Armed with pointed tips so sharp that neither cows nor deer will eat it, medusahead (Taeniatherum caput-medusae) is an invasive grass species that seems to have stepped right out of the Little Shop of Horrors. With no enemies, it is spreading rapidly throughout the western United States, outcompeting native grasses and even other grass invaders. Unless steps are found to control its spread, medusahead is likely to turn millions of hectares of grazing land into worthless fields, say researchers in a study that determined why this grass is so successful.
Armed with pointed tips so sharp that neither cows nor deer will eat it, medusahead (Taeniatherum caput-medusae) is an invasive grass species that seems to have stepped right out of the Little Shop of Horrors. With no enemies, it is spreading rapidly throughout the western United States, outcompeting native grasses and even other grass invaders. Unless steps are found to control its spread, medusahead is likely to turn millions of hectares of grazing land into worthless fields, say researchers in a study that determined why this grass is so successful.
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"It is a devilish species because it is absolutely not of any worth," says Seema Mangla, a plant ecologist at Oregon State University, Corvallis, who led the study. "Every animal avoids it."
That's because the medusahead's long, twisting, snakelike seed stems (which give the grass its name) are stiff and pointed like needles. Any animal that leans in for a snack gets jabbed in the eyes and mouth. The grass is loaded with inedible silica, too, providing few nutrients to would-be grazers. As a result, the grass steadily accumulates, forming mounds of thatch, Mangla says. "It's part of a huge change in vegetation structure," as native grasses are overwhelmed by invaders. Other studies have shown that medusahead is spreading at a rate of 12% per year in 17 western states. Although it invaded the United States from the Mediterranean in 1880 and is now found only on more than 1 million hectares, Mangla and others worry that it is picking up steam and may be outcompeting not only native grasses, but even cheatgrass (Bromus tectorum), a more nutritious invader.
Measures to control medusahead's spread—mowing or spraying with herbicides—aren't effective, because they only treat the top of the plants, not the thatch beneath, which protects their seeds, Mangla says. "We need to understand its growth dynamics, what makes it such a successful invader, then we can figure out better ways to disrupt it."
Article continues: http://news.sciencemag.org/sciencenow/2010/11/a-devilish-grass-invades-the-wes.html
