i:; 



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. 



of the vegetation or the physiography and composition 

 of the substrate— features that can be recognized 

 without the aid of detailed environmental measure- 

 ments. Vegetation is used at two different levels in the 

 classification. The life forms— trees, shrubs, emer- 

 gents, emergent mosses, and lichens— are used to 

 define classes because they are relatively easy to dis- 

 tinguish, do not change distribution rapidly, and have 

 traditionally been used as criteria for classification of 

 wetlands. 5 Other forms of vegetation, such as sub- 

 merged or floating-leaved rooted vascular plants, free- 

 floating vascular plants, submergent mosses, and 



5 Our initial attempts to use familiar terms such as marsh, 

 swamp, bog, and meadow at the class level were unsuc- 

 cessful 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 misunder- 

 standings and confusion that result from the use of the fa- 

 miliar terms. 



algae, though frequently more difficult to detect, are 

 used to define the class Aquatic Bed. Pioneer species 

 that briefly 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 

 advantages: (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 recognizable on a great variety of remote 

 sensing products (e.g., Radforth 1962; Anderson et al. 

 1976). If vegetation (except pioneer species) covers 

 30% or more of the substrate, we distinguish classes 

 on the basis of the life form of the plants that con- 

 stitute the uppermost layer of vegetation and that 

 possess an areal coverage 30% or greater. For 

 example, an area with 50% areal coverage of trees over 

 a shrub layer with a 60% areal coverage would be 

 classified as Forested Wetland; an area with 20% areal 

 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 



