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Medusahead Outcompeting Native Rangeland Grasses

Date Posted: 
November 19, 2010

An invasive grass that has been in the United States for more than a century is becoming increasingly aggressive in taking over western rangelands. Medusahead has been invading grasslands in Arizona, Utah, and Idaho west to the Pacific coast, as well as in a few states further east. It has two characteristics that make it highly undesirable for grazing animals: the ends of the grass contain pointed barbs and sharp seeds that can injure the eyes and mouths of animals, and it has a high ash and silica content compared to native and other invasive grasses, which makes it less nutritious.

The Journal of Arid Environments reports on a new study of the medusahead invasion in the West. Researchers from Oregon State University and USDA looked at the growth characteristics of medusahead versus native grasses and less undesirable invasive grasses such as cheatgrass over a wet and an unusually dry growing season. The native grass had greater biomass and relative growth rates than medusahead in the dry year, but the opposite occurred in the wet year, and in both years medusahead had a longer growth period and more total biomass than cheatgrass. According to the researchers, medusahead is now spreading at a rate of 12 percent per year; it has not received as much attention as a threat to rangelands compared to other invasives such as cheatgrass, but in fact it ultimately poses a far greater threat, having the potential to “eliminate more than 80 percent of the grazing value of the land,” reported ScienceDaily.