^ form distinctive belts, which may remain relatively stable, may undergo 



Z cyclic fluctuations, or may encroach upon one another, depending 



_i upon changes in the water table. If organic accumulation exceeds the 



Lij rate of recycling, shallow open water may eventually become a marsh 



^ dominated by submerged, floating, and emergent aquatics. Depending 



Q upon the water depth, this may lead to the formation of a deep or a 



< shallow marsh. The prairie potholes of the north-central United States, 



Z renowned for their high waterfowl productivity, are a classic example 



of deep marshes, where considerable areas of open water may be 

 present. If water levels are maintained, these marsh types may persist. 



With a lowering of the water table and/or organic accumulation, 

 however, marshes within forested regions may become shrub or tree 

 swamps, or a combination of the two. Although muck or peat soils un- 

 derlie marshes and swamps, mineral material is usually relatively near 

 the surface. Marshes and swamps generally exhibit stream drainage 

 patterns, although exceptions occur, as in the prairie pothole country. 

 Further vegetation development toward somewhat drier conditions in 

 swampy sites is dependent upon water table changes. As long as the 

 site is sufficiently wet to exclude upland species, a swamp vegetation 

 will prevail. 



Bogs represent a wetland type most frequently found within the 

 glaciated sections of North America. They can usually be distinguished 

 from swamps by their location in poorly drained depressions underlain 

 by considerable deposits of peat. Bog formation represents a classic ex- 

 ample of autogenic development, in which a lake, through continued 

 accumulation of dead plant material, gradually becomes transformed 

 into a bog. Bogs usually exhibit a distinctive evergreen-shrubby and/or 

 coniferous-tree cover. The spruce bogs scattered across the northeast- 

 ern United States represent an excellent example. They exhibit a 

 distinctive flora, including insectivorous plants — the sundew and 

 pitcher plant — bog orchids, and a diversity of evergreen shrubs belong- 

 ing to the heath family— leatherleaf, bog laurel, bog rosemary, and 

 Labrador tea. Within the eastern deciduous forest region, they 

 represent outliers of a more boreal biota. 



The transition between bogs and swamps is often not clear cut. For 

 example, red maple, a typical swamp species, may invade a bog and 

 eventually become the dominant tree, despite the fact that the wetland 

 is underlain by deep peat deposits. The southern white cedar on the 

 Atlantic Coastal Plain is frequently found growing in poorly drained 

 depressions along with a typical bog flora. Being less tolerant of shade 

 than the red maple, it may be gradually replaced by the maple. 



The wet meadow is another fresh-water, wetland type, somewhat 

 marsh-like but drier than the wetlands previously mentioned. Although 

 the soil is wet, flooding is rare. This site frequently exhibits a diversity 

 of herbaceous plants, including sedges and showy forbs such as purple 



