Pollinator-friendly flora in rangelands following control of cheatgrass (Bromus tectorum): A case study

Authors: Seshadri, Arathi; HARDIN, JANET - Colorado State University

Submitted to: Invasive Plant Science and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/20/2021
Publication Date: 12/27/2021
Citation: Seshadri, A.H., Hardin, J. 2021. Pollinator-friendly flora in rangelands following control of cheatgrass (Bromus tectorum): A case study. Invasive Plant Science and Management. 14(4):270-277. https://doi.org/10.1017/inp.2021.33.
DOI: https://doi.org/10.1017/inp.2021.33

Interpretive Summary: Cheatgrass (Bromus tectorum L.) is a widespread annual invasive grass that has taken over much of the fragile western rangelands. Spread of cheatgrass in this ecosystem has resulted in suppression and elimination of several natural forbs specifically pollinator-friendly flowering species that are critical nesting and food resources for the native bee pollinators. This is a report of a case study describing the positive impacts of controlling and eliminating cheatgrass in the rangelands of Colorado. We report the resurgence of native flora within a year of cheatgrass control. Continued control and elimination of cheatgrass will enable native flowering forbs to establish and increase flowering intensities. We hypothesize that such increase in flowering resources will bring back native pollinator species and in a few years we are likely to observe increased foraging and nesting activities in areas where cheatgrass has been eliminated.

Technical Abstract: Invasive species pose one of the largest threats to regional biodiversity, including impacting populations of pollinator-friendly flora that are inadvertently displaced by competitively superior invasive plants. Amongst the several known invasive plants, winter annual grasses such as cheatgrass (Bromus tectorum L.) wreak havoc in the rangelands in western United States. In addition to displacing native flora, cheatgrass results in increased risk of wildfires as dead stems are excellent fuel in the already dry and arid regions of the west. Control of cheatgrass has largely depended on grazing, prescribed burning, or use of broad-spectrum herbicides that are non-selective in nature. Indaziflam (Esplanade), herbicide recently approved for use in controlling invasive annual grasses on rangelands and open spaces, has been shown to target cheatgrass. Efficient control and eventual elimination of cheatgrass facilitates the restoration of the native rangeland flora that are crucial for the sustenance of pollinator populations. Here we evaluate the impacts of indaziflam application on cheatgrass control and restoration of native flora in natural areas of Boulder county, Colorado. This case study describes two seasons of monitoring following indaziflam application. Sites treated with indaziflam during the winter of 2016 were monitored over spring and summer of 2017 and 2018. Indaziflam treated plots showed an increase in frequency of flowering plants as compared to controls. Plots receiving indaziflam treatment had higher proportions of flowering species unique to the treated plots. Our study provides evidence that controlling cheatgrass allows for native flowering plants to be restored. Over the long term, continued control and elimination will allow for flowering forbs to reestablish their populations through reduced competition. Further studies are necessary to document the reproductive success and reseeding potential of the forbs, resulting pollinator activity and to determine the duration of indaziflam efficacy and need for re-application.