Long-Term Persistence of Cool-Season Grasses Planted to Suppress Broom Snakeweed,Downy Brome,and Weedy Forbs

Invasive plants are spreading throughout arid and semiarid rangelands of western North America. Long-lived perennial plants that can persist under harsh environmental conditions are needed to compete with invasive species. The objective of this study was to conduct a long-term evaluation of native and introduced grass species planted to suppress and prevent reinvasion of downy brome (Bromus tectorum L.), snakeweed (Gutierrezia sarothrae Pursh] Britt. & Rusby), and annual forbs. Seeding treatments comprised three introduced grasses: crested wheatgrass (Agropyron cristatum L.] Gaertner × A. desertorum Fisch. Ex Link] Schultes), pubescent wheatgrass (Elytrigia intermedia spp. trichophorum Host] Beauv.), and Russian wildrye (Psathyrostachys junceus Fisch.] Nevski); a mix of these introduced grass species, three native grasses: bluebunch wheatgrass (Pseudoroegneria spicata Pursh]), western wheatgrass (Pascopyrum smithii Rybd.] A. Löve), and squirreltail (Elymus multisetus J.G. Sm.] Jones); and a mix of these native grass species, or forage kochia (Bassia prostrata L.] A.J. Scott). The treatments were seeded in October 2003. Frequency and biomass were measured in 2015 and 2017 in Howell, Utah and in 2015 and 2016 in Nephi, Utah. Crested wheatgrass persisted at both locations (> 62% frequency) along with the rhizomatous grass species, pubescent (> 65%) and western wheatgrasses (> 72%). Russian wildrye was still present at Howell (30%) with little remaining at Nephi (7%). Squirreltail frequency was 13% at Howell and 12% at Nephi. Bluebunch wheatgrass was no longer present at either location (< 1%). Forage kochia remained at Nephi (36%) with little remaining at Howell (4%). Downy brome was present at both locations and was suppressed relative to control plots, at Nephi, by crested wheatgrass and the introduced grass mix (< 9%). Downy brome was > 93% in all plots, at Howell, in 2017. In summary, crested, pubescent, and western wheatgrasses were able to persist over 12 yr at both locations.