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 SpreadREMOTE SENSING,LIDAR AND GIS INFORM LANDSCAPE AND POPULATION ECOLOGY,WILLAPA BAY,WASHINGTONJ.C. CIVILLE 1,4 ,S.D.SMITH 2 AND D.R. STRONG 31 Department <strong>of</strong> Evolution and Ecology, University <strong>of</strong> California, Davis, One Shields Ave., Davis, CA 95616-87552 True North GIS, 4857 Grand Fir Lane, Olympia, WA 985023 Department <strong>of</strong> Evolution and Ecology, University <strong>of</strong> California, Davis, One Shields Ave., Davis, CA 95616-87554 Current address: 2731 Be<strong>the</strong>l St. NE, Olympia, WA 98506; jciville@comcast.netKeywords: Spartina alterniflora, Willapa Bay, photogrammetry, mappingThe spread <strong>of</strong> Spartina alterniflora Loisel. (smoothcordgrass, hereafter referred to as Spartina) in PacificNorthwest estuaries presents a unique opportunity toexamine ecological interactions between an invasive clonalorganism and local abiotic factors. Willapa Bay is a large,shallow, tidal basin on <strong>the</strong> southwest coast <strong>of</strong> WashingtonState. The bay is approximately 360 square kilometers (km 2 )at mean high tide, with well over 190 km 2 <strong>of</strong> s<strong>of</strong>t mud andsand tideflats exposed at mean low tide (Civille 2005). Themixed diurnal tides <strong>of</strong> <strong>the</strong> nor<strong>the</strong>rn Pacific coast distinguishWashington estuaries from those on <strong>the</strong> Atlantic coast whereS. alterniflora is <strong>the</strong> predominant native salt marsh species.Spartina species are <strong>the</strong> principle components <strong>of</strong> Atlanticand Gulf coast estuaries, but <strong>the</strong> introduction <strong>of</strong> Spartina to<strong>the</strong> Willapa Bay estuary and its open mudflats has led to <strong>the</strong>rapid conversion <strong>of</strong> thousands <strong>of</strong> intertidal hectares intodense stands <strong>of</strong> upper tidal meadows (Sayce 1988; Daehlerand Strong 1996; Civille et al. 2005). The rapid expansion <strong>of</strong>this robust clonal grass across <strong>the</strong> open habitat <strong>of</strong> intertidalmudflats is a textbook example <strong>of</strong> unimpeded colonization,and presents challenges not only to management efforts, butto ecologists as well.The initial questions relevant to this research weregenerated by biologists and land managers in <strong>the</strong> state <strong>of</strong>Washington, who needed to understand Spartina expansionfor environmental impact analyses, adaptive managementplans, and to direct control efforts in <strong>the</strong> most efficientmanner (Sayce 1988; Aberle 1990; Aberle 1993; Civille1993). These questions included: where were plantsspreading fastest, where was intertidal habitat being lostmost rapidly, and whe<strong>the</strong>r stopping seed production wasmore effective than removing as many new plants aspossible (Moody and Mack 1988). Ecologists studyinginvasive population growth dynamics ask similar questions.What is regulating <strong>the</strong> growth <strong>of</strong> Spartina on Willapa Baymudflats? Are <strong>the</strong>se regulators density dependent orindependent? With <strong>the</strong> seemingly limitless expanse <strong>of</strong>habitat available for colonization, why is it that some areasare filling in more quickly than o<strong>the</strong>rs? Are <strong>the</strong>re factorsintrinsic to <strong>the</strong> biology and mating system <strong>of</strong> Spartina thatinfluence its spread, or are abiotic factors more important inshaping <strong>the</strong> colonization fronts? Does competition betweenSpartina plants limit <strong>the</strong> population, and will availability <strong>of</strong>resources affect <strong>the</strong>ir growth? Have evolutionary changestaken place in <strong>the</strong> Willapa Bay population that allowSpartina to compete more effectively? Many <strong>of</strong> <strong>the</strong>sequestions have been addressed in experimental and<strong>the</strong>oretical work by members <strong>of</strong> <strong>the</strong> Spartina BiocomplexityGroup at <strong>the</strong> University <strong>of</strong> California at Davis, (Davis et al.2004a; Davis et al. 2004b; Taylor 2004; Taylor and Hastings2004; Civille 2005; Davis 2005; Civille 2006) and werepresented at this conference by <strong>the</strong>ir primary authors (Daviset al.; Taylor et al.; this volume).Spartina was probably brought to <strong>the</strong> Willapa estuarythrough <strong>the</strong> transplanting <strong>of</strong> eastern oysters to bolster <strong>the</strong>flagging oyster industry <strong>of</strong> Willapa Bay in <strong>the</strong> 1890s andearly 1900s. The California gold rush had fueled <strong>the</strong>depletion <strong>of</strong> native oysters from <strong>the</strong> bay, and an effort wasmade by <strong>the</strong> United States Fisheries Bureau to replant <strong>the</strong>bay with Chesapeake stock. The completion <strong>of</strong> <strong>the</strong>transcontinental railway allowed <strong>the</strong> trip to be made in abouta week (Townsend 1896; Scheffer 1945; Civille et al. 2005),and eastern oysters continued to be brought via railcar toWillapa until around 1917. The climate was apparently toocool for eastern oysters, and although <strong>the</strong>y grew well, <strong>the</strong>ywere never able to reproduce successfully in Willapa atcommercially viable levels. Spartina, however, was able toestablish in small colonies that were close to beds used torear eastern oysters (Civille et al. 2005).The first written and photographic evidence <strong>of</strong> Spartinapresence in <strong>the</strong> estuary was ga<strong>the</strong>red at <strong>the</strong> Willapa NationalWildlife Refuge by T.H. Scheffer in 1940 (Scheffer 1945).A photograph taken by Scheffer shows several “greenislands,” and was donated to <strong>the</strong> California Academy <strong>of</strong>Science Herbarium to document his findings. If an averageheight <strong>of</strong> one meter (m) is assumed, <strong>the</strong> large plant in <strong>the</strong>photo is about 42 m in diameter, covering approximately1,367 square meters (m 2 ) <strong>of</strong> mudflat. The first aerialphotographs <strong>of</strong> <strong>the</strong> bay were taken by <strong>the</strong> Army Corps <strong>of</strong>Engineers in 1945, and Spartina plants <strong>of</strong> a similar size to-83-