Downy brome control and impacts on perennial grass abundance: a systematic review spanning 64 years

Authors: Monaco, Thomas; MANGOLD, JANE - Montana State University; MEALOR, BRIAN - University Of Wyoming; MEALOR, RACHEL - University Of Wyoming; BROWN, CYNTHIA - Colorado State University

Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/1/2016
Publication Date: 5/1/2017
Citation: Monaco, T.A., Mangold, J., Mealor, B.A., Mealor, R.D., Brown, C. 2017. Downy brome control and impacts on perennial grass abundance: a systematic review spanning 64 years. Rangeland Ecology and Management. 70:396-404.

Interpretive Summary: Reducing annual grass abundance is for rangeland restoration in the Intermountain West, USA. In this study, we sought to identify limitations and strengths of annual grass and woody plant reduction methods and refine future management strategies. We systematically reviewed all published journal articles spanning a 64-year period (1948 to 2012; n = 119) reporting data on research efforts to either directly or indirectly reduce the abundance of the most common invasive annual grass, downy brome (Bromus tectorum L.). We found conflicting evidence regarding the assumption that reducing downy brome abundance is necessary to augment the growth and establishment of perennial grasses. Analyses suggest that all methods, with the exception of woody plant removal, significantly reduced downy brome in the short term, but that downy brome abundance generally increased over time except for herbicide and revegetation studies. Results also indicate that only burning, herbicide, and soil distubance led to long-term increases in perennial grass abundance. Based on our assessment, we present a conceptual diagram identifying how future research should prioritize a broader array of ecological processes to improve control efficacy and promote the reestablishemnt of desirable rangeland plant communities.

Technical Abstract: Given the high cost of restoration and the underlying assumption that reducing annual grass abundance is a necessary precursor to rangeland restoration in the Intermountain West, USA, we sought to identify limitations and strengths of annual grass and woody plant reduction methods and refine future management strategies. We systematically reviewed all published journal articles spanning a 64-year period (1948 to 2012; n = 119) reporting data on research efforts to either directly or indirectly reduce the abundance of the most common invasive annual grass, downy brome (Bromus tectorum L.). Our review revealed that seven control methods were most frequently studied in the literature: herbicide, burning, revegetation, woody removal, defoliation or grazing, soil disturbance, and soil amendment. In addition, the majority of control methods were (1) applied at scales of 10 to 100 m2, (2) sampled within small plots (i.e., 0.1 to l.0 m2), (3) implemented only once, and (4) monitored at time scales that rarely exceeded 5 years. We also performed summary analysis to assess how these control methods affect downy brome and perennial grass abundance (i.e., cover, density, biomass). We found conflicting evidence regarding the assumption that reducing downy brome abundance is necessary to augment the growth and establishment of perennial grasses. Analyses suggest that all methods, with the exception of woody plant removal, significanlty reduced downy brome in the short term, but that downy brome abundance generally increased over time except for herbicide and revegetation studies. Results also indicate that only burning, herbicide, and soil disturbance led to long-term increases in perennial grass abundance. Based on our assessment, we present a conceptual diagram identifying how future research should prioritize a broader array of ecological processes to improve control efficacy and promote the reestablishment of desirable rangeland plant communities.