Cheatgrass (Bromus tectorum, downy brome) is an exotic species that appeared in North American in the late nineteenth century and has since become a dominant plant in the arid rangelands between the Sierra Nevada, Cascades, and Rocky Mountains. A shallow-rooted annual, it is the first grass to appear after the region's long, cold winters and has become an important forage plant for livestock and wildlife. It is also a major environmental hazard...