Bogs form in highly acidic areas of saturated soil and standing water, factors which limit the growth of all but a few highly specialized plants. Because decay is minimal, a layer of peat accumulates beneath the bog vegetation. Many bogs are located in northerly areas, and they are also common in mountainous regions, including western Maryland. However, bogs on the coastal plain are uncommon, and Anne Arundel County has more than any other county.
Several are located in the Severn watershed, and are unique and fragile habitats of unusual lifeforms. Local bogs are considered to be of two types, sphagnum bogs and cedar bogs.
These are characterized by a thick surface mat of sphagnum moss, herbaceous plants and low shrubs. Local sites are usually very small and are shaded by surrounding woodland growth which limits plant diversity. Under such conditions, plant growth may be limited to sphagnum moss and royal ferns. An exception is Round Bay Bog, in the Maynadier Creek watershed, where shrub growth was cleared away for an electric transmission line right-of-way. The resulting bog growth is vigorous and diverse. Re-establishment of the original shrub growth is limited by the moisture-retentive capacity of the sphangum mat. Plant growth here also includes the carnivorous pitcher plant, bog fern, Virginia chainfern, northeastern marshfern, rose pogonia orchid, maleberry and cranberry. The surrounding swamp and woodland are dominated by pin oak, willow oak, sweet gum and sour gum, with a dense shrub layer of swamp azalea, buttonbush, swamp magnolia and clethra. This cover is botanically interesting and forms a prime nesting area for birds. The Arden Bog, in the Plum Creek watershed, was recently partly destroyed by development of a nearby recreational area. Neither the Round Bay Bog nor the Arden Bog is accessible to the public.
These sites are characterized by Atlantic white cedar which sometimes forms a dense, dark stand. Associated plants include sphagnum moss, swamp magnolia, sour gum, blackberry, highbush blueberry, swamp leucothoe, and royal fern. The surrounding borders often contain pitch pine, smooth winterberry, clethra and red maple. Because Atlantic white cedar has been much prized as lumber for boat construction for centuries, it is now quite uncommon throughout its former range and particularly on the western shore of Maryland. Several such white cedar bogs can be found in the Severn watershed, with the largest at Sullivan's Cove (survey). The species is currently being restored in the Howard's Branch watershed near the community of Sherwood Forest.
Bogs are fragile areas, requiring unusually careful protection. Maintenance of stable, moist conditions is a basic consideration. Any influx of sediment or reduction of acidity may cause loss of the bog by invasion by common woody pests, and protection of surrounding watershed for some distance is essential to preservation of these unique sites.