Downy Brome: Intruder in the Plant Succession of Big Sagebrush Communities in the Great Basin

We investigated succession on six big sagebrush sites of different potential ranging from the edge of the salt desert shrub to seral communities in the pinon/juniper woodland where the brush overstory had been removed by hand cutting. Depending upon the site, herbaceous communities that developed after elimination of overstory cover were composed of either a diversity or a relatively limited number of species of native annual forbs. Alien annual forbs were initial dominants on sites where seed source of these species was available. Dominance by downy brome caused a marked reduction of native annual species. Downy brome was seeded for 3 consecutive years in each of six different big sagebrush communities. On the majority of the sites, providing a seed source resulted in establishment and near total dominance by downy brome. The established populations have persisted and continued to dominate the communities. Some sites were outside the seedbed potential of downy brome, and seeding resulted in establishment only once in 3 years. Presence of plant litter and a rough microtopography were key seedbed characteristics permitting downy brome establishment on these sites.