Established Perennial Vegetation Provides High Resistance to Reinvasion by Exotic Annual Grasses

Exotic annual grasses have invaded millions of hectares of sagebrush (Artemisia L.) steppe in the Great Basin region and degraded wildlife habitat, reduced forage production, and promoted increasingly frequent wildfires. Revegetation after control of exotic annual grasses is needed to restore ecosystem services and break the annual grass-fire cycle. The ability of different common revegetation species and combinations of species to limit reinvasion of annual grasses is relatively unknown. We evaluated five species/combinations of perennial native and introduced bunchgrass and shrub species planted as seedlings after exotic annual grass control at two sites in southeast Oregon. To evaluate resistance to reinvasion, exotic annual grasses were seeded into all treatment plots in the fall two growing seasons after planting. Vegetation characteristics were measured in the third and fourth years after annual grass seeding. Exotic annual grass cover and density were greatly reduced in all treatments where perennial seedlings were planted compared with the control (no seedlings planted). Treatments including crested wheatgrass (Agropyron desertorum [Fisch. Ex Link] Schult) generally limited annual grasses more than other treatments. Most notably, forage kochia (Bassia prostata [L.] A. J. Scott) reduced exotic annual grasses less than crested wheatgrass and crested wheatgrass planted with forage kochia. This suggests that if forage kochia will be planted, it should be used in conjunction with perennial bunchgrasses in efforts to revegetate exotic annual grass − invaded sagebrush steppe. Established native vegetation also greatly reduced exotic annual grass reinvasion. Though some differences existed among established vegetation treatments, our study highlights that established perennial vegetation prevents redomination by invasives after exotic annual grass control.