Summer Pop-up Seminar - A Prickly Problem: Saving the Suisun Thistle from Extinction


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EOS Center Pop-up Summer Seminar – July 29, 2020 at 3:30 PM

Watch here if you missed it!

A Prickly Problem: Saving the Suisun Thistle from Extinction

Dr. Michael Vasey (presenter), Richard Graham-Bruno, Morgan Stickrod, Rosa Schneider, Ryan Anderson, Carly Miranda, Sarah Estrella, Jeb Bjork, Megan Keever, Dr. Jason Cantley, Dr. Karen Thorne, Dr. Kathy Boyer, Dr. Tom Parker

Abstract: The Suisun Thistle (Cirsium hydrophilum var. hydrophilum) was once widespread in brackish tidal marshes that frame the northern edge of Suisun Bay. Over time, 87% of these marshes were transformed into managed ponds. The few remaining tidal marshes in the region are relatively small and fragmented. The Suisun Thistle declined over time and was considered extinct until the discovery of a population near Rush Ranch Open Space Preserve in 1989. It was then listed as Endangered under the Federal Endangered Species Act in 1997. It is found today at Rush Ranch and Hill Slough, and potentially may be at Peytonia Slough, its former type locality. Despite its highly restricted range, a 2003 survey at Rush Ranch found it to be relatively widespread and abundant, particularly along shallow channels created by previous mosquito ditching to “drain” standing water on the marsh plain. Since 2003, populations have continued to persist at Rush Ranch but numbers appear to have declined significantly. This decline has occurred despite protection from disturbance by the designation of Rush Ranch as part of the SF Bay NERR. A study by Schneider suggested that physical disturbance might be needed to create opportunities for the Suisun Thistle to recruit. Unlike most long-lived rhizomatous species that dominate tidal marsh habitats, the Suisun Thistle is short-lived and light dependent. Further, recent studies have demonstrated that its seed output is heavily impacted by an introduced weevil. It appears that the Suisun Thistle is a “gap opportunist” that potentially may be threatened with too little disturbance over time! A current focus of the USFWS Tidal Marsh Recovery Team is to explore the potential of pilot reintroduction projects associated with tidal wetland habitat restoration opportunities to address this problem.

Bio: My background and research interests are in environmental studies and conservation biology. I originally came to San Francisco State in 1990 as Coordinator for the then-new SFSU Conservation Biology Program. In the early 1990’s, I was Acting Manager for the SF Bay NERR and led the effort to have it officially designated in 2003. Also during that time, I worked on tidal wetland vegetation projects from South SF Bay to the Delta. I recently received my PhD in Environmental Studies at UC Santa Cruz, where I conducted research on the influence of the summer marine layer on maritime chaparral. For the last 20 years, I have worked with colleagues to develop a systematic treatment for the woody genus Arctostaphylos.