Bald cypress swamps in North America can take on several forms, depending on their latitude and location. As they occur in Maryland, forested wetlands that contain Bald cypress (Taxodium distichum) as a dominant species are called Chesapeake Bay Cypress Gum Swamps, according to the International Vegetation Classification (IVC)*. These swamps are characterized by a canopy dominated by Bald cypress and swamp tupelo (Nyssa biflora). Occasionally other species such as pumpkin ash (Fraxinus profunda) or green ash (Fraxinus pensylvanica) attain canopy stature. The shrub layer is exceptionally diverse and usually contains winterberry (Ilex verticillata), swamp azalea (Rhododendron viscosum), sweet pepperbush (Clethra alnifolia), and Northern arrow-wood (Viburnum recognitum). Herbaceous plant diversity in swamps is generally high based on several environmental factors including: hummock-and-hollow microtopography, species recruitment from adjacent habitats, and the frequency and duration of flooding. Regularly flooded hollows typically support flood-tolerant swamp species such as jewelweed (Impatiens capensis), arrow-arum (Peltandra virginica), halberd-leaf tearthumb (Polygonum arifolium), blue flag (Iris versicolor) and Lizard’s-tail (Saururus cernuus). Hummocks, which are slightly elevated, provide habitat for less flood tolerant species such as Jack-and-the-pulpit (Arisaema triphyllum), marsh blue violet (Viola cucullata), wood reedgrass (Cinna arundinacea), water hemlock (Cicuta maculata), false nettle (Boehmeria cylindrica), weak stellate sedge (Carex seorsa), brome-like sedge (Carex bromoides), tussock sedge (Carex stricta) and ferns such as royal fern (Osmunda regalis var. spectabilis), cinnamon fern (Osmunda cinnamomea), netted chain fern (Woodwardia areolata) and marsh fern (Thelypteris palustris).
On the Eastern Shore, the bald cypress swamps such as those along Nassawango Creek and Pocomoke River may also include canopy species such as loblolly pine (Pinus taeda), red maple (Acer rubrum) and sweetgum (Liquidambar styraciflua). These swamps included a more diverse understory, with a subcanopy of sweetbay magnolia (Magnolia virginica), and red maple, plus several vine species. This increased species mix is most likely due to extended dry periods, compared to consistent flooding, or to higher light penetration due to a more open canopy.
Soils in all Maryland bald cypress swamps are saturated and poorly drained, containing high amounts of peaty organic matter. There is almost always standing water, with water levels seasonally or tidally influenced by lunar tide cycles. These swamps occur along channels of blackwater rivers. (Blackwater rivers are those with deep, slow-moving channels flowing through forested swamps and wetlands. Water in these rivers is dark in color, like clear tea or coffee, caused by the leaching of acidic tannins from bordering vegetation.) Surface water is important in the maintenance of these community types; Bald cypress seeds are too heavy to be dispersed far by wind and so depend upon flowing water for dispersal. Swamps like these most likely began to form approximately 10,000 years ago, at the end of the last ice age, although there is evidence supporting the existence of Bald cypress in what is now Maryland prior to the last ice age. An ancient cypress log was unearthed by contractors in the course of building the stadium for the Baltimore Ravens.
Maryland’s bald cypress swamps are some of the northern most occurrences of this community type, the range of which is centered on the southeastern United States.
The consummate bald cypress swamp just oozes with Southern mystique – picture Spanish-moss cascading from the branches into murky light and alligators drifting in the dark tannic water, weaving amongst the roots. Indeed, the bald cypress tree is the State Tree of Louisiana. Were it not for one developmental glitch of this tree, it might be found all the way north to Minnesota. Bald cypress trees are conifers, which have seeds borne in cones. Seeds require oxygen, and therefore some drawdown in water levels, to germinate and survive the first year. The one-year old seedlings are prone to damage from ice if water levels are too high. If larger seedlings are planted, they can thrive in more northern environments. But remember, you will find no alligators or cottonmouth water moccasins in Maryland swamps.
The basic structure of a swamp tree is largely determined by its hydrology and soil composition. Because wet soil is not very supportive, trees have developed structures to assist in stabilizing themselves. Generally, there is a swelling of the base of the trunk, called buttressing. As with cathedrals, this buttressing increases basal area and distributes the weight of the tree more widely. Bald cypress and black gum have developed additional structures, called pneumatophores, although most people call them knees. Knees are modified roots that grow up out of the water. Some scientists believe these knees add structural support. Some believe they assist in gas exchange, transporting both oxygen and carbon dioxide throughout the root system.
Wetlands are studied for their role in various ecological processes. Wetlands, including Bald cypress Swamps, can absorb additional water. This allows them to act as a buffer for uplands in the event of flooding. They act as a filter for runoff, slowing it down to reduce erosion and absorbing many harmful chemicals before they reach rivers and bays. Thanks to those knees, bald cypress swamps are also the subject of an investigation by the United States Geological Survey’s National Wetlands Research Center into carbon storage and its effect on increased greenhouse gases, namely carbon dioxide, in the air.
Although the range of distribution has remained relatively unchanged, the number and size of bald cypress swamps has declined, largely due to harvesting of the wood and changes in hydrology due to development. Bald cypress trees are tall and massive, achieving heights in excess of 50 meters, growing slowly but living to the ripe old age of 600 years or more. (The oldest recorded bald cypress was 1200 years old.) Bald cypress wood is prized for construction and furniture. It is naturally resistant to rot and disease, earning the nickname “the eternal wood”. It also makes an excellent landscaping tree in wetter soils. Its soft green needles provide shade in the summer but then turn a bright gold in the autumn, before falling off.
Bald cypress swamps are also important habitats for many rare, threatened or endangered species of plants and animals. Uncommon plants and trees recently reported from bald cypress swamps include catchfly cutgrass (Leersia lenticularis), red bay (Persea palustris), southern twayblade (Listera australis), and Virginia least trillium (Trillium pusillum var. virginianum). Macrobenthic invertebrates (large bottom-dwelling creepy crawlies) are also well represented by several species of crayfish. This habitat, with the fluctuating water levels, is also a good place to find many reptiles and amphibians, including the State-listed carpenter frog.
There are several excellent examples of bald cypress Swamps in Maryland. Battle Creek Cypress Swamp, part of the Calvert County Park and Recreation Program, provides a boardwalk through the swamp and a nature center with interpretive displays. Nassawango Creek Preserve in Worcester County is privately-owned and maintained by The Nature Conservancy. You can see an historic village demonstrating how humans have used the resources of the swamp; there is also a canoe launch, with canoe rentals available in nearby Snow Hill. Nassawango is a particularly good place to observe birds, especially warblers. Many state lands along the Pocomoke River in Worcester County (Pocomoke River State Park, State Forest and Wildlife Management Area) and the Great Cypress Swamp, shared with Delaware, provide many ways to enjoy the swamps.
* IVC or International Vegetation Classification is based on vegetation as it currently exists on the landscape. Landforms, soils and other features are not considered as part of the classification criteria.
The IVC was developed by NatureServe, its natural heritage member programs and The Nature Conservancy. It is the system accepted by the Federal Geographic Data Committee to be used by all U.S. federal agencies.