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 SpartinaA. Meadow first B. Outlying clones firstTime to eradication (years)403530252015105A.Yearly effort5001000150001 2Meadow firstOutliers firstFig. 1 Meadow-first (left) and outlier-first (right) approaches to controllingSpartina. Shown is <strong>the</strong> remaining Spartina at times 22, 25 and 30years. Removal <strong>of</strong> 500 occupied squares each year began on year 20.Fig. 1. Meadow-first (left) and outlier-first (right) approaches to controllingSpartina. Shown is <strong>the</strong> remaining Spartina (black areas) at times 2, 5,and 10 years. Removal <strong>of</strong> 500 occupied squares each year began on year20.(native marsh), (2) approaching from <strong>the</strong> upper tide zone andmoving toward <strong>the</strong> lower tide zone, and (3) approachingfrom one end <strong>of</strong> <strong>the</strong> meadow and moving parallel to shore to<strong>the</strong> o<strong>the</strong>r end. Each year a fixed amount <strong>of</strong> Spartina wasremoved.Is seed suppression effective?Seed suppression, through mowing or low concentrationherbicide spray, can be carried out at a much lower cost thancompletely killing <strong>the</strong> plants. To test <strong>the</strong> effectiveness <strong>of</strong>seed suppression, three start conditions were used (a 15-year-old invasion, a 20-year-old invasion, and a 15-year-oldmeadow without outliers). Seeds were suppressed at threelevels: 0%, 50%, or 100%. In each case, seeds weresuppressed every year, while established plants wereallowed to spread vegetatively.RESULTSThe outliers-first strategy achieved eradication substantiallysooner and with less total effort than <strong>the</strong> meadow firstTotal cost (m 2 controlled)20000180001600014000120001000080006000strategy. The difference was especially great when <strong>the</strong> availableyearly effort was low (Fig. 2).For oblong meadows, Spartina was eliminated fastest,and with <strong>the</strong> least total effort, when control work was appliedfirst to one end <strong>of</strong> <strong>the</strong> meadow and <strong>the</strong>n moved across<strong>the</strong> meadow in subsequent years. Slightly less effective was<strong>the</strong> approach <strong>of</strong> moving from lower to upper intertidal zone.The least effective strategy was to control from <strong>the</strong> uppertide zone, because this opened up an additional growingedge. Again, <strong>the</strong> largest difference in strategy effectivenesswas found when <strong>the</strong> yearly control effort was low.B.Yearly effort500100015001 2Meadow firstOutliers firstFig. 2. Comparison <strong>of</strong> <strong>the</strong> amount <strong>of</strong> time (A) and amount <strong>of</strong> effort (B)needed to eradicate a Spartina population using a meadow-first or outliersfirstapproach. Plots show mean and standard error <strong>of</strong> 10 replicate trials foreach strategy and yearly effort combination.- 204 -