Rough soil surface lessens annual grass invasion in disturbed rangeland.
Effective manipulations to prevent the spread of invasive species are needed. Downy brome (Bromus tectorumL.) is an annual invader that often expands after disturbances, compromising restoration of big sagebrush (Artemisia tridentata Nutt.) communities in western North America. This study examined the effects of two manipulations that may slow seed dispersal: soil microtopography (roughened with 50-cm relief or flat) and woody debris (0.024 m3.m-2or none) on restoration of four disturbed mountain big sagebrush (A. tridentata Nutt. ssp. vaseyana) sites in Colorado. Treatments were crossed with seeding in a fully factorial experiment (n=3). Microtopography and woody debris treatments were also crossed in a seed dispersal experiment using fluorescently marked downy brome seeds. In the restoration study, downy brome invaded two sites, one pervasively and one patchily. Seeding limited downy brome cover at both of these sites and also increased perennial grass and forb cover while limiting shrub cover. At the pervasively invaded site, the rough surface reduced unseeded plot downy brome cover from 13% to 3% by 5 yr post treatment. Woody debris increased shrub and perennial grass cover but had little effect on downy brome. In the seed dispersal experiment, the rough surface reduced downy brome mean dispersal distance twofold to threefold and 95% quantile distance threefold to sixfold. Woody debris slightly reduced downy brome dispersal only within rough surface plots. A rough surface may aid restoration by trapping downy brome seeds near the parent plant, limiting their spatial distribution, increasing intraspecific competition, and reducing propagule pressure. Designing landscapes to slow seed dispersal may help control invasives and promote establishment of seeded species.