The Classification System 



The basic framework of the classification system is as 

 follows: 



Soil 

 element 



Vegetation 

 element 



Water (aquatic) 

 element 4 



Order 



Class 



System 



Suborder 



Subclass 



Subsystem 



Great group 



Group 



Class 



Subgroup 



Formation 



Subclass 



Family 



Series 



Dominance type 



Series 



Association 





Information within each class level becomes increasingly 

 specific from the highest to the lowest levels of the hier- 

 archies. The lowest levels of the hierarchies and combina- 

 tions of them are well suited for detailed project plan- 

 ning; higher levels are more appropriate for State, re- 

 gional, or national assessments and planning. 



The soil system is Soil Taxonomy (USDA, Soil Con- 

 servation Service, 1975) used by the National Coopera- 

 tive Soil Survey throughout the United States. It is also 

 used in other nations and is closely related in concept and 

 development to other modern soil classification systems 

 (Buol and others 1980). Soil surveys provide the physical 

 setting of described and classified soils, including geo- 

 graphic location, physiographic position, topography, 

 parent material, and moisture and temperature regimes. 



The vegetation system is patterned after a worldwide 

 vegetation classification developed by UNESCO (UNESCO 

 1973) and has been provisionally described in relation to 

 the United States by Driscoll and others (1983). It con- 

 sists of two parts: the identification and description of 

 potential natural vegetation (Kuchler 1967, Tuxen 1957) 

 defined according to modern ecological principles (Dau- 

 benmire 1978, Mueller-Dombois and Ellenberg 1974); 

 and the identification of successional communities re- 

 lated to climax vegetation by describing secondary suc- 

 cession and relating it to soils (Shiflet 1973). Appendix A 

 presents the top four levels of the vegetation element of 

 this classification system. 



No fully developed and evaluated classification system 

 exists that classifies water according to its ability to sup- 

 port life on and in the water. However, a new hierarchical 

 classification of wetlands and deep water habitats (Cow- 

 ardin and others 1979) presents a hierarchy that defines 

 general water systems at the highest level and sorts them 

 according to specific dominance types of vegetation or 

 animals directly associated with wetlands at the lowest 

 level. Water regime, water chemistry, vegetation, and soil 



'From Cowardin and others (1979). 



modifiers were used to develop the system. These modi- 

 fiers lead to an interpretation of water as a life support 

 system. The dominance type of vegetation provides the 

 direct link to nonwetland ecosystems and is presented as 

 an element of the ecological land classification framework. 



In the absence of a complete landform classification 

 hierarchy, definitions of landform and geologic terms 

 important for describing the land are presented in appen- 

 dix B. They deal with land surface configuration, surfi- 

 cial material, and genesis. These terms, with legal or 

 other location descriptions, should be used as appropri- 

 ate to describe the physical location of plant communities 

 and soils of those elements. 



Integration relates to determining relationships 

 among individual elements; for example, relating vegeta- 

 tion and soils to landform and climate. These relation- 

 ships are important in establishing basic geographic units 

 and defining their biotic potentialities. The objective is to 

 provide for interpretation and to describe ecological units 

 (Driscoll and others 1983) that appear synonymous to 

 habitat types (Daubenmire 1978). Aggregation of these 

 units provides regional zonations under the general influ- 

 ence of macroclimate and land surface features (Bailey 

 1980a, Wiken and Ironside 1977). 



Soil Element 



The soil taxonomy system developed by the USDA, 

 Soil Conservation Service (1975) is complete with respect 

 to the framework, format, and definitions of most cate- 

 gories and classes. It is a hierarchical system in which 

 soils are precisely defined by observable and measurable 

 soil properties. The properties are determined by parent 

 material being acted upon over time by organisms, relief, 

 and climate. Brief descriptions of the six categories of the 

 soil taxonomy follow. 



Orders — There are currently 10 orders defined by the 

 presence or absence of identifiable horizons that reveal or 

 have marks of the major soil- forming processes, such as 

 accumulation of organic matter, availability of water for 

 plant growth, or translocation of clays. 



Suborders — There are currently 44 suborders de- 

 fined by important properties that influence soil develop- 

 ment and plant growth, such as wetness, parent material, 

 and temperature. 



Great groups — There are currently 189 great groups 

 defined by similarities in kind, arrangement, and distinc- 

 tiveness of horizons, as well as close similarities in mois- 

 ture and temperature regimes, and base status. 



Subgroups — There are currently 1,008 subgroups 

 defined by characteristics already described for the higher 



