Proceedings of the 2003 Georgia Water Resources Conference, held April 23-24, 2003, at the University of Georgia.This study was designed to examine the forest composition, structure and species richness of vegetation among undeveloped back-barrier islands near Sapelo Island, Georgia.  Known colloquially as “marsh hammocks,” back-barrier islands are completely or partially encircled by estuarine saltmarsh. There are upwards of 1200 hammocks along the Georgia coast, comprising approximately 6900 ha.  In the face of increased development pressure, the cumulative impacts caused by small-scale construction of homes, roads, bridges, and septic fields may alter natural hydrologic and ecological processes. We surveyed vegetation on 11 undeveloped hammocks in four size classes and found that overall species diversity is low, but the diversity of vascular plants may increase with island size. Local and regional planners and conservation organizations may use this information to help develop land-based projects that are consistent with the sustainable use of coastal resources

Alber, Merryl

Albers, Gayle

Scholarly Materials And Research @ Georgia Tech

A VEGETATIVE SURVEY OF BACK-BARRIER ISLANDSNEAR SAPELO ISLAND, GEORGIAGayle Albers1 and Merryl Alber2AUTHORS:  1Graduate Student, Institute of Ecology and 2Associate Professor, Dept. of Marine Sciences, University of Georgia, Athens, GA30602.REFERENCE:  Proceedings of the 2003 Georgia Water Resources Conference, held April 23-24, 2003, at the University of Georgia.  KathrynJ. Hatcher, editor, Institute of Ecology, The University of Georgia, Athens, Georgia.    Abstract.  This study was designed to examine theforest composition, structure and species richness ofvegetation among undeveloped back-barrier islandsnear Sapelo Island, Georgia.  Known colloquially as“marsh hammocks,” back-barrier islands arecompletely or partially encircled by estuarine saltmarsh.  There are upwards of 1200 hammocks alongthe Georgia coast, comprising approximately 6900 ha.In the face of increased development pressure, thecumulative impacts caused by small-scale constructionof homes, roads, bridges, and septic fields may alternatural hydrologic and ecological processes.  Wesurveyed vegetation on 11 undeveloped hammocks infour size classes and found that overall species diversityis low, but the diversity of vascular plants may increasewith island size.  Local and regional planners andconservation organizations may use this information tohelp develop land-based projects that are consistentwith the sustainable use of coastal resources.INTRODUCTIONA complex of primary and secondary barrierislands stretches along Georgia’s 100-mile coast.Barrier islands are dynamic habitats resulting fromgeologic interactions driven by long-term sea level riseand retreat, wave-driven erosion, accretion, andoverwash processes caused by storms and seasonal tidalevents (Johnson and Barbour, 1990; Hoyt, 1967).Johnson et al. (1974) described Georgia’s Sea Islandsas compound barrier islands of relatively recent (4000-5000 years) Holocene landmasses welded onto a coreof older Pleistocene ridges.  Age differences are basedon soil development. The topographic signature andfloristic profile of barrier islands are evidence for bothphysical disturbance and plant succession.Georgia’s secondary, or back-barrier islands, maybe completely or partially encircled by salt marsh andare often referred to colloquially as “marshhammocks.”  Georgia’s back-barrier islands totalapproximately 6900 hectares of upland area, with thoselocated in McIntosh County comprising 20% of thearea (CMHAC, 2002).Due to increased development pressure in coastalGeorgia, back-barrier islands have become a topic ofdebate.  An administrative court suit resulted in theappointment of Georgia’s coastal marsh hammockadvisory council (CMHAC) in February 2001 to assesshammock development issues and define Georgia’scoastal marsh hammocks.  The working definitionadopted by the CMHAC was:Back–barrier islands are all other1 islands betweenthe landward boundary of the barrier islandcomplexes and the mainland.  Natural back-barrierislands are erosional remnants of pre-existingupland, whereas man-made back barrier islandsare comprised of dredge spoil matter or ballaststones.  These islands may or may not haveexisting connections to the mainland by bridges,causeways, or other man-made structures. (Note:While we recommend that the term “hammock”not be used in any legal definition in the state ofGeorgia, we recognize the informal colloquial useof the term “hammock” to describe many back-barrier islands) (CMHAC, 2002).Although some features of Georgia’s primarybarrier islands have been well-studied, the ecologicalsignificance of the approximately 1,200 back-barrierislands is poorly documented in the scientific literatureand can only be derived from studies executed on largerislands within the southeastern region. In 1986, Odumand others identified research needs specifically relatedto the physical characteristics of interior wetlands ofbarrier island communities, including microtopographicsurveys and mapping to locate wetland habitat,1 The Georgia Barrier Island Complexes and their component unitsare:  Cumberland Island (Cumberland Island and LittleCumberland Island) Jekyll Island, St. Simons Island (St. SimonsIsland, Sea Island and Little St. Simons Island), Wolf Island,Sapelo Island (Sapelo Island and Blackbeard Island), St.Catherines Island, Ossabaw Island, Wassaw Island and TybeeIsland (Tybee Island and Williamson Island) (CMHAC, 2002).measurement of surface-water drainage andgroundwater transmissivity, modeling of groundwaterdynamics and water quality studies.   Beginning inOctober 2001, the Southern Environmental Law Centerand The Georgia Conservancy have organized a semi-annual volunteer survey of hammock areas, noting theirparticular importance to roosting and migratory birds.The purpose of this study was to examine thefloristic composition, structure, and species richnessamong a subset of back-barrier islands of different sizesnear Sapelo Island.  We expected that species diversityof vascular plants would increase with island size inaccordance with the theory of island biogeography(MacArthur and Wilson, 1968). Our goal was toinventory and quantify the vegetation that comprisesupland areas adjacent to Georgia marshlands, thusproviding the framework for monitoring long-termconditions of back-barrier islands.  This informationmay be helpful to the natural resource managementcommunity and conservation organizations that makedecisions regarding coastal resources.METHODSSite SelectionWe conducted a series of field observationswithin and near the Georgia Coastal Ecosystems LongTerm Ecological Research (GCE LTER) site at SapeloIsland, Georgia, during the summer and fall of 2002(Fig 1). The back-barrier islands were selected on thebasis of accessibility, minimal impact from residentialor agricultural development, natural origin (as opposedto dredge spoil) and size.  Back-barrier islands wereidentified using an ESRI ArcView v.3.2 map databaseprovided by the Georgia Dept. of Natural ResourcesCoastal Research Division (GADNR CRD).  The back-barrier islands that were included in this study rangedin size from 0.01 to 41.8 hectares (ha) and wereclassified into 4 size classes (Table 1).  Three islandswere sampled in each size class with the exception ofSize Class C (n=2) (we had difficulty identifying a thirdisland in Size Class C that we could sample).Vegetation SurveysFrom July to October 2002, we conductedvegetation surveys at each of the 11 back-barrierislands identified (Fig. 1).  Hammocks were accessedvia the GCE LTER V-tech boat. Some sites were onlyaccessible during high tide, when the tidal creeks weredeep enough for passage.  A series of 0.01 hatemporary plots was constructed on each back-barrierisland.  From 2 to 6 plots were sampled on each island;more plots were sampled on larger islands in order toobtain a more representative survey of the sites (Table1). Plots were randomly placed at or above the marsh-upland interface as indicated by the first woody tree orshrub.  The plots were marked semi-permanently using1.5” diameter x 12” length metal conduit stakes, sofuture observation in these areas may be possible.  Atotal of 41 plots were sampled.  Latitudinal andlongitudinal coordinates were recorded using a hand-held Global Positioning Satellite unit.  This informationwas used to plot onto the GADNR CRD database usingArcView GIS mapping techniques. Each site was alsophoto-documented with a 35 mm Nikon N65 camera.We followed the sampling protocol developed forNorth Carolina Vegetation Surveys (NCVS) (Peet etal., 1998). This methodology was chosen due to itsflexibility, ease of use, and successful application forrapid assessment in the SE region.  A 100 m measuringreel was used to demarcate the perimeter of a 10 x 10 mplot, and a hand held tape measure and 2 meter stickswere used to divide it into quadrats.  The vegetationwas sequentially assessed by nested quadrats in each ofthe corners of the module (labeled 1 to 4 in Fig. 2).Figure 1.  Back-barrier islands sampled in McIntoshCounty, GA are indicated by shading.Table 1.  Size Classes of Back-barrier Islands (BBI)Sampled Near Sapelo Island, GeorgiaBBI sizeclassBBI size(ha)# BBIssurveyed# Plots/BBIA <1.0 3 2B 1.0-2.0 3 3C 2.1-4.0 2 4D >4.0 3 6Sampling areas were 0.01 m2, 0.10 m2, 1.00 m2 , and10.00 m2.  Plants in the remaining cross-shaped areawere also evaluated. Figure 2 illustrates the samplingstrategy for a standard 100 m2 module.Vascular species were recorded as present orabsent within each subset of nested quadrats.  Theimpact to the site was minimal, although floristicsamples were collected for identification as necessary.In these cases, plants were dried and stored in plantpresses, frozen for 5 days to prevent contamination, andkeyed out and mounted at the University of GeorgiaPlant Sciences Herbarium, Athens, GA.   All vascularplants within plots were identified to species wheneverpossible: taxonomy followed Radford et al. (1968) andDuncan and Duncan (1987).  Due to difficulty inidentifying grasses and sedges in a vegetative state,they were excluded from these analyses. In this paper we present information on speciesrichness determined by tallying the number of speciesper plot.  Although the sampling protocol also allowsfor more thorough data analyses for cover, abundanceand biomass, this information is not presented here.RESULTSThis study revealed strong trends in thecomposition of the community on back-barrier islands.Yaupon holly (Ilex vomitoria) was the dominant woodyspecies, occurring in 93% of the plots sampled; spanishmoss (Tillandsia usenoides) is an epiphyte thatoccurred in 91% of all plots.   These plants were foundin association with live oak (Quercus virginiana),catbriar (Smilax bona-nox), cabbage palm (Sabalpalmetto ), red bay (Persea borbonia ) and saw palmetto(Serenoa repens), which are also common plants inmaritime forest communities.  Of a total of 43 speciesidentified, 25 were found in less than 10% of the 41individual plots sampled.  For these relativelyuncommon plants, 41% were found on back-barrierislands in the largest size class.   These floras includedHercules’ club (Xanthoxylem clava-herculis) andpassionflower (Passiflora lutea).  The tiny-leavedbuckthorn or shell mound buckthorn (Sageretiaminutiflora), a plant that is recognized as threatened bythe state of Georgia, was only observed on the threelargest hammocks in this study.Mean species richness increased with increasingsize category (Fig. 3).  Mean species richness valuesranged from 6.50 for back-barrier islands less than 1.0ha and rose to 9.94 for those greater than 4.0 ha.Although overall diversity is low for all back-barrierislands, these data suggest a positive relationshipbetween back-barrier island area and vascular plantdiversity, as predicted by the theory of islandbiogeography.  Future analyses will explore thedistance of the areas surveyed from potential seedsources, such as the mainland and barrier islands.DISCUSSIONThere are important science and policy reasonsfor evaluating the maritime vegetative communitiesfound on Georgia’s back-barrier islands.  Because oftheir significant ecological value, the state’s MarshlandProtection Act of 1970 protects Georgia’s coastalmarshlands from development; however, adjacent back-barrier islands are not currently offered the same10 0  m 210 m 21 m 20.1 m 20.01 m 22 13 45     1 0 .0 0 m  3 .1 6 m  1 .0 0 m  0 .3 2 m  0 .1 0 mFigure 2. Illustration of  0.01 m2, 0.1 m2, 1.0 m2and 10.0 m2 nested quadrats constructed withineach corner (1 to 4) of the 100 m2 plot module,with the length of quadrat sides indicated.9.948.887.336.5002468101214<1 ha 1-2 ha 2-4 ha >4 haSize CategorySpecies RichnessFigure 3.  Mean species richness of BBIs sampled inthis study.  Error bars represent standarddeviations.safeguards.  Although back-barrier island developmentcan be expensive, the potential to attract affluent buyershas stimulated interest in these areas.  In addition,private property owners are concerned that their rightsmay be threatened, so many are seeking permits tosecure future access to their land.  Although Georgia’sCoastal Zone Management Act of 1992 identifies bothmaritime forests and marsh hammocks as regions ofphysiographical significance, it may lack the legalframework to maintain their long-term sustainability.Inventories by Lopazanski and others (1988) andMathews and others (1980) indicated thatapproximately 39,000 ha of maritime forest remainsintact within North Carolina, Georgia and Florida froman unknown original total prior to human impacts. Ofthe remaining maritime forest, 65% is located inGeorgia.   This represents a density of 160 ha per linearkilometer of ocean shoreline.  Maritime forests may beimportant in maintaining fresh groundwater suppliesand providing wildlife habitat for resident andmigratory birds (Bellis and Keough, 1995).As back-barrier islands are developed, thecumulative impacts caused by small-scale constructionof homesites, roads, bridges, and septic fields may alterthe environment to such an extent that naturalhydrologic and ecological processes are no longerpossible.  Although the analyses presented here will berefined to include grasses and sedges, our preliminaryresults suggest that vascular plant diversity onundeveloped back-barrier islands increases withincreasing area and that their species composition isrepresentative of maritime forest vegetation on barrierislands.  This type of information can help coastalplanners target areas best suited for conservationeasements, land acquisition, and make better informedpolicy recommendations.ACKNOWLEDGMENTSWe thank our colleagues at the University ofGeorgia: Ken Helm, Susan White, Monica Moss, andMatt Ogburn for their field assistance; Wendy Zomleferfor herbarium services; and Karen Payne for GISexpertise. Fred Hay, GADNR Coastal ResourceDivision, graciously provided the map database.  TomWentworth and Kristen Rosenfeld, North CarolinaState University, offered guidance regarding the surveyprotocol.  Support was provided in part by The GeorgiaConservancy and the Georgia Coastal EcosystemsLTER Project (NSF Grant No. OCE 99-82133).LITERATURE CITEDBellis, VJ, and JR Keough, 1995.  Ecology of MaritimeForests of the Southern Atlantic Coast: ACommunity Profile, National Biological Service,Department of the Interior, Biological Report 30,May, Washington D.C. 95 pp.Coastal Marsh Hammock Advisory Council, March2002, Report of the Coastal Marsh HammockAdvisory Council, Georgia Department of NaturalResources, 25pp.Duncan WH and MB Duncan, 1987. Seaside Plants ofthe Gulf and Atlantic Coasts.  SmithsonianInstitution Press, Washington, D.C.Hoyt, 1967.  Barrier island formation.  GeologicalSociety of America Bulletin 78:1125-1136.Johnson, AF, and MG Barbour, 1990.  Dunes andmaritime forests. Pages 429-480 In R.L. Myers andJJ Ewel, editors. Ecosystems of Florida.  UniversityPress of Florida, Gainesville. 765 pp.Johnson, AS, HO Hillestad, SF Shanholtzer, and GFShanholzer, 1974.  An ecological survey of thecoastal region of Georgia.  U.S. National ParkService Scientific Monograph Series 3. Washington,D.C. 223 pp.Lopazanski, MJ, JP Evans, and RE Shaw, 1988.  Anassessment of the maritime forest resources of theNorth Carolina coast.  A final report submitted to theNorth Carolina Department of Natural Resourcesand Community Development, Division of CoastalManagement. Raleigh, N.C. 108 pp.Mathews, TD, FW Stapor, CR Richter, JV Miglarese,MD McKenzie, and LA Barclay, editors,  1980.Ecological characterization of the Sea Island coastalregion of South Carolina and Georgia, vol. 1:physical features of the characterization area. U.S.Fish and Wildlife Service, FWS/OBS79/40. 120 pp. MacArthur, RH and EO Wilson, 1967.  The theory ofisland biogeography. Princeton, NJ, PrincetonUniversity Press.Odum, WE, J Harvey, L Rozas, and R Chambers, 1986.The functional assessment of selected wetlands ofChincoteague Island, Virginia.  U.S. Fish andWildlife Service, National Wetlands Research CenterOpen File Report 86-7. Washington, D.C. 127 pp.Peet, RK, TR Wentworth and PS White, 1998. Aflexible, multipurpose method for recordingvegetation composition and structure.  Castanea63(3): 262-274.Radford,  AE, Aheles HE and CR Bell, 1986. Manualof the Vascular Flora of the Carolinas.  University ofNorth Carolina Press, Chapel Hill.

A Vegetative Survey of Back-Barrier Islands near Sapelo Island, Georgia

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A Vegetative Survey of Back-Barrier Islands near Sapelo Island, Georgia

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