Document: JUL-3-35-40

Natural resistance to cheatgrass invasion: The role of limiting resources.

BECKSTEAD, J.* and C.K.AUGSPURGER

University of Illinois, Urbana, IL, USA 61801 ¹

Abstract:
Cheatgrass (Bromus tectorum) is an aggressive invader in the Great Basin deserts. A shadscale shrub community in western Utah shows a mosaic of cheatgrass invasion that ranges from highly resistant patches (diameter = 5-15 m) with less than 15% cheatgrass cover to highly susceptible patches (diameter = 5-15 m) with greater than 90% cheatgrass cover. This study investigated whether resources in the highly resistant patches limit cheatgrass biomass. In ten patches at each of three life stages (establishment, overwintering, and active growth) and across all stages combined, resources were manipulated directly and indirectly. We applied four treatments (reduced competition from native grasses and forbs, or water, nitrogen, or litter additions), a combination of all four treatments, and an untreated control, and measured their effects on cheatgrass biomass. Life stage by itself had no significant effect on biomass. Patches that received a combination of all treatments had a 141% increase in cheatgrass biomass in comparison to the control. Of the four individual treatments, reduced competition from native species and nitrogen addition increased biomass by 164% and 38%, respectively; water and litter additions had no effect. These findings indicate that highly resistant patches do not provide adequate resources for cheatgrass. Competition from the native grasses and forbs appears to limit the population of cheatgrass at this spatial scale within this shadscale shrub community.

Keywords: biological invasion, cheatgrass, competition

This abstract is being presented at: 9:30 AM in session:
Oral Session #19: Grassland Restoration.