An overarching challenge in invasive species ecology is the ability to quantify how non-native plant species interact with their environments, including how this interaction determines which species are able to establish and persist and which plant communities are most susceptible to invasion. This project focuses on the non-native, invasive species Cirsium arvense (Canada thistle) in Yellowstone National Park (YNP). In 2006, we sampled five new sites and revisited 30 sites in young, lodgepole pine stands in the 1988 burned areas of YNP that had been previously sampled in 1999. Our objective was to understand which physiographic and environmental factors explain the variability in C.arvense establishment, persistence and abundance in post-fire forests. We found that C.arvense disappeared in 67% of the sites where it had been prevalent in 1999 and persisted in the remaining sites. Of the sites where C.arvense persisted, it exhibited decreased abundance in 33% of the sites and increased abundance in the remaining sites. C.arvense invaded 4 new sites since 1999. Mean stand density was highest where C.arvense had never been observed and lowest at newly invaded sites. Mean species richness, slope and pH were greatest where C.arvense persisted or recently invaded. Soil and community composition analyses may yield further insight into the susceptibility of plant communities to invasion by C.arvense. This project demonstrates the continued dynamic nature of an invasive species eighteen years following a major disturbance and reveals environmental and physiographic factors influencing the ability of an invasive species to establish and persist.
