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<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 SpreadFig. 3. Recruitment <strong>of</strong> S. alterniflora seedlings in plots varying insubstrate texture. Values are means ± 1 S.E.Seedlings/ha25002000150010005000NoneControlFig. 4. The influence <strong>of</strong> control efforts in 2003 on local seedlingrecruitment in 2004. Control methods included a variety <strong>of</strong> mechanicalmethods and herbicide application. Values are means ± 1S.E.did not receive control. The local reduction in seed productioninfluenced local (sub-region) seed recruitment <strong>the</strong> followingyear (Fig. 4). Areas such as <strong>the</strong> Palix and Cedar riversthat did not receive control in 2003 had high seed productionthat fall and correspondingly high seedling recruitment<strong>the</strong> following year. In contrast, sites that received controlin 2003 such as Tarlatt Slough and Diamond Point experiencedlow rates <strong>of</strong> seed production that fall and had correspondinglylow recruitment <strong>the</strong> following year.DISCUSSIONCauses <strong>of</strong> variabilitySpartina alterniflora recruitment in Willapa Bay ishighly variable across years and across sub-regions <strong>of</strong> <strong>the</strong>bay. The yearly variation observed in this study corroborateslonger-term data from historical aerial photographssuggesting that <strong>the</strong>re have been strong episodic bursts <strong>of</strong> S.alterniflora colonization (Civille et al. 2005). A significantcomponent <strong>of</strong> this yearly variation in recruitment appears tobe directly related to levels <strong>of</strong> seed production <strong>the</strong> previousyear. For <strong>the</strong> limited two years that we are able to makecomparisons, <strong>the</strong> average estuary-wide recruitment tracksaverage estuary-wide seed production <strong>the</strong> previous year. Inaddition, <strong>the</strong>re is evidence that S. alterniflora seed set is significantlyinfluenced by pollen availability, and that pollenavailability is significantly reduced by wet and cool conditions(Davis et al. 2004, and this volume). Yearly averagebay-wide recruitment is positively correlated with <strong>the</strong> number<strong>of</strong> August degree days (<strong>the</strong> cumulative number <strong>of</strong> growingdegree days in August) and negatively correlated withtotal August precipitation in <strong>the</strong> previous year (Lambrinos,unpublished data).Substrate characteristics appear to play an importantrole in <strong>the</strong> site-to-site variability in recruitment. Spartinaalterniflora seedlings are far less likely to establish at sandysites than at muddy sites. The mechanisms generating thispattern are still unclear. Spartina seeds may be less frequentlydeposited at more erosive sandy sites. In river systemsseed and sediment deposition are closely related(Goodson et al. 2003). In addition, seedlings may be lesslikely to establish at sandy sites because <strong>of</strong> higher erosionand physical stress. Alternatively, seedlings could performpoorly in sandy sediments because <strong>of</strong> nutritional limitations.Increasing sediment sand corresponds with decreasing sedimentnitrogen (N) content at <strong>the</strong>se sites (Tyler et al. 2007).Evidence from transplant experiments and common gardenexperiments indicate that S. alterniflora seedlings growpoorly on sand relative to mud irrespective <strong>of</strong> <strong>the</strong> ambienthydrological conditions (Lambrinos and Bando 2008).Undoubtedly, ano<strong>the</strong>r factor in <strong>the</strong> site-to-site variabilityin recruitment is seed supply. Spartina alterniflora can potentiallydisperse long distances (Howard and Sytsma 2010).However, <strong>the</strong> fact that regions that received control in 2003had correspondingly reduced recruitment levels in 2004,while no reductions in recruitment occurred in regions thatdid not receive control suggests that a sizeable portion <strong>of</strong>recruitment is derived from local seed sources.Implications for managementThe strongly episodic and spatially variable nature <strong>of</strong> S.alterniflora recruitment in Willapa Bay has important implicationsfor management. Years <strong>of</strong> poor recruitment haveprobably slowed <strong>the</strong> rate <strong>of</strong> <strong>the</strong> invasion in Willapa Bay.Both vegetative growth and recruitment by seed contribute-89-
Chapter 2: Spartina Distribution and Spread<strong>Proceedings</strong> <strong>of</strong> <strong>the</strong> <strong>Third</strong> <strong>International</strong> <strong>Conference</strong> on Invasive Spartinato <strong>the</strong> spatial expansion <strong>of</strong> <strong>the</strong> invasion. However, most <strong>of</strong><strong>the</strong> expansion in <strong>the</strong> bay has occurred through seedling recruitmentand subsequent growth <strong>of</strong> clones, not from <strong>the</strong>lateral growth <strong>of</strong> established meadows (Civille et al. 2005).With moderate and low annual budgets, <strong>the</strong> optimal controlstrategy in Willapa Bay is to target nascent populations(Taylor and Hastings 2004; Taylor et al., this volume).However, a “clone only” strategy may be incompatible witho<strong>the</strong>r management objectives such as restoring habitat formigratory birds. Periods <strong>of</strong> low recruitment may provideopportunities to target meadows with little reduction in controleffort against nascent clones. In contrast, periods <strong>of</strong>high recruitment would be poor times to allocate treatmentresources to established meadows.At <strong>the</strong> same time, periods <strong>of</strong> low recruitment may fostercomplacency. This is unlikely to occur with a comprehensiveand long-term management program such as <strong>the</strong> onecurrently being implemented in Willapa Bay. However, poorrecruitment years may hamper implementation <strong>of</strong> such comprehensivemanagement plans. For instance, if initial infestationsare followed by years <strong>of</strong> low recruitment <strong>the</strong>re maybe little impetus to expend resources on control because <strong>the</strong>spatial expansion <strong>of</strong> populations is limited. Even if controlis initiated at a particular site, <strong>the</strong> need to develop a regionalcontrol strategy may not be obvious. Untreated infestationsmay <strong>the</strong>n serve as significant seed sources during subsequentgood seed production years.The poor seedling recruitment at sandy sites comparedto muddy sites has allowed <strong>the</strong> S. alterniflora managementprogram in Willapa Bay to focus control efforts spatially.The sandy Long Beach Peninsula has been given a low priorityfor control, and control resources will only be spen<strong>the</strong>re during <strong>the</strong> final stages <strong>of</strong> <strong>the</strong> control program (K. Murphy,pers. comm.). The ability to prioritize estuaries in terms<strong>of</strong> susceptibility to S. alterniflora recruitment is an importantconsideration given <strong>the</strong> limited resources usually availableand <strong>the</strong> wide spatial extent <strong>of</strong> most estuaries.The ability to spatially allocate control resources is alsoaided by <strong>the</strong> fact that a significant proportion <strong>of</strong> local recruitmentis derived from local seed production. Controlefforts in one area are unlikely to be completely swamped byrecruitment coming from distant or hydrologically disjunctun-controlled areas. This suggests that S. alterniflora controlin different sub-regions <strong>of</strong> an estuary can be managedsomewhat independently (e.g., controlled sequentially) andstill be successful. Long-distance dispersal is certainly nottrivial, however, and long-term management will requireextensive monitoring and a better understanding <strong>of</strong> dispersalpathways.ACKNOWLEDGMENTSWe thank <strong>the</strong> kind and expert assistance <strong>of</strong> several peopleand agencies without whose assistance this work wouldnot have been possible: Brian Couch; Les Holcomb; KyleMurphy; Fritzie Grevstad; Kathleen Sayce; Brett Dumbauld;Dave Heimer; Charlie Stenvall; Todd Brownly; WendyBrown; The Washington Department <strong>of</strong> Fish and Wildlife;The Washington Department <strong>of</strong> Agriculture; The WashingtonDepartment <strong>of</strong> Natural Resources; The Willapa Bay NationalWildlife Refuge. Funding was provided by NSF Biocomplexitygrant DEB0083583.REFERENCESCiville, J.C., K. Sayce, S.D. Smith and D.R. Strong. 2005. Reconstructinga century <strong>of</strong> Spartina alterniflora invasion with historicalrecords and contemporary remote sensing. Ecoscience12(3):330-338.Civille, J.C., S.D. Smith, and D.R. Strong. 2005. Remote sensingLiDAR and GIS inform landscape and population ecology, WillapaBay, WA. In: Ayres, D.R., D.W. Kerr, S.D. Ericson andP.R. Ol<strong>of</strong>son, eds. <strong>Proceedings</strong> <strong>of</strong> <strong>the</strong> <strong>Third</strong> <strong>International</strong> <strong>Conference</strong>on Invasive Spartina, 2004 Nov 8-10, San Francisco,CA, USA. San Francisco Estuary Invasive Spartina Project <strong>of</strong> <strong>the</strong>California State Coastal Conservancy: Oakland, CA.Davis, H.G., C.M. Taylor, J.G. Lambrinos and D.R. Strong. 2004.Pollen limitation causes an Allee effect in a wind-pollinated invasivegrass (Spartina alterniflora). <strong>Proceedings</strong> <strong>of</strong> <strong>the</strong> NationalAcademy <strong>of</strong> Sciences USA 101:13804-13807.Goodson J.M., A.M. Gurnell, P.G. Angold, and I.P. Morrissey.2003. Evidence for hydrochory and <strong>the</strong> deposition <strong>of</strong> viableseeds within winter flow-deposited sediments: <strong>the</strong> River Dove,Derbyshire, UK. River Research & Applications 19:317-334.Howard, V., and M. Sytsma. 2010. Fragment propagules <strong>of</strong>Spartina alterniflora and potential eastern pacific dispersal. In:Ayres, D.R., D.W. Kerr, S.D. Ericson and P.R. Ol<strong>of</strong>son, eds.<strong>Proceedings</strong> <strong>of</strong> <strong>the</strong> <strong>Third</strong> <strong>International</strong> <strong>Conference</strong> on InvasiveSpartina, 2004 Nov 8-10, San Francisco, CA, USA. San FranciscoEstuary Invasive Spartina Project <strong>of</strong> <strong>the</strong> California StateCoastal Conservancy: Oakland, CA.Lambrinos, J.G. and K.J. Bando. 2008. Habitat modification inhibitsconspecific seedling recruitment in populations <strong>of</strong> an invasiveecosystem engineer. Biological Invasions 10:729-741.Sayce, K. 1988. Introduced cordgrass, Spartina alternifloraLoisel., in saltmarshes and tidelands <strong>of</strong> Willapa Bay, Washington.Report prepared for <strong>the</strong> Willapa National Wildlife Refuge.USFWS #FWSI-87058 (TS).Taylor, C. M., and A. Hastings. 2004. Finding optimal controlstrategies for an invasive grass using a density-structured model.Journal <strong>of</strong> Applied Ecology. 41:1049–1057Tyler, A.C., J.G. Lambrinos, and E.D. Grosholz. 2007 Nitrogeninputs promote <strong>the</strong> spread <strong>of</strong> an invasive marsh grass. EcologicalApplications 17:1886–1898.With, K.A. 2002. The landscape ecology <strong>of</strong> invasive spread. ConservationBiology 16:1192-1203.-90-
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FORWARD & ACKNOWLEDGEMENTSThe <stro
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CHAPTER ONESpartina Biology
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