Large-Scale Downy Brome Treatments Alter Plant-Soil Relationships and Promote Perennial Grasses in Salt Desert Shrublands
Hirsch-Schantz, M.C., T.A. Monaco, C.A. Call and R.L. Sheley. 2014.
Abstract
Because invasive annual grasses can strongly influence soil resource availability and disturbance regimes to favor their own
persistence, there is a great need to understand the interrelationships among invasive plant abundance, resource availability, and
desirable species prominence. These interrelationships were studied in two salt desert sites where the local abundance of downy
brome (Bromus tectorum L.) varied spatially and increased more than 12-fold over a 3-yr period. We measured downy brome
percentage cover, resource availability, and soil chemical and physical properties within 112 plots per site and found significant
negative associations between downy brome abundance and both soil water content (P < 0.05; r=-27 to -0.49) and nitrate
accumulation (P < 0.05; r=-0.34 to -0.45), which corroborated with the direction and strength of multivariate factor loadings
assessed with principal component analysis. We then applied factorial combinations of prescribed burning and preemergence
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
determine their impact on downy brome, soil resources, and resident plant species. Burning and herbicide applications,
especially when combined, significantly reduced downy brome cover (P=0.069 to 0.015), which in turn increased soil nitrate
accumulation and water content in the spring. Furthermore, for one shrubland site that was seeded 6 yr previously, the
combination of burning and herbicide treatments significantly increased perennial grass percentage cover in the 2 yr
posttreatment (P < 0.05). Results not only demonstrate the strong relationships between downy brome abundance, soil
resources, and residence species for impoverished salt desert shrub ecosystems, but also suggest that restoration and
management efforts must include tactics that facilitate resource use by the residual plant community or establish a greater
abundance of species capable of high resource acquisition in the spring.
Key Words
cheatgrass, disturbance ecology, ecosystem resilience, restoration ecology, soil resource dynamics, spatial and temporal variation
