IIA. Prose Description of Site. 



This 40 acre area is remarkable for containing eight taxa (four 

 species and four hybrids)of rare shield ferns ( Dryopteris spp.). It was 

 discovered in 1974 during the compilation of a preliminary flora of Dismal 

 Swamp (Musselman et al. 1977), and has been the subject of two journal 

 articles (Nickrent et al. 19785 McGraw et al. 1979) and a book chapter 

 (Wagner and Musselman 1978). It is sometimes referred to enthusiastically 

 by Dr. Musselman and his students as the Dismal Swamp "fern supersite". 



The area occurs at the toe of the Suffolk Scarp, a relict wave-cut 

 shoreline which forms the western boundary of the Dismal. At this point, 

 US 158 decends about 25 ft. from the farmland along the top of the scarp 

 to the old sea floor now occupied by swamp forest. This marine feature 

 probably dates to the height of the Sangamon Interglacial around 90,000 

 years ago. Sea level at that time is believed to have been around 25 ft. 

 higher than at present, which would correspond with the elevation at the 

 bottom of the escarpment. 



Much of Dismal Swamp is underlain by peat, up to 12 feet thick, over 

 a sandy basal deposit of marine origin. In most of the swamp the age of this 

 sand should correspond the beginning of recession of the sea around the end 

 of the Sangamon, perhaps 70,000 to 80,000 years ago. Shallow drainage 

 patterns bably formed on this exposed surface during the early Wisconsin 

 ice age. The peat deposits are much younger, having been formed beginning 

 around 11,000 to 12,000 years ago at the end of the Wisconsin. 



As the scarp is approached on the west, organics are shallower and 

 peat grades into a mineral soil with high organic content, which then 

 feathers out onto the toe of the scarp. Underlying the fern site are fine- 

 textured soils, probably derived from colluvial downwash from the scarp, 

 continually mixed over a long period of time with organic material formed 

 on the site. The soil 



Organic soils are formed when the water table is high enough to prevent 

 complete decomposition of plant litter. Under the previous hydrologic 

 regime and in the absence of a sediment source from the nearby scarp, this 

 site would have developed a thin layer of peat, which would have increased 

 in thickness eastward into the swamp. The mineral content, however, 

 probably precludes it being classified as a histosol. 



Color infrared photography shows that the hydrology of the site was 

 considerably interrupted by construction of US 158. In the undisturbed 

 swamp, water was collected by the small swamp which crosses US 158 at 

 Acorn Hill and flows downhill through a stream cut in the scarp just 

 north of the highway. From there it moved south along a low area near the 

 toe of the scarp into the headwaters of the Perquimans River. 



US 158 has acted as a dam, preventing southward flow and causing the 



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