Chairperson, Graduate Committee: Lisa RewWilliams, Amanda2024-12-102020https://scholarworks.montana.edu/handle/1/18961Humans have spread plant species to novel ranges throughout history, but the rate of new introductions has drastically increased with globalization. These introduced species are often viewed as a threat to native species richness. Linaria vulgaris (yellow toadflax) was introduced to North America in the 1600s as a useful and ornamental plant and has since spread across the continent. It is mandated for control in much of the intermountain west and is thought to form monocultures to the detriment of native species. Despite L. vulgaris' long residence time on the continent, causal links to negative effects have not been established. Land managers are typically faced with a long list of species mandated for control and limited resources and thus must prioritize high impact species for control. Herbicide is the management choice for non-native plants in Yellowstone National Park, but it may have negative effects. Therefore, managers need to be sure that treatment is worthwhile, and that the effects of treatment do not exceed the effects of non-native plants. Consequently, I selected 10 sample sites in the West Yellowstone, Montana area: five with a recent history of herbicide treatment and five without. Data were collected on plant species richness and abundance within and immediately adjacent to L. vulgaris patches. Species richness and diversity did not vary between sites based on treatment history. Species diversity did increase where L. vulgaris was present, indicating that it may act as a "plus one" in communities and does not dominate where it occurs. Treatment history was not linked to a reduction in L. vulgaris abundance, but the abundance of other non-natives was greater in treated sites. These results indicate that land managers should not assume that L. vulgaris negatively effects native species richness and diversity in their location and should pair management efforts with rigorous monitoring. In the West Yellowstone area, L. vulgaris likely should not be a high priority for herbicide treatments. However, this study is observational and not sufficient to establish causal links.en-USCopyright 2020 by Amanda WilliamsIntroduced organismsHerbicidesYellowstone National ParkSpecies diversityThesis