Understanding the causes and consequences of cheatgrass die-offs in the Great Basin. USDI BLM Integrated Die-off Project. Annual Summary Report: FY2013

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The segment of the USDI BLM Integrated Die-off Study entitled ‘Understanding the Causes and Consequences of Cheatgrass Die-offs in the Great Basin’ was initiated in late summer 2011. This report summarizes our research progress in FY2013. The primary objectives of the project were: (1) to examine patterns of cheatgrass die-off and recovery on a landscape scale, (2) to determine the causal agents responsible for die-offs, and (3) to examine potential post-die-off successional trajectories including ecological restoration. The project has three principal sets of studies. First, we use methods from remote sensing and landscape ecology to study die-off patterns on the landscape. Second, we use field, laboratory and greenhouse experiments to study putative die-off causal organisms. Third, we use field experiments to study successional trajectories, including rates of post-die-off recovery of cheatgrass stands as well as the potential for establishment of native species into die-offs. Under our first objective, we have used field validation data to train a remote sensing model for detecting die-off and recovery as indicated by changes in cheatgrass cover across years, and we have successfully applied this model in the Winnemucca NV area to detect meaningful differences in cheatgrass cover that are very likely indicative of die-off and recovery. Under our second objective, we have isolated possible die-off causal organisms (plant pathogenic fungi) from field soils, seeds, and plant tissue and demonstrated in rigorous pathogenicity trials that these organisms can cause diseases that contribute to the die-off phenomenon. These organisms include seed pathogens related to Fusarium tricinctum that can kill germinating seeds or seedlings as well as reducing the fitness of surviving seedlings. A second seed pathogen, Pyrenophora semeniperda, is not implicated directly in die-offs but probably plays a major role in rates of post-die-off recovery through its impacts on the persistent seed bank. A third pathogen, related to Roetstromia floccosa (causal agent of dollar spot disease of turf grasses), causes a disease we have named ‘bleach blonde syndrome’. This pathogen infects the crowns of developing cheatgrass plants and causes seed abortion and premature death, resulting in the development of dense mats of litter late in the summer. In addition to drastically reducing seed set, this pathogen produces litter that appears to set the stage for epidemic levels of pathogens that directly kill seeds and cause stand failure. We successfully predicted a die-off in Skull Valley UT in 2013 based on data from plots where a bleach blonde epidemic had occurred in 2012. Under objective three, we have determined that die-offs are usually transient events that pose no direct obstacle to cheatgrass establishment in subsequent years. Persistent die-offs are most likely caused by loss of the in situ seed bank, probably because of high P. semeniperda-caused mortality. Artificial seeding of cheatgrass into both recent and persistent die-offs has consistently resulted in successful establishment. We were also able to seed native grasses directly into a previous-year die-off and obtain successful emergence as well as high survival and growth due to decreased cheatgrass competition. This suggests that die-offs may represent opportunities for ecological restoration in a setting where increased success is likely. Residual levels of the pathogens that caused the previous-year die-off appear to present little problem either to cheatgrass or to seeded native species.

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Reference Code: U13MEY01IDUS

Full Citation: Meyer, S., B. Geary, Z. Aanderud, E. Leger, P. Weisberg, and J. Beckstead. 2013. Understanding the causes and consequences of cheatgrass die-offs in the Great Basin. USDI BLM Integrated Die-off Project. Annual Summary Report: FY2013. USDI Bureau of Land Management, Boise, ID. 45 pp.

Location: ELECTRONIC FILE BOTANY: PLANT SPECIES: {Bromus tectorum}