants, horses, all-terrain vehicles, trucks and trains. Others simply fly with the wind or ride on river currents.
Spotted knapweed came here from central Europe, mixed in with shipments of alfalfa and clover seeds. In Montana alone, it has crowded out native plants on 4.5 million acres, thriving on soil disturbed by logging, grazing, flooding or fire. By sending down stout taproots, knapweed gets the jump on other plants with its early spring growth; then it snatches up most of the available space, sun, water and nutrients.
Each knapweed plant produces more than a thousand seeds and can often be found in amazing densities of up to two million plants per acre. Infestations frequently reduce native grasses and forbs by as much as 90 percent; in fact, botanists now believe that the plant may release a chemical substance that inhibits the growth of surrounding vegetation.
Since the mammals, birds, insects and fungi that prey on these plants in their homeland didn't follow them to North America, exotics have a distinct competitive edge. In the same way that deer, elk and pronghorn can proliferate in the absence of predation, noxious weeds thrive in a land with no enemies. Spotted knapweed now blankets many of the low-elevation, south-facing slopes in Montana, Idaho, Oregon, Washington and British Columbia, the very places that elk and deer prefer to winter in. The aftermath of a weed invasion in these areas is sadly predictable: "It can be expected that knapweed takeover of fall, winter and spring range would result in a significant decline in deer and elk numbers," says a report from British Columbia's Knapweed Action Committee.
Noxious weeds not only harm elk and deer; they also harm everything up and down the food chain. Simply put, the loss of native grasses equates to a loss to all the creatures that depend on those grasses for food, cover and nesting—from voles and larkspurs to the coyotes and Cooper's hawks that eat them. And because weeds fail to hold soil as well as native vegetation does, erosion increases dramatically where weeds like knapweed dominate. So the earth sloughs into streams and fouls spawning and rearing habitat critical for trout and other fish. Deteriorating habitat also threatens ranchers and farmers and the private lands that help sustain cattle and wildlife.
"It's easy to get depressed about noxious weeds," says Jim Olivarez, a retired weed-program manager for the U. S. Forest Service's Northern Region. Steve Kilpatrick, a Wyoming biologist, echoes that sentiment, telling Wyoming Wildlife magazine that if he were a habitat biologist in Idaho, where cheatgrass has created a vast desert monoculture, "I think I'd shoot myself." But we have to keep fighting back, says Olivarez, because "these public lands are national treasures."
But given the scale of the problem, the question is: How do we fight back? One answer is cooperative action. Throughout the West, county, state and federal governments have joined forces with ranchers, farmers and environmental groups to wage an integrated attack against weeds.
We've already begun to knock back knapweed, thanks to a careful balance of herbicide use, sheep grazing, pulling up plants and introducing beetles and weevils that prey on the weeds in their native lands. It's also important for people to clean and keep their vehicles, clothing and recreational equipment free of weed seeds to avoid spreading them. And we all need to learn to identify the invaders, so we can report them to wildlife agencies when we see them, and, ideally, stop them before they spread farther. We're probably never going to win this war on weeds, but at least we can strive for containment.
David Stalling is a contributor to Writers on the Range, a service of High Country News (hcn.org). He is a writer in Missoula, Montana.