Technical Abstract: Interference from crested wheatgrass (Agropyron cristatum [L.} Gaertn.) seedlings is considered a major obstacle to native species establishment; however, estimates of interference at variable seedling densities have not been fully defined. We conducted greenhouse experiments using an addition series design to characterize interference between crested wheatgrsss and for imporant native species. Crested wheatgrass strongly interfered with the aboveground growth of Wyoming big sagebrush (Artemisia tridentata Nutt. ssp. wyomingenis Beetle & Young), rubber rabbitbrush (Ericameria nauseosa [Pall. ex Pursh] G.L. Nesom & Baird ssp. consimilis [Greene] G.L. Neson & Baird), and to a lesser extent with bluebunch wheatgrass (Pseudoroegneria spicata [Pursh} A. Love. Alternatively, bottlebrush squirreltail (Elymus elymoides [Raf.] Swezey ssp. elymoides and crested wheatgrass had similar effects on each other's growth. Results indicate that the native grasses more readily establish in synchrony with crested wheatgrass than these native shrubs, but that once established, the native shrubs are more likely to coexist and persist with crested wheatgrass because of high niche differentiation. Results also suggest that developing strategies to minimize interference from crested wheatgrass seedlings emerging from seed banks will enhance the establishment of native species seeded into crested wheatgrass-dominated communities.