11 



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 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 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 



