Pine flatwoods are the most extensive terrestrial ecosystem in Florida and prescribed burning is a common management practice, as frequent surface fires maintain low understory growth in this fire-adapted ecosystem. However, open space and resource availability from burning can also open the door for invasion of exotic plants like Caesar’s weed (Urena lobata), a Category I invasive spreading throughout subtropical and tropical ecosystems. It is a rapid growing annual plant that is often observed following prescribed fires. Additionally, disturbed soils such as tilled fire breaks or rootings of feral swine (Sus scrofa) often have high densities of Caesar’s weed. However, the distribution responses to burning and soil disturbance that may control Caesar’s weed spread are poorly understood. To better inform land management practices, we assessed the response of Caesar’s weed germination to seed heating and soil disturbance. Using a factorial field manipulation, we quantified invasion success in response to soil disturbance and winter prescribed burning, as well as whether soil seed banks or post-disturbance dispersal was responsible for invasion. We also quantified heat tolerance of Caesar’s weed seeds both in the canopy and soil seed bank to determine if the timing or intensity of prescribed burning influences germination success.
Results/Conclusions
Soil disturbance has a greater effect on the spread of Caesar’s weed than burning, particularly in rootings of feral swine. Caesar’s weed produces burred seeds that are likely dispersed and then buried by swine during rooting. Seed heating compromised seed germination, although greater fire intensities were required for soil heating compared to canopy held seeds, suggesting soil seed banks may protect seeds under typical winter prescribed burning conditions. With this information, land managers can make science-based decisions regarding the timing of prescribed burning to maximize removal and minimize facilitation of Caesar’s weed in pine flatwoods. Additionally, synergism between invasive soil disturbers (i.e., feral swine) and invasive plants results in novel ecology that may require novel conservation strategies in managed ecosystems.