Abstract: Background/Questions/Methods In the past two decades, brackish wetland ecosystems around San Francisco Bay, California have been increasingly invaded by the noxious weed, Phragmites australis In Suisun Marsh, P. australis is not only a detriment to wildlife that depend on these unique habitats, but also a fire hazard and nuisance for people who utilize these areas for recreational purposes. Long-term management methods consist of herbicide spraying, mowing, discing, and occasional burns, but have been largely unsuccessful, as managers have seen more than 300% growth in the invasion extent since 2000. Some parcels in Suisun Marsh have been intensively treated for the last two decades, while others have been subject to low levels of treatment or none at all. In this poster we analyze the effects of high-intensity invasive plant management on propagule pressure of P. australis. Sites with a total of 10 or more years of spraying were classified as high-intensity treatment while sites with low (< 3 year) or no spraying were classified as low-intensity treatment. Within sites of each management approach, 0.25 m2 quadrats were used to estimate inflorescence density within patches of P. australis. We collected five inflorescences per patch were collected to determine the mean inflorescence and spikelet weight, as well as the mean number of seeds per spikelet.
Results/Conclusion
Inflorescences collected from high-intensity sites were on average, 1.098 g compared with inflorescences collected from low-intensity sites that were 0.900 g on averge (t = -2.07; p = 0.0393). Estimates of mean inflorescence within a patch were also different between treatment groups, being higher in the low-intensity group by 3.01 inflorescences per m2. High treatment sites also had, on average, an estimated 84,670 fewer seeds of P. australis per m2 compared to low-intensity sites ( t = -2.5216, p = 0.01225). These results suggest that intensive management practices have diminished P. australis propagule pressure within managed properties of Suisun Marsh, although the invasion continues to spread.
