Proceedings of the Third International Conference on Invasive ...

Chapter 4: Spartina Control and Management<strong>Proceedings</strong> <strong>of</strong> <strong>the</strong> <strong>Third</strong> <strong>International</strong> <strong>Conference</strong> on Invasive SpartinaCordgrasses are capable <strong>of</strong> reproducing by vegetativefragments (Landin 1990; Stiller & Denton 1995; Daehler &Strong 1996; Sayce et al. 1997; Patten & Stenvall 2002).Disturbances to Spartina’s extensive below-groundstructure, such as those caused by rototilling, couldpotentially produce rhizome fragments. While invasivecordgrasses are known for <strong>the</strong> resiliency <strong>of</strong> <strong>the</strong>ir rhizomes(Reeder & Hacker 2004; Patten 2003), <strong>the</strong> viability <strong>of</strong>mechanically produced rhizome fragments and <strong>the</strong>ir role indispersal has not been closely examined (i.e., evidence isanecdotal) (Randall & Milne unpublished; Pfauth et al.2003).Research has focused on <strong>the</strong> sexual reproductivecapacity <strong>of</strong> Spartina (Broome et al. 1974; Sayce 1988;Daehler 1996; Plyer & Proseus 1996; Sayce & Dumbauld1997; Daehler 1999; Davis et al. 2004), ra<strong>the</strong>r than asexualproduction, since this is considered to be <strong>the</strong> primary source<strong>of</strong> new clones (Stiller and Denton 1995; Sayce et al. 1997).Seed as well as rhizome fragments could disperse Spartinalocally or across long distances if carried by tides and oceancurrents (Daehler and Strong 1996; Stenvall and Patten2002, Pfauth et al. 2003). Repeated reports <strong>of</strong> Spartinafragments washing ashore near Ft. Stevens (near Astoria,Oregon) suggest transport <strong>of</strong> wrack from nearby WillapaBay, Washington (Grevstad and Graves pers. comm.;Howard et al. unpublished report 2004). Huiskes et al.(1995) collected seeds <strong>of</strong> S. anglica in floating and standingnets in a tidal salt marsh in <strong>the</strong> Ne<strong>the</strong>rlands. Eighty-eightpercent <strong>of</strong> <strong>the</strong> seeds collected were captured in floating nets,indicating that tidal transport <strong>of</strong> seed was primarily on <strong>the</strong>water surface ra<strong>the</strong>r than along <strong>the</strong> sediment. In an earlierstudy in <strong>the</strong> same location, Koutsaal et al. (1987) releaseddyed sunflower seeds on outgoing and incoming tides totrack tidal movement <strong>of</strong> seeds in <strong>the</strong> salt marsh. Seeds werefound as far as 45 km away within one week <strong>of</strong> release. Thefinal location <strong>of</strong> seeds was determined by <strong>the</strong> wind velocityand direction as well as by tidal currents.Oregon’s Spartina Response Plan (Pfauth et al. 2003)was developed to prevent <strong>the</strong> introduction and spread <strong>of</strong> anySpartina species in Oregon. Areas requiring fur<strong>the</strong>r researchwere identified , including an investigation <strong>of</strong> <strong>the</strong> likelihood<strong>of</strong> <strong>the</strong> ability <strong>of</strong> Spartina fragments to resprout and anexamination <strong>of</strong> potential transport <strong>of</strong> propagules via oceancurrents.Preliminary results from three studies addressing <strong>the</strong>seresearch needs are presented here. First, a field study wasperformed to assess <strong>the</strong> production <strong>of</strong> Spartina fragments byrototillng. Secondly, a greenhouse experiment examined <strong>the</strong>ability <strong>of</strong> rhizome fragments to resprout. <strong>Third</strong>ly,preliminary data from a propagule dispersal study arepresented.MATERIALS AND METHODSField Study <strong>of</strong> Rototilling EffectsSamples were collected on January 16, 2004 along <strong>the</strong>south shore <strong>of</strong> <strong>the</strong> Naselle River, which flows into <strong>the</strong>sou<strong>the</strong>astern end <strong>of</strong> Willapa Bay, Washington. Staff <strong>of</strong>Willapa National Wildlife Refuge (NWR) was mechanicallytreating <strong>the</strong> site between high tides with a rototillingattachment towed by a Wilco amphibious vehicle. TheWilco operator made single passes within a solid meadow <strong>of</strong>Spartina alterniflora and tilled to a depth <strong>of</strong> approximately15 cm. Immediately following rototilling, three quadrats(0.25 m 2 ) were randomly chosen approximately 30 m apartand excavated to a depth <strong>of</strong> 10 cm. Excavated material wasrinsed clean and all fragments were measured for culmlength, number <strong>of</strong> culms, and rhizome diameter and length.Fragments were divided into two rhizome sizes, small andlarge, by <strong>the</strong> median value for rhizome length. The meanvalue <strong>of</strong> each <strong>of</strong> <strong>the</strong>se rhizome class sizes was <strong>the</strong>n roundedto <strong>the</strong> nearest half centimeter and used as <strong>the</strong> experimentalrhizome sizes for <strong>the</strong> greenhouse study <strong>of</strong> fragment viability.Greenhouse StudyA 2x3x3 factorial design was used to evaluatesurvivorship <strong>of</strong> S. alterniflora fragments. Factors were initialrhizome size (large or small), immersion duration (3, 8 or 15days), and salinity (freshwater, 15 ppt, or 35 ppt). Samplesfrom two populations were compared. Rhizome fragmentsfrom San Francisco were collected on March 26, 2004 from<strong>the</strong> shoreline <strong>of</strong> Elsie Roemer Bird Sanctuary on AlamedaIsland (San Francisco Bay, California). Two to threesamples were dug from each <strong>of</strong> ten clones. Samples fromWillapa Bay were collected on April 5, 2004 from fourriverbank locations (two along <strong>the</strong> Naselle River, one on <strong>the</strong>Niawiakum River, and one on <strong>the</strong> Palix River). Seven to tensamples were dug from each location. Sampling locationshad not been subjected to any previous chemical ormechanical treatment.Samples were returned to Portland State University andrinsed clean <strong>of</strong> all mud and organic matter within two days<strong>of</strong> field collection. Within 20 minutes <strong>of</strong> rinsing, fragmentswere cut to fit one <strong>of</strong> two rhizome class sizes (large ~7.5 cmor small ~2.5 cm). Fragments were <strong>the</strong>n placed in openplastic tubs containing water at 0 ppt, 15 ppt or 35 ppt(Instant Ocean ® aquarium salts). Tubs were maintainedunder ambient greenhouse conditions. Salinityconcentrations were monitored daily and adjusted as needed.After floating for a period <strong>of</strong> 3, 8 or 15 days (referred to asimmersion duration), each fragment was measured todetermine rhizome length, rhizome diameter, number <strong>of</strong>attached culms and culm length. The 8-day immersionduration was eliminated from <strong>the</strong> San Francisco treatmentdesign due to limited plant material. Fragments were <strong>the</strong>nindividually potted in six-inch diameter pots with a sterile- 256 -