Proceedings of the Third International Conference on Invasive ...

<strong>Proceedings</strong> <strong>of</strong> <strong>the</strong> <strong>Third</strong> <strong>International</strong> <strong>Conference</strong> on Invasive SpartinaChapter 2: Spartina Distribution and SpreadHYBRID CORDGRASS (SPARTINA) AND TIDAL MARSH RESTORATION IN SAN FRANCISCO BAY:IF YOU BUILD IT, THEY WILL COMED. R. AYRES 1 AND D. R. STRONG 21,2Evolution and Ecology, University <strong>of</strong> California, Davis, CA 956161drayres@ucdavis.edu; 2 drstrong@ucdavis.eduKeywords: invasive species, salt pondsRestoration sites built on former salt ponds (Fig. 1) presentan ideal combination <strong>of</strong> biotic and abiotic conditions forSpartina regeneration by seed. First, <strong>the</strong>y are unvegetated soseedlings grow unhindered by competition with establishedplants. Second, <strong>the</strong>y are graded to present a range <strong>of</strong> intertidalelevations enhancing <strong>the</strong> opportunity for colonization at elevationsthat are nei<strong>the</strong>r too saline, nor receive too much tidalinnundation for cordgrass seedling germination and growth.<strong>Third</strong>, tidal waters enter through levee breaches (see Fig. 1),muting <strong>the</strong> force <strong>of</strong> <strong>the</strong> waves and reducing seedling loss dueto physical removal by tidal action. And finally, many <strong>of</strong> <strong>the</strong>restored marshes in <strong>the</strong> sou<strong>the</strong>rn and eastern regions <strong>of</strong> <strong>the</strong>Bay are near marshes invaded by hybrids, or are actually fedby tidal water which travels though hybrid Spartina-chokedchannels (i.e. Alameda Creek and Alameda Flood ControlChannel; se e # in Fig. 2), thus ensuring a tidally-borne seedbank rich in floating hybrid Spartina seed.The result is that recent restoration sites in <strong>the</strong> area havebeen quickly colonized by large numbers <strong>of</strong> hybrid Spartina(Table 1). This pattern can be expected to continue as morenew marshes are opened until hybrid cordgrass is controlled.Hybrid cordgrass thus presents a substantial challenge tomarsh restoration that is particularly relevant in light <strong>of</strong> <strong>the</strong>planned restoration <strong>of</strong> 25 square miles <strong>of</strong> salt ponds in <strong>the</strong>South Bay (Fig. 2).Fig. 1. Cogswell Marsh in Hayward, CA is a former salt pond opened to tidal action (note levee breaches along<strong>the</strong> shoreline and within marsh denoted by ^ ) in 1980. Non-working salt ponds are at <strong>the</strong> left and top <strong>of</strong> <strong>the</strong>photo (photos provided by California Coastal Conservancy).- 125 -