Advancing management and restoration practices of Bromus tectorum invaded rangelands of southwestern Montana

Abstract

Bromus tectorum L. (cheatgrass), an invasive annual grass, has reduced biodiversity, decreased forage quality and quantity, and altered ecosystem function of western rangelands. These impacts make B. tectorum and other invasive annual grasses a management priority. Management is typically approached with herbicides, but new herbicides and non-herbicide methods are desired. When evaluating these new tools, it is important to assess their ability to control the abundance of B. tectorum, their impacts to the surrounding plant community, and how these effects differ over time and space. Another important aspect of management is restoring the plant community following control. Dryland seed restoration is a notoriously difficult task, and better understanding of the factors influencing success is needed. I evaluated the efficacy of novel management and restoration approaches on both B. tectorum and the surrounding plant community in semi-arid rangelands of southwestern Montana. First, I assessed the impact of novel management treatments (non-treated control, biofumigant, soil amendment, and a relatively new herbicide) on B. tectorum abundance and the surrounding plant community for four years at three different sites. All management methods decreased B. tectorum abundance, with the herbicide, indaziflam, having the most consistent control. There was no consistent spatial or temporal response of other vegetation. Secondly, I assessed the impact of the same management treatments on the diversity of the plant community. Impacts to diversity differed with treatments, and my study showed using several diversity metrics provided a more nuanced understanding of the management effects. Thirdly, I assessed variations in broadcast seeding (seasonality of seeding, seeding technologies, and inclusion of herbicide) and their interactions with biotic and abiotic limitations to seedling recruitment. I found the composition of pre-existing vegetation and the seasonality of seeding influenced success. Finally, I evaluated a novel seed technology for restoration success in both controlled and field settings. Seed pellet size and composition both influenced seedling recruitment. Altogether these studies have advanced our understanding of several novel management and restoration approaches for semi-arid rangelands invaded by B. tectorum. This knowledge provides a strong base to further inform and refine management and research in this field.