Large-Scale Downy Brome Treatments Alter Plant-Soil Relationships and Promote Perennial Grasses in Salt Desert Shrublands

To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. This is the publisher’s final pdf. The published article is copyrighted by the Society for Range Management and can be found at: http://www.srmjournals.org/loi/rama.Because invasive annual grasses can strongly influence soil resource availability and disturbance regimes to favor their own\ud persistence, there is a great need to understand the interrelationships among invasive plant abundance, resource availability, and\ud desirable species prominence. These interrelationships were studied in two salt desert sites where the local abundance of downy\ud brome (Bromus tectorum L.) varied spatially and increased more than 12-fold over a 3-yr period. We measured downy brome\ud percentage cover, resource availability, and soil chemical and physical properties within 112 plots per site and found significant\ud negative associations between downy brome abundance and both soil water content (P < 0.05; r = -0.27 to -0.49) and nitrate\ud accumulation (P < 0.05; r = -0.34 to -0.45), which corroborated with the direction and strength of multivariate factor loadings\ud assessed with principal component analysis. We then applied factorial combinations of prescribed burning and preemergence\ud herbicide at management-relevant scales (i.e., 6 to 46 ha) as well as biomass removal to smaller plots (12.25 m²) at both sites to\ud determine their impact on downy brome, soil resources, and resident plant species. Burning and herbicide applications,\ud especially when combined, significantly reduced downy brome cover (P = 0.069 to 0.015), which in turn increased soil nitrate\ud accumulation and water content in the spring. Furthermore, for one shrubland site that was seeded 6 yr previously, the\ud combination of burning and herbicide treatments significantly increased perennial grass percentage cover in the 2 yr\ud posttreatment (P < 0.05). Results not only demonstrate the strong relationships between downy brome abundance, soil\ud resources, and residence species for impoverished salt desert shrub ecosystems, but also suggest that restoration and\ud management efforts must include tactics that facilitate resource use by the residual plant community or establish a greater\ud abundance of species capable of high resource acquisition in the spring