318 Q 2000 Estuarine Research Federation Estuaries Vol. 23, No. 3, p. 318–327 June 2000 Marsh Vegetation Types of the Chenier Plain, Louisiana, USA JENNEKE M. VISSER 1 CHARLES E. SASSER Coastal Ecology Institute Louisiana State University Baton Rouge, Louisiana 70803 ROBERT H. CHABRECK School of Forestry, Wildlife, and Fisheries Louisiana State University Agricultural Center Baton Rouge, Louisiana 70803 R. G. LINSCOMBE Louisiana Department of Wildlife and Fisheries 2415 Darnall Road New Iberia, Louisiana 70560 ABSTRACT: The Chenier Plain of Louisiana contains 3,085 km 2 of coastal marshes and stretches from the Texas border to Vermilion Bay at approximately 918309W. The objective of this study was to describe the vegetation types of the Chenier Plain in 1997, compare the vegetation types of the Chenier Plain with those described previously for the Mississippi River Deltaic Plain, and compare the distribution and composition to previous descriptions of vegetation types in the region. Two-way Indictor Species Analysis (TWINSPAN) revealed seven major vegetation types that occurred in the region in 1997: fresh bulltongue, fresh maidencane, oligohaline bullwhip, oligohaline paspalum, oligohaline wire- grass, mesohaline wiregrass, and mesohaline mixture. These vegetation types are a logical expansion of the habitats previously described for the region. Five of the seven vegetation types were also identified by similar analyses and descriptions for the Mississippi River Deltaic Plain. Vegetation in the fresh marsh substantially changed since it was first described by O’Neil in the 1940s. The largest change was the disappearance of the sawgrass habitat, although this change occurred before 1968. We show a continued trend in increase of oligohaline marsh at the expense of mesohaline wiregrass marsh, although it is not clear if this change is genuine or arises from the difference in classification methods among years. The mesohaline mixture, labeled saline marsh in previous studies, has remained relatively stable over time. Introduction The Louisiana coast consists of a band of marsh- es that varies in width from 20 to 75 km and stretches from the Texas border eastward to the Mississippi border for a total of 9,715 km 2 of coast- al marshes (Field et al. 1991). Based on geomor- phology, the Louisiana coast is divided into two re- gions: the Mississippi River Deltaic Plain and the Chenier Plain. The Deltaic Plain is the eastern re- gion of the Louisiana coast and includes the area from the Mississippi border, at approximately 898 009 W, to Vermilion Bay, at approximately 918309W. This part of the coast formed with sedi- ments from the former deltas of the Mississippi River (Scruton 1960; Coleman and Gagliano 1964; Kolb and van Lopik 1966; Wright 1985) and is characterized by large interdistributary estuaries. The Chenier Plain is the western region of the Louisiana coast, and includes the area from Ver- milion Bay (918309W) westward to the Texas bor- der (948009W). It was also formed with sediments 1 Corresponding author: tele: 225/388-6515; fax: 225/388- 6376; e-mail: [email protected]. from the Mississippi River. The Chenier Plain sed- iments were transported by the westward coastal current in the Gulf of Mexico and reworked in periods of low deposition (Byrne et al. 1959; Gould and McFarland 1959). The Chenier Plain is char- acterized by beach ridges and stranded beach ridg- es, locally called cheniers, that limit tidal exchange to a few narrow inlets at the mouths of the rivers (Sabine River, Calcasieu River, and Mermentau River). Due to this difference in geomorphology, we expect the vegetation of the Chenier Plain coastal wetlands to be different from the vegeta- tion in the Deltaic Plain described in Visser et al. (1998). The Chenier Plain contains 3,085 km 2 of coastal marshes (Field et al. 1991). Few descriptions exist of the diverse plant communities in this large area of wetlands. O’Neil (1949) published the first map of major vegetation associations for coastal Loui- siana, including the Chenier Plain, as an inventory of muskrat habitat. Chabreck (1970, 1972) delin- eated and mapped 4 vegetation zones (fresh, in- termediate, brackish, and saline) in the Louisiana coastal zone mainly on the basis of Penfound and Hathaway’s (1938) descriptions of the major veg-
Transcript
318Q 2000 Estuarine Research Federation
Estuaries Vol. 23, No. 3, p. 318–327 June 2000
Marsh Vegetation Types of the Chenier Plain, Louisiana, USA
JENNEKE M. VISSER1
CHARLES E. SASSER
Coastal Ecology InstituteLouisiana State UniversityBaton Rouge, Louisiana 70803
ROBERT H. CHABRECK
School of Forestry, Wildlife, andFisheries
Louisiana State UniversityAgricultural Center
Baton Rouge, Louisiana 70803
R. G. LINSCOMBE
Louisiana Department of Wildlifeand Fisheries
2415 Darnall RoadNew Iberia, Louisiana 70560
ABSTRACT: The Chenier Plain of Louisiana contains 3,085 km2 of coastal marshes and stretches from the Texas borderto Vermilion Bay at approximately 918309W. The objective of this study was to describe the vegetation types of theChenier Plain in 1997, compare the vegetation types of the Chenier Plain with those described previously for theMississippi River Deltaic Plain, and compare the distribution and composition to previous descriptions of vegetationtypes in the region. Two-way Indictor Species Analysis (TWINSPAN) revealed seven major vegetation types that occurredin the region in 1997: fresh bulltongue, fresh maidencane, oligohaline bullwhip, oligohaline paspalum, oligohaline wire-grass, mesohaline wiregrass, and mesohaline mixture. These vegetation types are a logical expansion of the habitatspreviously described for the region. Five of the seven vegetation types were also identified by similar analyses anddescriptions for the Mississippi River Deltaic Plain. Vegetation in the fresh marsh substantially changed since it was firstdescribed by O’Neil in the 1940s. The largest change was the disappearance of the sawgrass habitat, although this changeoccurred before 1968. We show a continued trend in increase of oligohaline marsh at the expense of mesohaline wiregrassmarsh, although it is not clear if this change is genuine or arises from the difference in classification methods amongyears. The mesohaline mixture, labeled saline marsh in previous studies, has remained relatively stable over time.
Introduction
The Louisiana coast consists of a band of marsh-es that varies in width from 20 to 75 km andstretches from the Texas border eastward to theMississippi border for a total of 9,715 km2 of coast-al marshes (Field et al. 1991). Based on geomor-phology, the Louisiana coast is divided into two re-gions: the Mississippi River Deltaic Plain and theChenier Plain. The Deltaic Plain is the eastern re-gion of the Louisiana coast and includes the areafrom the Mississippi border, at approximately898009W, to Vermilion Bay, at approximately918309W. This part of the coast formed with sedi-ments from the former deltas of the MississippiRiver (Scruton 1960; Coleman and Gagliano 1964;Kolb and van Lopik 1966; Wright 1985) and ischaracterized by large interdistributary estuaries.The Chenier Plain is the western region of theLouisiana coast, and includes the area from Ver-milion Bay (918309W) westward to the Texas bor-der (948009W). It was also formed with sediments
from the Mississippi River. The Chenier Plain sed-iments were transported by the westward coastalcurrent in the Gulf of Mexico and reworked inperiods of low deposition (Byrne et al. 1959; Gouldand McFarland 1959). The Chenier Plain is char-acterized by beach ridges and stranded beach ridg-es, locally called cheniers, that limit tidal exchangeto a few narrow inlets at the mouths of the rivers(Sabine River, Calcasieu River, and MermentauRiver). Due to this difference in geomorphology,we expect the vegetation of the Chenier Plaincoastal wetlands to be different from the vegeta-tion in the Deltaic Plain described in Visser et al.(1998).
The Chenier Plain contains 3,085 km2 of coastalmarshes (Field et al. 1991). Few descriptions existof the diverse plant communities in this large areaof wetlands. O’Neil (1949) published the first mapof major vegetation associations for coastal Loui-siana, including the Chenier Plain, as an inventoryof muskrat habitat. Chabreck (1970, 1972) delin-eated and mapped 4 vegetation zones (fresh, in-termediate, brackish, and saline) in the Louisianacoastal zone mainly on the basis of Penfound andHathaway’s (1938) descriptions of the major veg-
Chenier Plain Vegetation Types 319
etation types of the Mississippi River Delta region.Within these salinity zones several vegetation as-sociations can be distinguished (O’Neil 1949; Shif-tlet 1963).
The objectives of this study were to describe thevegetation types of the Chenier Plain as they oc-curred in 1997, compare the distribution and com-position to previous descriptions of vegetationtypes in the region, and compare the vegetationtypes of the Chenier Plain with those described forthe Deltaic Plain.
Study AreaThe climate of the Chenier Plain is humid sub-
tropical with an average of 13 freeze days a year(Gosselink et al. 1979). Mean monthly tempera-ture is 148C in December/January, and 308C in thesummer. Average annual precipitation decreasesfrom east to west in the Chenier Plain from 144 to113 cm yr21 (Gosselink et al. 1979). Winds alongthe Louisiana coast are predominantly from thesoutheast. Tropical disturbances affect the area fre-quently, tropical storms once per 1.6 yr and hur-ricanes once every 3.3 yr, from late spring throughearly fall (Roth 1999). Hurricanes that have madelandfall in the study area include Audrey—1957,Cindy—1963, Edith—1971, Carmen—1974, Dan-ny—1985, and Juan—1985.
Louisiana experiences the most severe land lossin the United States, with loss rates estimated from6,000 to 12,450 ha yr21 (Turner 1990; Britsch andDunbar 1993). This land loss is due to a combi-nation of natural processes and human activitiesthat are well documented (Craig et al. 1979; Everset al. 1992; Boesch et al. 1994). Land loss in theChenier Plain is substantially lower than in the Del-taic Plain (Dunbar et al. 1992) due to the muchsmaller subsidence rate in the Chenier Plain asso-ciated with the thinner Holocene sediment layerin this region (Penland and Ramsey 1990). Themost severe land loss in the study area occurred inthe period between 1956 and 1974 (Dunbar et al.1992) and was concentrated in the marshes flank-ing Calcasieu Lake (Barras et al. 1994). The lossof 127 km2 of wetlands in the Calcasieu Lake areabetween 1952 and 1974 has been attributed to thewidening and deepening of the Calcasieu shipchannel in the mid 1940s (12 m depth) and againin the mid 1960s (15 m depth) that changed thehydrology and salinity in the area (Gosselink et al.1979). The study area is expected to lose an ad-ditional 510 km2 of land in the next 50 yr, whichrepresents 32% of the projected coastal land lossin the state (Louisiana Coastal Wetlands Conser-vation and Restoration Task Force and WetlandsConservation and Restoration Authority 1998).
The Chenier Plain provides important wildlife
habitat especially for wintering waterfowl. Severallarge tracts are managed as wildlife refuges by theState of Louisiana (Rockefeller and Russell Sage),the United States government (Sabine and Lacas-sine), and the Audubon Society (Rainey).
MethodsThe vegetation survey consisted of 75 north-
south transects spaced at approximately 3 km in-tervals from 918579300W to 938539400W. Along thetransects, stations were located by GPS at 0.8 kmintervals and extended from the Gulf of Mexiconorthward to the upland boundary of the coastalzone. Vegetation was surveyed from a helicopterhovering above the station in the late summer of1997 (August and September). Each species oc-curring in an approximately 30 m radius from thestation was recorded and assigned an abundancevalue (3 5 abundant, 2 5 common, and 1 5 pre-sent). Helicopter surveys were chosen over tradi-tional ground surveys to cover the extensive Lou-isiana marshes. These surveys are good for theidentifying large specimens and dominant species,but tend to omit inconspicuous species. Nomen-clature follows the International Taxonomic Infor-mation Service (http://www.itis.usda.gov). Eachstation was classified as natural marsh, forested(shrubs or trees), de-watered marsh, open water,beach, natural levee or ridge, spoil bank, or devel-oped.
Only stations classified as natural marsh (1,735stations) were used for the two-way indicator-spe-cies analysis (TWINSPAN; Hill 1979). All sub-merged, free-floating, and tree species were re-moved from the data set so that only emergentmarsh vegetation was included. Some species thatwere difficult to identify correctly using helicoptersurveys, for example grasses and sedges, weregrouped by genus. Species occurring in less than5 stations (0.3% of all the natural marsh stations)were removed to reduce the influence of rare spe-cies and instability in the analysis (Tausch et al.1995). The TWINSPAN program was run using 3cut levels (1, 2, and 3), a minimum size of divisionof 50, and 3 weights for the cut levels (1, 2, and3); all other settings followed the default setting ofthe program. TWINSPAN was chosen over otherclassification strategies because this technique bestreflects the intuitive phytosociologic classificationof vegetation types (Dale 1995).
Nomenclature of vegetation types follows Visseret al. (1998) and is based on the local commonnames of the dominant species and estuarine salin-ity zone in which it occurs following Odum et al.(1984). Odum et al. (1984) classified the following5 salinity zones: fresh (average annual salinity ,0.5‰), oligohaline (average annual salinity be-
320 J. M. Visser et al.
Fig. 1. Major divisions of vegetation types as derived with TWINSPAN using species abundance. Species at each fork are importantindicator species for the division, however not all indicator species used in the division are listed. Numbers indicate the number ofstations within each vegetation type.
Fig. 2. Occurrence of vegetation types in the Chenier Plain,based on the 75 vegetation transects and the 1,735 stations.
tween 0.5‰ and 5.0‰), mesohaline (average an-nual salinity between 5.0‰ and 18.0‰), polyha-line (average annual salinity between 18.0‰ and30.0‰), and euhaline (average annual salinity .30.0‰).
Average number of species per plot calculationsfor each vegetation type were based on the samedata reductions used for TWINSPAN, except thatspecies occurring in less than 5 stations were re-tained. This richness estimate is conservative be-cause several species could only be identified tothe genus level and smaller species may have beenobscured from view.
ResultsTWINSPAN revealed 7 major vegetation types
within the Chenier Plain. The first division sepa-rates the fresh marsh stations from stations withsome salinity (Fig. 1). Fresh marsh stations repre-sented 28% of the natural marsh (Fig. 2) and weredivided into two major vegetation types: the Sagit-taria lancifolia-dominated bulltongue type, and thePanicum hemitomon-dominated maidencane type.Within the stations with some salinity the first di-
vision isolated the stations of the mesohaline mix-ture vegetation type, which is co-dominated bySpartina alterniflora and Distichlis spicata. The re-maining stations divide into two groups of two veg-etation types. Two wiregrass vegetation types weredominated by Spartina patens. Oligohaline wire-grass was characterized by the frequent presenceof Typha spp. and a higher number of taxa thanthe mesohaline wiregrass. Mesohaline wiregrasswas co-dominated by Schoenoplectus americanus (pre-viously known as Scirpus olneyi) and Spartina patens.The remaining stations were divided into oligoha-line bullwhip dominated by Schoenoplectus californicus(previously known as Scirpus californicus) and oligo-haline paspalum dominated by Paspalum vaginatum.A more detailed description of each vegetation typefollows below and complete species lists for eachvegetation type are provided in Table 1.
VEGETATION TYPES
Fresh bulltongue represented 11% of the marshand was dominated by Sagittaria lancifolia with Lud-wigia spp. and Typha spp. frequently present. Othercommonly occurring species were Cladium jamai-cense, Sesbania drummondii, Panicum hemitomon, andSacciolepis striata. Fresh bulltongue had 4.7 taxa perstation and 46 taxa observed (Table 2). Fresh bull-tongue was found in the center of Sabine Refuge,along the east shore of Grand Lake, along thesoutheastern shore of White Lake, and the north-eastern corner of Vermilion Bay (Fig. 3).
Fresh maidencane represented 17% of themarsh and was dominated by Panicum hemitomon.Other frequently occurring taxa were Sagittaria lan-cifolia, Eleocharis spp., Typha spp., and Cladium ja-maicense. Fresh maidencane had 4.5 taxa per sta-tion and a total of 44 taxa observed. Fresh mai-dencane was mostly found in the area west and
Chenier Plain Vegetation Types 321
north of Grand Lake and north of White Lake(Fig. 3).
Oligohaline paspalum was dominated by Paspal-um vaginatum with Spartina patens as a frequent co-dominant and was relatively rare, covering 3% ofthe marsh. Frequently occurring taxa in this typewere Sesbania drummondii and Echinochloa spp. Oli-gohaline paspalum had 4.7 taxa per station and 28taxa observed. Oligohaline paspalum was foundmostly fringing the cheniers (Fig. 3).
Oligohaline bullwhip was dominated or co-dom-inated by Schoenoplectus californicus and Echinochloaspp. and was also relatively rare, covering 3% ofthe marsh. Cyperaceae, Spartina patens, and Typhaspp. were common taxa in this vegetation type. Oli-gohaline bullwhip had 4.4 taxa per station and 21taxa observed. Oligohaline bullwhip was found inthe southern part of Sabine Refuge and northwestof White Lake.
Oligohaline wiregrass, dominated by Spartinapatens, was the most widespread vegetation type inthe Chenier Plain, representing 45% of the marsh-es. Frequently occurring taxa were Typha spp.,Phragmites australis, Vigna luteola, and Sagittaria lan-cifolia. Oligohaline wiregrass had 4.7 taxa per sta-tion and 58 taxa observed.
Mesohaline wiregrass was co-dominated by Spar-tina patens and Schoenoplectus americanus. The onlyother frequently occurring species in this type wasVigna luteola. Mesohaline wiregrass represented14% of the area and had 3.2 taxa per station and29 taxa observed. Mesohaline wiregrass was mostlyfound in the marshes fringing Vermilion Bay, butwas also present along the east shore of CalcasieuLake and south of Sabine Lake (Fig. 3).
Mesohaline mixture was co-dominated by Spar-tina alterniflora and Distichlis spicata. The only otherfrequently occurring species in this type was Spar-tina patens. Mesohaline mixture had 2.8 taxa perstation and 14 taxa observed. Mesohaline mixturewas found in the marshes fringing the Gulf of Mex-ico, as well as the western shore of Calcasieu Lake.
Discussion
CHANGE IN VEGETATION IN THE LAST 50 YEARS
Historical Data
The oldest data on the vegetation of the Loui-siana coastal zone came from O’Neil’s (1949) mapand description of muskrat habitats in coastal Lou-isiana (Fig. 4). O’Neil performed a ground survey(by boat and on foot) of the coastal zone between1940 and 1945. His map of muskrat habitats wasbased on these ground surveys and can be usedfor general distribution of major habitats in theearly 1940s. Because the survey routes used byO’Neil are not documented, it was impossible to
assess the accuracy of habitat assignments for in-dividual points on the map. O’Neil’s (1949) habitatdescriptions in the map legend consisted mostly ofa list of common species that occurred within eachhabitat. His accompanying text provided more de-tail for some selected areas of the coast.
Chabreck et al. (1968) produced the first mapshowing 4 salinity zones along the Louisiana coastbased on helicopter surveys of the vegetation along39 north-south transects. The assignment of eachstation to one of the 4 salinity zones was based onPenfound and Hathaway’s (1938) descriptions ofthe major vegetation types of the Mississippi RiverDelta region. The species composition, surface wa-ter salinity, and major and minor soil nutrients foreach salinity zone were reported by Chabreck(1972).
Fresh Marsh TypesWithin the Chenier Plain, 3 fresh marsh types—
fresh marsh, floating fresh marsh, and sawgrassmarsh—were described by O’Neil (1949). O’Neil’smap showed that fresh floating marsh dominatedby Panicum hemitomon was relatively rare in the ear-ly 1940s, only occurring in a small area north ofWhite Lake (Fig. 4). The fresh marsh described byO’Neil was a mixture of Panicum hemitomon, Typhaspp., Sagittaria lancifolia, Eleocharis spp., Zizaniopsismiliacea, Cladium jamaicense, Phragmites australis,and Schoenoplectus californicus. This type occurredmostly in a band along the upland boundary of thecoast and a small patch southwest of Grand Lake(Fig. 4). O’Neil (1949) suggested that the freshbulltongue marsh replaced areas previously occu-pied by fresh maidencane marsh as a result ofheavy grazing by cattle and periodic burns. Thesetwo types were not separated on the map, probablybecause fresh marsh was considered inferior musk-rat habitat in the Louisiana coastal zone.
The sawgrass marsh was dominated by Cladiumjamaicense with Typha spp., Schoenoplectus californi-cus, Phragmites australis, Sagittaria lancifolia, Spartinacynosuroides, and Eleocharis spp. as common occur-ring taxa. In the 1940s, the largest areas of thesawgrass marsh were found around White Lakeand Grand Lake (Fig. 4). The disappearance ofthis marsh type has been attributed to the stormsurge of Hurricane Audrey in 1957 that increasedsoil salinities (Shiftlet 1963) and killed the Cladiumjamaicense (Valentine 1976). Chabreck (1970)showed that Cladium jamaicense was relatively rarein the Chenier Plain in 1968, occurring in less than1% of the fresh marsh stations. Our data show thatthis species is increasing and occurred in 28% ofthe fresh marsh stations in 1997.
The fresh marsh dominated by Zizaniopsis mili-acea occurred on the north flank of the major
322 J. M. Visser et al.
TABLE 1. Species composition of the different vegetation types. Consistency classes are as follows: 1 is ,5% of the stations withineach vegetation type, I is 5–20%, II is 21–40%, III is 41–60%, IV is 61–80%, and V is 81–100%. MM 5 Mesohaline Mixture, MW 5Mesohaline Wiregrass, OW 5 Oligohaline Wiregrass, OP 5 Oligohaline Paspalum, OB 5 Oligohaline Bullwhip, FM 5 Fresh Maiden-cane, and FB 5 Fresh Bulltongue.
Species
Vegetation Type
FB FM OP OB OW MW MM
Aeschynomene indica L. 1 1 1Alternanthera philoxeroides (Mart.) Griseb. I 1 II 1Amaranthus australis (Gray) Sauer IAndropogon virginicus L. 1 1Aster L. spp. 1 1 IBaccharis halimifolia L. 1 1 1Bacopa caroliniana (Walt.) Robins 1Bacopa monnieri (L.) Pennell 1Batis maritima L. 1 IBidens laevis (L.) B.S.P. 1 I I I 1Borrichia frutescens (L.) DC. 1 IBrasenia schreberi Gmel. 1 1Cephalanthus occidentalis L. I ICicuta mexicana Coult. & Rose 1 1Cladium jamaicense Crantz II II I 1Colocasia esculenta (L.) Schott I 1 1 1Crinum americanum L. 1 IICyperaceae 1 1 I III II 1Decodon verticillatus (L.) Elliott 1Distichlis spicata (L.) Greene 1 1 IVEchinochloa Beauv. spp. I 1 II IV IEleocharis parvula (R. & S.) Link ex Buff 1 1 1Eleocharis R.Br. spp. I II I 1 1Erianthus giganteus (Walt.) Hubbard, non Muhl. 1Hibiscus lasiocarpus Cav. 1 1Hydrocotyle L. spp. 1 1 1 1 1Ipomoea sagittata Poir. 1 1 1 1Iris L. spp. IIva frutescens L. 1 1 1Juncus roemerianus Scheele 1 1 1 I I IIKostelezkya virginica Presl. 1 1 1 ILeersia Sw. spp. I 1 I 1 1Leptochloa fascicularis (Lam.) Gray I 1Limnobium spongia (Bosc.) Rich. ex Steud. 1 1 1 1Ludwigia L. spp. III II 1 II I 1Lythrum lineare L. 1 1 1 1Mikania scandens (L.) Willd. 1 1 IMorella cerifera (L.) Small 1 1 1Nelumbo lutea Wild. 1 1 1Nymphaea odorata Ait. 1 I 1Panicum hemitomon Schultes V I 1Panicum L. spp. 1 1 1 1 IPaspalum vaginatum Sw. 1 V I 1 1Phragmites australis (Cav.) Trin. ex Steud. 1 I I I II 1 1Pluchea Cass. spp. 1 II 1 1Polygonum L. spp. I 1 I 1 1Pontederia cordata L. 1 1 1Sacciolepis striata (L.) Nash II 1 I 1Sagittaria lancifolia L. V IV I 1 II ISagittaria latifolia Willd. 1 I 1Sagittaria platyphylla (Engelm.) J.G.Sm. 1Schoenoplectus americanus (Pers.) Volk. ex Schintz & Keller 1 1 I I I VSchoenoplectus californicus (C. Meyer) Palla II II IV II 1Bolboschoenus robustus (Pursh.) Sojk. I 1 ISesbania drummondii (Rydb.) Cory. I II I I 1Sesbania herbacea (Mill.) McVaugh. 1 I 1 1Setaria Beauv. spp. I 1Solidago L. sp. 1Spartina alterniflora Loisel 1 1 IVSpartina cynosuroides (L.) Roth 1 1 1 I ISpartina patens (Ait.) Muhl. 1 IV III V V IVSpartina spartinae (Trin.) Hitchc. 1
Chenier Plain Vegetation Types 323
TABLE 1. Continued.
Species
Vegetation Type
FB FM OP OB OW MW MM
Sphenoclea zeylandica Gaertn. 1 1Thelypteris noveboracensis (L.) Nieuwl. 1 1Typha L. spp. II I III III IVigna luteola ( Jacq.) Benth. 1 II II IZizaniopsis miliacea (Michx.) Doele & Aschers I I 1 1
TABLE 2. Number of taxa of the vegetation types in the two geomorphic provinces of the Louisiana coast.
1 Deltaic Plain were collected using the same survey technique as used in this study and are described in Visser et al. (1998).
cheniers according to Shiftlet (1963) but was notidentified in our analysis. O’Neil (1949) also men-tioned this vegetation type, but suggested that it isreplaced by bulltongue marsh in the presence ofheavy grazing. Most of the flanks of the chenierswere converted to pasture in the 1950s and 1960s.Therefore, Zizaniopsis miliacea was rare in theChenier Plain in 1968 (Chabreck 1972).
A comparison of the 3 records of vegetation dis-tribution in the Chenier Plain (O’Neil 1949; Cha-breck 1972; this study) shows that the area of freshmarsh has decreased substantially since the early1940s (Fig. 5). The largest decrease in fresh marsh(50% to 34%) occurred between the 1940s and1968 and arose from the conversion of sawgrassmarsh to intermediate marsh along the Chenierridges that has been attributed to Hurricane Au-drey. The further decline (34% to 28%) was a re-sult of the conversion of fresh marsh south ofGrand Lake to oligohaline wiregrass marsh.
Oligohaline Marsh TypesO’Neil (1949) described an intermediate salinity
habitat that was mostly found in the southern halfof Sabine Refuge west of Calcasieu Lake (Fig. 4)that represented only 7% of the Chenier Plain(Fig. 5). The dominant taxa in this habitat wereCladium jamaicense, Phragmites australis, Typha spp.,and Schoenoplectus californicus with Schoenoplectusamericanus, Spartina patens, Sagittaria lancifolia, andSpartina cynosuroides as other common species. Cha-
breck et al. (1968) showed that the majority of thismarsh type was still in the same area, but that thistype also occurred in a band between the fresh andbrackish marshes in most of the remainder of theChenier Plain, an area occupied by sawgrass marshin the 1940s. Chabreck (1972) described the Chen-ier Plain intermediate marsh as dominated by Spar-tina patens and occupying 29% of the area. Thiswas a significant increase that mostly came at theexpense of fresh marsh, but also included someconversion of brackish marsh (Fig. 5). We classified51% of the marshes as oligohaline based on thespecies composition, but recognized 3 different as-sociations of which the type dominated by Spartinapatens was the most common. The large increasein intermediate marsh between 1968 and 1997(29% to 51%) was because we classified most ofthe marsh south of the cheniers and east of SabineLake as oligohaline (Fig. 3), while Chabreck et al.(1968) classified these areas as brackish. Sincethese areas are dominated by Spartina patens it isunclear if this reflects a true change in vegetationtype or a difference in classification. Further re-search is needed to answer this question.
Mesohaline Marsh TypesO’Neil (1949) showed a thin band of salt marsh
just behind the beach along most of the coast,along Southwest Pass, and on the north shore ofMarsh Island (Fig. 4). However, the legend ofO’Neil’s map stated that salinities in this habitat
324 J. M. Visser et al.
Fig. 3. Distribution of vegetation types in 1997.
type ranged from extremely saline to brackish andthat the vegetation consisted of Juncus roemerianus,Spartina patens, and Spartina alterniflora. In O’Neil’stext, this habitat in the Chenier Plain was de-scribed as a mixture of Distichlis spicata and Spartinapatens. Chabreck (1970) described the salinemarsh in the Chenier Plain in 1968 as dominatedby Distichlis spicata with Spartina alterniflora as a co-dominant. This makes the saline marsh as de-scribed for the 1940s and in 1968 similar to ourmesohaline mixture. We used mesohaline insteadof polyhaline, because soil salinities did not exceed18‰ in Chenier Plain salt marshes (Chabreck1972). We use our mesohaline mixture as salinemarsh in the comparison with historical data (Fig.5). This marsh type has remained relatively stablesince the 1940s (Fig. 5).
O’Neil (1949) recognized 2 brackish vegetationtypes in the Chenier Plain: the brackish three-cor-nered grass marsh and the leafy three-corneredgrass marsh. The brackish three-cornered grassmarsh was pre-dominantly Schoenoplectus american-us, but reverted to Spartina patens dominatedmarsh if it is not burned at least every other year.The leafy three-square marsh was dominated bySpartina patens with Bolboschoenus robustus (previ-ously known as Scirpus robustus) as a co-dominant.O’Neil’s map shows these marsh types along theedge of Sabine and Calcasieu Lake as well as Ver-
milion Bay and the center of Marsh Island andmost of the coastal rim south of the major cheniers(Fig. 4). Between the 1940s and 1968 the brackishmarsh in the Chenier Plain was reduced by 4%.This reduction came as a result of conversion tointermediate marsh (Fig. 5). This trend apparentlycontinued and brackish marsh was reduced fromthe 34% estimated in 1968 to 14% in 1997. As de-scribed in the oligohaline marsh type section, it isunclear if this change was genuine or reflected adifference in classification.
COMPARISON OF CHENIER PLAIN AND DELTAICPLAIN VEGETATION TYPES
Even though soils in the Chenier Plain are gen-erally more mineral then the soils in the DeltaicPlain (Rainey 1979) and the geomorphological set-ting is different, almost all vegetation types de-scribed in this study of the Chenier Plain havebeen previously described for the Deltaic Plain(Visser et al. 1998).
Fresh MarshAlthough the fresh maidencane vegetation type
was dominated by Panicum hemitomon in both re-gions of the coast, the number of taxa observedwas higher in the Deltaic Plain (Table 2). Sagittarialancifolia was much more common in the ChenierPlain maidencane marsh, while Eleocharis spp. and
Chenier Plain Vegetation Types 325
Fig. 4. Chenier Plain muskrat habitats in the 1940s (after O’Neil 1949).
Hydrocotyle spp. were much more frequently pre-sent in the Deltaic Plain (Visser et al. 1998). Thesedifferences may have resulted from the high per-centage of organic soils (86%) in the Deltaic Plainfresh marsh and the more mineral soils of theChenier Plain fresh marsh (Table 3). The hydrol-ogy of the fresh maidencane marsh in the 2 geo-morphic regions is very different. Ninety-five per-cent of the maidencane marsh in the Deltaic Plainis floating marsh (Evers et al. 1996), while most ofthe fresh marsh is attached in the Chenier Plain.In the Deltaic Plain large areas of maidencanemarsh have converted to spike rush marsh (Visseret al. 1999). This fresh spike rush marsh type wasnot observed in the Chenier Plain.
Fresh bulltongue marsh in the Deltaic Plain wasco-dominated by Panicum hemitomon (Visser et al.
1998) and appeared similar to the fresh maiden-cane marsh of the Chenier Plain. Fresh bulltonguemarsh in the Chenier Plain contained less Panicumhemitomon, was truly dominated by Sagittaria lanci-folia, and was characterized by the frequent pres-ence of Ludwigia spp. These differences may havebeen caused by the floating nature of half of thebulltongue marshes in the Deltaic Plain (Evers etal. 1996).
Oligohaline MarshThe difference between the oligohaline wire-
grass marshes in the 2 regions were in the com-monly occurring taxa rather than the dominants.In the Chenier Plain, Typha spp. and Phragmitesaustralis were commonly found in this type, butthese taxa were rare in the Deltaic Plain and were
326 J. M. Visser et al.
Fig. 5. Change in distribution of the vegetation over thefour salinity zones as defined by Chabreck (1972). The data forthe 1940s was based on digitization of O’Neil’s map (Fig. 5).For the 1940s data, we combined fresh marsh, fresh floatingmarsh, and sawgrass marsh as fresh marsh, brackish three-cor-nered grass and leafy three-square marsh as brackish marsh, andused intermediate marsh and saline marsh by themselves. Datafor 1968 combined data reported for the Chenier Plain hydro-logic units (7, 8, and 9 see Chabreck 1972). For the data fromthis study (1997), we combined the two fresh vegetation typesfor fresh marsh, the three oligohaline vegetation types for in-termediate marsh, and used mesohaline wiregrass for brackishmarsh and mesohaline mixture for saline marsh.
TABLE 3. Soil classification of the salinity zones (after Brup-bacher et al. 1973).
SalinityZone
Chenier Plain
Mineral Organic1
Deltaic Plain
Mineral Organic
FreshBrackishSaline
52%38%
100%
48%62%0%
14%24%51%
86%76%49%
1 Brupbacher et al. (1973) define organic soils as those con-taining .16% organic matter.
replaced by Eleocharis spp. and Cyperus spp. as theother most common taxa (Visser et al. 1998). Theother oligohaline vegetation type observed in theDeltaic Plain was the oligohaline mixture, whichwas co-dominated by Sagittaria lancifolia and Cype-rus spp. This vegetation type was very differentfrom the oligohaline bullwhip and oligohaline pas-palum vegetation types that occurred in the Chen-ier Plain.
Mesohaline MarshThe mesohaline wiregrass marshes in the 2 re-
gions differed in co-dominants. In the Deltaic Plainthe co-dominant was Distichlis spicata (Visser et al.1998), while Schoenoplectus americanus was the com-mon co-dominant in the Chenier Plain. The muchlower abundance of Schoenoplectus americanus in theDeltaic Plain may have been due to higher grazingpressure from the introduced rodent, nutria (My-ocastor coypus) in this region. Taylor et al. (1994)showed that the biomass of Schoenoplectus american-us increased significantly in the absence of grazingby nutria in a Deltaic Plain wiregrass marsh. Only4% of the area damaged by nutria grazing in coast-al Louisiana occurs in the Chenier Plain (Kinlerand Linscombe 1998). Mesohaline mixture marsh-es in both regions were co-dominated by Spartinaalterniflora and Distichlis spicata, with Spartina patenscommonly present. We concluded that this typewas similar in both regions.
ConclusionOur 7 vegetation types for the Chenier Plain are
a logical expansion of the habitats previously de-
scribed for the region. Five of the seven vegetationtypes were also identified by similar analyses anddescriptions for the Deltaic Plain (Visser et al.1998). Our results show that vegetation in the freshmarsh has substantially changed since these marsh-es were first described by O’Neil (1949). The larg-est change was the disappearance of the sawgrasshabitat, although this change clearly occurred be-fore 1968, as evident from the vegetation map de-veloped by Chabreck et al. (1968). We also show acontinued trend in increase of oligohaline marshat the expense of mesohaline wiregrass marsh. Itis not clear if this change is genuine or arises fromthe difference in classification methods amongyears. The mesohaline mixture—labeled salinemarsh in previous studies—has remained relativelystable over time.
ACKNOWLEDGMENTS
The 1997 coastwide vegetation survey was funded by the Min-erals Management Service and U.S. Army Corps of Engineers.The analysis of the data was funded by the Louisiana Depart-ment of Natural Resources, Coastal Restoration Division. Wewould like to thank D. Elaine Evers for her assistance with thepreparation of the figures and her review of an earlier draft ofthis paper. Eura DeHart digitized the areas of different habitattypes from O’Neil’s map. This paper improved with the com-ments of two anonymous reviewers.
LITERATURE CITED
BARRAS, J. A., P. E. BOURGEOIS, AND L. R. HANDLEY. 1994. LandLoss in Coastal Louisiana 1956–90. National Biological Survey,National Wetland Research Center, Open File Report 94–01.Lafayette, Louisiana.
BOESCH, D. F., M. N. JOSSELYN, A. J. MEHTA, J. T. MORRIS, W. K.NUTTLE, C. A. SIMENSTAD, AND D. J. P. SWIFT. 1994. Scientificassessment of coastal wetland loss, restoration and manage-ment in Louisiana. Journal of Coastal Research Special Issue 20.
BRITSCH, L. D. AND J. B. DUNBAR. 1993. Land loss rates: Louisi-ana Coastal Plain. Journal of Coastal Research 9:324–338.
BRUPBACHER, R. H., J. E. SEDBERRY, JR., AND W. H. WILLIS. 1973.The coastal marshlands of Louisiana: Chemical properties ofthe soil materials. Louisiana State University Agricultural Experi-ment Station Bulletin No. 672. Louisiana State University, BatonRouge, Louisiana.
BYRNE, J. V., D. O. LEROY, AND C. M. RILEY. 1959. The ChenierPlain and its stratigraphy, southwest Louisiana. Transactions ofthe Gulf Coast Association of the Geological Society 9:237–259.
CHABRECK, R. H. 1970. Marsh zones and vegetative types in theLouisiana coastal marshes. Ph.D. Dissertation, Louisiana StateUniversity, Baton Rouge, Louisiana.
Chenier Plain Vegetation Types 327
CHABRECK, R. H. 1972. Vegetation, water, and soil characteristicsof the Louisiana coastal region. Louisiana State University Ag-ricultural Experiment Station Bulletin No. 664. Louisiana StateUniversity, Baton Rouge, Louisiana.
CHABRECK, R. H., J. T. JOANEN, AND A. W. PALMISANO. 1968. Veg-etative Type Map of the Louisiana Coastal Marshes. LouisianaWildlife and Fisheries Commission, New Orleans, Louisiana.
COLEMAN, J. M. AND S. M. GAGLIANO. 1964. Cyclic sedimentationin the Mississippi River Deltaic Plain. Transactions of the GulfCoast Association of the Geological Society 14:67–80.
CRAIG, N. J., R. E. TURNER, AND J. W. DAY, JR. 1979. Land lossin coastal Louisiana (USA). Environmental Management 3:133–144.
DALE, M. B. 1995. Evaluating classification strategies. Journal ofVegetation Science 6:437–440.
DUNBAR, J. B., L. D. BRITSCH, AND E. B. KEMP, III. 1992. LandLoss Rates: Report 3, Louisiana Coastal Plain. Technical Re-port GL-90–2, U.S. Army Corps of Engineers, New Orleans,Louisiana.
EVERS, D. E., J. G. GOSSELINK, C. E. SASSER, AND J. M. HILL. 1992.Wetland loss dynamics in southwestern Barataria basin, Lou-isiana (USA), 1945–1985. Wetlands Ecology and Management 2:103–118.
EVERS, D. E., G. O. HOLM, AND C. E. SASSER. 1996. Digitizationof the Floating Marsh Maps in the Barataria and TerrebonneBasins, Louisiana. Barataria-Terrebonne National EstuarineProgram Publication No. 28, Barataria-Terrebonne NationalEstuarine Program, Thibodaux, Louisiana.
FIELD, D. W., A. J. REYER, P. A. GENOVESE, AND B. D. SHEARER.1991. Coastal Wetlands of the United States: An Accountingof a Valuable National Resource. Special National Oceanicand Atmospheric Administration 20th Anniversary Report,National Oceanic and Atmospheric Administration and U.S.Fish and Wildlife Service, Washington, D.C.
GOSSELINK, J. G., C. L. CORDES, AND J. W. PARSONS. 1979. AnEcological Characterization Study of the Chenier Plain Coast-al Ecosystem of Louisiana and Texas. 3 Volumes. U.S. Fishand Wildlife Service, Office of Biological Services. FWS/OBS-78/9 through 78/11. Washington, D.C.
GOULD, H. R. AND E. MCFARLAN, JR. 1959. Geologic history ofthe Chenier Plain, Southwest Louisiana. Transactions of theGulf Coast Association of the Geological Society 9:261–270.
HILL, M. O. 1979. Twinspan—A FORTRAN Program for Ar-ranging Multivariate Data in an Ordered Two-way Table byClassification of the Individuals and Attributes. Cornell Uni-versity Press, Ithaca, New York.
KINLER, N. AND G. LINSCOMBE. 1998. A Survey of Nutria Herbiv-ory Damage in Coastal Louisiana in 1998. Report submittedto the Louisiana Department of Natural Resources, BatonRouge, Louisiana.
KOLB, C. R. AND J. R. VAN LOPIK. 1966. Depositional environ-ments of the Mississippi River deltaic plain—SoutheasternLouisiana, p. 17–61. In M. L. Shirley (ed.), Deltas in TheirGeologic Framework. Houston Geological Society, Houston,Texas.
LOUISIANA COASTAL WETLANDS CONSERVATION AND RESTORATION
TASK FORCE AND WETLANDS CONSERVATION AND RESTORATION
AUTHORITY. 1998. Coast 2050: Towards a Sustainable CoastalLouisiana. Louisiana Department of Natural Resources, BatonRouge, Louisiana.
ODUM, W. E., T. J. SMITH, III, J. K. HOOVER, AND C. C. MCIVOR.1984. The Ecology of Tidal Freshwater Marshes of the UnitedStates East Coast: A Community Profile. U.S. Fish and WildlifeService. FWS/OBS-83/17. Washington, D.C.
O’NEIL, T. 1949. The Muskrat in the Louisiana Coastal Marshes.Louisiana Wildlife and Fisheries Commission, New Orleans,Louisiana.
PENFOUND, W. T. AND E. S. HATHAWAY. 1938. Plant communitiesin the marshland of southeastern Louisiana. Ecological Mono-graphs 8:1–56.
PENLAND, S. AND K. E. RAMSEY. 1990. Relative sea-level rise inLouisiana and the Gulf of Mexico: 1908–1988. Journal of Coast-al Research 6:323–342.
RAINEY, G. B. 1979. Factors affecting nutrient chemistry distri-bution in Louisiana coastal marshes. M.S. Thesis, LouisianaState University, Baton Rouge, Louisiana.
ROTH, D. M. 1999. A Historical Study of Tropical Storms andHurricanes that have Affected Southwest Louisiana andSoutheast Texas. National Oceanic and Atmospheric Admin-istration, www.srh.noaa.gov/FTPROOT/LCH/lchhur.htm.
SCRUTON, P. C. 1960. Delta building and the deltaic sequence,p. 82–102. In F. P. Shepard, F. B. Phleger, and T. H. van Andel(eds.), Recent Sediments, Northwest Gulf of Mexico. Ameri-can Association of Petroleum Geologists, Tulsa, Oklahoma.
SHIFTLET, T. N. 1963. Major ecological factors controlling plantcommunities in Louisiana marshes. Journal of Range Manage-ment 16:231–235.
TAUSCH, R. J., D. A. CHARLET, D. A. WEIXELMAN, AND D. C. ZA-MUNDIO. 1995. Patterns of ordination and classification insta-bility resulting from changes in input data order. Journal ofVegetation Science 6:897–902.
TAYLOR, K. L., J. B. GRACE, G. R. GUNTENSPERGEN, AND A. L.FOOTE. 1994. The interactive effects of herbivory and fire onan oligohaline marsh, Little Lake, Louisiana, USA. Wetlands14:82–87.
TURNER, R. E. 1990. Landscape development and coastal wet-land losses in the northern Gulf of Mexico. American Zoology30:89–105.
VALENTINE, JR., J. M. 1976. Plant succession after saw-grass mor-tality in southwestern Louisiana. Proceedings of the SoutheasternAssociation of Fish and Wildlife Agencies 30:630–640.
VISSER, J. M., C. E. SASSER, R. H. CHABRECK, AND R. G. LINS
COMBE. 1998. Marsh vegetation types of the Mississippi RiverDeltaic Plain, USA. Estuaries 21:818–828.
VISSER, J. M., C. E. SASSER, R. H. CHABRECK, AND R. G. LINSCOMBE.1999. Long-term vegetation change in Louisiana tidal marsh-es, 1968–1992. Wetlands 19:168–175.
WRIGHT, L. D. 1985. River deltas, p.1–76. In R. A. Davis, Jr. (ed.),Coastal Sedimentary Environments. Springer Verlag, NewYork.
Received for consideration, April 23, 1998Accepted for publication, January 13, 2000
