Spatial Variation in Germination of Two Annual Brome Species in the Northern Great Plains

Downy brome or cheat grass (Bromus tectorum L.) and field brome (B. arvensis L.; Synonym = Bromus japonicus Thunb. ex Murr.; Japanese brome) are two annual exotic species that have increased the intensity and frequency of fire cycles in the Intermountain West of the United States, with millions of dollars in associated costs (DiTomaso 2000). These invasive brome species have a different impact in the Northern Great Plains of North America where they commonly co-occur in disturbed sites (White and Currie 1983, Haferkamp et al. 1993). In these mixed-grass prairie rangelands, annual bromes compete against other forage species (Haferkamp et al. 1997) and reduce litter decomposition rates (Ogle et al. 2003), which negatively impacts ecosystem services of biomass production and soil nutrient availability. In central plains croplands, downy brome invades alfalfa fields (Kapusta and Strieker 1975), wheat fields (Wicks 1984, Ostlie and Howatt 2013), and perennial grass pastures and seed production areas (Wicks 1984). Downy brome is a regulated plant in Montana (Montana Noxious Weed List, December 2013) and has been found in all counties of Montana since 1950 (Menalled et al. 2008). Field brome is found in all North American states and provinces (USDA Plants Database http://plants.usda.gov). It is used as a winter cover crop in vegetable plots and orchards in the Northeastern United States (NRCS 2006). Field brome has no formal designation in the state of Montana, although downy brome and field brome are commonly grouped together and are referred to colloquially as “cheatgrass” in the state