Management strategies determine how invasive plant impacts on rangeland provisioning services change net revenue on California annual rangeland

Authors: JAMES, JEREMY - California Polytechnic State University; BROWNSEY, PHILIP - University Of California; DAVY, JOSH - University Of California; FORERO, LARRY - University Of California; STACKHOUSE, JEFF - University Of California; SHAPERO, MATTHEW - University Of California; BECCHETTI, THERESA - University Of California; Rinella, Matthew - Matt

Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/1/2022
Publication Date: 3/5/2022
Citation: James, J.J., Brownsey, P., Davy, J., Forero, L., Stackhouse, J., Shapero, M., Becchetti, T., Rinella, M.J. 2022. Management strategies determine how invasive plant impacts on rangeland provisioning services change net revenue on California annual rangeland. Rangeland Ecology and Management. 82:29-36. https://doi.org/10.1016/j.rama.2022.02.001.
DOI: https://doi.org/10.1016/j.rama.2022.02.001

Interpretive Summary: The expectation that invasive plants decrease livestock production is extensively used as a justification for invasive plant management on rangelands across the globe even though we largely lack direct evidence backing these assumptions. This study experimentally manipulated the abundance of the invasive plant medusahead in pastures to directly evaluate how this species may impact livestock production. This study found that medushaead significantly decreases livestock production but also shows that the actual impacts of medusahead on livestock production may be lower than impacts perceived by managers and that relatively simple adaptation strategies could further reduce how invasive plant impacts on livestock production scale to impacts on profitability.

Technical Abstract: 1. Invasive plants have long been viewed as a universal threat to ranching enterprises because invasive plants could alter forage quantity or quality for livestock and therefore reduce profitability. These concerns are almost entirely based on how invasive plants alter forage production in small plots rather than direct measures of invasive plant impacts on livestock production. 2. In this study we quantify impacts of the invasive annual grass medusahead (Taeniatherum caput-medusahead L.) on livestock production and evaluate how management buffers or exacerbates impacts to gross profitability. To do this we tracked changes in yearling steer weights across the growing season (March to May) for two years in 11 2.1-ha pastures where medusahead abundance was experimentally manipulated. We then integrated these field results with market data to estimate changes in profitability due to a change in medusahead abundance and common management strategies that may be used to respond to changes in invasive plant abundance, including altering grazing season length or altering animal density. 3. We found that medusahead significantly lowered livestock production, but this decrease was significantly lower than that reported in the literature based on indirect measures of invasive plant impacts. 4. We also illustrate that invasive plant impacts on livestock production do not necessarily scale directly to impacts on profitability. Responding to a 10% increase in medusahead by shortening the grazing season reduced gross profitability -102.97 USD per hectare compared to a baseline, whereas responding to this increase by reducing animal density and selling some animals early resulted in a gross profitability of +2.71 USD per hectare compared to baseline. 5. Synthesis and application: Our study shows that the actual impacts of invasive plant species on livestock production may be lower than impacts perceived by managers and that relatively simple adaptation strategies could further reduce how invasive plant impacts on livestock production scale to impacts on profitability.