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 ManagementTime to eradication (years)30252015105*A.Yearly effort200300600Area occupied1400012000100008000600040002000Seeds suppressed after year 150% seed suppression50% seed suppression100% seed suppression0Upper to lower Lower to upper End onApproach direction00 5 10 15 20 25 30 35 40 45Time (years)14000Relative cost <strong>of</strong> eradication(m 2 controlled)50004000300020001000*B.Yearly effort200300600Area occupied12000100008000600040002000Seeds suppressed after year 200% seed suppression50% seed suppression100% seed suppression00 5 10 15 20 25 30 35 40 45Time (years)0Upper to lower Lower to upper End onApproach directionFig. 3. 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 in <strong>the</strong> case <strong>of</strong> an oblong meadowadjacent to <strong>the</strong> native marsh using three approach directions. Plots showmean and standard error <strong>of</strong> 10 replicate trials for each strategy and yearlyeffort combination.When <strong>the</strong> mudflat was already dotted with patches <strong>of</strong>Spartina, seed suppression only slightly reduced <strong>the</strong> rate <strong>of</strong>invasion and it took many years to see an effect. Seed suppressionwas somewhat more effective in <strong>the</strong> meadow-onlycase. However, in all cases, <strong>the</strong> area occupied by Spartinacontinued to increase.CONCLUSIONSIn a situation where only a fraction <strong>of</strong> <strong>the</strong> invasion canbe controlled each year, strategic placement <strong>of</strong> controltreatments can greatly reduce <strong>the</strong> time and effort needed toeradicate Spartina. Control is more effective if it first targetsoutlying clones in <strong>the</strong> lower tide zone and <strong>the</strong>n moves up <strong>the</strong>tidal gradient to target <strong>the</strong> larger meadow. These results areconsistent with expectations based on <strong>the</strong> more generalizedstudy by Moody and Mack (1988); <strong>the</strong>y also agree with aArea occupied12000100008000600040002000Meadow only infestationSeeds suppressed after year 150% seed suppression50% seed suppression100% seed suppression00 5 10 15 20 25 30 35 40 45Time (years)Fig. 4. Growth <strong>of</strong> simulated S. alterniflora populations for which seedswere suppressed at levels <strong>of</strong> 0%, 50% and 100% every year for a 20 yearperiod. Seed suppression treatment was applied to <strong>the</strong> invading populationafter year 15 in (A) and after year 20 in (B). In (C) seed suppression wasapplied to a 15-year-old meadow surrounded by an uninfested mudflat.model <strong>of</strong> Spartina control by Taylor et al. (this volume). Theoutliers-first approach eliminates Spartina in <strong>the</strong> areas wherevegetative spread is greatest. In addition, it avoids openingup a new growing edge in <strong>the</strong> upper intertidal zone and also- 205 -