27 



and for the degree of detail attainable. It is necessary for 

 the user to develop a specific set of mapping conventions 

 for each application and to demonstrate their relationship 

 to the generalized classification described here. For ex- 

 ample, there are a number of possible mapping conven- 

 tions for a small wetland basin 50 m (164 feet) in diam- 

 eter with concentric rings of vegetation about the deepest 

 zone. At a scale of 1:500 each zone may be classified and 

 mapped; at 1:20,000 it might be necessary to map the en- 

 tire basin as one zone and ignore the peripheral bands; 

 and at 1:100,000 the entire wetland basin may be smaller 

 than the smallest mappable unit, and such a small-scale 

 map is seldom adequate for a detailed inventory and must 

 be supplemented by information gathered by sampling. 

 In other areas, it may be necessary to develop mapping 

 conventions for taxa that cannot be easily recognized; for 

 instance, Aquatic Beds in turbid waters may have to be 

 mapped simply as Unconsolidated Bottom. 



Hierarchical Levels and Modifiers 



We have designed the various levels of the system for 

 specific purposes, and the relative importance of each will 

 vary among users. The Systems and Subsystems are most 

 important in applications involving large regions or the 

 entire country. They serve to organize the Classes into 

 meaningful assemblages of information for data storage 

 and retrieval. 



The Classes and Subclasses are the most important part 

 of the system for many users and are basic to wetland 

 mapping. Most Classes should be easily recognizable by 

 users in a wide variety of disciplines. However, the Class 

 designations apply to average conditions over a period of 

 years, and since many wetlands are dynamic and subject 

 to rapid changes in appearance, the proper classification 

 of a wetland will frequently require data that span a period 

 of years and several seasons in each of those years. 



The Dominance Type is most important to users in- 

 terested in detailed regional studies. It may be necessary 

 to identify Dominance Types in order to determine which 

 modifying terms are appropriate, because plants and 

 animals present in an area tend to reflect environmental 

 conditions over a period of time. Water regime can be 

 determined from long-term hydrologic studies where these 

 are available. The more common procedure will be to 

 estimate this characteristic from the Dominance Types. 

 Several studies have related water regimes to the pres- 

 ence and distribution of plants or animals (e.g., Stephen- 

 son and Stephenson 1972; Stewart and Kantrud 1972; 

 Chapman 1974). 



Similarly, we do not intend that salinity measurements 

 be made for all wetlands except where these data are re- 

 quired; often plant species or associations can be used to 

 indicate broad salinity classes. Lists of halophytes have 

 been prepared for both coastal and inland areas (e.g., 



Duncan 1974; MacDonald and Barbour 1974; Ungar 1974), 

 and a number of floristic and ecological studies have 

 described plants that are indicators of salinity (e.g., Pen- 

 found and Hathaway 1938; Moyle 1945; Kurz and Wagner 

 1957; Dillon 1966; Anderson et al. 1968; Chabreck 1972; 

 Stewart and Kantrud 1972; Ungar 1974). 



In areas where the Dominance Types to be expected 

 under different water regimes and types of water chem- 

 istry conditions have not been identified, detailed regional 

 studies will be required before the classification can be ap- 

 plied in detail. In areas where detailed soil maps are 

 available, it is also possible to infer water regime and 

 water chemistry from soil series (U.S. Soil Conservation 

 Service, Soil Survey Staff 1975). 



Some of the Modifiers are an integral part of this system 

 and their use is essential; others are used only for detailed 

 applications or for special cases. Modifiers are never used 

 with Systems and Subsystems; however, at least one 

 Water Regime Modifier, one Water Chemistry Modifier, 

 and one Soil Modifier must be used at all lower levels in 

 the hierarchy. Use of the Modifiers listed under mixosaline 

 and mixohaline (Table 2) is optional but these finer 

 categories should be used whenever supporting data are 

 available. The user is urged not to rely on single observa- 

 tions of water regime or water chemistry. Such measure- 

 ments give misleading results in all but the most stable 

 wetlands. If a more detailed Soil Modifier, such as soil 

 order or suborder (U.S. Soil Conservation Service, Soil 

 Survey Staff 1975) can be obtained, it should be used in 

 place of the Modifiers, mineral and organic. Special 

 Modifiers are used where appropriate. 



Relationship to Other 

 Wetland Classifications 



There are numerous wetland classifications in use in the 

 United States. Here we relate this system to three pub- 

 lished classifications that have gained widespread accep- 

 tance. It is not possible to equate these systems directly 

 for several reasons: (1) the criteria selected for establish- 

 ing categories differ; (2) some of the classifications are 

 not applied consistently in different parts of the country; 

 and (3) the elements classified are not the same in various 

 classifications. 



The most widely used classification system in the United 

 States is that of Martin et al. (1953) which was republished 

 in U.S. Fish and Wildlife Service Circular 39 (Shaw and 

 Fredine 1956). The wetland types are based on criteria 

 such as water depth and permanence, water chemistry, 

 life form of vegetation, and dominant plant species. In 

 Table 4 we compare some of the major components of our 

 system with the type descriptions listed in Circular 39. 



In response to the need for more detailed wetland 

 classification in the glaciated Northeast, Golet and Lar- 

 son (1974) refined the freshwater wetland types of 



