Anatomy of a medusahead invasion
by Cally Carswell
Medusahead, an invasive annual grass, is poised to become a major rangeland menace. "It's just starting its major advancement," says Roger Sheley, an Agricultural Research Service ecologist in Oregon. Sheley believes most Western rangelands are vulnerable, especially those already plagued by invasives. "Medusahead represents another step in the decline of these systems."
Devilish and useless: That's how most range managers and ecologists see medusahead. Unlike some noxious weeds, it's shunned by livestock and wildlife except in early spring when it's green. As it matures, its barbed points can pierce the mouths and faces of animals, and its high silica content -- five to 10 times that of most grasses -- makes it hard to digest.
Medusahead outcompetes many native and invasive plants. That may be because it grows faster and longer, according to a recent Oregon State University study. It's a prolific seed producer, and because it isn't grazed, dead medusahead accumulates in a thick thatch -- impenetrable to most seeds except its own.
Medusahead has invaded at least a few million acres in the West, and is expanding by 12 to 20 percent yearly. Scientists believe the weed, a Mediterranean native, could even overtake cheatgrass, which has overwhelmed some 100 million acres. Medusahead cuts grazing capacity by almost 80 percent. It annihilates native habitat, threatening species like sage grouse. And, like cheatgrass, it alters natural fire cycles, feeding frequent range blazes that leave soil bare -- and primed for yet another weedy colonization.