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 1: Spartina BiologyThese vegetative adaptive traits are also complementedby a number <strong>of</strong> important reproductive adaptations thatinclude: (1) wind pollination; (2) asynchronous flowering;i.e. protogyny (i.e. females flower first, <strong>the</strong>n males comeinto bloom) which promotes out-crossing yet allows someoverlap in flowering time so that individuals can partiallyself-fertilize (reproductive insurance); (3) production <strong>of</strong>large numbers <strong>of</strong> small seeds that can be dispersed byflotation (hydrochory); (4) seeds with awns and o<strong>the</strong>rstructures that make <strong>the</strong>m available for attachment to birdfea<strong>the</strong>rs and potential avian dispersal (Vivian-Smith andStiles 1994); (5) vegetative rhizome fragments that can betransported by water to fur<strong>the</strong>r spread individual genotypes;(6) phenology cued into optimal conditions for flowering(late summer), seed set (fall) and dispersal during winterstorm events; and (7) timing <strong>of</strong> dispersal coinciding withfresh conditions in <strong>the</strong> estuary during winter flooding, suchthat fresh water conditions promote germination andestablishment.The unique suite <strong>of</strong> vegetative and reproductiveadaptations <strong>of</strong> S. foliosa have resulted in its successfuloccupation <strong>of</strong> an important low marsh niche within westcoast tidal wetlands found in <strong>the</strong> California FloristicProvince (and beyond through south-central BajaCalifornia). In fact, as I will argue below, S. foliosa could beviewed as a “foundation species” i.e. a species that has apr<strong>of</strong>ound effect on tidal wetland functions such assuccession, productivity, and habitat structure. Thesefunctions ultimately facilitate <strong>the</strong> occupation <strong>of</strong> such tidalwetlands by a myriad <strong>of</strong> microbial, algal, plant, invertebrate,fish, and bird species.SPARTINA FOLIOSA AS A FOUNDATION SPECIESThe concept <strong>of</strong> a foundation species has been articulatedby Dayton (1972), Bruno and Bertness (2001), and Bruno etal. (2003) in <strong>the</strong> context <strong>of</strong> recognizing facilitation as anessential element <strong>of</strong> contemporary ecological <strong>the</strong>ory. Unlikekeystone species, which are proportionately rare incommunities and yet exert a disproportionate influence overcommunity structure through processes such as predation orecological engineering, foundation species are habitatformingdominant species that provide <strong>the</strong> framework for <strong>the</strong>assembly <strong>of</strong> an entire community. California cordgrassappears to be an excellent example <strong>of</strong> a foundation species.The importance <strong>of</strong> S. foliosa as an initiator <strong>of</strong> tidalwetland succession in San Francisco Bay tidal wetlands haslong been appreciated. For example, Howell (1949) makes<strong>the</strong> following comment: “Pacific (i.e. California) cord grassis generally <strong>the</strong> first plant to appear on tidal flats where itfrequently establishes broad pure stands. Later it issucceeded by Salicornia and a more diversified salt marshassociation as higher ground is built up around it. In thislater association Spartina still occurs as a narrow fringealong tidal sloughs and also occasionally as a localizedcolony in low areas”. In recently restored tidal wetlands in<strong>the</strong> bay today, such as Carl’s Marsh in Sonoma County orPond 2A in Napa County, this exact pattern has beenobserved. Spartina foliosa is usually <strong>the</strong> first species tocolonize barren mud flats by floating seeds and rhizomefragments. As clones grow and establish, rhizomatous matstrap sediment and facilitate <strong>the</strong> incremental rise <strong>of</strong> a marshplain. As elevations become suitable, o<strong>the</strong>r vascular plantspecies colonize <strong>the</strong> emerging marsh plain and eventuallydisplace S. foliosa to <strong>the</strong> accreting edges <strong>of</strong> <strong>the</strong> marsh,margins <strong>of</strong> drainage channels, or it persists in lowdepressions in <strong>the</strong> marsh where duration <strong>of</strong> inundationapparently detracts o<strong>the</strong>r marsh plain species from becomingestablished (personal observation).Once established, dense low marsh stands <strong>of</strong> S. foliosaprovide a key role in marsh productivity. Each year, S.foliosa rhizomes put out fresh shoots that rapidly grow intotall, mature stems and leaves. A considerable phase <strong>of</strong>carbon fixation <strong>the</strong>n takes place before flowering begins inmid summer (June). After fruiting in <strong>the</strong> fall, stems die backand much <strong>of</strong> <strong>the</strong> vegetative matter <strong>of</strong> <strong>the</strong> stand contributes to<strong>the</strong> detritus base <strong>of</strong> <strong>the</strong> wetland food web. Fur<strong>the</strong>r, stemwrack is washed up to <strong>the</strong> marsh/upland transition zone,providing habitat and nutrients for a variety <strong>of</strong> organismsthat inhabit this interface. Along with this direct contributionto <strong>the</strong> wetland food web, S. foliosa also provides animportant indirect contribution because its rhizomatous massprovides key habitat for a diverse assemblage <strong>of</strong> algae,including nitrogen-fixing cyanobacteria. Dawson and Foster(1982) describe this phenomenon as follows: “The mudbeneath and between California cord grass is covered withvarious algae, including films <strong>of</strong> golden-colored, unicellulardiatoms, <strong>the</strong> brownish-green Enteromorpha, redPolysiphonia, <strong>the</strong> brownish-green, siphonous Vaucheria, andblue-green algae. All <strong>of</strong> <strong>the</strong>se kinds <strong>of</strong> algae can beimportant contributors to marsh productivity and, inaddition, some <strong>of</strong> <strong>the</strong> blue-greens can convert nitrogen gasinto o<strong>the</strong>r nitro-nutrients for <strong>the</strong> algae as well as <strong>the</strong>flowering plants.”Stands <strong>of</strong> S. foliosa also provide habitat structure that isimportant for a number <strong>of</strong> species that occupy tidalwetlands. The relationship between California cordgrass andCalifornia and light-footed clapper rails (both subspecies <strong>of</strong>Rallus longirostris) is an excellent case in point. Both forcover and nesting habitat, California cordgrass is essentialfor <strong>the</strong> success <strong>of</strong> this species. Boyer and Zedler (1996) alsopoint out that insects occupy stands <strong>of</strong> S. foliosa and <strong>the</strong>seundoubtedly provide food resources for passerine birds (e.g.marsh wrens and song sparrows) that live in salt marshhabitats.Finally, because <strong>of</strong> its importance as a foundationspecies, particularly in terms <strong>of</strong> succession, S. foliosa is alsoan essential element for tidal wetland restoration projects.Seeds, rhizome fragments, and plugs <strong>of</strong> S. foliosa can beused to revegetate formerly diked wetlands that are restored-5-