-:', 



Wetlands in this subclass generally occur on mineral 

 soils or highly decomposed organic soils. 



Needle-leaved Deciduous.— The southern repre- 

 sentatives of the Needle-leaved Deciduous subclass 

 include bald cypress and pond cypress {Taxodium 

 ascendens), which are noted for their ability to tolerate 

 long periods of surface inundation. Tamarack is 

 characteristic of the Boreal Forest Region, where it 

 occurs as a dominant on organic soils. Relatively few 

 other species are included in this subclass. 



Broad-leaved Evergreen. — In the Southeast, 

 Broad-leaved Evergreen wetlands reach their greatest 

 development. Red bay {Persea borbonia), loblolly bay 

 (Gordonia lasianthus), and sweet bay {Magnolia vir- 

 giniana) are prevalent, especially on organic soils. This 

 subclass also includes red mangrove, black mangrove 

 {Avicennia germinans), and white mangrove (Lagun- 

 cularia racemosa), which are adapted to varying levels 

 of salinity. 



Needle-leaved Evergreen.— Black spruce, growing 

 on organic soils, represents a major dominant of the 

 Needle-leaved Evergreen subclass in the North. 

 Though black spruce is common on nutrient-poor soils, 

 Northern white cedar (Thuja occidentalis) dominates 

 northern wetlands on more nutrient-rich sites. Along 

 the Atlantic Coast, Atlantic white cedar (Chamae- 

 cyparis thyoides) is one of the most common domi- 

 nants on organic soils. Pond pine is a common needle- 

 leaved evergreen found in the southeast in association 

 with dense stands of broad-leaved evergreen and decid- 

 uous shrubs. 



Dead. —Dead Forested wetlands are dominated by 

 dead woody vegetation taller than 6 m (20 feet). Like 

 Dead Scrub-Shrub Wetlands, they are most common 

 in, or around the edges of, man-made impoundments 

 and beaver ponds. The same factors that produce 

 Dead Scrub- Shrub Wetlands produce Dead Forested 

 Wetlands. 



Modifiers 



To fully describe wetlands and deepwater habitats, 

 one must apply certain modifiers at the class level and 

 at lower levels in the classification hierarchy. The 

 modifiers described below were adapted from existing 

 classifications or were developed specifically for this 

 system. 



Water Regime Modifiers 



Precise description of hydrologic characteristics 

 requires detailed knowledge of the duration and timing 

 of surface inundation, both yearly and long-term, as 

 well as an understanding of groundwater fluctuations. 

 Because such information is seldom available, the 

 water regimes that, in part, determine characteristic 

 wetland and deepwater plant and animal communities 



are described here in only general terms. Water 

 regimes are grouped under two major headings, Tidal 

 and Nontidal. 



Tidal water regime modifiers are used for wetlands 

 and deepwater habitats in the Estuarine and Marine 

 systems and Nontidal modifiers are used for all 

 nontidal parts of the Palustrine, Lacustrine, and Riv- 

 erine systems. The Tidal Subsystem of the Riverine 

 System and tidally influenced parts of the Palustrine 

 and Lacustrine systems require careful selection of 

 water regime modifiers. We designate subtidal and 

 irregularly exposed wetlands and deepwater habitats 

 in the Palustrine, Riverine, and Lacustrine systems as 

 permanently flooded-tidal rather than subtidal, and 

 Palustrine, Riverine and Lacustrine wetlands regu- 

 larly flooded by the tide as regularly flooded. If 

 Palustrine, Riverine, and Lacustrine wetlands are only 

 irregularly flooded by tides, we designate them by the 

 appropriate nontidal water regime modifier with the 

 word tidal added, as in seasonally flooded-tidal. 



Tidal 



The water regimes are largely determined by oceanic 

 tides. 



Subtidal. The substrate is permanently flooded with 

 tidal water. 



Irregularly Exposed. The land surface is exposed by 

 tides less often than daily. 



Regularly Flooded. Tidal water alternately floods 

 and exposes the land surface at least once daily. 



Irregularly Flooded. Tidal water floods the land 

 surface less often than daily. 



The periodicity and amplitude of tides vary in dif- 

 ferent parts of the United States, mainly because of 

 differences in latitude and geomorphology. On the 

 Atlantic Coast, two nearly equal high tides are the rule 

 (semidiurnal). On the Gulf Coast, there is frequently 

 only one high tide and one low tide each day (diurnal); 

 and on the Pacific Coast there are usually two unequal 

 high tides and two unequal low tides (mixed semi- 

 diurnal). 



Individual tides range in height from about 9.5 m (31 

 feet) at St. John, New Brunswick (U. S. National 

 Oceanic and Atmospheric Administration 1973) to less 

 than 1 m (3.3 feet) along the Louisiana coast (Chabreck 

 1972). Tides of only 10 cm (4.0 inches) are not un- 

 common in Louisiana. Therefore, though no hard and 

 fast rules apply, the division between regularly flooded 

 and irregularly flooded water regimes would probably 

 occur approximately at mean high water on the 

 Atlantic Coast, lowest level of the higher high tide on 

 the Pacific Coast, and just above mean tide level of the 

 Gulf Coast. The width of the intertidal zone is deter- 

 mined by the tidal range, the slope of the shoreline, 

 and the degree of exposure of the site to wind and 

 waves. 



