2360-Classification of Wetlands and Deep-water Habitats of the United States

7/31/2019 2360-Classification of Wetlands and Deep-water Habitats of the United States

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1Classifi cation of Wetlandsand Deepwater Habitatsof theUnited States

By

L ewis M . Cowar din1, Virginia Car ter 2, Fr ancis C. Golet3, and Edwar d T. L aRoe4

U.S. Depar tment of the I nter ior

Fi sh and Wildl ife Servi ce

Office of Biological Services

Washington, D.C. 20240

Classification of Wetlands and

Deepwater Habitats of theUnited States


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2 Classification of Wetlandsand Deepwater Habitatsof theUnited States

Abstract

This classification, to beused in a new inventory of wetlands and deepwater habitats of theUnited States, isintended to describe ecological taxa, arrangethem in a system useful to resourcemanagers, furnish units formapping, and provideuniformity of conceptsand terms. Wetlands are defined by plants (hydrophytes), soils(hydric soils), and frequency of flooding. Ecologically related areas of deep water, traditionally not consid-ered wetlands, are included in the classification as deepwater habitats.

Systemsform thehighest level of the classification hierarchy; five are definedMarine, Estuarine, Riverine,Lacustrine, and Palustrine. Marineand EstuarineSystemseach have two Subsystems, Subtidal and Inter-tidal; theRiverine System has four Subsystems, Tidal, Lower Perennial, Upper Perennial, and Intermittent;theLacustrinehas two, Littoral and Limnetic; and thePalustrinehas no Subsystems.

Within the Subsystems, Classes are based on substratematerial and flooding regime, or on vegetative lifeform. The sameClasses may appear under oneor more of the Systems or Subsystems. Six Classes are basedon substrateand flooding regime: (1) Rock Bottom with a substrate of bedrock, boulders, or stones; (2)Unconsolidated Bottom with a substrateof cobbles, gravel, sand, mud, or organic material; (3) Rocky Shorewith the samesubstrates as Rock Bottom; (4) Unconsolidated Shore with the samesubstrates as Unconsoli-

dated Bottom; (5) Streambed with any of the substrates; and (6) Reef with a substrate composed of theli ving and dead remainsof invertebrates (corals, moll usks, or worms). Thebottom Classes, (1) and (2)above, are fl ooded all or most of thetimeand theshore Classes, (3) and (4), are exposed most of thetime.TheClass Streambed is restricted to channels of intermittent streamsand tidal channels that are dewatered atlow tide. Thelif e form of thedominant vegetation defi nes thefi ve Classes based on vegetative form: (1)Aquatic Bed, dominated by plantsthat grow principally on or below thesurface of the water; (2) Moss-Lichen Wetland, dominated by mosses or lichens; (3) Emergent Wetland, dominated by emergent herba-ceousangiosperms; (4) Scrub-Shrub Wetland, dominated by shrubs or small trees; and (5) Forested Wetland,dominated by largetrees.

TheDominance Type, which is named for thedominant plant or animal forms, is thelowest level of the

classification hierarchy. Only examples are provided for this level; DominanceTypes must be developed byindividual users of theclassification.

Modifying terms applied to the Classes or Subclasses are essential for use of the system. In tidal areas, thetype and duration of flooding are described by four Water Regime Modifiers: subtidal, irregularly exposed,regularly fl ooded, and irregularly fl ooded. In nontidal areas, eight Regimes are used: permanently fl ooded,intermittently exposed, semipermanently f looded, seasonally f looded, saturated, temporaril y f looded, inter-mittently flooded, and arti ficially f looded. A hierarchical system of Water Chemistry Modifiers, adaptedfrom theVeniceSystem, is used to describethesalinity of thewater. Fresh waters are further divided on thebasis of pH. Use of a hierarchical system of soil modifiers taken directly f rom U.S. soil taxonomy is alsorequired. Special modif iers are used where appropriate: excavated, impounded, diked, partl y drained,farmed, and artifi cial.

Regional differences important to wetland ecology are described through a regionalization that combines asystem developed for inland areas by R. G. Bail ey in 1976 with our Marineand Estuarineprovinces.

Thestructure of the classification allows it to beused at any of several hierarchical levels. Special datarequired for detailed application of the system are frequently unavailable, and thusdata gathering may be


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prerequisite to classification. Development of rules by the user will be required for specif ic map scales.DominanceTypes and relationships of plant and animal communities to environmental characteristicsmustalso bedeveloped by users of theclassification. Keys to theSystemsand Classes are furnished as a guide,and numerous wetlands and deepwater habitatsare illustrated and classified. Theclassification system isalso compared with several other systemscurrently in use in theUnited States.

This r esource is based on the following source (Nor ther n Pr air ie Publication 0421):

C o w a r d i n , L . M. , V . C a r t e r , F . C . Go l e t , E . T . L a R o e . 1 9 7 9 . C l a s s i f i c a t i o n o fw e t l a n d s a n d d e e p w a t e r h a b i t a t s o f t h e U n i t e d S t a t e s . U . S . D e p a r t me n t o f

t h e I n t e r i o r , F i s h a n d Wi l d l i f e Se r v i c e , Wa s h i n g t o n , D . C . 1 3 1 p p .

This resource should be cit ed as:

C o w a r d i n , L . M. , V . C a r t e r , F . C . Go l e t , E . T . L a R o e . 1 9 7 9 . C l a s s i f i c a t i o n o fw e t l a n d s a n d d e e p w a t e r h a b i t a t s o f t h e U n i t e d S t a t e s . U . S . D e p a r t me n t o ft h e I n t e r i o r , F i s h a n d Wi l d l i f e Se r v i c e , Wa s h i n g t o n , D . C .

J a me s t o wn , ND: No r t h e r n Pr a i r i e Wi l d l i f e Re s e a r c h Ce n t e r Ho me Pa g e .h t t p : / / www . n p wr c . u s g s . g o v / r e s o u r c e / 1 9 9 8 / c l a s s we t / c l a s s we t . h t m

( V e r s i o n 0 4 DEC 9 8 ) .


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Table of Contents

Foreword Preface Introduction Wetlandsand Deepwater Habitats TheClassification System Hierarchical Structure MarineSystem EstuarineSystem RiverineSystem LacustrineSystem PalustrineSystem Classes, Subclasses, and DominanceTypes Rock Bottom Unconsoli dated Bottom Aquatic Bed Reef

Streambed Rocky Shore Unconsolidated Shore Moss-Lichen Wetland Emergent Wetland Scrub-Shrub Wetl and Forested Wetland Modifiers Water Regime Modifiers Water Chemistry Modifiers Soil Modifiers Special Modifiers Regionalization for the Classification System Use of theClassification System Acknowledgments References Appendix A. Scientific and common names of plants Appendix B. Scientif ic and common names of animals Appendix C. Glossary of terms Appendix D. Criteria for distinguishing organic soils from mineral soils Appendix E. Artificial key to Systemsand Classes

Tables

Table 1 Distribution of Subclasses within theclassif ication hierarchy Table 2 Sali nity Modifi ers used in theclassifi cation system Table 3 pH Modifi ers used in theclassification system Table 4 Comparison of wetland types Table 5 Comparison of zones devised by Stewart and Kantrud (1971)


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Figures

Figure1 Classification hierarchy of wetlands and deepwater habitats Figure 2 Distinguishing features of habitats in theMarineSystem Figure 3 Distinguishing features of habitats in theEstuarineSystem Figure 4 Distinguishing features of habitats in theRiverineSystem Figure 5 Distinguishing features of habitats in theLacustrineSystem Figure 6 Distinguishing features of habitats in thePalustrineSystem Figure 7 Ecoregions of theUnited States Figure 8 Comparison of water chemistry subclasses

Plates

Plates1-4 Plates5-8 Plates9-12 Plates13-16 Plates17-20 Plates21-24 Plates25-28 Plates29-32 Plates33-36 Plates37-40 Plates41-44 Plates45-48 Plates49-52 Plates53-56 Plates57-60 Plates61-64

Plates65-68 Plates69-72 Plates73-76 Plates77-80 Plates81-84 Plates85-86

1U.S. Fish and Wildlife Service, Northern Prairie Wildlife Research Center, Jamestown, North Dakota584012U.S. Geological Survey, Reston, Virginia 220923Department of Natural Resources Science, University of Rhode Island, Kingston, RhodeIsland 028814U.S. National Oceanographic andAtmospheric Administration, Officeof Coastal ZoneManagement,Washington, D.C. 20235


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Classification of Wetlands and Deepwater Habitatsof the United States

Foreword

Wetlandsand deepwater habitats are essential breeding, rearing, and feeding groundsfor many speciesoffi sh and wildlife. They may also perform fl ood protection and poll ution control functions. Increasing Na-

tional and international recognition of these values has intensifi ed theneed for reliable information on thestatus and extent of wetland resources. To develop comparable information over largeareas, a clear defini-tion and classification of wetlands and deepwater habitatsis required.

Theclassification system contained in this report was developed by wetland ecologists, with theassistanceof many private individuals and organizations and local, State, and Federal agencies. An operational draftwas published in October 1977, and a noticeof intent to adopt the system for all pertinent Serviceactivitieswas published December 12, 1977 (42 FR 62432).

TheFish and Wildlife Serviceis officiall y adopting this wetland classifi cation system. Futurewetland databases developed by the Service, including theNational Wetlands Inventory, will utilizethis system. A one-year transition period will allow for training of Servicepersonnel, amendment of administrative manuals,

and further development of theNational WetlandsInventory data base. During this period, Servi cepersonnelmay continue to use the old wetland classif ication described in Fish and Wildli fe Service Circular 39 forFish and Wildlife CoordinationAct reports, wetland acquisition priority determinations, and other activitiesin conjunction with thenew system, where immediate conversion is not practicable.

Upon completion of thetransition period, theCircular 39 system will no longer beoffi cially used by theFish and Wildlife Serviceexcept where theapplicable lawsstill reference that system or when theonlyinformation available is organized according to that system and cannot be restructured without new fi eldsurveys.

Other Federal and State agencies are encouraged to convert to the use of this system. No specif ic legal

authorities require theuse of this system or any other system for that matter. However, it is expected thatthebenefits of National consistency and a developing wetland data base utilizing this system will result inacceptance and use by most agencies involved in wetland management. Training can beprovided to users bytheService, depending on the availabil ity of resources. Congressional committees will be notified of thisadoption action and will be encouraged to facil itate general adoption of the new system by amending anylaws that reference the Circular 39 system.


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This is a new system and users will need to study and learn theterminology. TheServiceis preparing adocument to aid in comparing and translating the new system to the Services former classification system.In the coming year, the Fish and Wildli fe Service, in conjunction with the Soil Conservation Service, alsoplansto develop initial l istsof hydrophytic plantsand hydric soils that wil l support interpretation and use ofthis system.

We beli eve that this system will providea suitable basis for information gathering for most scientific, educa-

tional, and administrative purposes; however, it will not f it all needs. For instance, historical or potentiallyrestorable wetlands are not included in this system, nor was the system designed to accommodate all therequirementsof the many recently passed wetland statutes. No attempt was madeto definetheproprietary orjurisdictional boundaries of Federal, State, or l ocal agencies. Nevertheless, the basic design of the classif ica-tion system and the resulti ng data base should assist substantially in the administration of these programs.

This report represents themost current methodology available for wetland classification and culminates along-term effort involvi ng many wetland scientists. Although it may require revision from time to time, itwill serve uswell in theyears ahead. We hopeall wetland personnel in all levels of government and theprivate sector cometo know it and use it for theultimate benefit of Americas wetlands.

Lynn Greenwalt, DirectorU.SFish and Wildlife Service


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Preface

Since its publication in 1979, Classi fication of Wetlands and D eepwater Habitats of the Uni ted States hasbeen used in theNational inventory of wetlands conducted by theU.S. Fish and Wildlife Service. Thesystem has been widely used throughout the United States and is often cited in thescientific literature. Therehas also been considerable international interest in use of theclassification.

Copies from thefi rst printing have been expended and demand requires this reprinting. We have taken thisopportunity to correct anumber of minor typographical errors, bring plant names into conformity with the

National List of Scientific Plant Names (U.S. Dept. Agriculture1982), and to upgradethequality of plates aswell as furnish additional plates. No changes have been madethat either alter the structure of theclassifica-tion or themeaning of the definiti ons. Such major revisions must be deferred until certain prerequisite tasksare accomplished.

Completion of theli st of hydrophytes and other plantsoccurring in wetlands and theli st of hydric soils hasbeen a task of far greater complexity than we envisioned when writing the classification. These lists havereceived extensive review and are being prepared as computer data bases. In addition, theli sts will contain agreat deal of ancillary information that will make possible the development of methodologies for their use inboth thedelineation and classifi cation of wetlands. When thelistsand methodologiesare completed, re-viewed, and tested we wil l revise the classif ication and use the li sts to add precision to the defi nitions. At the

sametime, we will address specific technical problemsthat have arisen during application of the classifica-tion.

Theplates at theend of this publication are included primarily to ill ustrate a variety of examplesof wetlandclassification. Wehave attempted to include photographs from various regionsof the country insofar aspossible; however, final selection of plates was based on the availabil ity of both high-quality photographsand thedetailed field data required for accurate classifi cation. While on sabbatical leave from theUniversityof Rhode Island in 1985, Dr. Frank Golet took numerous photographs of Alaskan wetlands. Addition ofmany of these and several photographsfrom other regions helpssomewhat to correct a regional imbalance.

Weacknowledgetheassistance of Dr. J. Henry Sather who served as editor for thereprinting. He spent

many hours compiling minor errors and inconsistencies and preparing final copy for the printer. We thankMr. Jon Hall, National Wetlands Inventory Coordinator for theAl aska region, for his assistance to Dr. Goletduring his stay in Al aska.

Lewis M. CowardinVirginiaCarterFrancis C. GoletEdward T. LaRoeSeptember 24, 1985


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Introduction

TheU.S. Fish and Wildlife Serviceconducted an inventory of thewetlands of the United States (Shaw andFredine 1956) in 1954. Since then, wetlands have undergoneconsiderable change, both natural and manrelated, and their characteristicsand natural values have becomebetter defined and more widely known.During this interval, State and Federal l egislation has been passed to protect wetlands, and some Statewidewetland surveyshave been conducted.

In 1974, the U.S. Fish and Wildli fe Service directed its Office of Biological Services to design and conduct a

new National inventory of wetlands. Whereas thesingle purpose of the1954 inventory was to assess theamount and types of valuable waterfowl habitat, thescopeof thenew project i s considerably broader(Montanari and Townsend 1977). It will providebasic data on thecharacteristicsand extent of theNationswetlands and deepwater habitatsand should facil itate the management of these areas on a sound, multiple-use basis.

Before the1954 inventory was begun, Martin et al. (1953) had devised a wetland classif ication system toserve as a framework f or the National inventory. Theresults of theinventory and an illustrated description ofthe 20 wetland types were publi shed as U.S. Fish and Wildli fe Service Circular 39 (Shaw and Fredine1956). This circular has been one of themost common and most influential documents used in the continu-ous battle to preserve a critically valuable but rapidly diminishing National resource(Stegman 1976). How-

ever, theshortcomings of this work are well known (e.g., see Leitch 1966; Stewart and Kantrud 1971).

In attempting to simpli fy their classifi cation, Martin et al. (1953) not only i gnored ecologicall y criticaldifferences, such as thedistinction between fresh and mixosaline inland wetlands but also placed dissimilarhabitats, such as forests of boreal black spruce (Picea mar iana) and of southern cypress-gum (Taxodiumdistichum-Nyssa aquatica) in thesamecategory, with no provisions in thesystem for distinguishing betweenthem. Because of the central emphasis on waterfowl habitat, far greater attention was paid to vegetated areasthan to nonvegetated areas. Probably the greatest single disadvantageof theMartin et al. system was theinadequate definition of types, which led to inconsistenciesin appli cation.

Numerousother classifications of wetlands and deepwater habitats have been developed (Stewart and

Kantrud 1971; Golet and Larson 1974; Jeglum et al. 1974; Odum et al. 1974; Zoltai et al. 1975; Millar1976), but most of these are regional systemsand nonewould fully satisfy National needs. Because of theweaknesses inherent in Circular 39, and because wetland ecology has become significantly better under-stood since1954, theU.S. Fish and Wildlife Serviceelected to construct a new National classif icationsystem as thefirst step toward a new National inventory. Thenew classification, presented here, has beendesigned to meet four long-range objectives: (1) to describeecological units that have certain homogeneousnatural attri butes; (2) to arrange these units in a system that will aid decisions about resource management;(3) to furnish units for inventory and mapping; and (4) to provide unif ormity in conceptsand terminologythroughout the United States.


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Scientif ic and common names of plants(Appendix A) and animals (Appendix B) were taken from varioussources cited in thetext. No attempt has been madeto resolve nomenclatorial problemswhere there is ataxonomic dispute. Many of the termsused in this classifi cation have various meanings even in thescientificli teratureand in some instances our use of termsis new. We have provided a glossary (Appendix C) to guidethe reader in our usageof terms.


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Wetlands and Deepwater Habitats

Concepts and Defi nit ions

Marshes, swamps, and bogshave been well-known terms for centuries, but only relatively recently haveattempts been madeto group these landscapeunits under the single term wetlands. This general term hasgrown out of a need to understand and describethecharacteristicsand values of all types of land, and towisely and eff ectively managewetland ecosystems. There is no single, correct, indisputable, ecologicallysound definition for wetlands, primarily because of thediversity of wetlands and because the demarcationbetween dry and wet environments lies along a continuum. Because reasons or needsfor defining wetlandsalso vary, a great proliferation of defi nitions has arisen. Theprimary objective of this classif ication is toimpose boundaries on natural ecosystems for the purposes of inventory, evaluation, and management.

WetlandsIn general terms, wetlands are lands where saturation with water is thedominant factor determining thenatureof soil development and thetypes of plant and animal communities living in thesoil and on itssurface. The single feature that most wetlands share is soil or substrate that is at least periodically saturatedwith or covered by water. Thewater creates severe physiological problemsfor all plants and animals exceptthose that are adapted for l ife in water or in saturated soil.

WETLANDS are lands transi tional between terr estr ial and aquatic systems where the water table i s usuall yat or near the surface or the land is covered by shallow water. For purposes of this classification wetlands

must have one or more of the following three attributes: (1) at least periodically, the land supports predomi-nantly hydrophytes; 1 (2) the substrate is predominantly undrained hydric soil; 2 and (3) the substr ate isnonsoil and is saturated with water or covered by shallow water at some time during the growing season ofeach year.

Theterm wetland includes a variety of areas that fall into one of five categories: (1) areas with hydrophytesand hydric soils, such as those commonly known as marshes, swamps, and bogs; (2) areas without hydro-phytes but with hydric soilsfor example, fl ats where drastic fl uctuation in water level, wave action, turbid-ity, or high concentration of salts may prevent thegrowth of hydrophytes; (3) areas with hydrophytes butnonhydric soil s, such as marginsof impoundments or excavations where hydrophytes have become estab-lished but hydric soils have not yet developed; (4) areas without soils but with hydrophytes such as the

seaweed-covered portion of rocky shores; and (5) wetlands without soil and without hydrophytes, such asgravel beaches or rocky shoreswi thout vegetation.

Drained hydric soils that are now incapable of supporting hydrophytes because of a change in water regimeare not considered wetlands by our defi nition. These drained hydric soils furnish a valuable record of his-toric wetlands, as well as an indication of areas that may be suitable for restoration.

Wetlands as defined here include lands that areidentif ied under other categories in some land-use classifica-tions. For example, wetlands and farmlandsare not necessarily exclusive. Many areas that we defineas


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wetlands are farmed during dry periods, but if they are not till ed or planted to crops, a practicethat destroysthe natural vegetation, they will support hydrophytes.

Deepwater HabitatsDEEPWATER HABITATS are per manently fl ooded l ands lying below the deepwater boundary of wetlands.Deepwater habitats includeenvironments where surfacewater is permanent and often deep, so that water,rather than air, is theprincipal medium within which thedominant organismslive, whether or not they are

attached to the substrate. As in wetlands, thedominant plants are hydrophytes; however, thesubstrates areconsidered nonsoil because the water is too deep to support emergent vegetation (U.S. Soil ConservationServi ce, Soil Survey Staff 1975).

Wetlands and deepwater habitats are defined separately because traditi onally theterm wetland has notincluded deep permanent water; however, both must beconsidered in an ecological approach to classifica-tion. We define five major Systems: Marine, Estuarine, Riverine, Lacustrine, and Palustrine. Thefirst four ofthese include both wetland and deepwater habitats but thePalustrineincludes only wetland habitats.

Limits

Theupland limit of wetland is designated as (1) theboundary between land with predominantly hydrophyticcover and land with predominantly mesophytic or xerophytic cover; (2) the boundary between soil that ispredominantly hydric and soil that is predominantly nonhydric; or (3) in thecase of wetlands without veg-etation or soil, theboundary between land that is fl ooded or saturated at some timeduring thegrowingseason each year and land that is not.

Theboundary between wetland and deepwater habitat in theMarineand EstuarineSystemscoincides withthe elevation of the extremelow water of spring tide; permanently fl ooded areas are considered deepwaterhabitats in these Systems. Theboundary between wetland and deepwater habitat in theRiverine and Lacus-trineSystemsliesat a depth of 2 m (6.6 feet) below low water; however, if emergents, shrubs, or trees growbeyond this depth at any time, their deepwater edge is theboundary.

The2-m lower limit for inland wetlands was selected because it representsthemaximum depth to whichemergent plants normally grow (Welch 1952; Zhadin and Gerd 1963; Sculthorpe 1967). As Daubenmire(1968:138) stated, emergents are not true aquatic plants, but are amphibious, growing in both permanentlyfl ooded and wet, nonflooded soils. In their wetland classifi cation for Canada, Zoltai et al. (1975) also in-cluded only areas with water l ess than 2 m deep.

1TheU.S. Fish and Wildlife Serviceis preparing a list of hydrophytes and other plantsoccurring in wetlandsof the United States.2TheU.S. Soil Conservation Serviceis preparing a preliminary list of hydric soils for use in this classifi ca-tion system.


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Fig. 1. Classification hierarchy of wetlands and deepwater habitats, showing Systems, Sub-systems, and Classes. The Palustri neSystem does not include deepwater habitats.


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The Classification System

Thestructure of this classification is hierarchical, progressing from Systemsand Subsystems, at the mostgeneral levels, to Classes, Subclasses, and Dominance Types. Figure1 illustrates theclassification structureto theclass level. Table 1 li sts theClasses and Subclasses for each System and Subsystem. Arti fi cial keys totheSystemsand Classes are given in Appendix E . Modifi ers for water regime, water chemistry, and soilsare applied to Classes, Subclasses, and DominanceTypes. Special modifiers describewetlands anddeepwater habitats that havebeen either created or highly modif ied by man or beavers.


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Systems and Subsystems

The term SYSTEM refers here to a complex of wetlandsand deepwater habitatsthat share the influence ofsimilar hydrologic, geomorphologic, chemical, or biological factors. Wefurther subdivi deSystemsintomore specif ic categories called SUBSYSTEMS.

Thecharacteristicsof thefive major SystemsMarine, Estuarine, Riverine, Lacustrine, and Palustrinehave been discussed at length in the scientific literature and the concepts are well recognized; however, thereis frequent disagreement as to which attri butes should beused to bound the Systemsin space. For example,both theli mit of ti dal influence and thelimit of ocean-derived salinity have been proposed for bounding the

upstream end of theEstuarineSystem (Caspers 1967). As Bormann and Likens(1969) pointed out, bound-aries of ecosystems are defined to meet practical needs.


Hierarchical Structure

M ar ine System

Definition. TheMarineSystem (Fig. 2) consistsof theopen ocean overlying thecontinental shelf and itsassociated high-energy coastl ine. Marinehabitats are exposed to thewaves and currents of the open oceanand thewater regimes are determined primarily by theebb and fl ow of oceanic tides. Sali nities exceed 30, with li ttle or no dilution except outside themouths of estuaries. Shallow coastal indentations or bayswithout appreciable freshwater inflow, and coasts with exposed rocky islands that provide the mainland withlittle or no shelter from wind and waves, are also considered part of theMarineSystem because they gener-

ally support typical marinebiota.

Limits. TheMarineSystem extends from the outer edge of thecontinental shelf shoreward to one of threelines: (1) the landward limit of tidal inundation (extremehigh water of spring tides), including thesplashzonefrom breaking waves; (2) theseaward limit of wetland emergents, trees, or shrubs; or (3) theseawardlimit of theEstuarineSystem, where this limit is determined by factors other than vegetation. Deepwaterhabitats lying beyond theseaward limit of theMarineSystem are outsidethescopeof this classif icationsystem.

Description. Thedistribution of plantsand animals in theMarineSystem primarily refl ectsdiff erences infour factors: (1) degree of exposure of thesite to waves; (2) textureand physicochemical nature of the

substrate; (3) amplitude of thetides; and (4) l atitude, which governswater temperature, the intensity andduration of solar radiation, and the presence or absence of ice.

Subsystems.

Subtidal. Thesubstrate is continuously submerged.Intertidal. Thesubstrate is exposed and fl ooded by tides; i ncludes the associated splash zone.

Classes. Rock Bottom, Unconsolidated Bottom, Aquatic Bed, Reef, Rocky Shore, and UnconsolidatedShore.


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Fig. 2. Distinguishing features and examplesof habitats in theMarineSystem. EHWS= extremehighwater of spring tides; ELWS = extreme low water of spring tides.

Estuar ine System

Definition. The EstuarineSystem (Fig. 3) consists of deepwater tidal habitatsand adjacent tidal wetlandsthat are usually semienclosed by land but have open, partl y obstructed, or sporadic access to the open ocean,and in which ocean water is at least occasionally diluted by freshwater runoff from theland. Thesalinitymay beperiodically increased above that of the open ocean by evaporation.Along somelow-energy coast-li nes there is appreciable dilution of sea water. Offshoreareas with typical estuarineplantsand animals, suchas red mangroves (Rhizophora mangle) and eastern oysters (Crassostrea virginica), are also included in theEstuarineSystem.3

Limits. TheEstuarineSystem extends (1) upstream and landward to where ocean-derived salts measurelessthan 0.5 during theperiod of averageannual low fl ow; (2) to an imaginary lineclosing themouth of ariver, bay, or sound; and (3) to theseaward limit of wetland emergents, shrubs, or trees where they are notincluded in (2). TheEstuarineSystem also includes offshore areas of continuously diluted sea water.


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Description. TheEstuarineSystem includes both estuaries and lagoons. It is more strongly influenced by itsassociation with land than is theMarineSystem. In termsof wave action, estuaries are generall y consideredto below-energy systems(Chapman 1977:2).

Estuarinewater regimes and water chemistry areaff ected by one or moreof thefollowing forces: oceanictides, precipitation, freshwater runoff from land areas, evaporation, and wind. Estuarinesaliniti es range fromhyperhaline to oligohaline (Table 2). Thesali nity may bevariable, as in hyperhaline lagoons (e.g., Laguna

Madre, Texas) and most brackish estuaries (e.g., Chesapeake Bay, Virginia-Maryl and); or it may be rela-tively stable, as in sheltered euhalineembayments(e.g., Chincoteague Bay, Maryland) or brackishembayments with partly obstructed access or small tidal range (e.g., Pamlico Sound, North Caroli na). (Foran extended discussion of estuaries and lagoons see Lauff 1967.)

Subsystems.

Subtidal. Thesubstrate is continuously submerged.Intertidal. Thesubstrate is exposed and fl ooded by tides; i ncludes the associated splash zone.

Classes. Rock Bottom, Unconsolidated Bottom, Aquatic Bed, Reef, Streambed, Rocky Shore, Unconsoli-dated Shore, Emergent Wetland, Scrub-Shrub Wetland, and Forested Wetland.

Fig. 3. Distinguishing features and examples of habitatsin the EstuarineSystem. EHWS = extremehigh water of spring tides; ELWS= extreme low water of spring tides.

3The Coastal Zone Management Act of 1972 defines an estuary as that part of a river or stream or other body of water having

unimpaired connection with theopen sea, where thesea-water is measurably diluted with freshwater derived from landdrainage.TheA ct further states that theterm includes estuary-type areas of theGreat L akes. However, in thepresent system we do not

consider areas of the Great Lakesas Estuarine.


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development.Intermittent. In this Subsystem, the channel contains fl owing water for only part of the year.When thewater is not flowing, it may remain in isolated pools or surfacewater may beabsent.

Classes. Rock Bottom, Unconsolidated Bottom, Aquatic Bed, Streambed, Rocky Shore, UnconsolidatedShore, and Emergent Wetl and (nonpersistent).

Fig. 4. Distinguishing features and examples of habitatsin theRiverine System.

L acustr ine System

Definition. TheLacustrineSystem (Fig. 5) i ncludes wetlands and deepwater habitats with all of thefollow-

ing characteristics: (1) situated in a topographic depression or a dammed river channel; (2) lacking trees,shrubs, persistent emergents, emergent mosses or lichens with greater than 30% areal coverage; and (3) totalarea exceeds8 ha(20 acres). Similar wetland and deepwater habitats totaling less than 8 haare also includedin theLacustrineSystem if an active wave-formed or bedrock shorelinefeature makes up all or part of theboundary, or if thewater depth in the deepest part of thebasin exceeds2 m (6.6 feet) at low water. Lacus-trinewaters may betidal or nontidal, but oceanderived sali nity is always less than 0.5 .


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Limits. TheLacustrineSystem is bounded by upland or by wetland dominated by trees, shrubs, persistentemergents, emergent mosses, or l ichens. Lacustri neSystems formed by damming a river channel arebounded by acontour approximating the normal spil lway elevation or normal pool elevation, except wherePalustrinewetlands extend lakeward of that boundary. Where a river enters a lake, the extension of theLacustrineshorelineforms theRiverine-Lacustrineboundary.

Description. TheLacustrineSystem includes permanently flooded lakes and reservoirs (e.g., Lake Supe-

rior), intermittent l akes (e.g., playa lakes), and tidal lakes with ocean-derived salinities below 0.5 (e.g.,Grand Lake, Louisiana). Typically, there are extensive areas of deep water and there is considerable waveaction. Islands of Palustrinewetland may lie within the boundaries of theLacustrineSystem.

Subsystems.

Limnetic. All deepwater habitatswithin theLacustrineSystem; many small LacustrineSystemshave no Limnetic Subsystem.Littoral. All wetland habitats in the LacustrineSystem. Extendsf rom the shoreward boundary ofthesystem to a depth of 2 m (6.6 feet) below l ow water or to themaximum extent of nonpersistentemergents, if these grow at depthsgreater than 2 m.

Classes. Rock Bottom, Unconsolidated Bottom, Aquatic Bed, Rocky Shore, Unconsolidated Shore, andEmergent Wetland (nonpersistent).

Fig. 5. Distinguishing features and examples of habitatsin theLacustrineSystem.


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Palustr ine System

Definition. The PalustrineSystem (Fig. 6) i ncludes all nontidal wetlands dominated by trees, shrubs, persis-tent emergents, emergent mosses or lichens, and all such wetlands that occur in tidal areas where salinitydue to ocean-derived salts is below 0.5 . It also includes wetlands lacking such vegetation, but with all ofthe following four characteristics: (1) area less than 8 ha(20 acres); (2) active wave-formed or bedrock

shorelinefeatures lacking; (3) water depth in the deepest part of basin less than 2 m at low water; and (4)salinity due to ocean-derived salts less than 0.5 .

Limits. ThePalustrineSystem is bounded by upland or by any of theother four Systems.

Description. ThePalustrineSystem was developed to group thevegetated wetlands traditionally called bysuch names as marsh, swamp, bog, fen, and prairie, which are found throughout theUnited States. It alsoincludes the small, shallow, permanent or intermittent water bodies often called ponds. Palustrinewetlandsmay besituated shoreward of lakes, river channels, or estuaries; on river floodplains; in isolated catchments;or on slopes. They may also occur asislands in lakes or rivers. Theerosive forces of wind and water areofminor importance except during severe floods.

Theemergent vegetation adjacent to rivers and lakes is often referred to as theshore zone or the zoneofemergent vegetation (Reid and Wood 1976), and is generally considered separately from theriver or lake.As an example, Hynes (1970:85) wrote in reference to riverinehabitats, We will not here consider thelonglist of emergent plants which may occur along thebanksout of the current, as they do not belong, strictlyspeaking, to therunning water habitat. There are often great similarities between wetlands lying adjacentto lakes or rivers and isolated wetlands of thesameclass in basinswithout open water.

Subsystems. None.

Cl asses. Rock Bottom, Unconsolidated Bottom, Aquatic Bed, Unconsolidated Shore, Moss-Lichen Wetland,Emergent Wetland, Scrub-Shrub Wetland, and Forested Wetland.


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Fig. 6. Distinguishing features and examples of habitatsin the PalustrineSystem.


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Classes, Subclasses, and Dominance Types

TheCLASS is the highest taxonomic unit below theSubsystem level. It describes the general appearance ofthehabitat in termsof either thedominant l ife form of thevegetation or the physiography and compositionof the substrate features that can berecognized without the aid of detailed environmental measurements.Vegetation is used at two diff erent levels in theclassif ication. Theli fe forms trees, shrubs, emergents,

emergent mosses, and lichens are used to defineClasses because they are relatively easy to distinguish,do not change distribution rapidly, and have traditionally been used as criteria for classif ication of wetlands.4

Other formsof vegetation, such as submerged or floating-leaved rooted vascular plants, free-floating vascu-lar plants, submergent mosses, and algae, though frequently moredifficult to detect, are used to definetheClassAquatic Bed. Pioneer speciesthat briefly invadewetlands when conditions are favorable are treated atthe Subclass level because they are transient and often not true wetland species.

Use of life formsat theClass level has two major advantages: (1) extensive biological knowledgeis notrequired to distinguish between various li fe forms, and (2) it has been established that various li fe forms areeasily recognizable on a great variety of remote sensing products(e.g., Radforth 1962; Anderson et al.1976). If vegetation (except pioneer species) covers 30% or more of thesubstrate, we distinguish Classes on

the basis of the life form of the plants that constitute the uppermost layer of vegetation and that possess anareal coverage30% or greater. For example, an area with 50% areal coverageof trees over a shrub layerwith a 60% areal coveragewould beclassified as Forested Wetland; an area with 20% areal coverageoftrees over thesame(60%) shrub layer would beclassified as Scrub-Shrub Wetland. When trees or shrubsalonecover less than 30% of an area but in combination cover 30% or more, thewetland is assigned to theClass Scrub-Shrub. When trees and shrubs cover less than 30% of the area but thetotal cover of vegetation(except pioneer species) i s 30% or greater, the wetland is assigned to the appropriate Class for the predomi-nant lif e form below theshrub layer. Finer diff erences in lif e forms are recognized at the SUBCLASS level.For example, Forested Wetland is divi ded into the Subclasses Broad-leaved Deciduous, Needle-leavedDeciduous, Broad-leaved Evergreen, Needle-leaved Evergreen, and Dead. Subclasses are named on thebasis of thepredominant l ife form.

If vegetation covers less than 30% of the substrate, thephysiography and composition of thesubstrate arethe principal characteristicsused to distinguish Classes. Thenature of the substratereflects regional andlocal variations in geology and theinfluence of wi nd, waves, and currentson erosion and deposition ofsubstrate materials. Bottoms, Shores, and Streambedsare separated on the basis of duration of inundation. Inthe Riverine, Lacustrine, and PalustrineSystems, Bottoms are submerged all or most of the time, whereasStreambedsand Shores are exposed all or most of thetime. In the Marineand EstuarineSystems, Bottomsare Subtidal, whereas Streambedsand Shoresare Interti dal. Bottoms, Shores, and Streambedsare furtherdivi ded at the Class level on the basis of theimportant characteristic of rock versusunconsolidated sub-strate. Subclasses are based on finer distinctions in substratematerial unless, as with StreambedsandShores, thesubstrate is covered by, or shaded by, an areal coverageof pioneering vascular plants (often

nonhydrophytes) of 30% or more; theSubclass is then simply vegetated. Further detail as to thetype ofvegetation must beobtained at thelevel of Dominance Type. Reefs are a unique class in which the substrateitself is composed primarily of living and dead animals. Subclasses of Reefs are designated on the basis ofthetypeof organism that formed thereef.

TheDOMI NANCE TYPE is thetaxonomic category subordinate to Subclass. Dominance Types are deter-mined on the basis of dominant plant species (e.g., Jeglum et al. 1974), dominant sedentary or sessile animaspecies (e.g., Thorson 1957), or dominant plant and animal species(e.g., Stephenson and Stephenson 1972).A dominant plant specieshas traditionally meant one that has control over the community (Weaver and


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Clements 1938:91), and this plant is also usually the predominant species (Cain and Castro 1959:29). WhentheSubclass is based on li fe form, we nametheDominance Typefor thedominant species or combination ofspecies(codominants) in the same layer of vegetation used to determinethe Subclass.5 For example, aNeedle-leaved Evergreen Forested Wetland with 70% areal cover of black spruce (Picea mar iana) and 30%areal cover of tamarack (Larix lari cina) would bedesignated as a Picea mariana DominanceType. Whentherelative abundance of codominant species is nearly equal, theDominance Typeconsists of a combinationof speciesnames. For example, an Emergent Wetland with about equal areal cover of common cattail (Typhalatifolia) and hardstem bulrush (Scir ious acutus) would bedesignated a Typha latifolia-Scirpus acutusDominanceType.

When the Subclass is based on substrate material, the Dominance Type is named for the predominant plantor sedentary or sessile macroinvertebrate species, without regard for li fe form. In theMarineand EstuarineSystems, sponges, alcyonarians, mollusks, crustaceans, worms, ascidians, and echinoderms may all bepartof the community represented by the Macoma balthica DominanceType. Sometimes it i s necessary todesignate two or more codominant speciesas a DominanceType. Thorson (1957) recommended guidelinesand suggested definiti ons for establishing community types and dominants on level bottoms.

4Our ini tial attempts to use familiar termssuch as marsh, swamp, bog, and meadow at theClass level were unsuccessful

primaril y because of wide discrepanciesi n theuse of these termsi n variousregionsof theUnited States. In an effort toresolve that diff iculty, we based theClasses on thefundamental components(lif e form, water regime, substrate type,

water chemistry) that give rise to such terms. We believe that this approach will greatly reducethemisunderstandings andconfusion that result f rom theuse of the familiar terms.5Percent areal cover i s seldom measured in theappli cation of this system, but the term must be defi ned in terms of area.Wesuggest 2 m2 for herbaceous and moss layers, 16 m2 for shrub layers, and 100 m2 for tree layers (Mueller-Domboisand Ellenberg 1974:74). When percent areal cover is thekey for establishing boundaries between units of theclassifi ca-

tion, it may occasionall y benecessary to measurecover on plots, in order to maintain unif ormity of ocular estimates made

in thefi eld or interpretations madefrom aerial photographs.

Rock Bottom

Definition. TheClass Rock Bottom includes all wetlands and deepwater habitatswith substrates having anareal cover of stones, boulders, or bedrock 75% or greater and vegetative cover of l ess than 30%. Waterregimes are restri cted to subtidal, permanently flooded, intermittently exposed, and semipermanentlyflooded.

Description. Therock substrate of therocky benthic or bottom zoneis one of themost important factors indetermining theabundance, variety, and distribution of organisms. Thestability of thebottom all owsa richassemblageof plantsand animals to develop. Rock Bottoms are usually high-energy habitatswith well-aerated waters. Temperature, salinity, current, and light penetration are also important factors in determiningthecomposition of thebenthic community.Animals that live on therocky surfaceare generall y firmly

attached by hooking or sucking devices, although they may occasionally moveabout over the substrate.Some may bepermanently attached by cement. A few animals hide in rocky crevices and under rocks, somemove rapidly enough to avoid being swept away, and others burrow into thefiner substrates between boul-ders. Plants are also firmly attached (e.g., by hold-fasts), and in theRiverineSystem both plantsand animalsare commonly streamlined or fl attened in response to high water velocities.

Subclasses and Dominance Types.

Bedrock. Bottomsin which bedrock covers 75% or more of the surface.Rubble. Bottomswith less than 75% areal cover of bedrock, but stones and boulders alone, or i n


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combination with bedrock, cover 75% or more of the surface.

Examples of Dominance Types for these two Subclasses in theMarineand EstuarineSystemsare theen-crusting sponges Hippospongia, the tunicate Cnemidocarpa, the sea urchin Strongylocentrotus, thesea starPisaster , the sea whip Muricea, and theAmerican lobster Homarus americanus. Examples of Lacustrine,Palustri ne, and RiverineDominanceTypes are the freshwater sponges Spongilla and Heteromeyenia, thepond snail Lymnaea, the mayfly Ephemerella, various midges of theChironomidae, thecaddisfly

Hydropsyche, the leech Helobdella, the riffle beetle Psephenus, the chironomid midgeEukiefferiella, thecrayfish Procambarus, and the black fl y Simulium.

Dominance Types for Rock Bottoms in theMarineand EstuarineSystemswere taken primarily from Smith(1964) and Ricketts and Calvin (1968), and those for Rock Bottoms in theLacustrine, Riverine, andPalustrineSystemsfrom Krecker and Lancaster (1933), Stehr and Branson (1938), Ward and Whipple(1959), Clarke(1973), Hart and Fuller (1974), Ward (1975), Slack et al. (1977), and Pennak (1978).

Unconsolidated Bottom

Definition. The Class Unconsolidated Bottom includes all wetland and deepwater habitats with at least 25%cover of particles smaller than stones, and a vegetative cover less than 30%. Water regimes are restricted tosubtidal, permanently f looded, intermittently exposed, and semipermanently f looded.

Description. Unconsolidated Bottoms are characterized by the lack of largestable surfaces for plant andanimal attachment. They areusually found in areas with lower energy than Rock Bottoms, and may be veryunstable. Exposureto wave and current action, temperature, salinity, and light penetration determines thecomposition and distribution of organisms.

Most macroalgae attach to the substrate by meansof basal hold-fast cells or discs; in sand and mud, how-ever, algae penetratethe substrateand higher plants can successfully root if wave action and currents are not

too strong. Most animals in unconsolidated sedimentsli ve within thesubstrate, e.g., Macoma and theam-phipod Melita. Some, such as thepolychaete worm Chaetopterus, maintain permanent burrows, and othersmay live on thesurface, especially in coarse-grained sediments.

In theMarineand EstuarineSystems, Unconsolidated Bottom communities are relatively stable. They varyfrom theArctic to thetropics, depending largely on temperature, and from theopen ocean to theupper endof theestuary, depending on salinity. Thorson (1957) summarized and described characteristic types of level-bottom communities in detail.

In theRiverineSystem, thesubstrate typeis largely determined by current velocity, and plantsand animalsexhibit a high degree of morphologic and behavioral adaptation to flowing water. Certain species are con-fined to specif ic substrates and some are at least moreabundant in one type of substrate than in others.According to Hynes (1970:208), Thelarger the stones, and hence themore complex thesubstratum, themore diverse is theinvertebrate fauna. In theLacustrineand PalustrineSystems, there is usually a highcorrelation, within a given water body, between thenature of thesubstrate and the number of species andindividuals. For example, in theprofundal bottom of eutrophic lakes where light i s absent, oxygen content islow, and carbon dioxideconcentration is high, thesedimentsare ooze-like organic materials and speciesdiversity is low. Each substrate type typically supports a relatively distinct community of organisms(Reidand Wood 1976:262).


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Cobble-Gravel. Theunconsolidated particles smaller than stones are predominantly cobble andgravel, although finer sediments may beintermixed. Examples of Dominance Types for theMarineand EstuarineSystemsare the mussels Modiolus and Mytilus, the brittle star Amphipholis, the soft-shell clam M ya, and theVenus clam Saxidomus. Examples for theLacustrine, Palustrine, and River-ineSystemsare themidge Diamesa, stonefly-midge Nemoura-Eukiefferiella (Slack et al. 1977),

chironomid midge-caddisfly-snail Chironomus-Hydropsyche-Physa (Krecker and Lancaster 1933),the pond snail Lymnaea, the mayfly Baetis, the freshwater spongeEunapius, theoligochaete wormLumbriculus, thescud Gammarus, and the freshwater mollusks Anodonta, Elliptio, and Lampsilis.Sand. Theunconsolidated particles small er than stones are predominantly sand, although fi ner orcoarser sediments may beintermixed. Examples of Dominance Types in the Marineand EstuarineSystemsare the wedgeshell Donax, the scall op Pecten, the telli n shell Tellina, theheart urchinEchinocardium, the lugworm Arenicola, the sand doll ar Dendraster , and thesea pansy Renilla.Examples for the Lacustrine, Palustrine, and Riverine Systemsare the snail Physa, the scudGammarus, theoligochaete worm Limnodrilus, the mayfly Ephemerella, thefreshwater mollusksElliptio and Anodonta, and thefi ngernail clam Sphaerium.Mud. Theunconsoli dated particles small er than stones are predominantly sil t and clay, although

coarser sediments or organic material may beintermixed. Organismsliving in mud must beable toadapt to low oxygen concentrations. Examples of Dominance Types for the Marineand EstuarineSystemsinclude theterebell id worm Amphitrite, the boring clam Platyodon, the deep-sea scallopPlacopecten, thequahog Mercenaria, themacomaMacoma, the echiurid worm Urechis, the mudsnail Nassarius, and the sea cucumber Thyone. Examples of Dominance Types for theLacustrine,Palustrine, and Riverine Systemsare the sewageworm Tubifex, freshwater mollusks Anodonta,Anodontoides, and Elli iotio, thefi ngernail clamsPisidium and Sphaerium, and the midgeChironomus.Organic. Theunconsoli dated material small er than stones is predominantly organic. The numberof species is li mited and faunal productivity is very low (Welch 1952). Examples of Dominance

Types for Estuarineand MarineSystemsare the soft-shell clam M ya, the falseangel wing Petricolapholadiformis, the clam worm Nereis, and themud snail Nassarius. Examples for theLacustrine,Palustrine, and Riverine Systemsare the sewageworm Tubifex, the snail Physa, theharpacticoidcopepod Canthocamptus, and theoligochaete worm Limnodrilus.

Dominance Types for Unconsolidated Bottoms in theMarineand EstuarineSystemswere taken predomi-nantly from Mi ner (1950), Smith (1964), Abbott (1968), and Ricketts and Calvi n (1968). Dominance Typesfor Unconsolidated Bottoms in the Lacustrine, Riverine, and PalustrineSystemswere taken predominantlyfrom Krecker and Lancaster (1933), Stehr and Branson (1938), Johnson (1970), Bri nkhurst and Jamieson(1972), Clarke(1973), Hart and Fuller (1974), Ward (1975), and Pennak (1978).

Aquatic Bed

Definition. TheClassAquatic Bed includes wetlands and deepwater habitatsdominated by plants that growprincipally on or below the surface of thewater f or most of the growing season in most years. Water regimesincludesubtidal, irregularly exposed, regularly flooded, permanently flooded, intermittently exposed,semipermanently flooded, and seasonally flooded.

Description. Aquatic Bedsrepresent a diverse group of plant communiti es that requires surface water foroptimum growth and reproduction. They are best developed in relatively permanent water or under condi-


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tions of repeated fl ooding. Theplantsare either attached to thesubstrate or f loat freely in thewater abovethebottom or on thesurface.


Algal. Algal Beds are widespread and diverse in the Marine and Estuarine Systems, where theyoccupy substratescharacterized by a widerangeof sediment depthsand textures. They occur in both

theSubtidal and Intertidal Subsystemsand may grow to depths of 30 m (98 feet). Coastal Algal Bedsare most luxuriant along the rocky shores of the Northeast and West. Kelp (Macrocystis) beds areespecially well developed on therocky substrates of thePacific Coast. Dominance Types such as therockweeds Fucus and Ascophyllum and the kelp Laminaria are common along both coasts. In tropi-cal regions, green algae, including formscontaining calcareous particles, are more characteristic;Halimeda and Penicillus are common examples. Thered algaLaurencia, and thegreen algaeCaulerpa, Enteromorpha, and Ulva are also common Estuarineand Marinedominance types;Enteromorpha and Ulva are tolerant of f resh water and flourish near the upper end of someestuaries.The stonewort Chara. is also found in estuaries.Inland, thestoneworts Chara, Nitella, and Tolypella are examples of algae that look much likevascular plants and may grow in similar situations. However, meadows of Chara may befound in

Lacustrinewater as deep as 40 m (131 feet) (Zhadin and Gerd 1963), where hydrostatic pressurelimits the survival of vascular submergents (phanaerogams) (Welch 1952). Other algae bearing lessresemblance to vascular plants are also common. Mats of f ilamentousalgae may cover the bottom indense blankets, may rise to thesurface under certain conditions, or may becomestranded on Uncon-solidated or Rocky Shores.Aquatic Moss. Aquatic mosses are far l ess abundant than algae or vascular plants. They occurprimarily in theRiverineSystem and in permanently flooded and intermittently exposed parts ofsomeLacustri nesystems. The most important DominanceTypes includegenera such as Fissidens,Drepanocladus, and Fontinalis. Fontinalis may grow to depths as great as 120 m (394 feet)(Hutchinson 1975). For simpli city, aquatic liverworts of thegenus Marsupella are included in thisSubclass.Rooted Vascular. Rooted Vascular Reds include a large array of vascular species in the Marineand EstuarineSystems. They have been referred to by others as temperate grass flats (Phil lips1974);tropical marinemeadows(Odum 1974); and eelgrass beds, turtl egrass beds, and seagrass beds(Akinsand Jefferson 1973; Eleuterius1973; Phil lips1974). Thegreatest number of species occur inshallow, clear tropical, or subtropical waters of moderate current strength in the Caribbean and alongtheFloridaand Gulf Coasts. Principal Dominance Types in these areas include turtlgrass (Thalassiatestudinum), shoalgrass (Halodule writghtii), manatee grass (Cyrnodocea filiformis), widgeon grass(Ruppia martima), sea grasses (Halophila spp.), and wil d celery (Vallisneria americana).Five major vascular speciesdominate along the temperatecoasts of North America: shoalgrass, surfgrasses(Phyllospadix scoulleri, P. torreyi ), widgeon grass, and eelgrass (Zostera marina). Eelgrass

bedshave the most extensive distribution, but they are limited primarily to themore sheltered estua-rineenvironment. In the lower salinity zones of estuaries, stands of widgeon grass, pondweed(Potamogeton), and wil d celery often occur, along with naiads(Najas) and water mil foil(Myriophyllum).In theRiverine, Lacustrine, and PalustrineSystems, rooted vascular aquatic plants occur at all depthswithin thephotic zone. They often occur in sheltered areas where there is little water movement(Wetzel 1975): however, they also occur in theflowing water of the Riverine System, where theymay be streamlined or flattened in response to high water velocities. Typical inland genera includepondweeds, horned pondweed (Zannichellia palustris), ditch grasses (Ruppia), wild celery, and


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waterweed (Elodea). The riverweed (Postostemum ceratophyllum) is included in this class despite itslack of truly recognizable roots (Sculthorpe l967).Someof the rooted vascular speciesare characterized by floating leaves. Typical dominants includewater l il ies (Nymphaea, Nuphar ), floating-leaf pondweed (Potamogeton natans), and water shield(Brasenia schreberi). Plants such as yell ow water li ly (Nuphar luteum) and water smartweed(Polygonum amphibium), which may stand erect abovethewater surface or substrate, may becon-sidered either emergents or rooted vascular aquatic plants, depending on thelife form adopted at aparticular site.Fl oating Vascular. Bedsof fl oating vascular plants occur mainly in the Lacustrine, Palustrine,and Riverine Systemsand in thefresher waters of the EstuarineSystem. Theplants float freely eitherin thewater or on its surface. Dominant plantsthat fl oat on thesurfaceinclude theduckweeds(Lemna, Spirodela), water lettuce (Pistia stratiotes), water hyacinth (Eichhornia crassipes), waternut (Trapa natans), water ferns (Salvinia spp.), and mosquito ferns(Azolla). These plantsare foundprimarily in protected portions of slow-flowing rivers and in theLacustrineand PalustrineSystems.They areeasily moved about by wi nd or water currents and cover a largearea of water i n some partsof the country, particularly the Southeast. Dominance Types for bedsfloating below thesurfaceinclude bladderworts (Utricularia), coontail s (Ceratophyllum), and watermeals (Wolffia) (Sculthorpe

1967; Hutchinson 1975).

Reef

Definition. TheClass Reef includes ridge-like or mound-li ke structures formed by the colonization andgrowth of sedentary invertebrates. Water regimesare restri cted to subtidal, irregularly exposed, regularlyflooded, and irregularly flooded.

Description. Reefs are characterized by their elevation above the surrounding substrate and their interfer-ence with normal wave fl ow; they are primarily subtidal, but parts of some reefs may beintertidal as well .

Although corals, oysters, and tube wormsare themost visible organismsand are mainly responsible for reefformation, other mollusks, foraminifera, coralli nealgae, and other forms of life also contribute substantiall yto reef growth. Frequently, reefs contain far more dead skeletal material and shell f ragmentsthan livingmatter.


Coral. Coral Reefs are widely distributed in shall ow waters of warm seas, in Hawaii , Puerto Rico,theVirgin Islands, and southern Florida. They were characterized by Odum (1971) as stable, well-adapted, highly diverse, and highly productive ecosystems with a great degree of internal symbiosis.Coral Reefs lie almost entirely within the Subtidal Subsystem of theMarineSystem, although theupper part of certain Reefs may beexposed. Examplesof Dominance Types are the corals Porites,Acropora, and Montipora. Thedistribution of these types refl ectsprimarily their elevation, waveexposure, theageof theReef, and its exposureto waves.Mollusk. This Subclass occurs in both the Intertidal and Subtidal Subsystems of the EstuarineSystem. These Reefs are found on thePacific, Atl antic, and Gulf Coasts and in Hawaii and theCaribbean. Moll usk Reefs may become extensive, affording a substrate for sedentary and boringorganisms and a shelter for many others. Reef mollusks are adapted to great variations in water level,salinity, and temperature, and these samefactors control their distribution. Examples of DominanceTypes for this Subclass are the oysters Ostrea and Crassostrea (Smith 1964; Abbott 1968; Rickettsand Calvin 1968).


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Worm. Worm Reefs are constructed by l arge colonies of Sabell arii d worms li ving in individualtubes constructed from cemented sand grains. Although they do not support as diverse a biota as doCoral and Mollusk Reefs, they providea distinct habitat which may cover l argeareas. Worm Reefsare generally confined to tropical waters, and are most common along the coasts of Florida, PuertoRico, and theVirgin Islands. They occur i n both theIntertidal and Subtidal Systemsof the Marineand EstuarineSystemswhere the salinity approximates that of sea water. Thereefworm Sabellaria is

an example of a Dominance Type for this Subclass (Ricketts and Calvi n 1968).

Str eambed

Definition. The Class Streambed includes all wetland contained within the Intermittent Subsystem of theRiverine System and all channels of theEstuarineSystem or of the Tidal Subsystem of the Riverine Systemthat are completely dewatered at low tide. Water regimes are restricted to irregularly exposed, regularlyflooded, irregularly flooded, seasonally flooded, temporarily flooded, and intermittently flooded.

Description. Streambedsvary greatly i n substrateand form depending on thegradient of the channel, thevelocity of thewater, and the sediment load. The substrate material frequently changes abruptly between

riff lesand pools, and complex patternsof bars may form on theconvex side of single channels or be in-cluded as islands within thebed of braided streams(Crickmay 1974). In mountainous areas theentire chan-nel may be cut through bedrock. In most cases streambedsare not vegetated because of thescouring effectof moving water, but, like Unconsolidated Shores, they may be colonized by pioneering annuals or peren-nials during periods of low flow or they may have perennial emergents and shrubsthat aretoo scattered toqualify thearea for classification as Emergent Wetland or Scrub-Shrub Wetland.


Bedrock. This Subclass is characterized by a bedrock substrate covering 75% or more of thestream channel. It occurs most commonly in theRiverineSystem in high mountain areas or inglaciated areas where bedrock is exposed. Examples of Dominance Types are the mollusk Ancylus,theoligochaete worm Limnodrilus, the snail Physa, thefingernail clam Pisidium, and the mayfli esCaenis and Ephemerella.Rubble. This Subclass is characterized by stones, boulders, and bedrock that i n combinationcover morethan 75% of thechannel. Like Bedrock Streambeds, Rubble Streambedsare most com-mon in mountainousareas and the dominant organisms are similar to those of Bedrock and are oftenformscapable of attachment to rocks in fl owing water.Cobble-Gravel. In this Subclass at least 25% of the substrate is covered by unconsoli dated par-ticles smaller than stones; cobbles or gravel predominate. TheSubclass occurs in riff le areas or in thechannels of braided streams. Examples of Dominance Types in theIntermittent Subsystem of theRiverine System are thesnail Physa, theoligochaete worm Limnodrilus, the mayfly Caenis, the

midge Chironomus, and the mosquito Anopheles. Examples of Dominance Types in theEstuarineSystem or Tidal Subsystem of theRiverine System are the mussels Modiolus and Mytilus.Sand. I n this Subclass, sand-sized particles predominate among the particles small er than stones.Sand Streambed often containsbars and beaches interspersed with Mud Streambed or it may beinterspersed with Cobble-Gravel Streambed in areas of fast f low or heavy sediment load. Examplesof Dominance Types in theRiverineSystem are thescud Gammarus, the snail s Physa and Lymnaea,and themidge Chironomus; in theEstuarineSystem theghost shrimp Callianassa is a commonDominanceType.


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Mud. I n this Subclass, the particles small er than stones are chiefl y sil t or clay. Mud Streambedsare common in arid areas where intermittent fl ow is characteristic of streamsof low gradient. Suchspecies as tamarisk (Tamarix gallica) may occur, but are not dense enough to qualify the area forclassification as Scrub-Shrub Wetland. Mud Streambedsare also common in the EstuarineSystemand theTidal Subsystem of theRiverine System. Examples of Dominance Types for Mud Stream-bedsinclude thecrayfish Procambarus, thepouch snail Aplexa, the fly Tabanus, the snail Lymnaea,the fingernail clam Sphaerium, and (in theEstuarineSystem) themud snail Nassarius.Organic. This Subclass is characterized by channels formed in peat or muck. Organic Streambedsare common in the small creeks draining EstuarineEmergent Wetlands with organic soils. Examplesof DominanceTypes are the mussel Modiolus in theEstuarineSystem and theoligochaete wormLimnodrilus in theRiverineSystem.Vegetated. These streambedsare exposed long enough to becolonized by herbaceousannuals orseedli ng herbaceousperennials (pioneer plants). This vegetation, unlike that of Emergent Wetlands,is usually kill ed by rising water levels or sudden fl ooding. A typical Dominance Typeis Panicumcapillare.

Dominance Types for Streambedsin theEstuarineSystem were taken primarily from Smith (1964), Abbott(1968), and Ricketts and Calvin (1968) and those for streambedsin theRiverineSystem from Krecker and

Lancaster (1933), Stehr and Branson (1938), van der Schalie (1948), Kenk (1949), Cumminset al. (1964),Clarke (1973), and Ward (1975).

Rocky Shore

Definition. The Class Rocky Shoreincludes wetland environments characterized by bedrock, stones, orboulders which singly or in combination have an areal cover of 75% or moreand an areal coveragebyvegetation of less than 30%. Water regimes are restricted to irregularly exposed, regularly flooded, irregu-larly flooded, seasonally flooded, temporarily flooded, and intermittently flooded.

Description. In Marineand EstuarineSystems, Rocky Shores are generally high-energy habitatswhich lieexposed as a result of continuouserosion by wind-driven waves or strong currents. Thesubstrate is stableenough to permit the attachment and growth of sessile or sedentary invertebrates and attached algae orlichens. Rocky Shores usually display a vertical zonation that is a function of tidal range, wave action, anddegree of exposureto the sun. In theLacustrineand Riverine Systems, Rocky Shores support sparse plantand animal communities.


Bedrock. These wetlands have bedrock covering 75% or more of the surface and less than 30%areal coverageof macrophytes.Rubble. These wetlands have less than 75% areal cover of bedrock, but stones and boulders alone

or in combination with bedrock cover 75% or moreof the area. Theareal coverageof macrophytes isless than 30%.

Communities or zones of M arineand EstuarineRocky Shores have been widely studied (Lewis 1964;Ricketts and Calvin 1968; Stephenson and Stephenson 1972). Each zonesupports a rich assemblageofinvertebrates and algae or lichensor both. Dominance Types of theRocky Shores often can becharacterizedby oneor two dominant genera from these zones.


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The uppermost zone (here termed the littorine-lichen zone) is dominated by periwinkles(Littorina andNerita) and lichens. This zonefrequently takes on a dark, or even black appearance, although abundantlichensmay lend a colorful tone. These organismsare rarely submerged, but are kept moist by sea spray.Frequently this habitat is invaded from thelandward sideby semimarinegenera such as theslater Ligia.

Thenext lower zone(the balanoid zone) i s commonly dominated by mollusks, green algae, and barnacles ofthe balanoid group. Thezoneappears white. Dominance Types such as thebarnacles Balanus, Chthamalus,

and Tetraclita may form an almost pure sheet, or these animals may beinterspersed with mollusks, tubeworms, and algae such as Pelvetia, Enteromorpha, and Ulva.

Thetransition between thelittorine-lichen and balanoid zones is frequently marked by the replacement ofthe periwinkles with li mpets such as Acmaea and Siphonaria. Thelimpet band approximates theupper li mitof theregularly f looded intertidal zone.

In themiddle and lower intertidal areas, which are fl ooded and exposed by tides at least oncedaily, lie anumber of other communities which can becharacterized by dominant genera. Mytilus and gooseneckbarnacles (Pollicipes) form communitiesexposed to strong wave action. Aquatic Bedsdominated by Fucusand Laminaria lie sli ghtly l ower, just abovethose dominated by corall ine algae (Lithothamnion). The Lami-

naria DominanceTypeapproximatesthe lower end of the Interti dal Subsystem; it is generally exposed atleast once daily. TheLithothamnion Dominance Typeforms thetransition to theSubtidal Subsystem and isexposed only irregularly.

In thePalustrine, Riverine, and Lacustrinevarious species of lichenssuch as Verrucaria spp. andDermatocarpon fluviatile, as well as blue-green algae, frequently form characteristic zones on RockyShores. Thedistribution of these species depends on theduration of flooding or wetting by spray and issimilar to thezonation of species in theMarineand EstuarineSystems(Hutchinson 1975). Though lessabundant than lichens, aquatic liverworts such as Marsupella emarginata var. aquatica or mosses such asFi ssidens j uli anus are found on theRocky Shores of lakes and rivers. If aquatic liverwortsor mosses cover30% or moreof thesubstrate, they should beplaced in theClassAquatic Bed. Other examplesof Rocky

Shore Dominance Types are thecaddisfly Hydropsyche and thefingernail clam Pisidium.

Unconsolidated Shore

Definition. The Class Unconsolidated Shore includes all wetland habitats having three characteristics: (1)unconsoli dated substrates with less than 75% areal cover of stones, boulders, or bedrock; (2) less than 30%areal cover of vegetation other than pioneering plants; and (3) any of thefollowing water regimes: irregu-larly exposed, regularly flooded, irregularly flooded, seasonally flooded, temporarily flooded, intermittentlyflooded, saturated, or arti ficially flooded. Intermittent or intertidal channels of the Riverine System andinterti dal channels of theEstuarineSystem are classified as Streambed.

Description. Unconsoli dated Shoresare characterized by substrates lacking vegetation except f or pioneer-ing plants that becomeestablished during brief periods when growing conditions are favorable. Erosion anddeposition by waves and currents producea number of landforms such as beaches, bars, and flats, all ofwhich are included in this Class. Unconsolidated Shores are found adjacent to Unconsolidated Bottomsinall Systems; in the Palustrineand LacustrineSystems, theClass may occupy theentire basin. As in Uncon-solidated Bottoms, the particle sizeof the substrate and the water regime are the important factors determin-ing the types of plant and animal communities present. Different substrates usually support characteristicinvertebrate fauna. Faunal distribution is controlled by waves, currents, interstitial moisture, salinity, andgrain size(Hedgpeth 1957; Ranwell 1972; Riedl and McMahan 1974).


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Cobble-Gravel. Theunconsolidated particles smaller than stones are predominantly cobble andgravel. Shell fragments, sand, and silt often fill the spaces between thelarger particles. Stones andboulders may befound scattered on some Cobble-Gravel Shores. In areas of strong wave and currentaction these shores take the form of beaches or bars, but occasionally they f orm extensive flats.Examples of DominanceTypes in theMarineand EstuarineSystemsare: the acorn barnacle Balanus,

theli mpet Patella, the periwinkle Littorina, therock shell Thais, themussels Mytilus and Modiolus,and theVenus clam Saxidomus. In theLacustrine, Palustrine, and RiverineSystemsexamplesofDominance Types are the freshwater mollusk Elliptio, the snail s Lymnaea and Physa, the toad bugGelastocoris, the leech Erpodella, and the springtail Agrenia.Sand. Theunconsolidated particles small er than stones are predominantly sand which may beeither calcareous or terrigenousin origin. They are prominent features of theMarine, Estuarine,Riverine, and LacustrineSystemswhere the substratematerial is exposed to thesorting and washingaction of waves. Examples of Dominance Types in the Marineand EstuarineSystemsare the wedgeshell Donax, thesoft-shell clam Mya, thequahog Mercenaria, the oli ve shell Oliva, the blood wormEuzonus, the beach hopper Orchestia, the pismo clam Tivela stultorum, the mole crab Emerita, andthelugworm Arenicola. Examplesof Dominance Types in theRiverine, Lacustrine, and Palustrine

Systems are the copepodsParastenocaris and Phyllognathopus, theoligochaete worm Pristina, thefreshwater mollusks Anodonta and Elliptio, and thefi ngernail clamsPisidium and Sphaerium.Mud. Theunconsoli dated particles small er than stones are predominantly sil t and clay. Anaerobicconditions often exist below the surface. Mud Shores have a higher organic content than Cobble-Gravel or Sand Shores. They are typically found in areas of minor wave action. They tend to havelittle slopeand are frequently call ed flats. Mud Shores support diverse populations of tube-dwelli ngand burrowing invertebrates that include worms, clams, and crustaceans(Gray 1974). They arecommonly colonized by algae and diatoms which may form a crust or mat.Irregularly flooded Mud Shores in theEstuarineSystem have been called salt fl ats, pans, or pannes.They are typically high in sali nity and are usuall y surrounded by, or lie on thelandward side of,

Emergent Wetland (Martin et al. 1953, Type15). In many arid areas, Palustrineand LacustrineMudShores are encrusted or saturated with salt. Martin et al. (1953) called these habitats inland sali neflats(Type9); they are also called alkali flats, salt flats, and salt pans. Mud Shores may also resultfrom removal of vegetation by man, animals, or f ire, or from thedischarge of thermal waters orpoll utants. Examples of Dominance Types in theMarineand EstuarineSystemsinclude thefiddlercrab Uca, the ghost shrimp Callianassa, the mud snail s Nassarius and Macoma, the clam wormNereis, thesea anemoneCerianthus, and the sea cucumber Thyone. In theLacustrine, Palustrine, andRiverine Systems, examples of Dominance Types are the fingernail clam Pisidium, the snails Aplexaand Lymaea, the crayfish Procambarus, theharpacticoid copepods Canthocamptus andBryocamptus, thefi ngernail clam Sphaerium, the freshwater mollusk Elliptio, the shore bug Saldula,theisopod Asellus, the crayfi sh Cambarus, and the mayfly Tortopus.

Organic. Theunconsoli dated material small er than stones is predominantly organic soil s offormerly vegetated wetlands. In theMarineand EstuarineSystems, Organic Shores are often domi-nated by microinvertebrates such as foraminifera, and by Nassarius, Littorina, Uca, Modiolus, M ya,Nereis, and the false angel wing Petricola pholadiformis. In theLacustrine, Palustrine, and RiverineSystems, examplesof DominanceTypes are Canthocamptus, Bryocamptus, Chironomus, and thebackswimmer Notonecta.Vegetated. Somenontidal shores are exposed for a sufficient period to becolonized by herbaceousannuals or seedli ng herbaceous perennials (pioneer plants). This vegetation, unlike that of EmergentWetlands, is usually ki ll ed by rising water l evels and may be gonebefore thebeginning of the next


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growing season. Many of the pioneer speciesare not hydrophytesbut are weedy mesophytes thatcannot tolerate wet soil or flooding. Examples of Dominance Types in the Palustrine, Riverine, andLacustri neSystemsare cocklebur (Xanthium strumarium) and barnyard grass (Echinochloacrusgalli).

DominanceTypes for Unconsolidated Shores in theMarineand EstuarineSystemswere taken primarilyfrom Smith (1964), Morris (1966), Abbott (1968), Ricketts and Calvi n (1968), and Gosner (1971). Domi-

nance Types for Unconsolidated Shores in theLacustrine, Riverine, and PalustrineSystemswere takenprimarily from Stehr and Branson (1938), Kenk (1949), Ward and Whipple (1959), Cumminset al. (1964),Johnson (1970), Ingram (1971), Clarke(1973), and Hart and Fuller (1974).

M oss-L ichen Wetland

Definition. The Moss-Lichen Wetland Class includes areas where mosses or lichenscover substrates otherthan rock and where emergents, shrubs, or trees make up less than 30% of the areal cover. Theonly waterregimeis saturated.

Description. Mosses and lichensare important components of theflora in many wetlands, especially in thenorth, but these plants usually form a ground cover under a dominant layer of trees, shrubs, or emergents. Insome instances higher plants are uncommon and mosses or lichensdominate the flora. Such Moss-LichenWetlands are not common, even in the northern United States where they occur most frequently.


Moss. M oss Wetlands are most abundant i n the far north. Areas covered with peat mosses (Sphag-num spp.) areusually called bogs(Golet and Larson 1974; Jeglum et al. 1974; Zoltai et al. 1975),whether Sphagnum or higher plants are dominant. In Alaska, Drepanocladus and the li verwortChil oscyphus fragi li s may dominate shallow pools with impermanent water; peat moss and othermosses(Campylium stellatum, Aulacomnium palustre, and Oncophorus wahlenbergi i) aretypical of

wet soil i n this region (Britton 1957; Drury 1962).Lichen. L ichen Wetlands are also a northern Subclass. Reindeer moss (Cladina rangiferina)formsthe most important DominanceType. Poll ett and Bri dgewater (1973) described areas withmosses and lichensas bogsor fens, thedistinction being based on theavail ability of nutrientsand theparticular plant speciespresent. Thepresence of Lichen Wetlands has been noted in theHudson BayLowlands (Sjrs 1959) and in Ontario (Jeglum et al. 1974).

Emer gent Wetland

Definition. The Emergent Wetland Class is characterized by erect, rooted, herbaceoushydrophytes, exclud-

ing mosses and lichens. This vegetation is present for most of thegrowing season in most years. Thesewetlands are usually dominated by perennial plants. All water regimes are included except subtidal andirregularly exposed.

Description. In areas with relatively stable climatic conditions, Emergent Wetlands maintain the sameappearance year after year. In other areas, such as theprairies of thecentral United States, violent climaticfluctuations cause them to revert to an open water phase in some years (Stewart and Kantrud 1972). Emer-gent Wetlands are found throughout theUnited States and occur in all Systemsexcept theMarine. EmergentWetlands are known by many names, including marsh, meadow, fen, prairie pothole, and slough. Areas that


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are dominated by pioneer plantswhich becomeestablished during periods of low water are not EmergentWetlandsand should beclassified as Vegetated Unconsoli dated Shoresor Vegetated Streambeds.


Persistent. Persistent Emergent Wetlands are dominated by species that normall y remain standingat least until thebeginning of thenext growing season. This Subclass is found only in theEstuarine

and Palustrine Systems.Persistent Emergent Wetlandsdominated by saltmarsh cordgrass (Spartina alterniflora), saltmeadowcordgrass (S. patens), big cordgrass (S. cynosuroides), needlerush (Juncus roemerianus), narrow-leaved cattail (Typha angusti fol ia), and southern wild rice(Zizaniopsis miliacea) are major compo-nentsof the Estuarinesystemsof theAtlantic and Gulf Coasts of the United States. On thePacificCoast, common pickleweed (Salicornica Virginica), sea blite (Suaeda californica), arrow grass(Triglochin maritimum), and Calif ornia cordgrass (Spartina foliosa) are common dominants.Palustri nePersistent Emergent Wetlandscontain a vast array of grasslike plantssuch as cattails(Typha spp.), bulrushes (Scirpus spp.), saw grass (Cladium jamaicense), sedges (Carex spp.); andtrue grasses such as reed (Phragmites australis), mannagrasses (Glyceria spp.), slough grass(Beckmannia syzigachne), and whitetop (Scolochloa festucacea). There is also a variety of broad-

leaved persistent emergents such as purple loosestri fe (Lythrum salicaria), dock (Rumex mexicanus),waterwillow (Decodon ver tici ll atus), and many speciesof smartweeds(Polygonum).Nonpersistent. Wetlands in this Subclass are dominated by plants which fall to the surfaceof thesubstrateor below the surface of the water at the end of the growing season so that, at certain seasonsof theyear, there is no obvious sign of emergent vegetation. For example, wild rice(Zizaniaaquatica) does not becomeapparent in the North Central States until midsummer and fall, when itmay form dense emergent stands. Nonpersistant emergents also include speciessuch as arrow arum(Peltandra virginica), pickerelweed (Pontederia cordata), and arrowheads(Sagittaria spp.). Move-ment of icein Estuarine, Riverine, or LacustrineSystemsoften removes all traces of emergentvegetation during thewinter. Where this occurs thearea should beclassified as Nonpersistant Emer-gent Wetland.

Scrub-Shrub Wetland

Definition. TheClass Scrub-Shrub Wetland includes areas dominated by woody vegetation less than 6 m(20 feet) tall. Thespecies include true shrubs, young trees, and trees or shrubsthat are small or stuntedbecause of environmental conditi ons. All water regimesexcept subtidal are included.

Description. Scrub-Shrub Wetlands may represent a successional stage leading to Forested Wetland, or theymay berelatively stable communities. They occur only in theEstuarineand PalustrineSystems, but are oneof the most widespread classes in the United States (Shaw and Fredine 1956). Scrub-Shrub Wetlands are

known by many names, such as shrub swamp (Shaw and Fredine 1956), shrub carr (Curtis 1959), bog(Heinselman 1970), and pocosin (Kologiski 1977). For practical reasons we have also included forestscomposed of young trees less than 6 m tall .

7/31/2019 2360-Classification of Wetlands and Deep-water Habitats of the United State

2360-Classification of Wetlands and Deep-water Habitats of the United States

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