Biological invasion is one of the most important problems facing modern ecologists, and while research has shown the detrimental effects caused by many invasive species, the impact of the majority of invaders in largely unknown. I investigated the effects of the ubiquitous exotic plant species common mullein (Verbascum thapsus) on plant communities in northern Colorado. Additionally, I studied the impact of a second common invasive species, cheatgrass (Bromus tectorum), and examined its interactions with mullein. I conducted a field experiment over two years, manipulating mullein and cheatgrass presence at two sites, either removing the aboveground biomass of one or both of the exotic plants, or leaving them intact. I measured a number of plant community and abiotic characteristics as responses to these treatments. I found that mullein invasion has few negative impacts, and that the benefits associated with management are lost within a year. Removal of mullein acts as a disturbance, creating physical and ecological openings for cheatgrass and other exotics to occupy. Percent cover of exotic species was highest when mullein was removed and cheatgrass was left intact. Since cheatgrass invasion is associated with undesired changes in the community, I suggest that resources should be used for its management rather than the management of mullein, and that mullein removal in areas with cheatgrass should be accompanied by an aggressive strategy addressing cheatgrass invasion.