- CHAPTER 4 



STRUCTURE AND FUNCTION OF THE SUBSTRATE 



4.1 HYDROLOGY 



The hydrology of cedar wetlands is a con- 

 trolling factor in aeration of the root zone, availability 

 and movement of nutrients, soil temperature regime, 

 and the availability of moisture. Data on all quantita- 

 tive and functional aspects of cedar forest water 

 regimes are sparse and fragmentary. Some water 

 regime information is included in other studies on 

 cedar wetlands, e.g., Laderman (1975, 1980) for MA; 

 Little (1950), Markley (1979), Schneider and Ehren- 

 feld (1987), and reviewed by Roman et al. (unpubi.) 

 for NJ; Dill et al. (unpubi.) for Delman/a; reviewed in 

 USFWS (1986b,c) for VA and NO; and Dunn et al. 

 (1987) for FL. The most comprehensive information 

 available on hydrological functions in a cedar wet- 

 land relates to the Great Dismal Swamp (see Section 

 2.4.1). 



4.1.1 Annual Hydrological C ycle 



Although the natural water regime varies 

 from year to year, from site to site, and with the 

 development of a stand, a summary of a generalized 

 annual cycle (Otte 1981; Golet and Lowry 1987) 

 would be as follows; 



In late winter and early spring, cedar swamp 

 waters are highest. In late spring and early summer, 

 evapotranspiration removes large quantities of 

 water; the water table begins to drop below the 

 ground surface in places. In autumn, swamps are 

 driest, with standing water and water tables at their 

 annual low point. Most water loss is via evapo- 

 transpiration. In flowing systems, downstream flow 

 is reduced or absent. In the winter, with declining 

 temperatures and reduced evapotranspiration, the 

 water table rises; in flowing systems, stream flow 

 swells and lateral subsurface and surface flow in- 

 creases. 



4.1.2 Classification of Water Regimes 



Chamaecyparis thyoides usually grows on 

 hummocks slightly elevated above and surrounded 

 by hollows where water level may be up to 1.2 m 

 deep, or as low as 0.3 m below the surface. The hol- 

 lows are saturated or hold standing water for ex- 

 tended periods during the growing season. Cedars 

 themselves are stressed and do not thrive when the 

 bole is under water, but classification (USFWS sys- 

 tem, Cowardin et al. 1979) of cedar-dominated wet- 

 lands is determined by the water regime in the 

 hollows. Atlantic white cedars are found with the fol- 

 lowing water regimes: 



a. Nontidal: Almost all Atlantic white cedars grow 

 beyond tidal movements. In the living swamps 

 where there is tidal influence (e.g., on the coastal 

 fringes of New Jersey, Delaware, Maryland, North 

 Carolina), tidal flux is very small and infrequent (see 

 Section 7.2.6). 



b. Seasonally Flooded: Surface water is present for 

 extended periods especially early in the growing 

 season but is absent by the end of the season in most 

 years. When surface water Is absent, the water table 

 is near the land surface. 



c. Saturated: The substrate is saturated to the sur- 

 face for extended periods during the growing 

 season, but surface water is seldom present. Cedars 

 growing on seepage slopes, or on slopes adjacent 

 to hummock and hollow terrain, also fall in this 

 category. 



d. Semipermanently Flooded: Surface water per- 

 sists throughout the growing season in most years. 



e. Permanently Flooded: Water covers the land sur- 

 face throughout the year in all years. 



Some Atlantic white cedars grow in artificial- 

 ly or naturally modified wetlands which are classified 

 with special modifiers to indicate their status: Ex- 

 cavated (with artificially altered channels or basins); 

 Impounded (created by a barrier or dam made by 



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