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 SpreadIMPLICATIONS OF VARIABLE RECRUITMENT FOR THE MANAGEMENT OF SPARTINAALTERNIFLORA IN WILLAPA BAY,WASHINGTONJ.G. LAMBRINOS 1,2 ,D.R.STRONG 3,5 ,J.C.CIVILLE 3,4 AND J. BANDO 1,61 Department <strong>of</strong> Environmental Science and Policy, University <strong>of</strong> California, Davis, CA 956162 Current address: Department <strong>of</strong> Horticulture, 4017 Ag and Life Sciences Building, Oregon State University,Corvallis, OR 97331; lambrinj@hort.oregonstate.edu3 Department <strong>of</strong> Evolution and Ecology, University <strong>of</strong> California, Davis, CA 956164 Current address: 2731 Be<strong>the</strong>l St. NE, Olympia, WA 98506; jciville@comcast.net5 drstrong@ucdavis.edu; 6 jun.bando@gmail.comThe spatial expansion <strong>of</strong> Spartina alterniflora populations in Willapa Bay, Washington has beendriven primarily by seedling recruitment. We measured this recruitment at <strong>the</strong> landscape scale usinga series <strong>of</strong> precision GPS guided airboat censuses. Recruitment is highly variable across both spaceand time. Over <strong>the</strong> four years <strong>of</strong> observation, yearly average estuary-wide recruitment varied from alow <strong>of</strong> 12 per hectare (ha) to a high <strong>of</strong> 500/ha. Variability across individual census plots was evengreater, ranging from 0 per ha to over 4000/ha. Several factors influence this variability. 1) Localrecruitment tracks variation in local seed production. 2) Tidal elevation and hydrological conditionsinfluence <strong>the</strong> spatial pattern <strong>of</strong> seed deposition and retention, and this is reflected in micro-spatialrecruitment patterns. 3) Substrate characteristics independent <strong>of</strong> elevation and hydrology significantlyinfluence seedling survivorship and growth. These results have broad implications for <strong>the</strong>management <strong>of</strong> invasive Spartina populations. Poor recruitment years afford windows <strong>of</strong> opportunityfor effective control, but could equally lead to complacency and an inadequate response duringrecruitment pulses. The strong relationship between local seed production and local recruitmentsuggests that control strategies that do not explicitly account for inter-regional dispersal can still besuccessful over <strong>the</strong> short-term, even if long-term management requires an explicit understanding <strong>of</strong>regional dispersal pathways. Finally, <strong>the</strong> strong differences in recruitment and growth patternscaused by substrate differences may allow <strong>the</strong> categorization <strong>of</strong> sites by recruitment risk.Keywords: heterogeneity, invasion, spread, wetlandINTRODUCTIONSpartina alterniflora has spread over 60 square kilometers(km 2 ) <strong>of</strong> <strong>the</strong> approximately 190 km 2 <strong>of</strong> intertidal habitat in WillapaBay, Washington (Civille et al., 2005; Civille et al. 2010).This large-scale invasion threatens to disrupt many importantecosystem services such as habitat for oysters and migratorybirds, nutrient cycling, and storm water run<strong>of</strong>f control (Sayce1988). A consortium <strong>of</strong> local residents, state agencies and <strong>the</strong>Federal government is currently attempting to manage <strong>the</strong> invasionwith <strong>the</strong> ultimate goal <strong>of</strong> eradicating S. alterniflora from<strong>the</strong> estuary.There have been few attempts to comprehensively managesuch a large plant invasion. Property ownership, funding allocations,and <strong>the</strong> idiosyncratic interests <strong>of</strong> stakeholders usuallyforce management to occur on an ad hoc and project-specificbasis. However, given <strong>the</strong> large extent <strong>of</strong> many invasions <strong>the</strong>reis a growing appreciation for <strong>the</strong> need to manage invasiveplants at explicitly landscape scales (With 2002).The management <strong>of</strong> large-scale invasions takes time.Some invasions will likely require ongoing management,while <strong>the</strong> eradication <strong>of</strong> o<strong>the</strong>rs will take years. In <strong>the</strong> case <strong>of</strong>S. alterniflora in Willapa Bay, coordinated control activitiesbegan over 10 years ago.The effective management <strong>of</strong> landscape-scale invasions,<strong>the</strong>refore, requires an understanding <strong>of</strong> how basic properties<strong>of</strong> invasions vary across space and time. Here we report thattwo basic components <strong>of</strong> S. alterniflora demography, seedproduction and seedling recruitment, vary considerablyacross different habitats in <strong>the</strong> bay and across years. Wediscuss <strong>the</strong> consequences <strong>of</strong> this variability for <strong>the</strong> management<strong>of</strong> S. alterniflora in Willapa Bay.METHODSSeedling RecruitmentTo test <strong>the</strong> degree <strong>of</strong> spatial and temporal variation inseedling recruitment we established 44 permanent plots ontidal mudflat that was free <strong>of</strong> S. alterniflora. Plots covered<strong>the</strong> full spatial extent <strong>of</strong> <strong>the</strong> estuary and spanned a range <strong>of</strong>substrate characteristics, distance to established S. alterniflora,and tidal elevation. Plots were 15 m wide andvaried in length depending on local site characteristics. Werecorded <strong>the</strong> location <strong>of</strong> each plot using GPS equipment(Trimble Pathfinder Pro XRS). Beginning in June 2001 we-87-