Effects of disturbance history and habitat variables on H aurantiacum (orange hawkweed) invasion

Finding invasive species when their populations in are still in the nascent stage can be the key factor in preventing wide-spread invasion, but our understanding of which factors are associated with successful invasion are often based on anecdote rather than studies. Hieracium aurantiacum is an invasive weed which is considered to primarily invade disturbed and open areas, suppressing natives with huge mats of vegetative growth and using wind-born seeds to spread into new habitats. I tested whether (1) habitat variables affected H. aurantiacum presence, and (2) how resource allocation differed between habitat types. I preformed ground and canopy cover surveys in sites from four disturbance history types (burned and logged; logged; burned; meadow), and harvested plants at each site. The vegetative and reproductive biomass of collected plants were then weighed and compared between habitat types. Results suggest that H. aurantiacum is more likely to be found in highly disturbed (burned and logged) areas. Thatch was negatively associated with H. aurantiacum presence, while both moss and forbs were positively associated. Plants in burned and logged areas allocated more resources to vegetative growth. These results support the hypothesis that H. aurantiacum is more likely to invade highly disturbed areas. Once plants have entered a habitat, they allocate more resources to continued expansion and persistence, further effecting damaged native communities.