Using native grass seeding and targeted spring grazing to reduce low-level Bromus tectorum invasion on the Colorado Plateau

Authors: Porensky, Lauren; BAUGHMAN, OWEN - University Of Nevada; WILLIAMSON, MATTHEW - University Of California; PERRYMAN, BARRY - University Of Nevada; MADSEN, MATTHEWA - Brigham Young University; LEGER, ELIZAVETH - University Of Nevada

Submitted to: Biological Invasions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/26/2020
Publication Date: 2/23/2021
Citation: Porensky, L.M., Baughman, O., Williamson, M.A., Perryman, B.L., Madsen, M.D., Leger, E.A. 2021. Using native grass seeding and targeted spring grazing to reduce low-level Bromus tectorum invasion on the Colorado Plateau. Biological Invasions. 23:705-722. https://doi.org/10.1007/s10530-020-02397-0.
DOI: https://doi.org/10.1007/s10530-020-02397-0

Interpretive Summary: Reducing invasive species is important for maintaining healthy ecosystems. Relatively little research has explored how to resist or reduce cheatgrass (Bromus tectorum), a widespread, invasive annual grass, near the edge of its range. We asked what plants were associated with lower levels of cheatgrass at the edge of its range in the southern Colorado Plateau. We tested native grass seeding and targeted spring grazing as treatments for resisting or reversing low-level invasion. We seeded five native perennial grasses that included both warm-season and cool-season species. In unseeded, ungrazed communities, areas with high cool-season perennial grass cover and high shrub cover had less cheatgrass. Among grasses analyzed in more detail, adult muttongrass (Poa fendleriana) and western wheatgrass (Pascopyrum smithii) plants had the fewest cheatgrass individuals nearby. Two years after seeding, planted species establishment was 36% greater in high seed rate plots, which also had lower cheatgrass cover. One season after targeted spring grazing, there were no significantly negative and two marginally-significant positive effects of the treatment on desired outcomes. Early results suggest that high rate native perennial grass seedings and short-duration spring grazing should be further evaluated as potential tools for increasing site resistance and preventing ecosystem conversion along invasion fronts such as the Colorado Plateau.

Technical Abstract: Reducing the abundance of invasive species at the leading edge of invasions is important for maintaining diverse, high-functioning ecosystems. Focusing on a widespread, invasive annual grass, Bromus tectorum, at the edge of its range in the southern Colorado Plateau, we asked what plant community components were associated with lower levels of B. tectorum. We simultaneously tested the efficacy of native grass seeding and targeted spring grazing as treatments for resisting or reversing low-level invasion. We seeded five native perennial grass species spanning a range of life-history and photosynthetic strategies. Data were collected using a randomized, hierarchical design. 18 paired paddocks were arranged into 9 blocks. In 6 blocks, one paddock received a single, 2-week spring-grazing treatment 17 months after seeding. In unseeded, ungrazed communities, high C3 perennial grass cover and shrub cover were associated with lower B. tectorum abundance. Among grasses analyzed in more detail, adult Poa fendleriana and Pascopyrum smithii plants had the fewest B. tectorum individuals within 50 cm. Two years after seeding, planted species establishment was 36% greater in high seed rate plots, which also had lower B. tectorum cover. One season after targeted spring grazing, there were no significantly negative and two marginally-significant positive effects of the treatment on desired outcomes. Early results suggest that high rate native perennial grass seedings and short-duration spring grazing should be further evaluated as potential tools for increasing site resistance and preventing ecosystem conversion along invasion fronts such as the Colorado Plateau.