Targeted grazing for native forbs in annual grasslands

Authors: DAVY, JOSH - University Of California - Cooperative Extension Service; Rinella, Matthew - Matt

Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/9/2019
Publication Date: 3/12/2019
Citation: Davy, J.S., Rinella, M.J. 2019. Targeted grazing for native forbs in annual grasslands. Rangeland Ecology and Management. 72(3):501-504. https://doi.org/10.1016/j.rama.2019.01.003.
DOI: https://doi.org/10.1016/j.rama.2019.01.003

Interpretive Summary: We investigated cattle grazing for the goal of promoting flowering plants relied on by pollinators. The plants of interest were tarweed and vinegarweed, native annual forbs of annual grasslands that supply important late growing season nectar to pollinators. While tarweed and vinegarweed are desirable for pollinators, these species at high densities are undesirable for livestock because they have chemical and mechanical deterrents to grazing, and they can potentially reduce forage species. Therefore, we sought to promote low-density stands capable of supporting both pollinators and livestock production. A short period of grazing early in the growing season appeared to provide dominant annual grasses medusahead and soft brome time to recover and competitively suppress tarweed and vinegarweed. Therefore, early grazing may be useful for reducing dense stands of tarweed and vinegarweed. A single period of grazing after annual grasses senesced increased tarweed, while repeated grazing proved capable of increasing both forbs, and repeated grazing may have caused slightly larger increases in forbs. Combined with previous research, our study indicates repeated or continuous cattle grazing across a range of annual grass growth stages is the most reliable way to encourage flowering plants in annual grasslands. While flowering plant density increases were modest, recent research indicates modest increases can substantially benefit pollinators.

Technical Abstract: Targeted grazing can address a range of objectives, including controlling invasive and encroaching woody plants, increasing native plants and reducing wildfire risks. We investigated targeted cattle grazing for the goal of promoting flowering plants relied on by pollinators. The plants of interest were tarweed and vinegarweed, native annual forbs of annual grasslands that supply important late growing season nectar to pollinators. While tarweed and vinegarweed are desirable for pollinators, these species at high densities are undesirable for livestock because they have chemical and mechanical deterrents to grazing, and they can potentially reduce forage species. Therefore, we sought to promote low-density stands capable of supporting both pollinators and livestock production. A short period of grazing early in the growing season appeared to provide dominant annual grasses medusahead (Taeniatherum caput-medusae (L.) Nevski) and soft brome (Bromus hordeaceus L.) time to recover and competitively suppress tarweed and vinegarweed. Therefore, early grazing may be useful for reducing dense stands of tarweed and vinegarweed. A single period of grazing after annual grasses senesced increased tarweed, while repeated grazing proved capable of increasing both forbs, and repeated grazing may have caused slightly larger increases in forbs. Combined with previous research, our study indicates repeated or continuous cattle grazing across a range of annual grass growth stages is the most reliable way to encourage flowering plants in annual grasslands. While flowering plant density increases were modest, recent research indicates modest increases can substantially benefit pollinators.