An invasive species of weed called medusahead has the potential to overrun native grasses in the American West, which could disrupt native ecosystems and make millions of acres of grazing land almost worthless. 

"This is a devil species," said Seema Mangla, one of a group of researchers from Oregon State University that studied the species' potential for grassland domination.

Researchers looked at the growth rate of this invasive species and compared it to that of native grasses of the West and found that medusahead has a leg up on these other plants. Their study found that medusahead has a faster growth rate, a longer period of growth and produces more total biomass even than cheatgrass — another invading species that is a major problem in its own right, but not as devastating as medusahead.

"Medusahead is now spreading at about 12 percent a year over 17 western states," Mangla said. "Once established, it's very hard to get rid of. It displaces native grasses and even other invasive species that animals can still eat. Unless we do more to stop it, medusahead will take over much of the native grassland in the West."

Research is identifying some other grass species, including crested wheatgrass and Sandberg's bluegrass, that may be able to compete with medusahead, reduce its spread and preserve the grazing value of lands, Mangla said. They are also studying new ways of restoring medusahead-infested areas. But so far, medusahead has received very little attention compared to other threats such as cheatgrass, even though it ultimately poses a far greater threat to ecosystems across the West.

The new study, detailed in the Journal of Arid Environments, makes it clear that cheatgrass and native grasses may all eventually be replaced by medusahead, which eliminates more than 80 percent of the grazing value of land, making it incapable of supporting native animals, birds or livestock.

The sharp and twisting points on the tips of medusahead injure the eyes and mouths of animals, and give the plant its name — based on the female monster in Greek mythology that had hair composed of writhing snakes. The plant takes up other soil resources and its deep root system soaks up limited moisture. It creates fuel for wildfires, has a high silicon content that wears away the teeth of animals, is virtually inedible and prevents many other plants from germinating.

Medusahead is not a new problem — only a rapidly worsening one. Native to the Mediterranean region, it was imported to the United States in the late 1880s and has gradually established footholds since then.

It's now found on about 2.5 million acres in the United States — much less than other invading species such as cheatgrass — but it's widespread in the Pacific Northwest and most of Oregon, including the Willamette Valley.

"For too long we've treated these invasive species as something you just mow, spray with herbicides, or chop out somehow and then forget about them," Mangla said. "That just treats the symptoms, but doesn't get to the underlying problem. If we’re going to stop something like medusahead, we have to better understand its ecology and find ways to compete with it."

With this new study, researchers now have a better target to aim at in identifying plants that have some ecological characteristics that are similar to medusahead, but are useful species that, once established, may be able to better compete with the invasive weed.

"However, this plant is easier to keep out than it is to get rid of," Mangla said. "The time to stop it from taking over the West is now, before it becomes much more widely established. And it has not gotten the attention it deserves."

This article was reprinted with permission from OurAmazingPlanet.

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