But invasive species also extend to plant life. Residents of the South are well acquainted with kudzu, the fast-growing and disruptive vine originally intended as livestock feed and for erosion control. Purple loosestrife arrived in New England back in the 1800s as an ornamental plant, but now threatens to clog and dry out great areas of America's wetlands -- while reportedly costing communities across the country about $45 million a year in control efforts.
Here's yet another invasive plant species, and a particularly nasty one, to add to the list: Medusahead, aka medusa's head. It's a Mediterranean grass accidentally brought to the Western U.S. in the 1880s. Researchers at Oregon State University and the Agricultural Research Service have a new report warning that Medusahead is threatening to crowd out native grasslands in the West -- to the detriment of both wildlife and livestock.
"Medusahead is now spreading at about 12% a year over 17 Western states," says Seema Mangla, an OSU researcher. "Once established, it's very hard to get rid of."
It Puts Cattle on a Diet
The plant contains a high level of the mineral silica, which makes it inedible. Its spiky head and seeds cut the mouths of animals attempting to graze on it -- from cattle to deer to rodents. And Medusahead creates thick mulch that pushes out other plant life and increases the risk of wildfires.
Agriculture, experts say, doesn't have much to fear from Medusahead, thanks to the industry's regimen of herbicides, tilling, clearing and controlled burns. But the story is very different for livestock. Joseph DiTomaso, a specialist in noncrop weeds at UC Davis's Department of Plant Sciences, calls Medusahead a "landscape transformer." Two things happen, he says, for ranchers confronted with large areas of Medusahead.
"Your cattle will gain weight at a much slower rate because this is not a high-forage crop," he notes. "The second thing is that you will have to use more land to raise the same number of cattle because your cattle will go elsewhere to try and feed. So, this land becomes lower value, lower productivity, and you have to use more land to achieve the same [weight gain]. That's what ranchers are concerned with. It's not like they can go out and say we'll use more land. They have to raise fewer cattle, and that's the bottom line."
While the media may just be catching on to the challenges posed by Medusahead, control of the plant has been under study for years. The major issue is how cost-effective those control options are -- especially for ranchers. "A rancher can hardly put anything in and be profitable. They're already working on the margin as it is," says DiTomaso. "[If] you say, 'I have a chemical that will get rid of this thing, it'll only cost you $15 an acre,' they just look at you and say: 'I couldn't spend $4 an acre and make it profitable.'"