of water levels in the swamp throughout the summer. 

 Surface water runoff through the swamp is also a 

 major output event. Over the last two centuries 

 natural outiflow patterns have been almost complete- 

 ly obliterated, and surface water now drains from the 

 swamp through channelized outlets. Ground-water 

 discharge is significant: where the upper confining 

 layer is absent, freshwater wells up into the overlying 

 peat and Is removed by evapotranspiration; where 

 the aquifer is breached, ground water drains from the 

 swamp as surface flow through outlet channels. In 

 the latter case, the water is lost to the swamp; it may 

 be a major factor in the lowering of the swamp's 

 general water level. 



The net effect of all the modifications to the 

 swamp's surface and ground water systems is that 

 the majority of the peat soils in the swamp are drier 

 for a longer period of the annual cycle than would 

 occur naturally (Lichtler and Walker 1979; USFWS 

 1986b). 



Surface water . The water has a dark tannic 

 color, low mineral content, and a pH of 3.5 - 6.7. 

 Some areas have high iron and free carbon dioxide 

 content. Sediment from upstream agricultural and 

 timber lands, runoff from hog operations, and fer- 

 tilizers and pesticides used on corn, soybeans, and 

 peanuts are potential sources of surface water pollu- 

 tion. The proximity of the shallow aquifer to the sur- 

 face makes it highly susceptible to contamination 

 from agricultural, industrial, and domestic runoff. 



Biota. Atlantic white cedar covers 3,000 ha 

 or 7% of the refuge, primarily in the south central por- 

 tion of the swamp, with a few stands north of Lake 

 Drummond. At present, it is impossible to estimate 

 the area occupied by cedar a century or more earlier 

 (A. Carter, pers. comm.). In the Great Dismal, cedar 

 grows primarily either in pure, even-aged stands or 

 mixed with red maple, black gum, sweet bay, and red 

 bay {Persea borbonia) or pond pine {Pinus serotina). 



The Great Dismal contains three major 

 swamp forest communities in addition to the cedar 

 stands: 



a. f^aple-Gum, dominated by red maple and black 

 gum, often in association with red bay, sweet bay, 

 sweet gum {Liquidambar styraciflua), and the tulip- 

 tree {Liriodendron tulipifera). Maple-gum now 

 covers 60% of the Great Dismal, having increased 

 significantly in the past 40 years at the expense of 

 both cypress-gum and cedar associations. 



b. Cypress-Gum, dominated by cypress {Taxodum 

 distichum), tupelo gum {Nyssa aquatica), and black 



gum. This was formerly the most extensive associa- 

 tion in the swamp. 



c. Pine, dominated by either loblolly or pond pine. 



Over time, the composition of the swamp 

 forest varied. In the Great Dismal, the continuing ef- 

 fects of human activities in the swamp now override 

 natural influences on succession. Cedar has been 

 harvested on a large scale in the Dismal Swamp since 

 the 1 8th century when the Dismal Swamp Land Com- 

 pany began operations. Loggers often cut the cedar 

 but left the hardwoods to take over the site, or left so 

 much slash on the ground that cedar seedlings were 

 unable to develop in the resultant shade. Other im- 

 portant factors that have resulted in the gradual suc- 

 cession to hardwoods are suppression of wildfires 

 and changes in the water regime (see Chapter 6). 

 Frost (1 987 and unpubl.) and Ward (unpubl.) discuss 

 Great Dismal commercial cedar logging operations 

 in detail. 



Despite major disturbances, the swamp still 

 contains typical historical communities whose exist- 

 ence predates the extensive development of the 

 1940's and 1950's. Many of the historical species in 

 the swamp appear to have survived, but their relative 

 abundance has changed. The five herbaceous 

 species classified as rare or endangered in the cedar 

 wetlands of Virginia (Porter 1 979) all occur exclusive- 

 ly in the Delmarva peninsula. 



The vascular flora associated with cedar in 

 the Great Dismal, currently consisting of 19 tree, 34 

 shrub, and 7 herbaceous species (A. Laderman, un- 

 publ.) is included in Appendix A; some frequently 

 encountered species are illustrated in Figure 24. 

 Wildlife on the refuge is discussed in Section 5.3. A 

 list of Great Dismal flora and fauna is maintained by 

 the Refuge staff; the tabulation of 1979-1980 is con- 

 tained in the Refuge Master Plan (USFWS 1986b). 

 Levy and Walker (1 979) examined forest dynamics in 

 the Great Dismal's cedar wetlands. Day and his co- 

 workers have conducted a series of studies on com- 

 munity structure, biomass, productivity, and de- 

 composition rates of a Great Dismal cedar wetland 

 from 1977 to the present (synthesized and sum- 

 marized in Day 1987 and unpubl.). Extensive discus- 

 sions of all aspects of the Great Dismal, including 

 literature reviews, appear in the proceedings of a 

 1973 conference devoted to the subject (Kirk 1979) 

 as well as in USFWS (1984a and 1986a,b). For fur- 

 ther discussion of flora and fauna of the region, see 

 Chapter 5. 



Mana gement . Burning, grazing, and log- 

 ging that once maintained parts of the Great Dismal 

 Swamp in different stages of succession or climax 

 were curtailed or eliminated when the Refuge was es- 



21 



