29 



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

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

 entire 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 neces- 

 sary 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 sub- 

 systems 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 recog- 

 nizable 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 placement of a wetland in its proper 

 place 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 

 interested in detailed regional studies. It may be neces- 

 sary 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 presence and distribution of 

 plants or animals (e.g., Stephenson and Stephenson 

 1972; Stewart and Kantrud 1972; Chapman 1974). 



Similarly, we do not intend that salinity measure- 

 ments be made for all wetlands except where these 

 data are required; 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., Penfound 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 

 chemistry conditions have not been identified, detailed 

 regional studies will be required before the classifi- 

 cation can be applied 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 observations of water 

 regime or water chemistry. Such measurements 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 modi- 

 fiers 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 

 published classifications that have gained widespread 

 acceptance. It is not possible to equate these systems 

 directly for several reasons: (1) The criteria selected for 

 establishing categories differ; (2) some of the classifi- 

 cations 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 

 Larson (1974) refined the freshwater wetland types of 

 Circular 39 by writing more detailed descriptions and 

 subdividing classes on the basis of finer differences in 

 plant life forms. Golet and Larson's classes are 

 roughly equivalent to Types 1-8 of Circular 39, except 

 that they restricted Type 1 to river floodplains. The 



