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 ManagementSHOREBIRD USE OF SPARTINA-AFFECTED TIDELANDS –CAN WE ACHIEVE FUNCTIONALHABITAT POST-CONTROL?K. PATTEN AND C. O’CASEYWashington State University, Long Beach Research and Extension Unit.2907 Pioneer Road, Long Beach, WA 98631; pattenk@wsu.edu; ocasey@wsu.eduOne <strong>of</strong> <strong>the</strong> major threats <strong>of</strong> invasive Spartina is <strong>the</strong> loss <strong>of</strong> shorebird foraging habitat. The AudubonSociety lists <strong>the</strong> invasion <strong>of</strong> Willapa Bay (WB) by Spartina as <strong>the</strong> second most critical threat toshorebird habitat in <strong>the</strong> nation. Studies were conducted on how large-scale mechanical and chemicalcontrol efforts affect shorebird and waterfowl usage <strong>of</strong> Spartina meadows in WB. Food abundanceand accessibility, shorebird, waterfowl and bird <strong>of</strong> prey density, and bird behaviour were evaluatedon treated meadows and compared to untreated meadows and bare mudflats. Based on long-termpoint counts and remote video monitoring, <strong>the</strong>re was no bird usage (<strong>of</strong> any species) in Spartinameadows. Highest food abundance and accessibility was found in mudflats. Waterfowl and birds <strong>of</strong>prey preferred herbicide-treated sites over <strong>the</strong> tilled and mudflat sites. Shorebirds preferred mudflatsfollowed by tilling over that <strong>of</strong> herbicide-treated sites. Bird behaviour (feeding or resting) wasvariable and dependent on species, time <strong>of</strong> year and treatment. Although tilling appears to beinitially effective in expediting restoration for shorebirds, it is too costly to implement on a largescale. The most significant long-term concern for shorebird usage is <strong>the</strong> Spartina-induced increasein tidal elevations on <strong>the</strong>se meadows (>35 cm). Less than 20% <strong>of</strong> <strong>the</strong> gain in elevation wasattributable to sediment accretion; <strong>the</strong> rest was root biomass. Due to <strong>the</strong> change in bathymetry, onceSpartina was controlled at <strong>the</strong>se sites, native salt marsh plants (Salicornia, Triglochin and Spergula)immediately invaded more than 400 meters out into what were previously intertidal mudflats. Thispotentially permanent large scale conversion <strong>of</strong> mudflat to salt marsh will have pr<strong>of</strong>oundimplications for shorebird habitat. Some potential remedies will be suggested.Keywords: restoration, Dunlin, Western Sandpiper, birds <strong>of</strong> prey, native salt marsh, Willapa Bay,SpartinaINTRODUCTIONSpartina has colonized and eliminated much <strong>of</strong> <strong>the</strong>upper portion <strong>of</strong> <strong>the</strong> wide expansive intertidal mudflats <strong>of</strong>Willapa Bay. Species most threatened by Spartina are likelyto be <strong>the</strong> thirty species <strong>of</strong> shorebirds that rely upon WillapaBay’s 47,000 acres <strong>of</strong> tideland for food and shelter duringannual migrations to and from <strong>the</strong> Arctic. Much <strong>of</strong> <strong>the</strong> mostpreferredshorebird habitat <strong>of</strong> Willapa Bay, sheltered uppertidal mudflats in <strong>the</strong> sou<strong>the</strong>rn bay, has been displaced bySpartina. Peak winter and spring shorebird usage in sections<strong>of</strong> <strong>the</strong> bay has declined over 60 percent in <strong>the</strong> past decade asSpartina meadows have replaced <strong>the</strong> tidal mudflats (Jaques2002). Census studies on shorebird abundance in WillapaBay in 1991-1995, prior to <strong>the</strong> major increase in Spartinagrowth, found that 44 percent <strong>of</strong> <strong>the</strong> total bird usage waswithin two areas, <strong>the</strong> Bear River/Lewis Unit – South WillapaBay region and <strong>the</strong> Willapa River area (Buchanan andEvenson 1997). These two areas have become almostcontiguous Spartina meadows. Because <strong>of</strong> <strong>the</strong> loss <strong>of</strong> habitatcaused by Spartina, <strong>the</strong> Audubon Society has listed WillapaBay as <strong>the</strong> second most endangered shorebird habitat in <strong>the</strong>United States (Audubon 2004).The ongoing chemical and mechanical control effort is<strong>the</strong> first step in recovering that habitat. The ultimate goal <strong>of</strong>a control effort should not be limited to control, but alsoneeds to consider restoration <strong>of</strong> <strong>the</strong> affected habitat formaximal ecological value. Little information exists to dateon how <strong>the</strong> numerous chemical and mechanical controlmethods being used to manage Spartina have expeditedhabitat restoration. The long-term ecological impact <strong>of</strong>invasive Spartina on shorebirds in England has beenrecently reviewed by Lacambra et al. 2004. They concludethat a return <strong>of</strong> shorebirds to English estuaries followingSpartina removal is not axiomatic. In Washington, where<strong>the</strong>re have been long-term control efforts by variousagencies, use <strong>of</strong> <strong>the</strong> affected tideflats by shorebirds andwaterfowl increases dramatically within several years <strong>of</strong>removal <strong>of</strong> invasive Spartina from mudflats (Patten andO’Casey 2007). The objective <strong>of</strong> this study was to assess <strong>the</strong>likelihood and <strong>the</strong> limiting factors involved in achievingfunctional habitat at Spartina-affected mudflats after control.METHODSSite information:Direct and indirect assessments were made <strong>of</strong> shorebird,waterfowl and birds <strong>of</strong> prey usage <strong>of</strong> Spartina meadows(treated and untreated) in comparison to bare mudflats.These assessments were made for five sites: bare mudflat,- 207 -