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 4: Spartina Control and ManagementDistance from native marsh (m)10008006004002000Salicornia virginicaTriglochin maritimumCotula coronopifoliaSpergularia canadensisTilled 2001/2002Sprayed 2002/2003Fig. 3. The mean maximum distance from <strong>the</strong> shoreline that salt marshspecies were located after Spartina was controlled. Data were collected June2004.Standard soil science methodology was used to determineporosity, bulk density, and <strong>the</strong> core sample composition. Bywashing <strong>the</strong> trench wall it was possible to identify allgrowing point meristems and record <strong>the</strong>ir points <strong>of</strong> origin(depth). The change in depth from <strong>the</strong> first occurringmeristem to <strong>the</strong> current growing points over <strong>the</strong> 8-to-10-yearperiod this meadow had been growing was assumed to be achange in tidal elevation resulting from Spartina-inducedaccretion. Data on vascular plant density (#/m 2 ) by specieswere collected in June 2004 from multiple transects from <strong>the</strong>native marsh line out to 500 m through each treatment site.RESULTSShorebird foragingBased on visual and remote observation data during <strong>the</strong>time course <strong>of</strong> this study, none <strong>of</strong> <strong>the</strong> Spartina controlmethods resulted in shorebird usage comparable to <strong>the</strong> baremudflats (Figures 1 & 2). Flux density <strong>of</strong> shorebirds duringwinter and spring <strong>of</strong> 2003 was higher in <strong>the</strong> bare mudflatthan in <strong>the</strong> tilled areas based on remote sensing (Figure 1),but comparable between <strong>the</strong> sites based on visualobservations (Figure 2). Flux densities <strong>of</strong> shorebirds on <strong>the</strong>tilled site were higher than <strong>the</strong> sprayed or spray-mowed site(Figures 1 & 2). During 480 hours <strong>of</strong> video recordings, noshorebirds were ever observed at <strong>the</strong> Spartina meadow site.Shorebirds (Western sandpipers) were only noted once over14 visual observations in <strong>the</strong> Spartina meadow, and <strong>the</strong>yfloated in on a Spartina wrack. From a behavioralperspective, it appeared that <strong>the</strong> tilled site had <strong>the</strong> lowestpercentage <strong>of</strong> skittish feeding and <strong>the</strong> bare mudflat <strong>the</strong>lowest percentage <strong>of</strong> resting (data not shown).Based on short-term comparisons in shorebirdfootprints, fecal droppings and beak probe densities, <strong>the</strong>rewere major differences in shorebird microsite habitatpreferences (Table 1). All types <strong>of</strong> dead Spartina stubble orlive Spartina stems drastically interfered with shorebirdforaging. For three locations within Porter Point, <strong>the</strong>re wasalmost no evidence <strong>of</strong> any shorebird usage where <strong>the</strong>re wasTable 1. Shorebird usage <strong>of</strong> Spartina habitat at Porter Point based onfootprint, fecal dropping and beak print densities as a function <strong>of</strong>accessibility.*General sitelocationSprayedmeadow, 80 mfrom nativemarsh; stubble25-50cm highEdge <strong>of</strong> sprayedmeadowadjacent to baremudflat, 80 mfrom nativemarsh; stubble25 to 50 cm highTilled strips inbetween sprayedSpartina, 1000’from nativemarsh; stubblewas mowed at25 cm heightShorebirdaccessdescriptions Footprints*Live SpartinacanopyDensity (#/0.25m 2 )**FecaldroppingsBeakprints0 0 0.8±0.4Dead stubble 50±50 0.9±0.4 29±4ExposedmudflatLive Spartinacanopy134±11 1.8±0.3 68±100.2±0.1 0 3±2Dead stubble 8±2 6±0.3 13±4Exposedmudflat35±5 0.8±0.2 47±5Dead stubble 87±12 0.5±0.2 25±4Exposedmudflat130±19 1.3±0.3 76±9*Data collected 5-13-03; 5 replications per habitat per location, with 5subsample counts per replication. For each replication comparative habitats(treatments) were located with 20 feet <strong>of</strong> each o<strong>the</strong>r.** mean ± standard errorlive Spartina growing. The bare mud and dead stubblelocations usually displayed high counts <strong>of</strong> beak and footprints and fecal droppings. Bare mud usually had twice asmuch shorebird usage as dead stubble.Soil and plant dataSpartina meadows rapidly began a transition to nativemiddle to upper salt marsh as soon as <strong>the</strong> Spartina was killed(Figure 3). Within two years <strong>of</strong> treatment, four salt marshplant species extended 400 m out from <strong>the</strong>ir native marshhabitat. At this particular site, <strong>the</strong> transition from mudflat toSpartina meadow to salt marsh has all occurred with tenyears and represents a permanent loss <strong>of</strong> hundreds <strong>of</strong>hectares <strong>of</strong> prime shorebird habitat. In an analysis <strong>of</strong> soilparameters at this meadow (data not shown), we have found<strong>the</strong> dead Spartina root mat extends down to 35 cm, with <strong>the</strong>bulk <strong>of</strong> <strong>the</strong> soil volume being comprised <strong>of</strong> organic matterand pore space. Only 15% <strong>of</strong> <strong>the</strong> elevation rise could beaccounted for by sediment accretion.DISCUSSIONRestoring mudflats back to <strong>the</strong>ir original form andfunction will be extremely difficult. Even with tilling andseveral years <strong>of</strong> follow-up chemical control, as well as- 209 -