The park protects 22 square miles of forested wetland in the Great Dismal Swamp, the largest remaining swamp in the eastern United States. Historically, the swamp was much wetter than what you see today. Extensive ditching and logging have changed its character over the past 200 years. Today's Dismal is dominated by red maple in place of the bald cypress and tupelos that once flourished here. But make no mistake; the Dismal Swamp is still an area of great natural significance.
Populations of Atlantic White Cedar can be found along the western edge of the park. The cedar trees grow in deep peat soils common to the area. Hessel's Hairstreak, a rare butterfly species dependent on the white cedar, has been seen here. Black-throated green warblers may be found nesting among these conifers.
Only a few old logging roads and ditches break the vast forests of the park. The roadbeds serve as park trails and form habitat used by a wide variety of wildlife that live in the forests. Bobwhite and turkey are often seen feeding on seeds and insects here. Deer and marsh rabbits browse on the green herbs that thrive in the sunlight. Blackberry brambles and devil's-walking-stick are abundant along the roadsides. The fruits of these plants are favorite foods of the numerous black bears that live in the swamp. Persimmon, poke, blueberry, various oaks, black walnut and tall pawpaw also provide food for wildlife. Tracks of raccoons, opossums, and gray fox can be seen along the roads. Bobcats roam these open areas in search of prey.
Butterflies abound in the Dismal. Forty-three species have been identified in the park so far. Huge numbers of Palamedes and zebra swallowtails can be found 'puddling' along the roads during certain times of the year. Tiger swallowtails, Atlantic holly azures, and variegated fritillaries are also present in large numbers.
Along the forest edge supple-jack, grape, and greenbrier create dense tangles of vines. Neotropical songbirds such as the American redstart and the black-and-white warbler find these conditions perfect for nesting. Yellow-throated warblers and white-eyed vireos are often heard among the vines, but can be difficult to see. Swainson's warblers are known to nest within the swamp, but they are rarely seen. Prothonotary warblers and wood ducks can be spotted along the ditches that parallel the roadbeds. Seven species of woodpeckers are present in the park. Red-shouldered hawks can often be seen flying through the forest. Occasionally barred owls can be heard calling from deep in the swamp.
The high pocosin along the northern boundary of the park is dominated by dense stands of inkberry. Gallberry, shining fetterbush, and sweet pepperbush are also found here. High pocosin is a fire-dependent natural community. It is becoming rare in the Dismal today.