Rapid Invasion of a Great Lakes Coastal Wetland by Non ... - BioOne

J. Great Lakes Res. 33 (Special Issue 3):269–279Internat. Assoc. Great Lakes Res., 2007Rapid Invasion of a Great Lakes Coastal Wetland byNon-native Phragmites australis and TyphaMirela G. Tulbure * , Carol A. Johnston, and Donald L. AugerDepartment of Biology and Microbiology, Box 2140DSouth Dakota State UniversityBrookings, South Dakota 57007ABSTRACT. Great Lakes coastal wetlands are subject to water level fluctuations that promote themaintenance of coastal wetlands. Point au Sauble, a Green Bay coastal wetland, was an open waterlagoon as of 1999, but became entirely vegetated as Lake Michigan experienced a prolonged period ofbelow-average water levels. Repeat visits in 2001 and 2004 documented a dramatic change in emergentwetland vegetation communities. In 2001 non-native Phragmites and Typha were present but their coverwas sparse; in 2004 half of the transect was covered by a 3 m tall, invasive Phragmites and non-nativeTypha community. Percent similarity between plant species present in 2001 versus 2004 was approximately19% (Jaccard’s coefficient), indicating dramatic changes in species composition that took place inonly 3 years. The height of the dominant herbaceous plants and coverage by invasive species were significantlyhigher in 2004 than they were in 2001. However, floristic quality index and coefficient of conservatismwere greater in 2004 than 2001. Cover by plant litter did not differ between 2001 and 2004. Theprolonged period of below-average water levels between 1999 and early 2004 exposed unvegetatedlagoon bottoms as mud flats, which provided substrate for new plant colonization and created conditionsconducive to colonization by invasive taxa. PCR/RFLP analysis revealed that Phragmites from Point auSauble belongs to the more aggressive, introduced genotype. It displaces native vegetation and is tolerantof a wide range of water depth. Therefore it may disrupt the natural cycles of vegetation replacement thatoccur under native plant communities in healthy Great Lakes coastal wetlands.Phragmites australis, Great Lakes coastal wetlands, invasion, vegetation replace-INDEX WORDS:ment.INTRODUCTIONPhragmites australis (Cav.) Trin. ex Steud. (hereafterPhragmites) was historically infrequent inU.S. wetlands, but has expanded tremendously withthe introduction of Eurasian genotypes (Blossey2002). Phragmites is a cryptic invasive species(sensu Richardson et al. 2000) in the U.S., withboth native and non-native genotypes that differ intheir aggressiveness (Galatowitsch et al. 1999,Saltonstall 2002). Phragmites occurs throughout theentire U. S. and southern Canada in freshwater andbrackish to saline wetlands (Chambers et al. 1999),prevailing especially in tidal wetlands along the Atlanticcoast. However, recent expansion of Phragmitesoccurrence in the Great Lakes region has beenobserved (McNabb and Batterson 1991, Lynch andSaltonstall 2002, Wilcox et al. 2003). Phragmites is* Corresponding author. E-mail: Mirela.Tulbure@sdstate.educonsidered an indicator of wetland disturbance becauseit forms monospecific stands that displace nativespecies, reducing plant biodiversity and thehabitat available for associated fauna (Marks et al.1994, Chambers et al. 1999, Meyerson et al. 2000).Variations in climatic conditions (Minchinton2002), alteration of the hydrologic regime (Bart andHartman 2000, 2003), changes in land use (Lynchand Saltonstall 2002), and nutrient increase (Bertnesset al. 2002, Minchinton and Bertness 2003)may be responsible for Phragmites expansion.Saltonstall’s (2002) genetic study suggested that theinvasive haplotype M, introduced from Eurasia, isresponsible for the observed expansion. However,in areas where native and non-native populationsare sympatric, care should be taken to identify theorigins of populations subject to management. Thisis particularly important in the Midwest, where nativepopulations still thrive at many sites (Salton-269

270 Tulbure et al.stall 2003). For example, Lynch and Saltonstall(2002) documented the expansion of the nativePhragmites genotype at a Lake Superior wetland.Coastal wetlands along Lake Michigan’s GreenBay are known to be dynamic, experiencing vastchanges in the extent of emergent vegetation aswater levels fluctuate over decadal cycles (Epsteinet al. 2002). Emergent plants germinate on lakebedexposed during low-water years, persist during averagewater level conditions, and decline after a seriesof high-water years, the marshes reverting toopen water (Harris et al. 1977, Bosley 1978). Typhais commonly mentioned as a key genus involved inthese vegetation cycles, but Phragmites is not.Data about plant species in wetlands of GreenBay on Lake Michigan were collected by the GreatLakes Environmental Indicators project (GLEI)during mid-June 2001, when the water level ofLake Michigan was 54 cm below average (USCOE2006). During a repeat visit to wetlands of theGreen Bay area three years later, large stands ofPhragmites were observed in the Point au Saublelagoon where little or no Phragmites had occurredin 2001. During the interim between the two sampledates, Lake Michigan experienced a prolonged periodof below-average water levels.The goal of this paper is to document the rapidchange in wetland vegetation of a Green Bay lagoonover a 3-year period associated with the rapidinvasion of Phragmites. Specific objectives were tocompare vegetation structure and community compositionbefore and after Phragmites invasion, evaluateedaphic conditions within areas that were andwere not colonized by Phragmites, and determine ifthe expanding areas of Phragmites are of the invasivegenotype.METHODSStudy AreaThe 81 ha Point Au Sauble lagoon is located onthe eastern shore of Green Bay, 10 km northeast ofthe city of Green Bay in Brown County, Wisconsin.It is currently owned by the University of Wisconsin-GreenBay and has been preserved in a naturalstate by The Nature Conservancy and duck huntinggroups for many decades (UWGB Cofrin Center forBiodiversity 2004). Point au Sauble is covered by avariety of plant communities such as floodplain forest,shrub-carr, sedge meadow, emergent aquatic,and Great Lakes beach, but the area sampled wasdescribed by earlier accounts as an open-water lagoon(Epstein et al. 2002). Although wetlands arecommon along the western shore of Green Bay,Point au Sauble is one of only a few coastal wetlandson the eastern shore of Green Bay.Abiotic Data CollectionThe soils at each plot were examined to a depthof 30 cm below the litter layer using a soil probe,and assigned to one of the following broad categories:organic, sand, silt, or clay. “Organic” soilswere those composed of organic soil material (peator muck) in a histic epipedon (Soil Survey Staff1999); undecomposed plant litter overlying the soilsurface was excluded when making this determination.Only the surface 30 cm was considered. Wedid not attempt to discern if soils in the organic categorywere true histosols. The texture of mineralsoils (i.e., sand, silt, clay) was determined by feelusing standard field methods (Soil Survey Staff1951). The hand texturing was done by co-authorJohnston, who is a professional soil scientist certifiedby the American Society of Agronomy and experiencedat wetland soil characterization usingboth field and laboratory methods. Soil texture byplot in 2004 varied from silty to organic soils(Table 1).Lake level data recorded every 6 minutes atGreen Bay, Wisconsin (Station ID 9087079) wereobtained from the National Oceanic and AtmosphericAdministration (NOAA 2006), and were averagedover the time period from 0800 hours to1800 hours local standard time to determine averagewater levels on the days sampled. Monthly averageand monthly minimum lake levels, based ondata collected from 1918-2005, were obtained fromthe U.S. Army Corps of Engineers (USCOE 2006).Vegetation SamplingThe Point au Sauble lagoon was initially sampledon 19 Jun 01 as part of GLEI, a large, multi-investigatorproject designed to identify biotic indicatorsof human disturbance (Danz et al. 2005). The GLEIvegetation sampling protocol (Bourdaghs et al.2006, Johnston et al. 2007 this issue) was used inboth 2001 and 2004, when a repeat visit to the lagoonwas made on 7 Jul 04. A north-south trendingtransect was placed across the lagoon at Point auSauble, and 11 sampling locations (plots) were establishedat approximately 20 m intervals along thetransect (Fig. 1). At each sampling location, a 1 m 2plot was established and its geographic coordinates

Phragmites australis Invasion 271TABLE 1.plot.Point au Sauble wetland conditions byWater depthVariable/(cm)Substrate typePlot number 2001 2004 In 2004Plot 1 (at the North endof the peninsula) 10 26 SiltPlot 2 14 26 SiltPlot 3 15 27 SiltPlot 4 9 27 SiltPlot 5 8 20 SiltPlot 6 4 20 OrganicPlot 7 11 18 OrganicPlot 8 8 37 OrganicPlot 9 9 33 OrganicPlot 10 0 5 SandPlot 11 (at the South endof the peninsula) 0 0 Organicrecorded using a hand held Garmin GPSMAP 76unit (Garmin International Inc., Olathe, KS). Allvascular plant species observed within the plot wereidentified to the species or genus level; there wereno unidentified plants present. All GLEI projectfield crews met every summer and conducted fieldwork together to ensure that species identificationand the visual cover estimates were consistent betweenfield crews. The non-native cattail Typha angustifoliaand its hybrid Typha × glauca could notbe reliably distinguished because of the paucity offruiting heads, and were combined into a singleclass called “invasive Typha.” Sagittaria latifoliaWilld. was identified as Sagittaria sp. by the GLEIfield crew in 2001, but because we found Sagittarialatifolia in 2004 at the same plots, we felt confidentto call Sagittaria latifolia the one identified in2001. Cover class was estimated visually for eachtaxon using modified Braun-Blanquet cover classranges: < 1%, 1 to < 5%, 5 to < 25%, 25 to < 50%,50 to < 75%, and 75 to 100% (ASTM 1997). Summedindividual taxa percent cover in a quadratcould exceed 100% because canopies of differentspecies overlap one another. Cover estimates werealso recorded for herbaceous litter, open water (definedas water open to the sun in patches 10 cm ×10 cm or greater), and standing water (defined asany water above the soil surface, including waterbelow thatch and green vegetation). Water depthand canopy height were recorded at each samplinglocation. The height of the dominant herbaceousplant was determined as the average height of thedominant herbaceous plant per plot, measured toFIG. 1. Aerial photo of the Point au Sauble peninsula (BrownCounty, Wisconsin) taken on 4 Oct 99. Circles indicate silty substrates,triangles and diamond indicate organic and sand substrates,respectively. Image courtesy of the U.S. Geological Survey.

272 Tulbure et al.the nearest 5 cm. If a plant species could not beidentified in the field, it was collected, pressed, andidentified in the lab. Plant nomenclature conventionsin this study follow the Interagency TaxonomicInformation System (ITIS, http://www.itis.usda.gov), a national standardized plant nomenclaturesource. Prior to data analyses, cover classeswere converted to the midpoint percent cover ofeach class (e.g., 37.5% for the 50 to < 75% class).The average of midpoint percent cover was computedfor each plant species based on all plots in thetransect. Geographic coordinates of the initial 11sampling locations were uploaded into a GarminGPS unit, and used to return to the same locationson 7 Jul 04.Genetic Analysis of PhragmitesDNA was extracted from dried leaf tissues of oneramet (located in the center of the stand) of thePhragmites stand using Extract-N-Amp (Sigma-Aldrich, St. Louis, MO) according to manufacturer’sdirections. DNA from one ramet was judgedsufficient because all the Phragmites plants appearedto belong to the same clone, and shared morphologicalcharacteristics typical of the non-nativegenotype (Blossey 2002). Generally, in polyclonalreed stands, different clones are morphologicallydistinguishable (Koppitz 1999). Two non-codingchloroplast regions were amplified using the polymerasechain reaction (PCR). Amplification primerpairs used were trn and rbc (Saltonstall 2003). Two20 µL PCR reactions were made from each sample,generally according to the manufacturer’s directions.Instead of 4 µL of template, as recommendedby the manufacturer, it was determined that betterresults were obtained using 1 µL of template. Thedifference was made up by adding 3 µL of a 1:1mixture of the Extract-N-Amp extraction and dilutionreagents. Either 50 ng each of forward and reversetrn primers or 12.5 ng each of rbc primerswere used.The two PCR products were subjected to restrictionenzyme digests to detect restriction fragmentslength polymorphisms (RFLP). Each PCR productwas divided into two 10 µL portions; one was subjectedto restriction digest and the other held as acontrol. From each plant, the rbc PCR product wasdigested using the restriction enzyme HhaI, whichcuts only the non-native genotype, and the trn PCRproduct was digested with RsaI, which cuts only thenative genotype (Saltonstall 2003). Restriction fragmentswere electrophoresed in 2% TAE gel and visualizedwith ethidium bromide using a ChemiDocXRS Imaging Station (BioRAD, Hercules, CA).Data AnalysisSpecies composition similarity was calculated for2001 and 2004 using Jaccard’s similarity index(Greig-Smith 1964). Mean coefficient of conservatism(a numerical score that ranges from 0 to 10,assigned to each plant species in a local flora that reflectsthe likelihood that a species is found in naturalhabitats) and floristic quality index (FQI) valueswere also compared in 2001 versus 2004. FQI iscomputed by multiplying the mean coefficient ofconservatism of the species in a community (C – ) bythe square root of the total number of native species:FQI = C – * √N, C-values used were those assigned forthe state of Wisconsin (Bernthal 2003).Species diversity and evenness were compared in2001 versus 2004. We used Shannon-Weinerspecies diversity index:S∑H′ =− p ln pi−1and Pielou’s J index for evenness: H´ / lnS, where:S is species richness and p i is the relative abundanceof the ith species (Magurran 1988).Water depth and height of the dominant herbaceousplant in 2001 versus 2004 were comparedusing t-tests. Kruskal-Wallis nonparametric testswere used to compare the coverage by open water(defined as water open to the sun in patches 10 cm× 10 cm or greater), coverage by herbaceous litter,coverage by invasive species, and mean Phragmitescover per plot in 2001 versus 2004 (none of thedata sets were normally distributed). A one-wayANOVA followed by Tukey’s HSD comparison testwas used to compare 2004 Phragmites cover onthree different types of soil (i.e., silt, organic, andsand). Simple regression was used to test if therewas an effect of 2004 water depth on Phragmitescover. All tests were conducted at an alpha level of0.05 using the SAS ® 9.1 (SAS Institute 2001).RESULTSDigital orthophotography acquired on 10 Apr 99,when the lake level was 176.3 m (18 cm below average),showed an open water lagoon at Point auSauble (Fig. 1). The lake level dropped precipitouslylater in 1999, and was 27 to 54 cm below averagethroughout Jan 00 to Apr 04 (Fig. 2). Thelake level during the first field data collection on 16ii

Phragmites australis Invasion 273Jun 01 was 176.1 m, ~0.5 m below average. Lakelevel had rebounded to 176.5 m by the second fielddata collection date on 9 Jul 04 (Table 2).During initial vegetation sampling on 19 Jun 01,all 11 sample plots contained emergent wetlandvegetation. By 7 Jul 04 the water levels had reboundedto 176.5 m, mean water depth per plot wassignificantly greater, and mean coverage of openwater patches was lower. Despite the deeper water,all sample plots remained vegetated (Table 2).As of 2001, Sagittaria latifolia Willd. (arrowhead)was the predominant plant (Table 3). Sagittariaoccurred on both silty and sandy substrates.Two annual species, Bidens cernua L. (noddingbeggartick) and Impatiens capensis Meerb. (jewelweed)were also abundant. Bidens occurred towardsthe north edge of the transect, on silty substrates,with standing water as deep as 9 cm, while Impatiensgrew mainly on sandy substrates. Schoenoplectustabernaemontani (Torr.) M.T. Strong(softstem bulrush) was the fourth most abundantspecies with an average cover of 10.2%. InvasiveTypha was present but sparse (2.7% cover). It occurredin plots with sandy substrate, without standingwater. A few stems of Phragmites (cover classof 1 to 5%) were present in only a single plot.In 2004, the wetland was dominated by invasiveTypha and Phragmites (Table 2). Phragmites waspresent in four plots with a cover of 100%. Thesefour plots were located towards the north edge ofthe transect and the substrate was silty. Phragmiteswas also present with lower cover in two other plotswith silty (3% cover) and sandy substrate (37.5%cover). Invasive Typha was present in six plots,with a cover ranging from 60 to 100%. InvasiveTypha did not occur in the plots where Phragmitesoccurred except for the plot where Phragmites hadlow cover of 3%, and Typha generally grew on organicsoil substrates (five out of the six plots werecovered by organic substrate). Ricciocarpus natans,a free-floating liverwort, covered the water surfacebeneath the Phragmites, although it had not beenobserved in 2001. The species with the secondgreatest plant cover in 2001, Bidens cernua, wascompletely absent in 2004. Several other speciesFIG. 2. Monthly mean water levels (MWL) at Green Bay, Lake Michigan, WI from 1999to 2004 (USCOE 2006). Arrows denote dates of aerial photo acquisition and field sampling.

274 Tulbure et al.TABLE 2.P ≤ 0.05)Comparison of Point au Sauble wetland conditions between 2001 and 2004. (** significant atValue in Value in P- Degrees ofVariable 2001 2004 value Statistics freedomSpecies richness 15 29 — — —Mean water depth (cm) 8 22 0.0003 ** t = 5.5 1, 10Mean canopy height (cm) 112 234 0.0002 * t = 5.7 1, 10Mean coverage by herbaceous litter (%) 79 81 0.9611 χ 2 < 0.1 1Mean coverage by open water (%) 16 8 0.0413 * χ 2 = 4.2 1Mean coverage by invasive species per plot (%) 3 84

Phragmites australis Invasion 275TABLE 3. Species present at Point au Sauble wetland in 2001 and 2004 and their C-values(Bernthal 2003).Scientific name C-value Cover in 2001 Cover in 2004Bidens cernua L. 4 23.9 —Calamagrostis canadensis (Michx.) Beauv. 5 — 1.4Carex bebbii Olney ex Fern. 4 — < 0.1Carex hystericina Muhl. ex Willd. 3 — < 0.1Carex lacustris Willd. 6 — < 0.1Cirsium arvense (L.) Scop. * — 0.3Calystegia sepium ssp. sepium (L.) R. Br 2 — < 0.1Cynoglossum officinale L. * — 3.4Eleocharis erythropoda Steud. 3 0.2 < 0.1Epilobium ciliatum Raf. 3 0.2 —Eupatorium perfoliatum L. 6 < 0.1 < 0.1Impatiens capensis Meerb. 2 13.7 1.4Juncus balticus Willd. 5 — < 0.1Leersia oryzoides (L.) Sw. 3 0.3 0.3Lemna minor L. 4 4.8 —Lycopus americanus Muhl. ex W. Bart 4 — < 0.1Lysimachia thyrsiflora L. 7 — 4.8Lythrum salicaria L. * < 0.1 —Phalaris arundinacea L. * 0.3 1.4Phragmites australis (Cav.) Trin. ex Steud. * 0.3 35.5Ranunculus sp. 1.6 —Ricciocarpus natans L. — 16.0Sagittaria latifolia Willd. 3 24.5 4.6Schoenoplectus fluviatilis (Torr.) M.T. Strong 6 — 1.4Schoenoplectus tabernaemontani (K.C. Gmel.) Palla 4 10.2 1.7Solanum dulcamara L. * — < 0.1Sparganium eurycarpum Engelm. ex Gray 5 — < 0.1Taraxacum officinale G.H. Weber ex Wiggers * — < 0.1Typha latifolia L. 1 0.8 —Invasive Typha * 2.7 45.7Urtica dioica L. 1 — 3.4Verbena hastata L. 3 — 1.4Veronica anagallis-aquatica L. 4 — < 0.1* indicates an introduced species that was not assigned a C-value; species identified at genus level werenot assigned any C-values.sponse of wetland plant species to a three-year(1996-1998) water level change in coastal LakeHuron wetlands. In their study, stem density, perplotspecies richness, and Shannon diversity in thewet meadow and transition zones decreased aswater depth increased from 1996 to 1997. An increasein these same measures was noted in 1998with the decrease in water level (Gathman et al.2005).Periods of extremely low water expose unvegetatedlagoon bottoms as mud flats, providing a substratefor new plant colonization. Annuals and otheropportunistic species such as Schoenoplectus tabernamontanirapidly increase in abundance, and aretypically replaced by cattail as the plant communitymatures (Harris et al. 1977, Bosley 1978). From1997 to 2001, the water level dropped 1.25 m inLake Michigan, the largest drop since data recordswere kept (NOAA 2003).Some of the observed species changes at Point auSauble were predictable outcomes of succession asplants colonized the exposed lagoon bottom. Theannual species Bidens cernua and Impatiens capensisdo not grow vigorously and are usually found onexposed sandy or muddy shores (Chadde 1998).Their loss was expected as the site evolved from anewly established community dominated by annualsto a more mature community dominated by

276 Tulbure et al.FIG. 3. PCR/RFLP analysis of non-nativePhragmites population from Point au Sauble wetland.Lanes 1 and 2 contain the rbc primer withthe HhaI digested DNA and undigested DNA,respectively. Lanes 3 and 4 contain the trn primerwith the RsaI digested DNA and undigested DNA,respectively. Lane 5 contains a 100 bp ladder(Promega, Madison, WI). The rbc productdigested and the trn product did not, indicatingthe source DNA was from the invasive genotype.perennials. The decreased cover of Schoenoplectustabernaemontani and Sagittaria latifolia was presumablydue to shading by taller successionalplants.Prior authors have identified the dynamic natureof Point au Sauble and other Green Bay wetlands inresponse to such water level fluctuations (Epstein etal. 2002, UWGB 2004). The difference between ourobserved changes at Point au Sauble and previousreports, which point out the dominance of Typhaspp. as the water level increases (UWGB 2004), isthe dominance of Phragmites. The fact that Phragmitesexpanded so rapidly in only 3 years is a causeof concern. Moreover, Phragmites from Point auSauble was found to belong to the more aggressive,introduced genotype. Therefore it may disrupt thenatural cycles of vegetation replacement that occurunder native plant communities in healthy coastalwetlands.Although there was an increase in species richnessbetween 2001 and 2004, we believe that this istransient based on our data collected at this site. Weexpect to see a decrease in species richness in plotswith the continued expansion and densification ofPhragmites, similar to what we have seen at thefour plots where Phragmites had a 100% cover.Phragmites is an invasive taxon (sensu Richardsonet al. 2000) that is a clonal dominant (sensuBoutin and Keddy 1993). Under the predictions ofthe hump-backed model (Grime 2000, Moore andKeddy 1989), the large standing crop of this clonaldominant species would be expected to reducespecies richness because the greatest species richnessis usually reached at moderate standing crops.Phragmites forms monospecific stands with a consequentreduction in species diversity (Marks et al.1994). Such a reduction did occur in the four plotswhere Phragmites had a 100% cover in 2004,species richness being significantly lower in thesefour plots than in the plots where Phragmites wasnot present or had a low cover.“Mean coverage by invasive species” was an indicatorthat suggested a degradation of the lagoon.Species richness and other metrics commonly usedas wetland indicators (i.e., FQI and mean coefficientof conservatism) did not point out a degradationof this wetland. However, greater values of allthese three metrics are expected as the site evolvedfrom a newly established community dominated byannuals to a more mature community dominated byperennials. The greater height of the dominantherbaceous plants in 2004 can be explained by thedominance of Phragmites or Typha in almost all ofthe plots. These are invasive species in the U.S. andgrow taller than native species (Galatowitsch et al.1999). Plant size larger than that of associatespecies is a key trait that allows plant species todominate, such that tall stature is a characteristic ofcompetitive species (Grime 1973, Grime 2000).Monoculture is achieved by larger species throughtheir ability to compete for light (tall shoots), forwater and nutrients (high below ground biomass),and through the presence of a high density of herbaceouslitter throughout the year (Grime 2000). BothTypha and Phragmites form mono-dominant stands,and both are well adapted to sustained inundation(Haslam 1971, Shay and Shay 1986). These fea-

Phragmites australis Invasion 277tures promote Phragmites as a good competitor inthe stands where it occurs (Haslam 1971).While predicting invasion of a community is difficultbecause there is no unique theory to successfullyexplain plant invasions (Williamson 1999,Grime 2000, Zedler and Kercher 2004), fluctuationof resource availability may be one of the key factorsthat control invasibility (Davis et al. 2000).New substrate availability makes an area susceptibleto invasion (Grime 2000) and is one of the factorsthat make riparian areas more prone to invasion(Tickner et al. 2001).Establishment of Phragmites typically occurs onbare, unvegetated moist soils after water levels recede(Chambers et al. 1999, Galatowitsch et al.1999, Ailstock et al. 2001, Pengra et al. 2007). Thisspecies typically invades starting from the uplandfringe of the wetland via stolons and rhizomes. Alternatively,it may start on a high point within thewetland, such as a dike remnant, and then spreadinto the wetland plain. Unlike rhizomes, stolons arelocated aboveground and usually elongate morerapidly than rhizomes. Phragmites propagation byseeds is limited (Haslam 1970, 1971). Vegetativepropagation is efficient through rhizome portionstransported by water, man, or stolons from nearbycolonies (Haslam 1971). We observed long Phragmitesstolons on beach areas north of the lagoon,and believe that stolon growth was the primarymechanism of Phragmites expansion within the lagoon.The rapid invasion of Point au Sauble by Phragmitescannot and should not be considered representativeof all Great Lakes coastal wetlands.Although the extremely low water levels between1999 and early 2004 occurred throughout lakesMichigan and Huron, Phragmites stands observedelsewhere in Green Bay by co-author Tulbure as a2004 field assistant to Pengra (2005) were muchless extensive than those found at Point au Sable. Inthat study, Pengra and co-workers visited 82 GreenBay wetland locations with emergent vegetationand found that 34 of them had Phragmites presentin 2004. We believe that this could be because theAu Sauble wetland is a lagoon protected in the interiorof a hook-shaped peninsula, whereas other sitesare sandy peninsulas and associated embaymentsthat are more open to wave action (e.g., Little TailPoint, and Long Tail Point, Wisconsin DNR 2006).Also, other sites had organic substrates (e.g., SensibaWildlife Area) rather than silty substrate asPoint au Sauble, which might have been less proneto Phragmites invasion. We believe that the exposureof unvegetated silty mineral soils at Point auSauble, which suggests the presence of a depositionalenvironment, created conditions conducive toPhragmites colonization and may be atypical forthe region. Based on these results, we predict thatsites with exposed mineral soils are most susceptibleto Phragmites invasion, and future studiesshould further test this hypothesis.The GLEI project was designed to be conductedas single-sampling event, not an analysis of changeover time. However, these results illustrate the benefitsof the sampling and documentation protocolestablished by GLEI. Without the careful recordskept by the GLEI sampling crew in 2001, documentationof this rapid Phragmites expansion would nothave been possible.ACKNOWLEDGMENTSWe thank Dr. Elizabeth Lynch and an anonymousreviewer for helpful comments on an earlier draft.This research has been supported by a grant fromthe U.S. EPA’s Science to Achieve Results Estuarineand Great Lakes program through funding to theGreat Lakes Environmental Indicators project, U.S.EPA Agreement EPA/R-828675. Although the researchdescribed in this article has been fundedwholly by the U.S. EPA, it has not been subjectedto the agency’s required peer and policy review andtherefore does not necessarily reflect the views ofthe agency and no official endorsement should beinferred.REFERENCESAilstock, M.S., Norman, C.M., and Bushmann. P.J.2001. Common Reed, Phragmites australis: controland effects upon biodiversity in freshwater nontidalwetlands. Resour. Ecol. 9(1):49–59.ASTM (American Society for Testing and Materials).1997. ASTM E 1923, Standard Guide forSampling Terrestrial and Wetlands Vegetation. ASTMInternational, West Conshohocken, PA, USA.Bart, D., and Hartman, J.M. 2000. Environmental determinantsof Phragmites australis expansion in a NewJersey salt marsh: an experimental approach. Oikos89:59–69.———, and Hartman, J.M. 2003. The role of large rhizomedispersals and low salinity windows in theestablishment of common reed, Phragmites australis,in salt marshes: new links to human activities. Estuaries26(2B):436–443.Bernthal, T.W. 2003. Development of a floristic qualityassessment methodology for Wisconsin. Final reportto the U.S. Environmental Protection Agency. Region

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