19 



monly colonized by algae and diatoms which may form a 

 crust or mat. 



Irregularly flooded Mud Shores in the Estuarine System 

 have been called salt flats, pans, or pannes. They are 

 typically high in salinity and are usually surrounded by, 

 or lie on the landward side of, Emergent Wetland (Mar- 

 tin et al. 1953, Type 15). In many arid areas, Palustrine 

 and Lacustrine Mud Shores are encrusted or saturated 

 with salt. Martin et al. (1953) called these habitats inland 

 saline flats (Type 9); they are also called alkali flats, salt 

 flats, and salt pans. Mud Shores may also result from 

 removal of vegetation by man, animals, or fire, or from 

 the discharge of thermal waters or pollutants. 



Examples of Dominance Types in the Marine and Estu- 

 arine Systems include the fiddler crab Uca, the ghost 

 shrimp Callianassa, the mud snails Nassarius and 

 Macoma, the clam worm Nereis, the sea anemone Cerian- 

 thus, and the sea cucumber Thyone. In the Lacustrine, 

 Palustrine, and Riverine Systems, examples of Dominance 

 Types are the fingernail clam Pisidium, the snails Aplexa 

 and Lymnaea, the crayfish Procambarus, the harpacticoid 

 copepods Canthocamptus and Bryocamptus, the fingernail 

 clam Sphaerium, the freshwater mollusk Elliptio, the 

 shore bug Saldula, the isopod Asellus, the crayfish Cam- 

 barus, and the mayfly Tortopus. 



Organic.— The unconsolidated material smaller than 

 stones is predominantly organic soils of formerly vege- 

 tated wetlands. In the Marine and Estuarine Systems, 

 Organic Shores are often dominated by microinvertebrates 

 such as foraminifera, and by Nassarius, Littorina, Uca, 

 Modiolus, Mya, Nereis, and the false angel wing Petricola 

 pholadiformis. In the Lacustrine, Palustrine, and River- 

 ine Systems, examples of Dominance Types are Cantho- 

 camptus, Bryocamptus, Chironomus, and the backswim- 

 mer Notonecta. 



Vegetated.— Some nontidal shores are exposed for a 

 sufficient period to be colonized by herbaceous annuals or 

 seedling herbaceous perennials (pioneer plants). This 

 vegetation, unlike that of Emergent Wetlands, is usually 

 killed by rising water levels and may be gone before the 

 beginning of the next growing season. Many of the pioneer 

 species are not hydrophytes but are weedy mesophytes 

 that cannot tolerate wet soil or flooding. Examples of 

 Dominance Types in the Palustrine, Riverine, and Lacus- 

 trine Systems are cocklebur (Xanthium strumarium) and 

 barnyard grass (Echinochloa crusgalli). 



Dominance Types for Unconsolidated Shores in the Mar- 

 ine and Estuarine Systems were taken primarily from 

 Smith (1964), Morris (1966), Abbott (1968), Ricketts and 

 Calvin (1968), and Gosner (1971). Dominance Types for 

 Unconsolidated Shores in the Lacustrine, Riverine, and 

 Palustrine Systems were taken primarily from Stehr and 

 Branson (1938), Kenk (1949), Ward and Whipple (1959), 

 Cummins et al. (1964), Johnson (1970), Ingram (1971), 

 Clarke (1973), and Hart and Fuller (1974). 



Moss-Lichen Wetland 



Definition. The Moss-Lichen Wetland Class includes 

 areas where mosses or lichens cover substrates other than 

 rock and where emergents, shrubs, or trees make up less 

 than 30% of the areal cover. The only water regime is 

 saturated. 



Description. Mosses and lichens are important compo- 

 nents of the flora in many wetlands, especially in the north, 

 but these plants usually form a ground cover under a domi- 

 nant layer of trees, shrubs, or emergents. In some in- 

 stances higher plants are uncommon and mosses or lichens 

 dominate the flora. Such Moss-Lichen Wetlands are not 

 common, even in the northern United States where they 

 occur most frequently. 



Subclasses and Dominance Types. 

 Moss.— Moss Wetlands are most abundant in the far 

 north. Areas covered with peat mosses (Sphagnum spp.) 

 are usually called bogs (Golet and Larson 1974; Jeglum 

 et al. 1974; Zoltai et al. 1975), whether Sphagnum or 

 higher plants are dominant. In Alaska, Drepanocladus and 

 the liverwort Chiloscyphus fragilis may dominate shallow 

 pools with impermanent water; peat moss and other 

 mosses (Campylium stellatum, Aulacomnium palustre, 

 and Oncophorus wahlenbergii) are typical of wet soil in 

 this region (Britton 1957; Drury 1962). 



Lichen.— Lichen Wetlands are also a northern 

 Subclass. Reindeer moss (Cladina rangiferina) forms the 

 most important Dominance Type. Pollett and Bridgewater 

 (1973) described areas with mosses and lichens as bogs 

 or fens, the distinction being based on the availability of 

 nutrients and the particular plant species present. The 

 presence of Lichen Wetlands has been noted in the Hud- 

 son Bay Lowlands (Sjors 1959) and in Ontario (Jeglum et 

 al. 1974). 



Emergent Wetland 



Definition. The Emergent Wetland Class is charac- 

 terized by erect, rooted, herbaceous hydrophytes, ex- 

 cluding mosses and lichens. This vegetation is present for 

 most of the growing season in most years. These wetlands 

 are usually dominated by perennial plants. All water 

 regimes are included except subtidal and irregularly 

 exposed. 



Description. In areas with relatively stable climatic con- 

 ditions, Emergent Wetlands maintain the same appear- 

 ance year after year. In other areas, such as the prairies 

 of the central United States, violent climatic fluctuations 

 cause them to revert to an open water phase in some years 

 (Stewart and Kantrud 1972). Emergent Wetlands are 

 found throughout the United States and occur in all 

 Systems except the Marine. Emergent Wetlands are 

 known by many names, including marsh, meadow, fen, 

 prairie pothole, and slough. Areas that are dominated by 



