Evidence targeted grazing benefits to invaded rangelands can increase over extended time frames

Authors: Rinella, Matthew - Matt; Bellows, Susan - Bartlett

Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/9/2016
Publication Date: 4/5/2016
Citation: Rinella, M.J., Bellows, S.E. 2016. Evidence targeted grazing benefits to invaded rangelands can increase over extended time frames. Rangeland Ecology and Management. 69(3):169-172.

Interpretive Summary: Prescribed grazing uses livestock to address exotic weed invasions and other rangeland management issues Invasive weed responses to prescribed grazing have proven variable. In a previous study of the invasive forb leafy spurge, we imposed several simulated grazing treatments for three years to determine if variation in defoliation timings and intensities might explain variation in prescribed grazing responses. In that study, two treatments gave similarly promising responses, and the current study was conducted to determine if responses to those treatments remained similar or diverged over five additional years. The two treatments defoliated leafy spurge and grasses either prior to or during leafy spurge flowering. Defoliation levels mimicked sheep, the species most commonly used for prescribed grazing of invasive forbs. A third treatment, which served as a baseline for comparison, mimicked cattle, a species tending to avoid consuming leafy spurge. Accordingly, this treatment, which was carried out during leafy spurge flowering, defoliated only resident species. Pre-flowering defoliation of leafy spurge was clearly more damaging to leafy spurge than flowering stage defoliation, even though flowering stage defoliation removed greater leafy spurge biomass. Thus, defoliation timing appears to be a key variable regulating leafy spurge responses to prescribed grazing. By study’s end, simulated sheep grazing at the pre-flowering stage had reduced leafy spurge biomass 74%(52%, 86%) and increased resident species biomass 40%(14%, 74%) compared to simulated cattle grazing. Strong differences between pre-flowering and flower stage defoliation of leafy spurge were not apparent the first several years, illustrating long-term research is needed to accurately quantify differences between prescribed grazing treatments.

Technical Abstract: Prescribed grazing uses livestock to address rangeland management issues such as woody plant encroachment, accumulations of flammable biomass and exotic weed invasions. Invasive weed responses to prescribed grazing have proven variable. For instance, a given livestock species can sharply reduce abundances of an invader in some studies while having no observable effect on the same invader in other studies. In a previous study of the invasive forb leafy spurge (Euphorbia esula L.), we imposed several simulated grazing treatments for three years to determine if variation in defoliation timings and intensities might explain variation in prescribed grazing responses. In that study, two treatments gave similarly promising responses, and the current study was conducted to determine if responses to those treatments remained similar or diverged over five additional treatment years. The two treatments defoliated E. esula and resident species (mostly grasses) either prior to or during E. esula flowering. Defoliation levels mimicked sheep, the species most commonly used for prescribed grazing of invasive forbs. A third treatment, which served as a baseline for comparison, mimicked cattle, a species tending to avoid consuming E. esula. Accordingly, this treatment, which was carried out during E. esula flowering, defoliated only resident species. Pre-flowering defoliation of E. esula was clearly more damaging to E. esula than flowering stage defoliation, even though flowering stage defoliation removed greater E. esula biomass. Thus, defoliation timing appears to be a key variable regulating E. esula responses to prescribed grazing. By study’s end, simulated sheep grazing at the pre-flowering stage had reduced E. esula biomass 74%(52%, 86%) and increased resident species biomass 40%(14%, 74%) compared to simulated cattle grazing. Strong differences between pre-flowering and flower stage defoliation of E. esula were not apparent the first several years, illustrating long-term research is needed to accurately quantify differences between prescribed grazing treatments.