Classification of wetlands and deepwater habitats of the United States

              FWS/OBS-79131
DECEMBER 1979
Reprinted 1992
Classification of ~
Wetlands and
Deepwater Habitats
of the United States
QH- I Department of the Interior
540 .U56 h and Wildlife Service
no.7913 1
The Biological Services Program was established within the U.S. Fish and
Wildlife Service to supply scientific information and methodologies on key
environmental issues which have an impact on fish and wildlife resources and
their supporting ecosystems. The mission of the Program is as follows:
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respect to environmental impact assessment.
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3. To provide better ecological information and evaluation for Department
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Information developed by the Biological Services Program is intended for use
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Power plants
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Water resource analysis, including stream alterations and western water
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The Program consists of the Office of Biological Services in Washington, D.C.,
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FWSIOBS-79/31
December 1979
CLASSIFICATION OF WETLANDS AND DEEPWATER
HABITATS OF THE UNITED STATES
BY
Lewis M. Cowardin
U.S. Fish and Wildlife Service
Northern Prairie Wildlife Research Center
Jamestown, North Dakota 58401
Virginia Carter
U.S. Geological Survey
Reston, Virginia 22092
Francis C. Golet
Department of Natural Resources Science
University of Rhode Island
Kingston, Rhode Island 02881
and
Edward T. LaRoe
U.S. National Oceanographic and Atmospheric Administration
Office of Coastal Zone Management
Washington, D.C. 20235
Performed for
U.S. Department of the Interior
Fish and Wildlife Service
Office of Biological Services
Washington, D.C. 20240
For sale by the Superintendent of Documents, U.S. Guvernment Printing Office
Washington, D.C. 20402
i
Library of Congress Cataloging in Publication Data
United States, Fish and Wildlife Service
Classification of wetlands and deepwater habitats of the United States.
(Biological services program ; FWS/OBS-79/31)
1. Wetlands-United States-Classification. 2. Wetland ecology-United
States. 3. Aquatic ecology-United States. I. Cowardin, Lewis M. II. Title.
III. Series: United States. Fish and Wildlife Service. Biological services
program ; FWEYOBS-‘79/31.
QH76.U54a 79/31 [QH104] 574.5’0973s [574.5’2632] 79-607795
Foreward
Wetlands and deepwater habitats are essential breeding, rearing, and feeding grounds for many species of fish
and wildlife. They may also perform important flood protection and pollution control funtions. Increasing National
and international recognition of these values has intensified the need for reliable information on the status and ex-tent
of wetland resources. To develop comparable information over large areas, a clear definition and classification
of wetlands and deepwater habitats is required.
The classification system contained in this report was developed by wetland ecologists, with the assistance of many
private individuals and organizations and local, State, and Federal agencies. An operational draft was published in
October 1977, and a notice of intent to adopt the system for all pertinent Service activities was published December
12, 1977 (42 FR 62432).
The Fish and Wildlife Service is officially adopting this wetland classification system. Future wetland data bases
developed by the Service, including the National Wetlands Inventory, will utilize this system. A one-year transition
period will allow for training of Service personnel, amendment of administrative manuals, and further development
of the National Wetlands Inventory data base. During this period, Service personnel may continue to use the old
wetland classification described in Fish and Wildlife Service Circular 39 for Fish and Wildlife Coordination Act reports,
wetland acquisition priority determinations, and other activities in conjunction with the new system, where immediate
conversion is not practicable.
Upon completion of the transition period, the Circular 39 system will no longer be officially used by the Fish and
Wildlife Service except where applicable laws still reference that system or when the only information available is
organized according to that system and cannot be restructured without new field surveys.
Other Federal and State agencies are encouraged to convert to the use of this system. No specific legal authorities
require the use of this system-or any other system for that matter. However, it is expected that the benefits of
National consistency and a developing wetland data base utilizing this system will result in acceptance and use by
most agencies involved in wetland management. Training can be provided to users by the Service, depending on
availability of resources. Congressional committees will be notified of this adoption action and will be encouraged
to facilitate general adoption of the new system by amending any laws that reference the Circular 39 system.
This is a new system and users will need to study and learn the terminology. The Service is preparing a document
to aid in comparing and translating the new system to the Service’s former classification system. In the coming year,
the Fish and Wildlife Service, in conjunction with the Soil Conservation Service, also plans to develop initial lists
of hydrophytic plants and hydric soils that will support interpretation and use of this system.
We believe that this system will provide a suitable basis for information gathering for most scientific, educational,
and administrative purposes; however, it will not fit all needs. For instance, historical or potentially restorable wetlands
are not included in this system, nor was the system designed to accommodate all the requirements of the many recently
passed wetland statutes. No attempt was made to define the proprietary or jurisdictional boundaries of Federal, State,
or local agencies. Nevertheless, the basic design of the classification system and the resulting data base should assist
substantially in the administration of these programs.
This report represents the most current methodology available for wetland classification and culminates a long-term
effort involving many wetland scientists. Although it may require revision from time to time, it will serve us
well in the years ahead. We hope all wetland personnel in all levels of government and the private sector come to
know it and use it for the ultimate benefit of America’s wetlands.
Lynn ArGreenwalt, Director
U.S. Fish and Wildlife Service
111
Preface
Since its publication in 1979, Classification of Wetlands and Deepwater Habitats of the United States has been used
in the National inventory of wetlands conducted by the U.S. Fish and Wildlife Service. The system has been widely
used throughout the United States and is often cited in the scientific literature. There has also been considerable
international interest in use of the classification.
Copies from the first printing have been expended and demand requires this reprinting. We have taken this oppor-tunity
to correct a number of minor typographical errors, bring plant names into conformity with the National List
ofScientific Plant Names (U.S. Dept. Agriculture 1982), and to upgrade the quality of plates as well as furnish addi-tional
plates. No changes have been made that either alter the structure of the classification or the meaning of the
definitions. Such major revisions must be deferred until certain prerequisite tasks are accomplished.
Completion of the list of hydrophytes and other plants occurring in wetlands and the list of hydric soils (see page
3) has been a task of far greater complexity than we envisioned when writing the classification. These lists have
received extensive review and are being prepared as computer data bases. In addition, the lists will contain a great
deal of ancillary information that will make possible the development of methodologies for their use in both the delinea-tion
and classification of wetlands. When the lists and methodologies are completed, reviewed, and tested we will
revise the classification and use the lists to add precision to the definitions. At the same time, we will address specific
technical problems that have arisen during application of the classification.
The plates at the end of this publication are included primarily to illustrate a variety of examples of wetland classifica-tion.
We have attempted to include photographs from various regions of the country insofar as possible; however,
final selection of plates was based on the availability of both high-quality photographs and the detailed field data
required for accurate classification. While on sabbatical leave from the University of Rhode Island in 1985, Dr. Frank
Golet took numerous photographs of Alaskan wetlands. Addition of many of these and several photographs from
other regions helps somewhat to correct a regional imbalance.
We acknowledge the assistance of Dr. J. Henry Sather who served as editor for the reprinting. He spent many
hours compiling minor errors and inconsistencies and preparing final copy for the printer. We thank Mr. Jon Hall,
National Wetlands Inventory Coordinator for the Alaska region, for his assistance to Dr. Golet during his stay in Alaska.
Lewis M. Cowardin
Virginia Carter
Francis C. Golet
Edward T. LaRoe
September 24, 1985
iv
Contents
Page
Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Wetlands and Deepwater Habitats ..................................... 3
Concepts and Definitions ........................................... 3
Wetlands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Deepwater Habitats .............................................. 3
Limits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
The Classification System ............................................ 4
Hierarchical Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Systems and Subsystems. ......................................... 4
Marine System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Estuarine System .............................................. 4
Riverine System ............................................... 7
Lacustrine System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Palustrine System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Classes, Subclasses, and Dominance Types. . . . . . . . . . . . . . . . . . . . . . . . . . . 10
RockBottom . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Unconsolidated Bottom. ......................................... 14
Aquatic Bed.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Reef . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Streambed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Rocky Shore . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Unconsolidated Shore ........................................... 18
Moss-Lichen Wetland. .......................................... 19
Emergent Wetland . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Scrub-Shrub Wetland . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Forested Wetland.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Modifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Water Regime Modifiers ........................................ 21
Water Chemistry Modifiers ...................................... 22
Salinity Modifiers. ............................................ 22
pHModifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
SoilModifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Special Modifiers ............................................... 24
Regionalization for the Classification System ............................ 24
Use of the Classification System. ...................................... 26
Hierarchical Levels and Modifiers .................................... 27
Relationship to Other Wetland Classifications .......................... 27
Acknowledgments.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Appendix A. Scientific and common names of plants ..................... 35
Appendix B. Scientific and common names of animals .................... 38
Appendix C. Glossary of terms ........................................ 40
Appendix D. Criteria for distinguishing organic
soils from mineral soils ................................. 42
Appendix E. Artificial key to the Systems .............................. 44
Artificial key to the Classes ............................... 44
”
Tables
No.
1 Distribution of Subclasses within the classification hierarchy.
2 Salinity modifiers used in this classification system.
3 pH modifiers used in this classification system.
4 Comparison of wetland types described in U.S. Fish and Wildlife Service Circular
39 with some of the major components of this classification system.
5 Comparison of the zones of Stewart and Kantrud’s (1971) classification with the water
regime modifiers used in the present classification system.
Figures
No.
8
Classification hierarchy of wetlands and deepwater habitats, showing Systems, Sub-systems,
and Classes. The Palustrine System does not include deepwater habitats.
Distinguishing features and examples of habitats in the Marine System.
Distinguishing features and examples of habitats in the Estuarine System.
Distinguishing features and examples of habitats in the Riverine System.
Distinguishing features and examples of habitats in the Lacustrine System.
Distinguishing features and examples of habitats in the Palustrine System.
Ecoregions of the United States after Bailey (1976) with the addition of 10 Marine
and Estuarine Provinces proposed in our classification.
Comparison of the Water Chemistry Subclasses of Stewart and Kantrud (1972) with
Water Chemistry Modifiers used in the present classification system.
Classification of Wetlands and Deepwater
Habitats of the United States
Lewis M. Cowardin
U.S. Fish and Wildlife Service
Northern Prairie Wildlife Research Center
Jamestown, North Dakota 58401
Virginia Carter
U.S. Geological Survey, Reston, Virginia 22092
Francis C. Golet
Department of Natural Resources Science
University of Rhode Island, Kingston, Rhode Island 02881
and
Edward T. LaRoe
U.S. National Oceanographic and Atmospheric Administration
Office of Coastal Zone Management
Washington, D.C. 20235
Abstract
This classification, to be used in a new inventory of wetlands and deepwater habitats of the United
States, is intended to describe ecological taxa, arrange them in a system useful to resource managers,
furnish units for mapping, and provide uniformity of concepts and terms. Wetlands are defined by
plants (hydrophytes), soils (hydric soils), and frequency of flooding. Ecologically related areas of deep
water, traditionally not considered wetlands, are included in the classification as deepwater habitats.
Systems form the highest level of the classification hierarchy; five are defined-Marine, Estuarine,
Riverine, Lacustrine, and Palustrine. Marine and Estuarine Systems each have two Subsystems, Sub-tidal
and Intertidal; the Riverine System has four Subsystems, Tidal, Lower Perennial, Upper Peren-nial,
and Intermittent; the Lacustrine has two, Littoral and Limnetic; and the Palustrine has no
Subsystems.
Within the Subsystems, Classes are based on substrate material and flooding regime, or on vegetative
life form. The same Classes may appear under one or more of the Systems or Subsystems. Six Classes
are based on substrate and flooding regime: (1) Rock Bottom with a substrate of bedrock, boulders,
or stones; (2) Unconsolidated Bottom with a substrate of cobbles, gravel, sand, mud, or organic material;
(3) Rocky Shore with the same substrates as Rock Bottom; (4) Unconsolidated Shore with the same
substrates as Unconsolidated Bottom; (5) Streambed with any of the substrates; and (6) Reef with
a substrate composed of the living and dead remains of invertebrates (corals, mollusks, or worms).
The bottom Classes, (1) and (2) above, are flooded all or most of the time and the shore Classes, (3)
and (4), are exposed most of the time. The Class Streambed is restricted to channels of intermittent
streams and tidal channels that are dewatered at low tide. The life form of the dominant vegetation
defines the five Classes based on vegetative form: (1) Aquatic Bed, dominated by plants that grow
principally on or below the surface of the water; (2) Moss-Lichen Wetland, dominated by mosses or
lichens; (3) Emergent Wetland, dominated by emergent herbaceous angiosperms; (4) Scrub-Shrub
Wetland, dominated by shrubs or small trees; and (5) Forested Wetland, dominated by large trees.
The Dominance Type, which is named for the dominant plant or animal forms, is the lowest level
of the classification hierarchy. Only examples are provided for this level; Dominance Types must be
developed by individual users of the classification.
Modifying terms applied to the Classes or Subclasses are essential for use of the system. In tidal
areas, the type and duration of flooding are described by four Water Regime Modifiers: subtidal,
irregularly exposed, regularly flooded, and irregularly flooded. In nontidal areas, eight Regimes are
used: permanently flooded, intermittently exposed, semipermanently flooded, seasonally flooded,
saturated, temporarily flooded, intermittently flooded, and artificially flooded. A hierarchical system
of Water Chemistry Modifiers, adapted from the Venice System, is used to describe the salinity of
the water. Fresh waters are further divided on the basis of pH. Use of a hierarchical system of soil
modifiers taken directly from U.S. soil taxonomy is also required. Special modifiers are used where
appropriate: excavated, impounded, diked, partly drained, farmed, and artificial.
Regional differences important to wetland ecology are described through a regionalization that com-bines
a system developed for inland areas by R. G. Bailey in 1976 with our Marine and Estuarine
provinces.
The structure of the classification allows it to be used at any of several hierarchical levels. Special
data required for detailed application of the system are frequently unavailable, and thus data gather-ing
may be prerequisite to classification. Development of rules by the user will be required for specific
map scales. Dominance Types and relationships of plant and animal communities to environmental
characteristics must also be developed by users of the classification. Keys to the Systems and Classes
are furnished as a guide, and numerous wetlands and deepwater habitats are illustrated and classified.
The classification system is also compared with several other systems currently in use in the United
States.
The U.S. Fish and Wildlife Service conducted an inven-tory
of the wetlands of the United States (Shaw and
Fredine 1956) in 1954. Since then, wetlands have under-gone
considerable change, both natural and man related,
and their characteristics and natural values have become
better defined and more widely known. During this inter-val,
State and Federal legislation has been passed to
protect wetlands, and some Statewide wetland surveys
have been conducted.
In 1974, the U.S. Fish and Wildlife Service directed its
Office of Biological Services to design and conduct a new
National inventory of wetlands. Whereas the single pur-pose
of the 1954 inventory was to assess the amount and
types of valuable waterfowl habitat, the scope of the new
project is considerably broader (Montanari and Townsend
1977). It will provide basic data on the characteristics and
extent of the Nation’s wetlands and deepwater habitats
and should facilitate the management of these areas on
a sound, multiple-use basis.
Before the 1954 inventory was begun, Martin et al.
(1953) had devised a wetland classification system to serve
as a framework for the National inventory. The results
of the inventory and an illustrated description of the 20
wetland types were published as U.S. Fish and Wildlife
Service Circular 39 (Shaw and Fredine 1956). This cir-cular
has been one of the most common and most influen-tial
documents used in the continuous battle to preserve
a critically valuable but rapidly diminishing National
resource (Stegman 1976). However, the shortcomings of
this work are well known (e.g., see Leitch 1966; Stewart
and Kantrud 1971).
In attempting to simplify their classification, Martin et
al. (1953) not only ignored ecologically critical differences,
such as the distinction between fresh and mixosaline in-land
wetlands but also placed dissimilar habitats, such as
forests of boreal black spruce (Picea mariana) and of
southern cypress-gum (Taxodium distichum-Nyssa
aquatica) in the same category, with no provisions in the
system for distinguishing between them. Because of the
central emphasis on waterfowl habitat, far greater atten-tion
was paid to vegetated areas than to nonvegetated
areas. Probably the greatest single disadvantage of the
Martin et al. system was the inadequate definition of types,
which led to inconsistencies in application.
Numerous other classifications of wetlands and deep-water
habitats have been developed (Stewart and Kan-trud
1971; Golet and Larson 1974; Jeglum et al. 1974;
Odum et al. 1974; Zoltai et al. 1975; Millar 1976), but most
of these are regional systems and none would fully satisfy
National needs. Because of the weaknesses inherent in
Circular 39, and because wetland ecology has become
significantly better understood since 1954, the U.S. Fish
and Wildlife Service elected to construct a new National
classification system as the first step toward a new Na-tional
inventory. The new classification, presented here,
has been designed to meet four long-range objectives: (1)
to describe ecological units that have certain homogeneous
natural attributes; (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 pro-vide
uniformity in concepts and terminology throughout
the United States.
Scientific and common names of plants (Appendix A)
and animals (Appendix B) were taken from various sources
cited in the text. No attempt has been made to resolve
nomenclatorial problems where there is a taxonomic
dispute. Many of the terms used in this classification have
various meanings even in the scientific literature and in
some instances our use of terms is new. We have provided
a glossary (Appendix C) to guide the reader in our usage
of terms.
3
WETLANDSANDDEEPWATER
HABITATS
Concepts and Definitions
Marshes, swamps, and bogs have been well-known terms
for centuries, but only relatively recently have attempts
been made to group these landscape units under the single
term “wetlands.” This general term has grown out of a
need to understand and describe the characteristics and
values of all types of land, and to wisely and effectively
manage wetland ecosystems. There is no single, correct,
indisputable, ecologically sound definition for wetlands,
primarily because of the diversity of wetlands and because
the demarcation between dry and wet environments lies
along a continuum. Because reasons or needs for defin-ing
wetlands also vary, a great proliferation of definitions
has arisen. The primary objective of this classification is
to impose boundaries on natural ecosystems for the pur-poses
of inventory, evaluation, and management.
tion of salts may prevent the growth of hydrophytes; (3)
areas with hydrophytes but nonhydric soils, such as
margins of impoundments or excavations where hydro-phytes
have become established 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
as gravel beaches or rocky shores without vegetation.
Drained hydric soils that are now incapable of support-ing
hydrophytes because of a change in water regime are
not considered wetlands by our definition. These drained
hydric soils furnish a valuable record of historic wetlands,
as well as an indication of areas that may be suitable for
restoration.
Wetlands as defined here include lands that are iden-tified
under other categories in some land-use classifica-tions.
For example, wetlands and farmlands are not
necessarily exclusive. Many areas that we define as wet-lands
are farmed during dry periods, but if they are not
tilled or planted to crops, a practice that destroys the
natural vegetation, they will support hydrophytes.
Wetlands Deepwater Habitats
In general terms, wetlands are lands where saturation
with water is the dominant factor determining the nature
of soil development and the types of plant and animal com-munities
living in the soil and on its surface. The single
feature that most wetlands share is soil or substrate that
is at least periodically saturated with or covered by water.
The water creates severe physiological problems for all
plants and animals except those that are adapted for life
in water or in saturated soil.
WETLANDS are lands transitional between terrestrial
and aquatic systems where the water table is usually at
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 predominantly hydro-phytes;
l (2) the substrate is predominantly undrained
hydric s0i1;~ and (3) the substrate is nonsoil and is
saturated with water or covered by shallow water at some
time during the growing season of each year.
The term wetland includes a variety of areas that fall
into one of five categories: (1) areas with hydrophytes and
hydric soils, such as those commonly known as marshes,
swamps, and bogs; (2) areas without hydrophytes but with
hydric soils-for example, flats where drastic fluctuation
in water level, wave action, turbidity, or high concentra-
‘The U.S. Fish and Wildlife Service is preparing a list of hydro-phytes
and other plants occurring in wetlands of the United
States.
2The U.S. Soil Conservation Service is preparing a preliminary
list of hydric soils for use in this classification system.
DEEPWATER HABITATS are permanentlyflooded lands
lying below the deepwater boundary of wetlands, Deep-water
habitats include environments where surface water
is permanent and often deep, so that water, rather than
air, is the principal medium within which the dominant
organisms live, whether or not they are attached to the
substrate. As in wetlands, the dominant plants are hydro-phytes;
however, the substrates are considered nonsoil
because the water is too deep to support emergent vegeta-tion
(U.S. Soil Conservation Service, Soil Survey Staff
1975).
Wetlands and deepwater habitats are defined separately
because traditionally the term wetland has not included
deep permanent water; however, both must be considered
in an ecological approach to classification. We define five
major Systems: Marine, Estuarine, Riverine, Lacustrine,
and Palustrine. The first four of these include both wetland
and deepwater habitats but the Palustrine includes only
wetland habitats.
Limits
The upland limit of wetland is designated as (1) the boun-dary
between land with predominantly hydrophytic cover
and land with predominantly mesophytic or xerophytic
cover; (2) the boundary between soil that is predominant-ly
hydric and soil that is predominantly nonhydric; or (3)
in the case of wetlands without vegetation or soil, the
boundary between land that is flooded or saturated at
some time during the growing season each year and land
that is not.
The boundary between wetland and deepwater habitat
in the Marine and Estuarine Systems coincides with the
elevation of the extreme low water of spring tide; per-manently
flooded areas are considered deepwater habitats
in these Systems. The boundary between wetland and
deepwater habitat in the Riverine and Lacustrine Systems
lies at a depth of 2 m (6.6 feet) below low water; however,
if emergents, shrubs, or trees grow beyond this depth at
any time, their deepwater edge is the boundary.
The 2-m lower limit for inland wetlands was selected
because it represents the maximum depth to which emer-gent
plants normally grow (Welch 1952; Zhadin and Gerd
1963; Sculthorpe 1967). As Daubenmire (1968:138) stated,
emergents are not true aquatic plants, but are “amphib-ious,”
growing in both permanently flooded and wet,
nonflooded soils. In their wetland classification for
Canada, Zoltai et al. (1975) also included only areas with
water less than 2 m deep.
THE CLASSIFICATION SYSTEM
The structure of this classification is hierarchical,
progressing from Systems and Subsystems, at the most
general levels, to Classes, Subclasses, and Dominance
Types. Figure 1 illustrates the classification structure to
the class level. Table 1 lists the Classes and Subclasses
for each System and Subsystem. Artificial keys to the
Systems and Classes are given in Appendix E. Modifiers
for water regime, water chemistry, and soils are applied
to Classes, Subclasses, and Dominance Types. Special
modifiers describe wetlands and deepwater habitats that
have been either created or highly modified by man or
beavers.
Hierarchical Structure
Systems and Subsystems
The term SYSTEM refers here to a complex of wetlands
and deepwater habitats that share the influence of similar
hydrologic, geomorphologic, chemical, or biological fac-tors.
We further subdivide Systems into more specific
categories called SUBSYSTEMS .
The characteristics of the five major Systems-Marine,
Estuarine, Riverine, Lacustrine, and Palustrine-have
been discussed at length in the scientific literature and
the concepts are well recognized; however, there is fre-quent
disagreement as to which attributes should be used
to bound the Systems in space. For example, both the limit
of tidal influence and the limit of ocean-derived salinity
have been proposed for bounding the upstream end of the
Estuarine System (Caspers 1967). As Bormann and Likens
(1969) pointed out, boundaries of ecosystems are defined
to meet practical needs.
Marine System
Definition. The Marine System (Fig. 2) consists of the
open ocean overlying the continental shelf and its asso-ciated
high-energy coastline. Marine habitats are exposed
to the waves and currents of the open ocean and the water
regimes are determined primarily by the ebb and flow of
oceanic tides. Salinities exceed 30%0, with little or no
dilution except outside the mouths of estuaries. Shallow
coastal indentations or bays without appreciable fresh-water
inflow, and coasts with exposed rocky islands that
provide the mainland with little or no shelter from wind
and waves, are also considered part of the Marine System
because they generally support typical marine biota.
Limits. The Marine System extends from the outer
edge of the continental shelf shoreward to one of three
lines: (1) the landward limit of tidal inundation (extreme
high water of spring tides), including the splash zone from
breaking waves; (2) the seaward limit of wetland emer-gents,
trees, or shrubs; or (3) the seaward limit of the
Estuarine System, where this limit is determined by fac-tors
other than vegetation. Deepwater habitats lying
beyond the seaward limit of the Marine System are out-side
the scope of this classification system.
Description. The distribution of plants and animals in
the Marine System primarily reflects differences in four
factors: (1) degree of exposure of the site to waves; (2)
texture and physicochemical nature of the substrate; (3)
amplitude of the tides; and (4) latitude, which governs
water temperature, the intensity and duration of solar
radiation, and the presence or absence of ice.
Subsystems.
Subtidal.-The substrate is continuously submerged.
Intertidal. -The substrate is exposed and flooded by
tides; includes the associated splash zone.
Classes. Rock Bottom, Unconsolidated Bottom, Aquatic
Bed, Reef, Rocky Shore, and Unconsolidated Shore.
Estuarine System
Definition. The Estuarine System (Fig. 3) consists of
deepwater tidal habitats and adjacent tidal wetlands that
are usually semienclosed by land but have open, partly
obstructed, or sporadic access to the open ocean, and in
which ocean water is at least occasionally diluted by fresh-water
runoff from the land. The salinity may be periodical-ly
increased above that of the open ocean by evaporation.
Along some low-energy coastlines there is appreciable dilu-tion
of sea water. Offshore areas with typical estuarine
plants and animals, such as red mangroves (Rhizophora
5
System
~ Marine ~
- Estuarine __
L
~ Riverine4
~ Lacustrine ~
~ Palustrine
Subsystem Class
~Subtidal E &[{:ed B o t t o m
~IntertidalP/j!jZii;iledShore
- Rock Bottom
Subtidal--kiiiF%Bottom
i-
Aquatic Bed
Reef
Streambed
____ Intertidal PCcgky$ged Shore
t
Emergent Wetland
Scrub-Shrub Wetland
Forested Wetland
Rock Bottom
Unconsolidated Bottom
~ Tidal
Aquatic Bed
k
Streambed
Rocky Shore
Unconsolidated Shore
-- Emergent Wetland
F
Rock Bottom
Unconsolidated Bottom
~ Lower Perennial Aquatic Bed
Rocky Shore
- Intermittent
Limnetic -
Streambed
+$Z~~K~ed Bot to m
F
Rock Bottom
Unconsolidated Bottom
- L i t t o r a l - - - EAquatic Bed
Rocky Shore
Unconsolidated Shore
Emergent Wetland
Rock Bottom
Unconsolidated Bottom
Aquatic Bed
Unconsolidated Shore
Moss-Lichen Wetland
Emergent Wetland
Scrub-Shrub Wetland
Forested Wetland
Fig. 1. Classification hierarchy of wetlands and deepwater habitats, showing Systems, Subsystems, and Classes. The Palustrine
System does not include deepwater habitats.
6
Table 1. Distribution of Subclasses within the classification hierarchy.
Class/Subclass
Rock Bottom
Bedrock
Rubble
Unconsolidated Bottom
Cobble-Gravel
Sand
Mud
Organic
Aquatic Bed
Algal
Aquatic Moss
Rooted Vascular
Floating Vascular
Reef
Coral
Mollusk
Worm
Streambed
Bedrock
Rubble
Cobble-Gravel
Sand
Mud
Organic
Vegetated
Rocky Shore
Bedrock
Rubble
Unconsolidated Shore
Cobble-Gravel
Sand
Mud
Organic
Vegetated
Moss-Lichen Wetland
Moss
Lichen
Emergent Wetland
Persistent
Nonpersistent
Scrub-Shrub Wetland
Broad-leaved Deciduous
Needle-leaved Deciduous
Broad-leaved Evergreen
Needle-leaved Evergreen
Dead
Svstem and Subsvstem”
Marine Estuarine
ST IT ST IT
Riverine Lacustrine
TI LP UP IN LM LT
Palustrine
-
X
X
X
X
X
X
X X
X X
X
X
X
X X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X X
X X
X X X
X X X
X X X
X X
X X X
X X X
X X X
X X X
X X X
X X X
X X X
X X X
X X X
X X X
X X X
Xx
x X X
X X
X X
X X
X X
X X
X X
X X
X X
X X
X X
X
X
X
X
X
X
X
X
X
X
X
X
X X
X X
X X
X X
X X
X
X
X
X X
X
X
XX
X
7
Table 1. Continued.
System and Subsystem”
Marine Estuarine Riverine Lacustrine Palustrine
Class/Subclass ST IT ST IT TI LP UP IN LM LT -
Forested Wetland
Broad-leaved Deciduous X X
Needle-leaved Deciduous X X
Broad-leaved Evergreen X X
Needle-leaved Evergreen X X
Dead X X
“ST = Subtidal, IT = Intertidal, TI = Tidal, LP = Lower Perennial, UP = Upper Perennial, IN = Intermittent, LM = Limnetic,
LT = Littoral.
mangle) and eastern oysters (Crassostrea virginica), are
also included in the Estuarine System.3
Limits. The Estuarine System extends (1) upstream and
landward to where ocean-derived salts measure less than
0.5Y00 during the period of average annual low flow; (2)
to an imaginary line closing the mouth of a river, bay, or
sound; and (3) to the seaward limit of wetland emergents,
shrubs, or trees where they are not included in (2). The
Estuarine System also includes offshore areas of contin-uously
diluted sea water.
Description. The Estuarine System includes both es-tuaries
and lagoons. It is more strongly influenced by its
association with land than is the Marine System. In terms
of wave action, estuaries are generally considered to be
low-energy systems (Chapman 19772).
Estuarine water regimes and water chemistry are
affected by one or more of the following forces: oceanic
tides, precipitation, freshwater runoff from land areas,
evaporation, and wind. Estuarine salinities range from
hyperhaline to oligohaline (Table 2). The salinity may be
variable, as in hyperhaline lagoons (e.g., Laguna Madre,
Texas) and most brackish estuaries (e.g., Chesapeake Bay,
Virginia-Maryland); or it may be relatively stable, as in
sheltered euhaline embayments (e.g., Chincoteague Bay,
Maryland) or brackish embayments with partly obstructed
access or small tidal range (e.g., Pamlico Sound, North
Carolina). (For an extended discussion of estuaries and
lagoons see Lauff 1967.)
Subsystems.
Subtidal-The substrate is continuously submerged.
Intertidal.-The substrate is exposed and flooded by
tides; includes the associated splash zone.
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 the open sea, where the sea-water
is measurably diluted with freshwater derived from land
drainage.” The Act further states that “the term includes estuary-type
areas of the Great Lakes.” However, in the present system
we do not consider areas of the Great Lakes as Estuarine.
Classes. Rock Bottom, Unconsolidated Bottom, Aquatic
Bed, Reef, Streambed, Rocky Shore, Unconsolidated
Shore, Emergent Wetland, Scrub-Shrub Wetland, and
Forested Wetland.
Riverine System
Definition. The Riverine System (Fig. 4) includes all
wetlands and deepwater habitats contained within a chan-nel,
with two exceptions: (1) wetlands dominated by trees,
shrubs, persistent emergents, emergent mosses, or
lichens, and (2) habitats with water containing ocean-derived
salts in excess of 0.5”/00. A channel is “an open
conduit either naturally or artificially created which
periodically or continuously contains moving water, or
which forms a connecting link between two bodies of
standing water” (Langbein and Iseri 1960:5).
Limits. The Riverine System is bounded on the land-ward
side by upland, by the channel bank (including
natural and man-made levees), or by wetland dominated
by trees, shrubs, persistent emergents, emergent mosses,
or lichens. In braided streams, the system is bounded by
the banks forming the outer limits of the depression within
which the braiding occurs.
The Riverine System terminates at the downstream end
where the concentration of ocean-derived salts in the
water exceeds 0.5%0 during the period of annual average
low flow, or where the channel enters a lake. It terminates
at the upstream end where tributary streams originate,
or where the channel leaves a lake. Springs discharging
into a channel are considered part of the Riverine System.
Description. Water is usually, but not always, flowing
in the Riverine System. Upland islands or Palustrine wet-lands
may occur in the channel, but they are not included
in the Riverine System. Palustrine Moss-Lichen Wet-lands,
Emergent Wetlands, Scrub-Shrub Wetlands, and
Forested Wetlands may occur adjacent to the Riverine
System, often on a floodplain. Many biologists have sug-gested
that all the wetlands occurring on the river flood-plain
should be a part of the Riverine System because they
8
UPLAND
P!c
Soaward Llmlt of Marlno System ---a
INTERTIDAL
c c
SUSTIDAL INTERTIDAL
a lRREGULARLY FLOODED
b REGULARLY FLOODED
c IRREQULARLY EXPOSED
d SUBTIDAL
SUETIDAL
. c
_
j_
pig. 2. Distinguishing features and examples of habitats in the Marine System. EHWS = extreme high water of spring tides;
ELWS = extreme low water of spring tides.
consider their presence to be the result of river flooding.
However, we concur with Reid and Wood (1976:72,84) who
stated, “The floodplain is a flat expanse of land border-ing
an old river. . . . Often the floodplain may take the form
of a very level plain occupied by the present stream chan-nel,
and it may never, or only occasionally, be flooded. . . .
It is this subsurface water [the ground water] that con-trols
to a great extent the level of lake surfaces, the flow
of streams, and the extent of swamps and marshes.”
Subsystems. The Riverine System is divided into four
Subsystems: the Tidal, the Lower Perennial, the Upper
Perennial, and the Intermittent. Each is defined in terms
of water permanence, gradient, water velocity, substrate,
and the extent of floodplain development. The Subsystems
have characteristic flora and fauna (see Illies and Botosa-neau
1963; Hynes 1970; Reid and Wood 1976). All four
Subsystems are not necessarily present in all rivers, and
the order of occurrence may be other than that given
below.
nial Subsystem. The floodplain is typically well developed.
Lower Perennial.-The gradient is low and water veloc-ity
is slow. There is no tidal influence, and some water
flows throughout the year. The substrate consists mainly
of sand and mud. Oxygen deficits may sometimes occur,
the fauna is composed mostly of species that reach their
maximum abundance in still water, and true planktonic
organisms are common. The gradient is lower than that
of the Upper Perennial Subsystem and the floodplain is
well developed.
Upper Perennial.-The gradient is high and velocity of
the water fast. There is no tidal influence and some water
flows throughout the year. The substrate consists of rock,
cobbles, or gravel with occasional patches of sand. The
natural dissolved oxygen concentration is normally near
saturation. The fauna is characteristic of running water,
and there are few or no planktonic forms. The gradient
is high compared with that of the Lower Perennial Sub-system,
and there is very little floodplain development.
Tidal.-The gradient is low and water velocity fluctuates Intermittent. -In this Subsystem, the channel contains
under tidal influence. The streambed is mainly mud with flowing water for only part of the year. When the water
occasional patches of sand. Oxygen deficits may sometimes is not flowing, it may remain in isolated pools or surface
occur and the fauna is similar to that in the Lower Peren- water may be absent.
9
UPLAND ESTUARINE UPLAND ESTlJARlNE
INTERTIDAL SUBTIDAL INTERTIDAL INTERTIDAL SUBTIDAL
4
a IRREQULARLY FLOODED
b REGULARLY FLOODED
c IRREGULARLY EXPOSED
d SUBTIDAL
Fig. 3. Distinguishing features and examples of habitats in the Estuarine System. EHWS = extreme high water of spring tides;
ELWS = extreme low water of spring tides.
Classes. Rock Bottom, Unconsolidated Bottom, Aquatic
Bed, Streambed, Rocky Shore, Unconsolidated Shore, and
Emergent Wetland (nonpersistent).
Lacustrine System
Definition. The Lacustrine System (Fig. 5) includes wet-lands
and deepwater habitats with all of the following
characteristics: (1) situated in a topographic depression
or a dammed river channel; (2) lacking trees, shrubs, per-sistent
emergents, emergent mosses or lichens with
greater than 30% area1 coverage; and (3) total area ex-ceeds
8 ha (20 acres). Similar wetland and deepwater
habitats totaling less than 8 ha are also included in the
Lacustrine System if an active wave-formed or bedrock
shoreline feature makes up all or part of the boundary,
or if the water depth in the deepest part of the basin ex-ceeds
2 m (6.6 feet) at low water. Lacustrine waters may
be tidal or nontidal, but ocean-derived salinity is always
less than 0.5O/00.
emergents, emergent mosses, or lichens. Lacustrine
Systems formed by damming a river channel are bounded
by a contour approximating the normal spillway elevation
or normal pool elevation, except where Palustrine wet-lands
extend lakeward of that boundary. Where a river
enters a lake, the extension of the Lacustrine shoreline
forms the Riverine-Lacustrine boundary.
Description. The Lacustrine System includes perma-nently
flooded lakes and reservoirs (e.g., Lake Superior),
intermittent lakes (e.g., playa lakes), and tidal lakes with
ocean-derived salinities below 0.5%0 (e.g., Grand Lake,
Louisiana). Typically, there are extensive areas of deep
water and there is considerable wave action. Islands of
Palustrine wetland may lie within the boundaries of the
Lacustrine System.
Subsystems.
Limnetic.-All deepwater habitats within the Lacus-trine
System; many small Lacustrine Systems have no
Limnetic Subsystem.
Limits. The Lacustrine System is bounded by upland Littoral. -All wetland habitats in the Lacustrine
or by wetland dominated by trees, shrubs, persistent System. Extends from the shoreward boundary of the
10
Table 2. Salinity Modifiers used in this classification system.
Coastal Modifiers”
Hyperhaline
Euhaline
Mixohaline (Brackish)
Polyhaline
Mesohaline
Oligohaline
Fresh
Inland Modifiersb
Hypersaline
Eusaline
Mixosaline’
Polysaline
Mesosaline
Oligosaline
Fresh
Salinity (parts per thousand)
Approximate
specific conductance
bMhos at 25°C)
>40 >60,000
30.0-40 45,000-60,000
0.5-30 800-45,000
X0-30 30,000-45,000
5.0-18 8,000-30,000
0.5-5 800- 8,000
<0.5 <800
“Coastal Modifiers are used in the Marine and Estuarine Systems.
bInland Modifiers are used in the Riverine, Lacustrine, and Palustrine Systems.
‘The term Brackish should not be used for inland wetlands or deepwater habitats.
system to a depth of 2 m (6.6 feet) below low water or
to the maximum extent of nonpersistent emergents, if
these grow at depths greater than 2 m.
Classes. Rock Bottom, Unconsolidated Bottom, Aquatic
Bed, Rocky Shore, Unconsolidated Shore, and Emergent
Wetland (nonpersistent).
Palustrine System
Definition. The Palustrine System (Fig. 6) includes all
nontidal wetlands dominated by trees, shrubs, persistent
emergents, emergent mosses or lichens, and all such wet-lands
that occur in tidal areas where salinity due to ocean-derived
salts is below 0.5Y00. It also includes wetlands
lacking such vegetation, but with all of the following four
characteristics: (1) area less than 8 ha (20 acres); (2) ac-tive
wave-formed or bedrock shoreline features 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 O.~O/OO.
Limits. The Palustrine System is bounded by upland or
by any of the other four Systems.
Description. The Palustrine System was developed to
group the vegetated wetlands traditionally called by such
names as marsh, swamp, bog, fen, and prairie, which are
found throughout the United States. It also includes the
small, shallow, permanent or intermittent water bodies
often called ponds. Palustrine wetlands may be situated
shoreward of lakes, river channels, or estuaries; on river
floodplains; in isolated catchments; or on slopes. They may
also occur as islands in lakes or rivers. The erosive forces
of wind and water are of minor importance except dur-ing
severe floods.
The emergent vegetation adjacent to rivers and lakes
is often referred to as “the shore zone” or the “zone of
emergent vegetation” (Reid and Wood 1976), and is gen-erally
considered separately from the river or lake. As an
example, Hynes (1970:85) wrote in reference to riverine
habitats, “We will not here consider the long list of emer-gent
plants which may occur along the banks out of the
current, as they do not belong, strictly speaking, to the
running water habitat.” There are often great similarities
between wetlands lying adjacent to lakes or rivers and
isolated wetlands of the same class in basins without open
water.
Subsystems. None.
Classes. Rock Bottom, Unconsolidated Bottom, Aquatic
Bed, Unconsolidated Shore, Moss-Lichen Wetland, Emer-gent
Wetland, Scrub-Shrub Wetland, and Forested
Wetland.
Classes, Subclasses, and Dominance Types
The CLASS is the highest taxonomic unit below the Sub-system
level. It describes the general appearance of the
habitat in terms of either the dominant life form of the
vegetation or the physiography and composition of the
substrate-features that can be recognized without the aid
of detailed environmental measurements. Vegetation is
used at two different levels in the classification. The life
forms-trees, shrubs, emergents, emergent mosses, and
lichens-are used to define Classes because they are
relatively easy to distinguish, do not change distribution
rapidly, and have traditionally been used as criteria for
classification of wetlands.4 Other forms of vegetation, such
as submerged or floating-leaved rooted vascular plants,
free-floating vascular plants, submergent mosses, and
algae, though frequently more difficult to detect, are used
40ur initial attempts to use familiar terms such as marsh, swamp,
bog, and meadow at the Class level were unsuccessful primarily
because of wide discrepancies in the use of these terms in various
regions of the United States. In an effort to resolve that difficulty,
we based the Classes on the fundamental components (life form,
water regime, substrate type, water chemistry) that give rise to
such terms. We believe that this approach will greatly reduce the
misunderstandings and confusion that result from the use of the
familiar terms.
UPLAND PALUSTRINE RIVERINE PALUSTRINE UPLAND
HIGH WATER
AVERAGE WATER
LOW WATER
a TEMPORARILY FLOODED
b SEASONALLY FLOODED
c SEMIPERMANENTLY FLOODED
d INTERMITTENTLY EXPOSED
e PERMANENTLY FLOODED
Fig. 4. Distinguishing features and examples of habitats in the Riverine System.
to define the Class Aquatic Bed. Pioneer species that brief-ly
invade wetlands when conditions are favorable are
treated at the Subclass level because they are transient
and often not true wetland species.
Use of life forms at the Class level has two major advan-tages:
(1) extensive biological knowledge is not required
to distinguish between various life forms, and (2) it has
been established that various life forms are easily recog-nizable
on a great variety of remote sensing products (e.g.,
Radforth 1962; Anderson et al. 1976). If vegetation (ex-cept
pioneer species) covers 30% or more of the substrate,
we distinguish Classes on the basis of the life form of the
plants that constitute the uppermost layer of vegetation
and that possess an area1 coverage 30% or greater. For
example, an area with 50% area1 coverage of trees over
a shrub layer with a 60% area1 coverage would be classified
as Forested Wetland; an area with 20% area1 coverage
of trees over the same (60%) shrub layer would be
classified as Scrub-Shrub Wetland. When trees or shrubs
alone cover less than 30% of an area but in combination
cover 30% or more, the wetland is assigned to the Class
Scrub-Shrub. When trees and shrubs cover less than 30%
of the area but the total cover of vegetation (except
pioneer species) is 30% or greater, the wetland is assigned
to the appropriate Class for the predominant life form
below the shrub layer. Finer differences in life forms are
recognized at the SUBCLASS level. For example, Forested
Wetland is divided into the Subclasses Broad-leaved Decid-uous,
Needle-leaved Deciduous, Broad-leaved Evergreen,
Needle-leaved Evergreen, and Dead. Subclasses are
named on the basis of the predominant life form.
If vegetation covers less than 30% of the substrate, the
physiography and composition of the substrate are the
principal characteristics used to distinguish Classes. The
nature of the substrate reflects regional and local varia-tions
in geology and the influence of wind, waves, and cur-rents
on erosion and deposition of substrate materials.
Bottoms, Shores, and Streambeds are separated on the
basis of duration of inundation. In the Riverine, Lacus-trine,
and Palustrine Systems, Bottoms are submerged
all or most of the time, whereas Streambeds and Shores
are exposed all or most of the time. In the Marine and
Estuarine Systems, Bottoms are Subtidal, whereas
Streambeds and Shores are Intertidal. Bottoms, Shores,
and Streambeds are further divided at the Class level on
the basis of the important characteristic of rock versus
UPLAND LACUSTRINE
LIMNETIC
PALUSTRINE UPLAND
HIGH WATER
AVERAGE WATER
LOW WATER
-_-_____
a TEMPORARILY FLOODED
b SEASONALLY FLOODED
c SEMIPERMANENTLY FLOODED
d INTERMITTENTLY EXPOSED
e PERMANENTLY FLOODED
Fig. 5. Distinguishing features and examples of habitats in the Lacustrine System.
unconsolidated substrate. Subclasses are based on finer of vegetation used to determine the Subclass.6 For exam-distinctions
in substrate material unless, as with ple, a Needle-leaved Evergreen Forested Wetland with
Streambeds and Shores, the substrate is covered by, or 70% area1 cover of black spruce (Picea mariana) and 30%
shaded by, an area1 coverage of pioneering vascular plants area1 cover of tamarack (Lariz Zaticina) would be desig-
(often nonhydrophytes) of 30% or more; the Subclass is nated as a Picea mariana Dominance Type. When the
then simply “vegetated.” Further detail as to the type of relative abundance of codominant species is nearly equal,
vegetation must be obtained at the level of Dominance the Dominance Type consists of a combination of species
Type. Reefs are a unique class in which the substrate itself names. For example, an Emergent Wetland with about
is composed primarily of living and dead animals. equal area1 cover of common cattail (Typha ZatQ&a) and
Subclasses of Reefs are designated on the basis of the type hardstem bulrush (Scirpus acutzls) would be designated
of organism that formed the reef. a Typha latifolia-S&-pus acutus Dominance Type.
The DOMINANCE TYPE is the taxonomic category sub-ordinate
to Subclass. Dominance Types are determined
on the basis of dominant plant species (e.g., Jeglum et al.
1974), dominant sedentary or sessile animal species (e.g.,
Thorson 1957), or dominant plant and animal species (e.g.,
Stephenson and Stephenson 1972). A dominant plant
species has traditionally meant one that has control over
the community (Weaver and Clements 1938:91), and this
plant is also usually the predominant species (Cain and
Castro 1959:29). When the Subclass is based on life form,
we name the Dominance Type for the dominant species
or combination of species (codominants) in the same layer
When the Subclass is based on substrate material, the
Dominance Type is named for the predominant plant or
SPercent area1 cover is seldom measured in the application of this
system, but the term must be defined in terms of area. We sug-gest
2 m* for herbaceous and moss layers, 16 m2 for shrub
layers, and 100 m2 for tree layers (Mueller-Dombois and Ellen-berg
1974:74). When percent areal cover is the key for establishing
boundaries between units of the classification, it may occasion-ally
be necessary to measure cover on plots, in order to maintain
uniformity of ocular estimates made in the field or interpretations
made from aerial photographs.
UPLAND PALUSTRINE UPLAND PALUSTRINE UPLAND PALUSTRINE UPLAND
a TEMPORARILY FLOODED
b SEASONALLY FLOODED
c SEMIPERMANENTLY FLOODED
d INTERMITTENTLY EXPOSED
e PERMANENTLY FLOODED
f SATURATED
ERAGE WATEI
LOW WATEI
Fig. 6. Distinguishing features and examples of habitats in the Palustrine System.
sedentary or sessile macroinvertebrate species, without
regard for life form. In the Marine and Estuarine Systems,
sponges, alcyonarians, mollusks, crustaceans, worms, asci-dians,
and echinoderms may all be part of the community
represented by the Macoma balthica Dominance Type.
Sometimes it is necessary to designate two or more co-dominant
species as a Dominance Type. Thorson (1957)
recommended guidelines and suggested definitions for
establishing community types and dominants on level
bottoms.
Rock Bottom
Definition. The Class Rock Bottom includes all wetlands
and deepwater habitats with substrates having an area1
cover of stones, boulders, or bedrock 75% or greater and
vegetative cover of less than 30%. Water regimes are
restricted to subtidal, permanently flooded, intermittently
exposed, and semipermanently flooded.
Description. The rock substrate of the rocky benthic or
bottom zone is one of the most important factors in deter-mining
the abundance, variety, and distribution of organ-isms.
The stability of the bottom allows a rich assemblage
of plants and animals to develop. Rock Bottoms are usually
high-energy habitats with well-aerated waters. Tempera-ture,
salinity, current, and light penetration are also im-portant
factors in determining the composition of the ben-thic
community. Animals that live on the rocky surface
are generally firmly attached by hooking or sucking
devices, although they may occasionally move about over
the substrate. Some may be permanently attached by
cement. A few animals hide in rocky crevices and under
rocks, some move rapidly enough to avoid being swept
away, and others burrow into the finer substrates between
boulders. Plants are also firmly attached (e.g., by hold-fasts),
and in the Riverine System both plants and animals
are commonly streamlined or flattened in response to high
water velocities.
Subclasses and Dominance Types.
Bedrock.-Bottoms in which bedrock covers 75% or
more of the surface.
Rubble.-Bottoms with less than 75% area1 cover of
bedrock, but stones and boulders alone, or in combination
with bedrock, cover 75% or more of the surface.
Examples of Dominance Types for these two Subclasses
in the Marine and Estuarine Systems are the encrusting
14
sponges Hippospongia, the tunicate Cnemidocarpa, the
sea urchin Strongylocentrotus, the sea star Pisaster, the
sea whip Muricea, and the American lobster Homarus
americanus. Examples of Lacustrine, Palustrine, and
Riverine Dominance Types are the freshwater sponges
Spongilla and Heteromeyenia, the pond snail Lymnaea,
the mayfly Ephemerella, various midges of the Chirono-midae,
the caddisfly Hydropsyche, the leech Helobdella,
the riffle beetle Psephenus, the chironomid midge Eukief
feriella, the crayfish Procambarus, and the black fly
Simulium.
Dominance Types for Rock Bottoms in the Marine and
Estuarine Systems were taken primarily from Smith
(1964) and Ricketts and Calvin (1968), and those for Rock
Bottoms in the Lacustrine, Riverine, and Palustrine
Systems from 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 to subtidal,
permanently flooded, intermittently exposed, and semi-permanently
flooded.
Description. Unconsolidated Bottoms are characterized
by the lack of large stable surfaces for plant and animal
attachment. They are usually found in areas with lower
energy than Rock Bottoms, and may be very unstable. Ex-posure
to wave and current action, temperature, salinity,
and light penetration determines the composition and
distribution of organisms.
Most macroalgae attach to the substrate by means of
basal hold-fast cells or discs; in sand and mud, however,
algae penetrate the substrate and higher plants can suc-cessfully
root if wave action and currents are not too
strong. Most animals in unconsolidated sediments live
within the substrate, e.g., Macoma and the amphipod
Melita. Some, such as the polychaete worm Chaetopterus,
maintain permanent burrows, and others may live on the
surface, especially in coarse-grained sediments.
In the Marine and Estuarine Systems, Unconsolidated
Bottom communities are relatively stable. They vary from
the Arctic to the tropics, depending largely on temper-ature,
and from the open ocean to the upper end of the
estuary, depending on salinity. Thorson (1957) summarized
and described characteristic types of level-bottom com-munities
in detail.
In the Riverine System, the substrate type is largely
determined by current velocity, and plants and animals
exhibit a high degree of morphologic and behavioral adap-tation
to flowing water. Certain species are confined to
specific substrates and some are at least more abundant
in one type of substrate than in others. According to Hynes
(1970:208), “The larger the stones, and hence the more
complex the substratum, the more diverse is the inverte-brate
fauna.” In the Lacustrine and Palustrine Systems,
there is usually a high correlation, within a given water
body, between the nature of the substrate and the number
of species and individuals. For example, in the profundal
bottom of eutrophic lakes where light is absent, oxygen
content is low, and carbon dioxide concentration is high,
the sediments are ooze-like organic materials and species
diversity is low. Each substrate type typically supports
a relatively distinct community of organisms (Reid and
Wood 1976:262).
Subclasses and Dominance Types.
Cobble-Gravel. -The unconsolidated particles smaller
than stones are predominantly cobble and gravel, although
finer sediments may be intermixed. Examples of Domi-nance
Types for the Marine and Estuarine Systems are
the mussels Modiolus and Mytilus, the brittle star Am-phipholis,
the soft-shell clam Mya, and the Venus clam
Saxidomus. Examples for the Lacustrine, Palustrine, and
Riverine Systems are the midge 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 sponge Eunapius, the
oligochaete worm Lumbriculus, the scud Gammarus, and
the freshwater mollusks Anodonta, Elliptio, and
Lampsilis.
Sand. -The unconsolidated particles smaller than
stones are predominantly sand, although finer or coarser
sediments may be intermixed. Examples of Dominance
Types in the Marine and Estuarine Systems are the wedge
shell Donax, the scallop Pecten, the tellin shell Tellina, the
heart urchin Echinocardium, the lugworm Are&cola, the
sand dollar Dendraster, and the sea pansy Renilla. Ex-amples
for the Lacustrine, Palustrine, and Riverine
Systems are the snail Physa, the scud Gammarus, the
oligochaete worm Limnodrilus, the mayfly Ephemerella,
the freshwater mollusks Elliptio and Anodonta, and the
fingernail clam Sphaerium.
Mud.-The unconsolidated particles smaller than
stones are predominantly silt and clay, although coarser
sediments or organic material may be intermixed. Organ-isms
living in mud must be able to adapt to low oxygen
concentrations. Examples of Dominance Types for the
Marine and Estuarine Systems include the terebellid worm
Amphitrite, the boring clam Platyodon, the deep-sea
scallop Placopecten, the quahog Mercenaria, the macoma
Macoma, the echiurid worm Urechis, the mud snail
Nassarius, and the sea cucumber Thyone. Examples of
Dominance Types for the Lacustrine, Palustrine, and
Riverine Systems are the sewage worm TubiJex, fresh-water
mollusks Anodonta, Anodontoides, and Elliptio, the
fingernail clams Pisidium and Sphaerium, and the midge
Chironomus.
15
Organic-The unconsolidated material smaller than
stones is predominantly organic. The number of species
is limited and fauna1 productivity is very low (Welch 1952).
Examples of Dominance Types for Estuarine and Marine
Systems are the soft-shell clam Mya, the false angel wing
Petricola pholadiformis, the clam worm Nereis, and the
mud snail Nussurius. Examples for the Lacustrine, Palus-trine,
and Riverine Systems are the sewage worm Tubifex,
the snail Physa, the harpacticoid copepod Canthocamptus,
and the oligochaete worm Limnodrilus.
Dominance Types for Unconsolidated Bottoms in the
Marine and Estuarine Systems were taken predominant-ly
from Miner (1950), Smith (1964), Abbott (1968) and
Ricketts and Calvin (1968). Dominance Types for Uncon-solidated
Bottoms in the Lacustrine, Riverine, and Palus-trine
Systems were taken predominantly from Krecker
and Lancaster (1933), Stehr and Branson (1938), Johnson
(1970), Brinkhurst and Jamieson (1972), Clarke (1973),
Hart and Fuller (1974), Ward (1975) and Pennak (1978).
Aquatic Bed
Definition. The Class Aquatic Bed includes wetlands
and deepwater habitats dominated by plants that grow
principally on or below the surface of the water for most
of the growing season in most years. Water regimes in-clude
subtidal, irregularly exposed, regularly flooded,
permanently flooded, intermittently exposed, semiperm-anently
flooded, and seasonally flooded.
Description. Aquatic Beds represent a diverse group of
plant communities that requires surface water for opti-mum
growth and reproduction. They are best developed
in relatively permanent water or under conditions of re-peated
flooding. The plants are either attached to the
substrate or float freely in the water above the bottom
or on the surface.
Subclasses and Dominance Types.
Algal.-Algal Beds are widespread and diverse in the
Marine and Estuarine Systems, where they occupy sub-strates
characterized by a wide range of sediment depths
and textures. They occur in both the Subtidal and Inter-tidal
Subsystems and may grow to depths of 30 m (98 feet).
Coastal Algal Beds are most luxuriant along the rocky
shores of the Northeast and West. Kelp (Mucrocystis) beds
are especially well developed on the rocky substrates of
the Pacific Coast. Dominance Types such as the rockweeds
Fucus and Ascophyllum and the kelp Laminaria are com-mon
along both coasts. In tropical regions, green algae,
including forms containing calcareous particles, are more
characteristic; Halimeda and Penicillus are common ex-amples.
The red alga Laurencia, and the green algae
Caulerpa, Enteromorpha, and Ulva are also common
Estuarine and Marine dominance types; Enteromorpha
and Ulva are tolerant of fresh water and flourish near the
upper end of some estuaries. The stonewort Chara is also
found in estuaries.
Inland, the stoneworts Chara, Nitella, and Tolypella are
examples of algae that look much like vascular plants and
may grow in similar situations. However, meadows of
Chara may be found in Lacustrine water as deep as 40 m
(131 feet) (Zhadin and Gerd 1963) where hydrostatic
pressure limits the survival of vascular submergents
(phanaerogams) (Welch 1952). Other algae bearing less
resemblance to vascular plants are also common. Mats of
filamentous algae may cover the bottom in dense blankets,
may rise to the surface under certain conditions, or may
become stranded on Unconsolidated or Rocky Shores.
Aquatic Moss. -Aquatic mosses are far less abundant
than algae or vascular plants. They occur primarily in the
Riverine System and in permanently flooded and inter-mittently
exposed parts of some Lacustrine systems. The
most important Dominance Types include genera such as
Fissidens, Dreparwcladus, and Fontinalis. Fontinalis may
grow to depths as great as 120 m (394 feet) (Hutchinson
1975). For simplicity, aquatic liverworts of the genus Mur-supella
are included in this Subclass.
Rooted Vacular.-Rooted Vascular Beds include a
large array of vascular species in the Marine and Estu-arine
Systems. They have been referred to by others as
temperate grass flats (Phillips 1974); tropical marine
meadows (Odum 1974); and eelgrass beds, turtlegrass
beds, and seagrass beds (Akins and Jefferson 1973;
Eleuterius 1973; Phillips 1974). The greatest number of
species occur in shallow, clear tropical, or subtropical
waters of moderate current strength in the Caribbean and
along the Florida and Gulf Coasts. Principal Dominance
Types in these areas include turtle grass (Thalassia testu-d&
urn), shoalgrass (Halodule wrightii), manatee grass
(Cymodoceafiliformis), widgeon grass (Ruppia maritima),
sea grasses (Halophila spp.), and wild celery (Vallisneria
americana).
Five major vascular species dominate along the tem-perate
coasts of North America: shoalgrass, surf grasses
(Phyllospadix scoukri, P. torreyi), widgeon grass, and eel-grass
(Zostera marina). Eelgrass beds have the most ex-tensive
distribution, but they are limited primarily to the
more sheltered estuarine environment. In the lower salin-ity
zones of estuaries, stands of widgeon grass, pondweed
(Potamogeton), and wild celery often occur, along with
naiads (No&) and water milfoil (Myriophyllum).
In the Riverine, Lacustrine, and Palustrine Systems,
rooted vascular aquatic plants occur at all depths within
the photic zone. They often occur in sheltered areas where
there is little water movement (Wetzel 1975); however,
they also occur in the flowing water of the Riverine
System, where they may be streamlined or flattened in
response to high water velocities. Typical inland genera
include pondweeds, horned pondweed (Zannichellia
palustris), ditch grasses (Ruppia), wild celery, and water-weed
(Elodea). The riverweed (Podostemum ceratophyl-lum)
is included in this class despite its lack of truly
recognizable roots (Sculthorpe 1967).
16
Some of the rooted vascular species are characterized
by floating leaves. Typical dominants include water lilies
(Nymphoxa, Nuphar), floating-leaf pondweed (Potamoge-ton
natans), and water shield (Brasenia schreberi). Plants
such as yellow water lily (Nuphar Zuteum) and water
smartweed (Polygonum amphibium), which may stand
erect above the water surface or substrate, may be con
sidered either emergents or rooted vascular aquatic plants,
depending on the life form adopted at a particular site.
Floating Vascular.-Beds of floating vascular plants
occur mainly in the Lacustrine, Palustrine, and Riverine
Systems and in the fresher waters of the Estuarine Sys-tem.
The plants float freely either in the water or on its
surface. Dominant plants that float on the surface include
the duckweeds (Lemna, Spiro&la), water lettuce (Pistia
stratiotes), water hyacinth (Eichhornia crassipes), water
nut (Z’rupa natuns), water ferns (Salwinia spp.), and mos-quito
ferns (Azolla). These plants are found primarily in
protected portions of slow-flowing rivers and in the
Lacustrine and Palustrine Systems. They are easily moved
about by wind or water currents and cover a large area
of water in some parts of the country, particularly the
Southeast. Dominance Types for beds floating below the
surface include bladderworts (Utriculuria), coontails
(Ceratophyllum), and watermeals (Wolfja) (Sculthorpe
1967; Hutchinson 1975).
Reef
Definition. The Class Reef includes ridge-like or mound-like
structures formed by the colonization and growth of
sedentary invertebrates. Water regimes are restricted to
subtidal, irregularly exposed, regularly flooded, and
irregularly flooded.
Description. Reefs are characterized by their elevation
above the surrounding substrate and their interference
with normal wave flow; they are primarily subtidal, but
parts of some reefs may be intertidal as well. Although
corals, oysters, and tube worms are the most visible
organisms and are mainly responsible for reef formation,
other mollusks, foraminifera, coralline algae, and other
forms of life also contribute substantially to reef growth.
Frequently, reefs contain far more dead skeletal material
and shell fragments than living matter.
Subclasses and Dominance Types.
Coral.-Coral Reefs are widely distributed in shallow
waters of warm seas, in Hawaii, Puerto Rico, the Virgin
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 the Marine System, although
the upper part of certain Reefs may be exposed. Examples
of Dominance Types are the corals Porites, Acropora, and
Montipora. The distribution of these types reflects prim-arily
their elevation, wave exposure, the age of the Reef,
and its exposure to waves.
Mollusk.-This Subclass occurs in both the Intertidal
and Subtidal Subsystems of the Estuarine System. These
Reefs are found on the Pacific, Atlantic, and Gulf Coasts
and in Hawaii and the Caribbean. Mollusk Reefs may
become extensive, affording a substrate for sedentary and
boring organisms and a shelter for many others. Reef
mollusks are adapted to great variations in water level,
salinity, and temperature, and these same factors control
their distribution. Examples of Dominance Types for this
Subclass are the oysters Ostrea and Crassostrea (Smith
1964; Abbott 1968; Ricketts and Calvin 1968).
Worm.-Worm Reefs are constructed by large col-onies
of Sabellariid worms living in individual tubes con-structed
from cemented sand grains. Although they do
not support as diverse a biota as do Coral and Mollusk
Reefs, they provide a distinct habitat which may cover
large areas. Worm Reefs are generally confined to tropical
waters, and are most common along the coasts of Florida,
Puerto Rico, and the Virgin Islands. They occur in both
the Intertidal and Subtidal Systems of the Marine and
Estuarine Systems where the salinity approximates that
of sea water. The reefworm Sabellaria is an example of
a Dominance Type for this Subclass (Ricketts and Calvin
1968).
Streambed
Definition. The Class Streambed includes all wetland
contained within the Intermittent Subsystem of the River-ine
System and all channels of the Estuarine System or
of the Tidal Subsystem of the Riverine System that are
completely dewatered at low tide. Water regimes are
restricted to irregularly exposed, regularly flooded, irreg-ularly
flooded, seasonally flooded, temporarily flooded, and
intermittently flooded.
Description. Streambeds vary greatly in substrate and
form depending on the gradient of the channel, the veloc-ity
of the water, and the sediment load. The substrate
material frequently changes abruptly between riffles and
pools, and complex patterns of bars may form on the con-vex
side of single channels or be included as islands within
the bed of braided streams (Crickmay 1974). In mountain-ous
areas the entire channel may be cut through bedrock.
In most cases streambeds are not vegetated because of
the scouring effect of moving water, but, like Uncon-solidated
Shores, they may be colonized by “pioneering”
annuals or perennials during periods of low flow or they
may have perennial emergents and shrubs that are too
scattered to qualify the area for classification as Emer-gent
Wetland or Scrub-Shrub Wetland.
Subclasses and Dominance Types.
Bedrock. -This Subclass is characterized by a bedrock
substrate covering 75% or more of the stream channel.
17
It occurs most commonly in the Riverine System in high
mountain areas or in glaciated areas where bedrock is ex-posed.
Examples of Dominance Types are the mollusk An-ylus,
the oligochaete worm Limnodrilus, the snail Physa,
the fingernail clam Ptiidium, and the mayflies Caenis and
Ephemerella.
Rubble.-This Subclass is characterized by stones,
boulders, and bedrock that in combination cover more than
75% of the channel. Like Bedrock Streambeds, Rubble
Streambeds are most common in mountainous areas and
the dominant organisms are similar to those of Bedrock
and are often forms capable of attachment to rocks in flow-ing
water.
Cobble-Gravel.-In this Subclass at least 25% of the
substrate is covered by unconsolidated particles smaller
than stones; cobbles or gravel predominate. The Subclass
occurs in riffle areas or in the channels of braided streams.
Examples of Dominance Types in the Intermittent Subsys-tem
of the Riverine System are the snail Physa, the oligo-chaete
worm Limnodrilus, the mayfly Caenis, the midge
Chironomus, and the mosquito Anopheles. Examples of
Dominance Types in the Estuarine System or Tidal Sub-system
of the Riverine System are the mussels Modiolus
and Mytilus.
Sand. -In this Subclass, sand-sized particles predom-inate
among the particles smaller than stones. Sand
Streambed often contains bars and beaches interspersed
with Mud Streambed or it may be interspersed with
Cobble-Gravel Streambed in areas of fast flow or heavy
sediment load. Examples of Dominance Types in the
Riverine System are the scud Gammarus, the snails Physa
and Lymnaea, and the midge Chironomus; in the
Estuarine System the ghost shrimp Callianassa is a com-mon
Dominance Type.
Mud.-In this Subclass, the particles smaller than
stones are chiefly silt or clay. Mud Streambeds are com-mon
in arid areas where intermittent flow is character-istic
of streams of low gradient. Such species as tamarisk
(Tamarix gallica) may occur, but are not dense enough
to qualify the area for classification as Scrub-Shrub
Wetland. Mud Streambeds are also common in the Estu-arine
System and the Tidal Subsystem of the Riverine
System. Examples of Dominance Types for Mud Stream-beds
include the crayfish Procambarus, the pouch snail
Aplexa, the fly Tabanus, the snail Lymnaea, the finger-nail
clam Sphaerium, and (in the Estuarine System) the
mud snail Nassarius.
Organic. -This Subclass is characterized by channels
formed in peat or muck. Organic Streambeds are common
in the small creeks draining Estuarine Emergent Wet-lands
with organic soils. Examples of Dominance Types
are the mussel Modiolus in the Estuarine System and the
oligochaete worm Limnodrilus in the Riverine System.
Vegetated. -These streambeds are exposed long
enough to be colonized by herbaceous annuals or seedling
herbaceous perennials (pioneer plants). This vegetation,
unlike that of Emergent Wetlands, is usually killed by
rising water levels or sudden flooding. A typical Domi-nance
Type is Panicum capillare.
Dominance Types for Streambeds in the Estuarine Sys-tem
were taken primarily from Smith (1964), Abbott
(1968), and Ricketts and Calvin (1968) and those for
streambeds in the Riverine System from Krecker and Lan-caster
(1933), Stehr and Branson (1938), van der Schalie
(1948), Kenk (1949), Cummins et al. (1964), Clarke (1973),
and Ward (1975).
Rocky Shore
Definition. The Class Rocky Shore includes wetland en-vironments
characterized by bedrock, stones, or boulders
which singly or in combination have an area1 cover of 75%
or more and an area1 coverage by vegetation of less than
30%. Water regimes are restricted to irregularly exposed,
regularly flooded, irregularly flooded, seasonally flooded,
temporarily flooded, and intermittently flooded.
Description. In Marine and Estuarine Systems, Rocky
Shores are generally high-energy habitats which lie ex-posed
as a result of continuous erosion by wind-driven
waves or strong currents. The substrate is stable enough
to permit the attachment and growth of sessile or seden-tary
invertebrates and attached algae or lichens. Rocky
Shores usually display a vertical zonation that is a func-tion
of tidal range, wave action, and degree of exposure
to the sun. In the Lacustrine and Riverine Systems, Rocky
Shores support sparse plant and animal communities.
Subclasses and Dominance Types.
Bedrock.-These wetlands have bedrock covering 75%
or more of the surface and less than 30% area1 coverage
of macrophytes.
Rubble.-These wetlands have less than 75% area1
cover of bedrock, but stones and boulders alone or in com-bination
with bedrock cover 75% or more of the area. The
area1 coverage of macrophytes is less than 30%.
Communities or zones of Marine and Estuarine Rocky
Shores have been widely studied (Lewis 1964; Ricketts and
Calvin 1968; Stephenson and Stephenson 1972). Each zone
supports a rich assemblage of invertebrates and algae or
lichens or both. Dominance Types of the Rocky Shores
often can be characterized by one or two dominant genera
from these zones.
The uppermost zone (here termed the littorine-lichen
zone) is dominated by periwinkles (Littorina and Netita)
and lichens. This zone frequently takes on a dark, or even
black appearance, although abundant lichens may lend a
colorful tone. These organisms are rarely submerged, but
are kept moist by sea spray. Frequently this habitat is
invaded from the landward side by semimarine genera
such as the slater Ligia.
The next lower zone (the balanoid zone) is commonly
dominated by mollusks, green algae, and barnacles of the
balanoid group. The zone appears white. Dominance Types
18
such as the barnacles Balanus, Chthamalus, and Tetra-
&a may form an almost pure sheet, or these animals may
be interspersed with mollusks, tube worms, and algae such
as Pelvetia, Enteromorpha, and Ulva.
The transition between the littorine-lichen and balanoid
zones is frequently marked by the replacement of the
periwinkles with limpets such as Acmaea and Siphonaria.
The limpet band approximates the upper limit of the
regularly flooded intertidal zone.
In the middle and lower intertidal areas, which are
flooded and exposed by tides at least once daily, lie a
number of other communities which can be characterized
by dominant genera. Mytilus and gooseneck barnacles
(Pollicipes) form communities exposed to strong wave
action. Aquatic Beds dominated by Fwus and Laminaria
lie slightly lower, just above those dominated by coralline
algae (Lithothamnion). The Lam&aria Dominance Type
approximates the lower end of the Intertidal Subsystem;
it is generally exposed at least once daily. The Lithotham-nion
Dominance Type forms the transition to the Subtidal
Subsystem and is exposed only irregularly.
In the Palustrine, Riverine, and Lacustrine Systems
various species of lichens such as Vewucuria spp. and Dw-matocarpon
jluviatile, as well as blue-green algae, fre-quently
form characteristic zones on Rocky Shores. The
distribution of these species depends on the duration of
flooding or wetting by spray and is similar to the zona-tion
of species in the Marine and Estuarine Systems (Hut-chinson
1975). Though less abundant than lichens, aquatic
liverworts such as Marsupella emarginata var. aquatica
or mosses such as Fissidens julianus are found on the
Rocky Shores of lakes and rivers. If aquatic liverworts or
mosses cover 30% or more of the substrate, they should
be placed in the Class Aquatic Bed. Other examples of
Rocky Shore Dominance Types are the caddisfly Hydro-psyche
and the fingernail clam Pisidium.
Unconsolidated Shore
Definition. The Class Unconsolidated Shore includes all
wetland habitats having three characteristics: (1) uncon-solidated
substrates with less than 75% area1 cover of
stones, boulders, or bedrock; (2) less than 30% area1 cover
of vegetation other than pioneering plants; and (3) any
of the following water regimes: irregularly exposed,
regularly flooded, irregularly flooded, seasonally flooded,
temporarily flooded, intermittently flooded, saturated, or
artificially flooded. Intermittent or intertidal channels of
the Riverine System and intertidal channels of the Estu-arine
System are classified as Streambed.
Description. Unconsolidated Shores are characterized
by substrates lacking vegetation except for pioneering
plants that become established during brief periods when
growing conditions are favorable. Erosion and deposition
by waves and currents produce a number of landforms
such as beaches, bars, and flats, all of which are included
in this Class. Unconsolidated Shores are found adjacent
to Unconsolidated Bottoms in all Systems; in the Palus-trine
and Lacustrine Systems, the Class may occupy the
entire basin. As in Unconsolidated Bottoms, the particle
size of the substrate and the water regime are the impor-tant
factors determining the types of plant and animal
communities present. Different substrates usually support
characteristic invertebrate fauna. Fauna1 distribution is
controlled by waves, currents, interstitial moisture, salin-ity,
and grain size (Hedgpeth 1957; Ranwell 1972; Riedl
and McMahan 1974).
Subclasses and Dominance Types.
Cobble-Gravel.-The unconsolidated particles smaller
than stones are predominantly cobble and gravel. Shell
fragments, sand, and silt often fill the spaces between the
larger particles. Stones and boulders may be found scat-tered
on some Cobble-Gravel Shores. In areas of strong
wave and current action these shores take the form of
beaches or bars, but occasionally they form extensive flats.
Examples of Dominance Types in the Marine and Estu-arine
Systems are: the acorn barnacle Balunus, the limpet
Patella, the periwinkle Littorina, the rock shell Thais, the
mussels Mytilus and Modiolus, and the Venus clam Sax-idomus.
In the Lacustrine, Palustrine, and Riverine Sys-tems
examples of Dominance Types are the freshwater
mollusk Elliptio, the snails Lymnaea and Physa, the toad
bug Gelastocoris, the leech Erpodella, and the springtail
Agrenia.
Sand.-The unconsolidated particles smaller than
stones are predominantly sand which may be either cal-careous
or terrigenous in origin. They are prominent
features of the Marine, Estuarine, Riverine, and Lacus-trine
Systems where the substrate material is exposed to
the sorting and washing action of waves. Examples of
Dominance Types in the Marine and Estuarine Systems
are the wedge shell Donax, the soft-shell clam Mya, the
quahog Mercenuria, the olive shell Oliva, the blood worm
Euxonus, the beach hopper Orchestia, the pismo clam
Tivela stultorxm, the mole crab Emerita, and the lugworm
Arenicola. Examples of Dominance Types in the River-me,
Lacustrine, and Palustrine Systems are the copepods
Parastenocaris and Phyllognathopus, the oligochaete
worm Pristina, the freshwater mollusks Anodonta and
Elliptio, and the fingernail clams Pisidium and
Sphaerium.
Mud. -The unconsolidated particles smaller than
stones are predominantly silt and clay. Anaerobic condi-tions
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 have little slope and are frequently
called flats. Mud Shores support diverse populations of
tube-dwelling and burrowing invertebrates that include
worms, clams, and crustaceans (Gray 1974). They are com-
19
monly colonized by algae and diatoms which may form a Moss-Lichen Wetland
crust or mat.
Irregularly flooded Mud Shores in the Estuarine System
have been called salt flats, pans, or pannes. They are
typically high in salinity and are usually surrounded by,
or lie on the landward side of, Emergent Wetland (Mar-tin
et al. 1953, Type 15). In many arid areas, Palustrine
and Lacustrine Mud Shores are encrusted or saturated
with salt. Martin et al. (1953) called these habitats inland
saline flats (Type 9); they are also called alkali flats, salt
flats, and salt pans. Mud Shores may also result from
removal of vegetation by man, animals, or fire, or from
the discharge of thermal waters or pollutants.
Examples of Dominance Types in the Marine and Estu-arine
Systems include the fiddler crab Uca, the ghost
shrimp Callianassa, the mud snails Nassarius and
Macoma, the clam worm Nereis, the sea anemone Cerian-thus,
and the seascucumber Thyone. In the Lacustrine,
Palustrine, and Riverine Systems, examples of Dominance
Types are the fingernail clam Pisidium, the snails Aplexa
and Lymnaea, the crayfish Procambarus, the harpacticoid
copepods Canthocamptus and Bryocamptus, the fingernail
clam Sphaerium, the freshwater mollusk Elliptio, the
shore bug Sal&La, the isopod Asellus, the crayfish Cam-barus,
and the mayfly Tortopus.
Organic.-The unconsolidated material smaller than
stones is predominantly organic soils of formerly vege-tated
wetlands. In the Marine and Estuarine Systems,
Organic Shores are often dominated by microinvertebrates
such as foraminifera, and by Nassarius, Littorina, Uca,
Modiolus, Mya, Nereis, and the false angel wing Petricola
pholadiformis. In the Lacustrine, Palustrine, and River-ine
Systems, examples of Dominance Types are Cantho-camptus,
Bryocamptus, Chironomus, and the backswim-mer
Notonecta.
Vegetated.-Some nontidal shores are exposed for a
sufficient period to be colonized by herbaceous annuals or
seedling herbaceous perennials (pioneer plants). This
vegetation, unlike that of Emergent Wetlands, is usually
killed by rising water levels and may be gone before the
beginning of the next growing season. Many of the pioneer
species are not hydrophytes but are weedy mesophytes
that cannot tolerate wet soil or flooding. Examples of
Dominance Types in the Palustrine, Riverine, and Lacus-trine
Systems are cocklebur (Xanthium strumarium) and
barnyard grass (Echinochloa crusgalli).
Dominance Types for Unconsolidated Shores in the Mar-ine
and Estuarine Systems were taken primarily from
Smith (1964), Morris (1966), Abbott (1968), Ricketts and
Calvin (1968), and Gosner (1971). Dominance Types for
Unconsolidated Shores in the Lacustrine, Riverine, and
Palustrine Systems were taken primarily from Stehr and
Branson (1938), Kenk (1949), Ward and Whipple (1959),
Cummins et al. (1964) Johnson (1970), Ingram (1971),
Clarke (1973), and Hart and Fuller (1974).
Definition. The Moss-Lichen Wetland Class includes
areas where mosses or lichens cover substrates other than
rock and where emergents, shrubs, or trees make up less
than 30% of the area1 cover. The only water regime is
saturated.
Description. Mosses and lichens are important compo-nents
of the flora in many wetlands, especially in the north,
but these plants usually form a ground cover under a domi-nant
layer of trees, shrubs, or emergents. In some in-stances
higher plants are uncommon and mosses or lichens
dominate the flora. Such Moss-Lichen Wetlands are not
common, even in the northern United States where they
occur most frequently.
Subclasses and Dominance Types.
Moss.-Moss Wetlands are most abundant in the far
north. Areas covered with peat mosses (Sphagnum spp.)
are usually 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 liverwort Chiloscyphus fragilis may dominate shallow
pools with impermanent water; peat moss and other
mosses (Campylium stellatum, Aulacomnium palustre,
and Oncophorus wahlenbergii) are typical of wet soil in
this region (Britton 1957; Drury 1962).
Lichen.-Lichen Wetlands are also a northern
Subclass. Reindeer moss (Clad&a rangijikna) forms the
most important Dominance Type. Pollett and Bridgewater
(1973) described areas with mosses and lichens as bogs
or fens, the distinction being based on the availability of
nutrients and the particular plant species present. The
presence of Lichen Wetlands has been noted in the Hud-son
Bay Lowlands (Sjiirs 1959) and in Ontario (Jeglum et
al. 1974).
Emergent Wetland
Definition. The Emergent Wetland Class is charac-terized
by erect, rooted, herbaceous hydrophytes, ex-cluding
mosses and lichens. This vegetation is present for
most of the growing season in most years. These wetlands
are usually dominated by perennial plants. All water
regimes are included except subtidal and irregularly
exposed.
Description. In areas with relatively stable climatic con-ditions,
Emergent Wetlands maintain the same appear-ance
year after year. In other areas, such as the prairies
of the central United States, violent climatic fluctuations
cause them to revert to an open water phase in some years
(Stewart and Kantrud 1972). Emergent Wetlands are
found throughout the United States and occur in all
Systems except the Marine. Emergent Wetlands are
known by many names, including marsh, meadow, fen,
prairie pothole, and slough. Areas that are dominated by
20
pioneer plants which become established during periods
of low water are not Emergent Wetlands and should be
classified as Vegetated Unconsolidated Shores or Vege-tated
Streambeds.
Subclasses and Dominance Types.
Persistent.-Persistent Emergent Wetlands are domi-nated
by species that normally remain standing at least
until the beginning of the next growing season. This
Subclass is found only in the Estuarine and Palustrine
Systems.
Persistent Emergent Wetlands dominated by saltmarsh
cordgrass (Spurt&a alterniflora), saltmeadow cordgrass
(S. patens), big cordgrass (S. cynosuroides), needlerush
(Juncus roemerianus), narrow-leaved cattail (Typha
angustifolia), and southern wild rice (Zizaniopsis miliacea)
are major components of the Estuarine systems of the
Atlantic and Gulf Coasts of the United States. On the
Pacific Coast, common pickleweed (Salicornia virginica),
sea blite (Suueda californica), arrow grass (Triglochin
maritimum), and California cordgrass (Spartina foliosa)
are common dominants.
Palustrine Persistent Emergent Wetlands contain a vast
array of grasslike plants such as cattails (Typha spp.),
bulrushes (Stirpus spp.), saw grass (Cladi~mjamaicense),
sedges (Carex spp.); and true grasses such as reed
(Phragmites australis), manna grasses (Glyceria spp.),
slough grass (Beckmannia syzigachne), and whitetop
(Scolochloa festucacea). There is also a variety of broad-leaved
persistent emergents such as purple loosestrife
(Lythrum salicaria), dock (Rumex mexicanus), water-willow
(Decodon verticillatus), and many species of smart-weeds
(Polygonum).
Nonpersistent.-Wetlands in this Subclass are domi-nated
by plants which fall to the surface of the substrate
or below the surface of the water at the end of the grow-ing
season so that, at certain seasons of the year, there
is no obvious sign of emergent vegetation. For example,
wild rice (Zizania aquatica) does not become apparent in
the North Central States until midsummer and fall, when
it may form dense emergent stands. Nonpersistent emer-gents
also include species such as arrow arum (Peltandra
virginica), pickerelweed (Pontederia coro!ata), and arrow-heads
(Sagittaria spp.). Movement of ice in Estuarine,
Riverine, or Lacustrine Systems often removes all traces
of emergent vegetation during the winter. Where this
occurs, the area should be classified as Nonpersistent
Emergent Wetland.
Scrub-Shrub Wetland
Definition. The Class Scrub-Shrub Wetland includes
areas dominated by woody vegetation less than 6 m
(20 feet) tall. The species include true shrubs, young trees,
and trees or shrubs that are small or stunted because of
environmental conditions. All water regimes except sub-tidal
are included.
Description. Scrub-Shrub Wetlands may represent a
successional stage leading to Forested Wetland, or they
may be relatively stable communities. They occur only in
the Estuarine and Palustrine Systems, but are one of 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 poco-sin
(Kologiski 1977). For practical reasons we have also
included forests composed of young trees less than 6 m
tall.
Subclasses and Dominance Types.
Broad-leaved Deciduous.-In Estuarine System Wet-lands
the predominant deciduous and broad-leaved trees
or shrubs are plants such as sea-myrtle (Baccharis halimi-folia)
and marsh elder (1va frutescens). In the Palustrine
System typical Dominance Types are alders (Alnus spp.),
willows (Salix spp.), buttonbush (Cephalanthus occichm-talis),
red osier dogwood (Cornus stolonifera), honeycup
(Zenobia pulverulenta), spirea (Spiraea douglasii), bog
birch (Betula pumila), and young trees of species such as
red maple (Acer rubrum) or black spruce (Picea mariana).
Needle-leaved Deciduous.-This Subclass, consisting
of wetlands where trees or shrubs are predominantly
deciduous and needle-leaved, is represented by young or
stunted trees such as tamarack or bald cypress (Taxodium
distichum).
Broad-leaved Evergreen. --In the Estuarine System,
vast wetland acreages are dominated by mangroves
(Rhixophora mangle, Languncularia racemosa, Conocar-pus
erectus, and Avicennia germinans) that are less than
6 m tall. In the Palustrine System, the broad-leaved ever-green
species are typically found on organic soils. North-ern
representatives are labrador tea (Ledum groenlan-d&
urn), bog rosemary (Andromeda glaucophylla), bog
laurel (Kalmia polifolia), and the semi-evergreen leather-leaf
(Chamaedaphne calyculata). In the south, fetterbush
(Lyonia lucida), coastal sweetbells (Leucothoe axillaris),
inkberry (Ilex glabra), and the semi-evergreen black ti-ti
(Cyrilla racemiflora) are characteristic broad-leaved
evergreen species.
Needle-leaved Evergreen.-The dominant species in
Needle-leaved Evergreen Wetlands are young or stunted
trees such as black spruce or pond pine (Pinus serotina).
Dead.-Dead woody plants less than 6 m tall dominate
Dead Scrub-Shrub Wetlands. These wetlands are usual-ly
produced by a prolonged rise in the water table resulting
from impoundment of water by landslides, man, or
beavers. Such wetlands may also result from various other
factors such as fire, salt spray, insect infestation, air pollu-tion,
and herbicides.
Forested Wetland
Definition. The Class Forested Wetland is characterized
by woody vegetation that is 6 m tall or taller. All water
regimes are included except subtidal.
21
Description. Forested Wetlands are most common in
the eastern United States and in those sections of the West
where moisture is relatively abundant, particularly along
rivers and in the mountains. They occur only in the Palus-trine
and Estuarine Systems and normally possess an
overstory of trees, an understory of young trees or shrubs,
and a herbaceous layer. Forested Wetlands in the Estu-arine
System, which include the mangrove forests of
Florida, Puerto Rico, and the Virgin Islands, are known
by such names as swamps, hammocks, heads, and bottoms.
These names often occur in combination with species
names or plant associations such as cedar swamp or
bottomland hardwoods.
Modifiers
To fully describe wetlands and deepwater habitats, one
must apply certain Modifiers at the Class level and at lower
levels in the classification hierarchy. The Modifiers
described below were adapted from existing classifications
or were developed specifically for this system.
Water Regime Modifiers
Subclasses and Dominance Types.
Broad-leaved Deciduous. -Dominant trees typical of
Broad-leaved Deciduous Wetlands, which are represented
throughout the United States, are most common in the
South and East. Common dominants are species such as
red maple, American elm (ulmus americana), ashes (Frax-inus
pennsylvanica and F. nigra), black gum (Nyssa
sylvatica), tupelo gum (N. aquatica), swamp white oak
(Quercus bicolor), overcup oak (Q. lyrata), and basket oak
(Q. michausii). Wetlands in this subclass generally occur
on mineral soils or highly decomposed organic soils.
Precise description of hydrologic characteristics requires
detailed knowledge of the duration and timing of surface
inundation, both yearly and long-term, as well as an under-standing
of groundwater fluctuations. Because such in-formation
is seldom available, the water regimes that, in
part, determine characteristic wetland and deepwater
plant and animal communities are described here in only
general terms. Water regimes are grouped under two ma-jor
headings, Tidal and Nontidal.
Needle-leaved Deciduous-The southern representa-tive
of the Needle-leaved Deciduous Subclass is bald
cypress (Taxodium distichum), which is noted for its ability
to tolerate long periods of surface inundation. Tamarack
is characteristic of the Boreal Forest Region, where it
occurs as a dominant on organic soils. Relatively few other
species are included in this Subclass.
Broad-leaved Evergreen.-In the Southeast, Broad-leaved
Evergreen Wetlands reach their greatest develop-ment.
Red bay (Persea borbonia), loblolly bay (Gordonia
lasianthus), and sweet bay (Magnolia virginiana) are
prevalent, especially on organic soils. This Subclass also
includes red mangrove, black mangrove (Avicennia ger-minans),
and white mangrove (Languncularia racemosa),
which are adapted to varying levels of salinity.
Tidal Water Regime Modifiers are used for wetlands and
deepwater habitats in the Estuarine and Marine Systems
and Nontidal Modifiers are used for all nontidal parts of
the Palustrine, Lacustrine, and Riverine Systems. The
Tidal Subsystem of the Riverine System and tidally in-fluenced
parts of the Palustrine and Lacustrine Systems
require careful selection of Water Regime Modifiers. We
designate subtidal and irregularly exposed wetlands and
deepwater habitats in the Palustrine, Riverine, and Lacus-trine
Systems as pemnanently jlooded-tidal rather than
subtidal, and Palustrine, Riverine, and Lacustrine wet-lands
regularly flooded by the tide as regularly flooded.
If Palustrine, Riverine, and Lacustrine wetlands are on-ly
irregularly flooded by tides, we designate them by the
appropriate nontidal Water Regime Modifier with the
word tidal added, as in seasonally flooded-tidal.
Tidal
Needle-leaved Evergreen. -Black spruce, growing on
organic soils, represents a major dominant of the Needle-leaved
Evergreen Subclass in the North. Though black
spruce is common on nutrient-poor soils, Northern white
cedar (Thuja occidentalis) dominates northern wetlands
on more nutrient-rich sites. Along the Atlantic Coast,
Atlantic white cedar (Chamaecyparis thyoides) is one of
the most common dominants on organic soils. Pond pine
is a common needle-leaved evergreen found in the South-east
in association with dense stands of broad-leaved
evergreen and deciduous shrubs.
The water regimes are largely determined by oceanic
tides.
Subtidal. The substrate is permanently flooded with
tidal water.
Irregularly Exposed. The land surface is exposed by
tides less often than daily.
Regularly Flooded. Tidal water alternately floods and
exposes the land surface at least once daily.
Irregularly Flooded. Tidal water floods the land surface
less often than daily.
Dead.-Dead Forested Wetlands are dominated by
dead woody vegetation taller than 6 m (20 feet). Like Dead
Scrub-Shrub Wetlands, they are most common in, or
around the edges of, man-made impoundments and beaver
ponds. The same factors that produce Dead Scrub-Shrub
Wetlands produce Dead Forested Wetlands.
The periodicity and amplitude of tides vary in different
parts of the United States, mainly because of differences
in latitude and geomorphology. On the Atlantic Coast, two
nearly equal high tides are the rule (semidiurnal). On the
Gulf Coast, there is frequently only one high tide and one
low tide each day (diurnal); and on the Pacific Coast there
22
are usually two unequal high
tides (mixed semidiurnal).
tides and two unequal low
Individual tides range in height from about 9.5 m (31
feet) at St. John, New Brunswick (U.S. National Oceanic
and Atmospheric Administration 1973) to less than 1 m
(3.3 feet) along the Louisiana coast (Chabreck 1972). Tides
of only 10 cm (4.0 inches) are not uncommon in Louisi-ana.
Therefore, though no hard and fast rules apply, the
division between regularly flooded and irregularly flooded
water regimes would probably occur approximately at
mean high water on the Atlantic Coast, lowest level of
the higher high tide on the Pacific Coast, and just above
mean tide level of the Gulf Coast. The width of the inter-tidal
zone is determined by the tidal range, the slope of
the shoreline, and the degree of exposure of the site to
wind and waves.
Nontidal
Though not influenced by oceanic tides, nontidal water
regimes may be affected by wind or seiches in lakes. Water
regimes are defined in terms of the growing season, which
we equate to the frost-free period (see the U.S. Depart-ment
of Interior National Atlas 1970:110-111 for gen-eralized
regional delineation). The rest of the year is
defined as the dormant season, a time when even extended
periods of flooding may have little influence on the devel-opment
of plant communities.
Permanently Flooded. Water covers the land surface
throughout the year in all years. Vegetation is composed
of obligate hydrophytes.
Intermittently Exposed. Surface water is present
throughout the year except in years of extreme drought.
Semipermanently Flooded. Surface water persists
throughout the growing season in most years. When sur-face
water is absent, the water table is usually at or very
near the land surface.
Seasonally Flooded. Surface water is present for ex-tended
periods especially early in the growing season, but
is absent by the end of the season in most years. When
surface water is absent, the water table is often near the
land surface.
Saturated. The substrate is saturated to the surface for
extended periods during the growing season, but surface
water is seldom present.
Temporarily Flooded. Surface water is present for brief
periods during the growing season, but the water table
usually lies well below the soil surface for most of the
season. Plants that grow both in uplands and wetlands
are characteristic of the temporarily flooded regime.
Intermittently Flooded. The substrate is usually ex-posed,
but surface water is present for variable periods
without detectable seasonal periodicity. Weeks, months,
or even years may intervene between periods of inunda
tion. The dominant plant communities under this regime
may change as soil moisture conditions change. Some
areas exhibiting this regime do not fall within our defini-tion
of wetland because they do not have hydric soils or
support hydrophytes.
Artificially Flooded. The amount and duration of flood-ing
is controlled by means of pumps or siphons in com-bination
with dikes or dams. The vegetation growing on
these areas cannot be considered a reliable indicator of
water regime. Examples of artificially flooded wetlands
are some agricultural lands managed under a rice-soybean
rotation, and wildlife management areas where forests,
crops, or pioneer plants may be flooded or dewatered to
attract wetland wildlife. Neither wetlands within or
resulting from leakage from man-made impoundments,
nor irrigated pasture lands supplied by diversion ditches
or artesian wells, are included under this modifier.
Water Chemistry Modifiers
The accurate characterization of water chemistry in
wetlands and deepwater habitats is difficult, both because
of problems in measurement and because values tend to
vary with changes in the season, weather, time of day,
and other factors. Yet, very subtle changes in water
chemistry, which occur over short distances, may have a
marked influence on the types of plants or animals that
inhabit an area. A description of water chemistry, there-fore,
must be an essential part of this classification system.
The two key characteristics employed in this system are
salinity and hydrogen-ion concentration (pH). All habitats
are classified according to salinity, and freshwater habitats
are further subdivided by pH levels.
Salinity Modifiers
Differences in salinity are reflected in the species com-position
of plants and animals. Many authors have sug-gested
using biological changes as the basis for subdividing
the salinity range between sea water and fresh water
(Remane and Schlieper 1971). Others have suggested a
similar subdivision for salinity in inland wetlands (Moyle
1946; Bayly 1967; Stewart and Kantrud 1971). Since the
gradation between fresh and hypersaline or hyperhaline
waters is continuous, any boundary is artificial, and few
classification systems agree completely.
Estuarine and Marine waters are a complex solution of
salts, dominated by sodium chloride (NaCl). The term
haline is used to indicate the dominance of ocean salt. The
relative proportions of the various major ions are usually
similar to those found in sea water, even if the water is
diluted below sea water strength. Dilution of sea water
with fresh water and concentration of sea water by
evaporation result in a wide range of recorded salinities
in both surface water and interstitial (soil) water.
23
We have modified the Venice System, suggested at a
“Symposium on the Classification of Brackish Waters”
in 1958, for use in the Marine and Estuarine Systems
(Table 2). The System has been widely used during recent
years (Macan 1961, 1963; Burbank 1967; Carriker 1967;
Reid and Wood 1976), although there has been some
criticism of its applicability (den Hartog 1960; Price and
Gunter 1964).
The salinity of inland water is dominated by four major
cations, calcium (Ca), magnesium (Mg), sodium (Na), and
potassium (K); and three major anions, carbonate (CO,),
sulfate (SO,), and chloride (Cl) (Wetzel 1975). Salinity is
governed by the interactions between precipitation, sur-face
runoff, groundwater flow, evaporation, and some-times
evapotranspiration by plants. The ionic ratios of
inland waters usually differ appreciably from those in the
sea, although there are exceptions (Bayly 1967). The great
chemical diversity of these waters, the wide variation in
physical conditions such as temperature, and often the
relative impermanence of surface water, make it extreme-ly
difficult to subdivide the inland salinity range in a mean-ingful
way. Bayly (1967) attempted a subdivision on the
basis of animal life; Moyle (1945) and Stewart and Kan-trud
(1971) have suggested two very different divisions
on the basis of plant life. We employ a subdivision that
is identical to that used in the Estuarine and Marine
Systems (Table 2).
The term saline is used to indicate that any of a num-ber
of ions may be dominant or codominant. The term
brackish has been applied to inland waters of intermediate
salinity (Remane and Schlieper 1971; Stewart and Kan-trud
1971), but is not universally accepted (see Bayly
196784); therefore, mixosaline is used here. In some in-land
wetlands, high soil salinities control the invasion or
establishment of many plants. These salinities are ex-pressed
in units of specific conductance as well as percent
salt (Ungar 1974) and they are also covered by the salin-ity
classes in Table 2.
pH Modifiers
Acid waters are, almost by definition, poor in calcium
and often generally low in other ions, but some very soft
waters may have a neutral pH (Hynes 1970). It is difficult
to separate the effects of high concentrations of hydrogen
ions from low base content, and many studies suggest that
acidity may never be the major factor controlling the pre-sence
or absence of particular plants and animals. Never-theless,
some researchers have demonstrated a good
correlation between pH levels and plant distribution (Sjiirs
1950; Jeglum 1971). Jeglum (1971) showed that plants can
be used to predict the pH of moist peat.
There seems to be little doubt that, where a peat layer
isolates plant roots from the underlying mineral substrate,
the availability of minerals in the root zone strongly in-fluences
the types of plants that occupy the site. For this
reason, many authors subdivide freshwater, organic wet-lands
into mineral-rich and mineral-poor categories (Sjiirs
1950; Heinselman 1970; Jeglum 1971; Moore and Bellamy
1974). We have instituted pH modifiers for freshwater
wetlands (Table 3) because pH has been widely used to
indicate the difference between mineral-rich and mineral-poor
sites, and because it is relatively easy to determine.
The ranges presented here are similar to those of Jeglum
(1971), except that the upper limit of the circumneutral
level (Jeglum’s mesotrophic) was raised to bring it into
agreement with usage of the term in the United States.
The ranges given apply to the pH of water. They were
converted from Jeglum’s moist-peat equivalents by adding
0.5 pH units.
Soil Modifiers
Soil is one of the most important physical components
of wetlands. Through its depth, mineral composition,
organic matter content, moisture regime, temperature
regime, and chemistry, it exercises a strong influence over
the types of plants that live on its surface and the kinds
of organisms that dwell within it. In addition, the nature
of soil in a wetland, particularly the thickness of organic
soil, is of critical importance to engineers planning con-struction
of highways or buildings. For these and other
reasons, it is essential that soil be considered in the
classification of wetlands.
According to the U.S. Soil Conservation Service, Soil
Survey Staff (1975:1-2), soil is limited to terrestrial situa-tions
and shallow waters; however, “areas are not con-sidered
to have soil if the surface is permanently covered
by water deep enough that only floating plants are
present. .” Since emergent plants do not grow beyond
a depth of about 2 m in inland waters, the waterward limit
of soil is virtually equivalent to the waterward limit of
wetland, according to our definition. Wetlands can then
be regarded as having soil in most cases, whereas deep-water
habitats are never considered to have soil.
The most basic distinction in soil classification in the
United States is between mineral soil and organic soil (U.S.
Soil Conservation Service, Soil Survey Staff 1975). The
Soil Conservation Service recognizes nine orders of
mineral soils and one order of organic soils (Histosols) in
its taxonomy. Their classification is hierarchical and per-mits
the description of soils at several levels of detail. For
example, suborders of Histosols are recognized according
to the degree of decomposition of the organic matter.
Table 3. pH Modifiers used in this
classification system.
Modifier pH of Water
Acid <5.5
Circumneutral 5.5-7.4
Alkaline .7 4
24
We use the Modifiers mineral and organic in this
classification. Mineral soils and organic soils are differen-tiated
on the basis of specific criteria that are enumerated
in soil taxonomy (U.S. Soil Conservation Service, Soil
Survey Staff 1975:13-14, 65). These criteria are restated
in our Appendix D for ready reference. If a more detailed
classification is desired, the U.S. Soil Conservation Ser-vice
classification system should be used.
Special Modifiers
Many wetlands and deepwater habitats are man-made,
and natural ones have been modified to some degree by
the activities of man or beavers. Since the nature of these
modifications often greatly influences the character of
such habitats, special modifying terms have been included
here to emphasize their importance. The following Mod-ifiers
should be used singly or in combination wherever
they apply to wetlands and deepwater habitats.
Excavated
Lies within a basin or channel excavated by man.
Impounded
Created or modified by a barrier or dam which pur-posefully
or unintentionally obstructs the outflow of water.
Both man-made dams and beaver dams are included.
Diked
Created or modified by a man-made barrier or dike
designed to obstruct the inflow of water.
Partly Drained
The water level has been artificially lowered, but the
area is still classified as wetland because soil moisture is
sufficient to support hydrophytes. Drained areas are not
considered wetland if they can no longer support
hydrophytes.
Farmed
The soil surface has been mechanically or physically
altered for production of crops, but hydrophytes will
become reestablished if farming is discontinued.
Artificial
Refers to substrates classified as Rock Bottom, Uncon-solidated
Bottom, Rocky Shore, and Unconsolidated Shore
that were emplaced by man, using either natural materials
such as dredge spoil or synthetic materials such as dis-carded
automobiles, tires, or concrete. Jetties and break-waters
are examples of Artificial Rocky Shores. Man-made
reefs are an example of Artificial Rock Bottoms.
REGIONALIZATION FOR THE
CLASSIFICATION SYSTEM
In this classification system, a given taxon has no par-ticular
regional alliance; its representatives may be found
in one or many parts of the United States. However,
regional variations in climate, geology, soils, and vegeta-tion
are important in the development of different wetland
habitats; and management problems often differ greatly
in different regions. For these reasons, there is a need
to recognize regional differences. Regionalization is
designed to facilitate three activities: (1) planning, where
it is necessary to study management problems and poten-tial
solutions on a regional basis; (2) organization and
retrieval of data gathered in a resource inventory; and (3)
interpretation of inventory data, including differences in
indicator plants and animals among the regions.
We recommend the classification and map (Fig. 7) of
Bailey (1976) to fill the need for regionalization inland.
Bailey’s classification of ecoregions is hierarchical. The
upper four levels are domain (defined as including sub-continental
areas of related climates), division (defined as
including regional climate at the level of Koppen’s [1931]
types), province (defined as including broad vegetational
types), and section (defined as including climax vegeta-tion
at the level of Kiichler’s [1964] types). On the map,
the boundaries between the different levels are designated
by lines of various widths and the sections are numbered
with a four-digit code; digits 1 through 4 represent the
first four levels in the hierarchy. The reader is referred
to Bailey (1976, 1978) for detailed discussion and descrip-tion
of the units appearing on his map, reproduced in our
Fig. 7.
The Bailey system terminates at the ocean, whereas the
present wetland classification includes Marine and Estu-arine
habitats. Many workers have divided Marine and
Estuarine realms into series of biogeographic provinces
(e.g., U.S. Senate 1970; Ketchum 1972). These provinces
differ somewhat in detail, but the broader concepts are
similar. Figure 7 shows the distribution of 10 Marine and
Estuarine provinces that we offer for North America.
l Arctic Province extends from the southern tip of New-foundland
(Avalon Peninsula), northward around Canada
to the west coasts of the Arctic Ocean, Bering Sea, and
Baffin and Labrador basins. It is characterized by the
southern extension of floating ice, the 4°C summer iso-therm,
and Arctic biota.
l Acadian Province extends along the Northeast Atlan-tic
Coast from the Avalon Peninsula to Cape Cod and is
characterized by a well developed algal flora and boreal
biota. The shoreline is heavily indented and frequently
rocky. It has a large tidal range and is strongly influenced
by the Labrador Current.
l Virginian Province extends along the Middle Atlan-tic
Coast from Cape Cod to Cape Hatteras. The province
25
Fig. 7. Ecoregions of the United States after Bailey (1976) with the addition of 10 Marine and Estuarine Provinces proposed in
our classification.
“Domains, Divisions, Provinces, and Sections used on Bailey’s (1976) map and described in detail in Bailey (1978). Highland
ecoregions are designated M mountain, P plateau, and A altiplano.
3135 Ponderosa Shrub Forest
P313ll Colorado Plateau
P3131 Juniper-Pinyon Woodland + Sagebrush
Salthush Mosax
P3132 Grama-Gall&a steppe + Juniper-Plnyo”
Weedland Mosaic
26
is transitional between the Acadian and Carolinian
Provinces. The biota is primarily temperate, but has some
boreal representatives. The Labrador Current occasionally
extends down to Cape Hatteras and winter temperatures
may approach 4°C. The tidal range is moderate.
l Carolinian Province is situated along the South Atlan-tic
Coast from Cape Hatteras to Cape Kennedy. It con-tains
extensive marshes and well developed barrier
islands. Waters are turbid and productive. The biota is
temperate but has seasonal tropical elements. The Gulf
Stream is the primary influence, and winter temperatures
reach a minimum of 10°C; summer temperatures are
tropical (in excess of 20°C). The tidal range is small to
moderate.
l West Indian Province extends from Cape Kennedy to
Cedar Key, Florida, and also includes the southern Gulf
of Mexico, the Yucatan Peninsula, Central America, and
the Caribbean Islands. The shoreland is usually low-lying
limestone with calcareous sands and marls, except for
volcanic islands. The biota is tropical and includes reef cor-als
and mangroves. Minimum winter temperatures are
about 20°C and the tidal range is small.
l Louisianian Province extends along the northern
coast of the Gulf of Mexico from Cedar Key to Port Aran-sas,
Texas. The characteristics of the province are similar
to those of the Carolinian, reflecting the past submergence
of the Florida Peninsula. The biota is primarily temper-ate
and the tidal range is small.
l Californian Province extends along the Pacific Coast
from Mexico northward to Cape Mendocino. The shore-land
is strongly influenced by coastal mountains and the
coasts are rocky. Freshwater runoff is limited. In the
southern part volcanic sands are present; marshes and
swamps are scarce throughout the province. The climate
is Mediterranean and is influenced by the California Cur-rent.
The biota is temperate, and includes well developed
offshore kelp beds. The tidal range is moderate.
l Coluw&ian Province extends along the northern Pacific
Coast from Cape Mendocino to Vancouver Island. Moun-tainous
shorelands with rocky foreshores are prevalent.
Estuaries are strongly influenced by freshwater runoff.
The biota is primarily temperate with some boreal com-ponents,
and there are extensive algal communities. The
province is influenced by both the Aleutian and Califor-nia
Currents. The tidal range is moderate to large.
l Fjord Province extends along the Pacific Coast from
Vancouver Island to the southern tip of the Aleutian
Islands. Precipitous mountains, deep estuaries (some with
glaciers), and a heavily indented shoreline subject to winter
icing are typical of the coast. The biota is boreal to sub-
Arctic. The province is influenced by the Aleutian and
Japanese Currents, and the tidal range is large.
*Pacific Insular Province surrounds all the Hawaiian
Islands. The coasts have precipitous mountains and wave
action is stronger than in most of the other provinces. The
biota is largely endemic and composed of tropical and sub-tropical
forms. The tidal range is small.
Use of Bailey’s sections for the Riverine, Lacustrine,
and Palustrine Systems and the Provinces defined above
for the Marine and Estuarine Systems provides a regional
locator for any wetland in the United States.
USE OF THE CLASSIFICATION
SYSTEM
This System was designed for use over an extremely
wide geographic area and for use by individuals and organ-izations
with varied interests and objectives. The classi-fication
employs 5 System names, 8 Subsystem names,
11 Class names, 28 Subclass names, and an unspecified
number of Dominance Types. It is, of necessity, a com-plex
System when viewed in its entirety, but use of the
System for a specific purpose at a local site should be sim-ple
and straightforward. Artificial keys to the Systems
and Classes (Appendix E) are furnished to aid the user
of the classification, but reference to detailed definitions
in the text is also required. The purpose of this section
is to illustrate how the System should be used and some
of the potential pitfalls that could lead to its misuse.
Before attempting to apply the System, the user should
consider four important points:
(1) Information about the area to be classified must be
available before the System can be applied. This informa-tion
may be in the form of historical data, aerial photo-graphs,
brief on-site inspection, or detailed and intensive
studies. The System is designed for use at varying degrees
of detail. There are few areas for which sufficient infor-mation
is available to allow the most detailed application
of the System. If the level of detail provided by the data
is not sufficient for the needs of the user, additional data
gathering is mandatory.
(2) Below the level of Class, the System is open-ended
and incomplete. We give only examples of the vast number
of Dominance Types that occur. The user may identify
additional Dominance Types and determine where these
fit into the classification hierarchy. It is also probable that
as the System is used the need for additional Subclasses
will become apparent.
(3) One of the main purposes of the new classification
is to ensure uniformity throughout the United States. It
is important that the user pay particular attention to the
definitions in the classification. Any attempt a