Natural Communities - Coastal Plain Bogs in Maryland
When most people think of bogs, they think of huge quaking mats of sphagnum moss surrounded by evergreens in the far North ... or of the vast wet moors of northern Europe. Few Marylanders realize that we have a number of small bogs right here on our Coastal Plain. These unusual wetlands are important and threatened in our state.
Bogs are open, acidic, nutrient-poor wetlands with sphagnum moss, heath shrubs, wildflowers, and often with insect-eating plants. Bogs form when a mat of vegetation, especially sphagnum moss and sedges, develops on the edge of a pond, lake, wetlands, or slow-moving stream, and eventually grows over the surface of the water. As time passes, the dead, decaying plants form a dense, fibrous layer known as "peat." Living moss, sedges, and shrubs take root in the developing peat, holding it together and becoming part of it when they die.
As bogs develop, they become highly stressful environments for most plants. The still or slow-moving water is very acidic and contains a limited supply of nutrients, such as nitrogen, that are needed for plant growth. The partly decayed vegetation adds organic acids to the bog, slowing further decay and limiting the release of nutrients. If the peat layer is thick, it keeps water and nutrients from circulating freely. Most typical wetland plants cannot survive in the nutrient-poor, acidic environment, but a few plant species, such as cranberries, sundews, and sphagnum moss, are especially adapted for life in the bog.
Most of Maryland's original Coastal Plain bogs are believed to have formed when fires removed woody vegetation and humus from certain swamps during periods of drought. When the water table returned to normal, the lack of woody vegetation allowed bog species to invade the wetland edges, where wet, sandy soils provided the appropriate conditions. Coastal Plain bogs may also have developed in some "oxbow" lakes (the section of a meandering stream cut off when the stream changed course) and in old beaver ponds.
More than three centuries of human activity, including fire suppression, forest clearing, and the draining and filling of wetlands for agriculture and development, have radically altered the landscape of Maryland's Coastal Plain. These changes have destroyed many of Maryland's original Coastal Plain bogs and have confined most new bog formation to a few artificial sites that mimic the natural soil and water conditions required for bog formation. Maryland's few remaining Coastal Plain bogs harbor many species that are rare or endangered in the state, and these important habitats deserve our protection.
A Walk Through a Coastal Plain Bog
Bogs and the rare plants they harbor are very sensitive to human disturbance; just walking through a bog can destroy rare and fragile plants forever. For this reason, researchers studying bogs walk through them as little as possible. If you ever have the opportunity to visit a real Coastal Plain bog, please examine it only from the wooded perimeter.
But join us now on a flight of fancy: imagine that you can walk through a mature Coastal Plain bog and then magically erase your damaging footprints... Pushing aside branches of Red Maple and Black Gum, you step over thorny greenbrier vines and leave the shady forest.
At the bog's swampy edge, you struggle through a dense shrub thicket of Highbush Blueberry, Swamp Azalea, and Sweet Pepperbush. Curving limbs of Sweet Bay Magnolia arch overhead, bearing sweet-scented, creamy white blossoms. Tall, lush Cinnamon Ferns remind you of a primeval landscape where dinosaurs might have trod. The moist ground is plastered with fallen leaves, black with decay. Into the dark brown ooze your feet sink, releasing the pungent odor of marsh gases from decaying plants.
A few more careful steps and you emerge into the world of the bog. Sunlight floods a carpet of sphagnum moss interspersed with low shrubs and sedge hummocks. A maze of pools and open water channels winds through the sphagnum mat. As you step onto a squishy cushion of sphagnum, a frog leaps away so fast you only hear the splash as it enters the water.
Your feet sink a few inches into the moss, and cold water seeps into your tennis shoes. Quickly learning to step from hummock to hummock to find firmer footing, you notice plump berries dangling from tiny-leaved cranberry plants. Arching over the cranberries, branches of sturdy Leatherleaf shrubs bear a row of small, urn-shaped flowers near their tips.
Venturing farther into the bog, you spot strange low plants half-hidden in the sphagnum. The tubular greenish-red leaves of the Pitcher plant offer a watery grave to unwary insects. Here and there, White-fringed Orchids are beginning to open their lacy lower blossoms.
You pause to listen to the musical trills of bird song that ring out from the shrub swamp beyond the bog. Sunlight dances on the wings of dozens of dragonflies and smaller insects that hover and dart above the water lilies floating on the open water. Tiny, yellow bladderwort flowers poke their heads above the murky water, connected by a thread-like stalk to a feathery mass of underwater leaves. You step a bit closer to examine the flowers when ... splash! ... through the mat of sphagnum you go, one leg in up to the knee. Pulling your leg back to the sucking sound of the mucky peat, you beat a hasty retreat to the familiar woodland. You wave your magic wand and erase your footprints, but images of life in the bog linger with you.
Characteristic Species of Our Coastal Plain Bogs
Approximately 20 species of the genus sphagnum occur in Maryland. Each tiny leaf of sphagnum moss consists of a network of large and small cells that act as a sponge, allowing the moss to hold approximately twenty times its weight in water! Thriving in the bog's acidic environment, sphagnum grows out over the surface of the water to form a floating mat on which other bog plants grow. In a bog, what looks like solid ground may be only a few inches of floating sphagnum on top of open water!
"Insect-eating" plants may be the most unusual plants adapted to the stressful conditions of the bog. To make up for the lack of nutrients, the Northern Pitcher Plant (Sarracenia purpurea) traps insects in its strange, pitcher-shaped leaves. Insects land on downward-pointing hairs in the throat of the pitcher, slip into the water below, and drown. Strong enzymes secreted into the water by the pitcher plant leaf slowly digest the insects, releasing nutrients for absorption by the plant. The Northern Pitcher Plant grows in only a few Maryland bogs and is listed as Threatened in the state.
Spatulate and Round-leaved Sundew plants (Drosera intermedia and D. rotundifolia) also trap unwary insects. A sticky secretion formed on the end of stalked glands attracts insects and then entraps them much as flypaper would. Eventually the insect dies and the leaf curls around it to extract important nutrients. Round-leaved Sundews are not yet threatened in Maryland, but their numbers are declining.
Sedges are grasslike plants that cover large portions of our bogs and contribute to the formation of the vegetation mat. Sedges differ from grasses in the structure of their flowers and seeds, in stem shape (usually triangular instead of round), and in the arrangement of leaves on the stem (attaching at three positions on the stem instead of two). Among our bog sedges are many rare species. Coast Sedge, Carex exilis, bears thread-like leaves and grows in dense, hummocky clumps. Although common in the North, it is Endangered in Maryland, known from fewer than five sites in the state. White Beakrush (Rhynchospora alba) and Tawny Cottongrass (Eriophorum virginicum) stand tall above the sphagnum mat in late summer, dappling the bog with white. Their ranges extend north and south of us, but their numbers are declining in Maryland because they grow only in bogs.
Shrubs of the Heath Family
Leatherleaf (Chamaedaphne calyculata) is a common shrub in bogs of the far North, but in Maryland, near the southern limit of the species' range, it is listed as Threatened. Populations at the edge of a species' range are especially important to preserve because they often differ genetically from the rest of the species. The unique genetic makeup of outlying populations may help the species survive catastrophes such as disease outbreaks or climate changes due to global warming.
Deep red fruits of another heath shrub, the Large Cranberry (Vaccinium macrocarpon), stand out brightly among the sphagnum and sedges of several Maryland bogs. Bogs are so well suited to the growth of cranberries that they are widely used in the northern states to grow the tart fruit commercially.
Several species of these beautiful wildflowers, such as the uncommon Rose Pogonia (Pogonia ophioglossoides), occur primarily in bogs. The White-fringed Orchid (Platanthera blepitariglottis), which is Threatened in Maryland, and several related species were much more common in the early part of the century. Now these and many other orchids are rare due to the destruction of their boggy habitats and to the collection of orchids by people. Many people have tried to transplant beautiful orchids, but the orchids usually die. Orchids take a long time to grow, and they need specialized soil fungi growing with them. Original habitats are the right places for Maryland's native orchids. Transplanting usually kills the orchid, and digging up the orchid harms surrounding plants.
Animals of our Coastal Plain Bogs
Although many kinds of wildlife visit bogs from the surrounding forest, few except insects and amphibians make their permanent home in bogs. Some insect species are found nowhere else.
Usually less than 1/8" long, most species of "minute bog beetles" (family Hydraenidae) live exclusively in sphagnum bogs and seeps. Several species of "predaceous diving beetles" (family Dytiscidae) live primarily in bogs, but are also found occasionally in small, silty ponds. Scientists studying pitcher plants have learned that not all insects need to fear the deathtraps of these carnivorous plants. More than a dozen insect species live successfully on or in pitcher plants, eating the leaves or roots or living as larvae in the pitcher's water, somehow surviving its dangerous enzymes.
History and Distribution
One million years ago, ancient sediments deposited beneath the ocean were uplifted to form Maryland's Coastal Plain. Sea levels continued to fluctuate with climate changes, and as the seas advanced and retreated, a vast pinelands ecosystem --- pines on the sand hills and sphagnum bogs in the low areas --- migrated back and forth across the Coastal Plain. Today, our Coastal Plain bogs are among the few remnants of the pinelands ecosystem in Maryland.
No one knows exactly how widespread Maryland's Coastal Plain bogs were prior to humankind's drastic alteration of the landscape. Our earliest detailed accounts of the bogs come from naturalists writing in the early part of this century. They suggest that, although Maryland's Coastal Plain may never have supported as many bogs as occur in the New Jersey pinelands, small bogs and bog-like depressions were once more common here than they are today.
In 1918, naturalist W.L. McAtee listed 34 "magnolia bogs!" in Prince Georges and Anne Arundel Counties that were similar in species composition to our current Coastal Plain bogs. Even at that early date, he reported that a number of additional bogs had already been obliterated. Only a few remnants of these "magnolia bogs" exist today. Several of the rare plants that McAtee reported have also been destroyed and are no longer found in the state.
Although fire suppression has limited new bog formation, several bogs have developed within this century in artificial habitats. A few, very restricted areas where power lines cross certain swamps simulate natural bog conditions and support some rare bog species. The removal of woody vegetation during power line right-of-way maintenance mimics the effect of fire at these unusual sites. Several bogs have also formed at the upstream ends of abandoned millponds that have soils and water regimes similar to those of natural bogs. Only a small proportion of power line swamps and millponds develops into Coastal Plain bogs. Hydrology and soils must be just right, mimicking the natural bog-promoting conditions that were once more abundant.
Anne Arundel County has more Coastal Plain bogs than any other county in Maryland, yet even Anne Arundel has fewer than ten. Several bogs and bog-like openings are located in Prince Georges County, and a few others occur in scattered locations on the Eastern Shore. These sites support many species that have become rare in the state. Bogs are so rare on Maryland's Coastal Plain today that we need to protect this habitat type wherever we can if we want this element of our natural heritage to be here for our grandchildren, and theirs.
How Can Our Threatened Bogs Be Protected?
Changes in the quantity or quality of water are one of the major threats to our Coastal Plain bogs. If a bog dries out, its unique vegetation is replaced by species more tolerant of dry conditions. Development too close to a bog produces impervious surfaces such as parking lots and buildings that change flow patterns and the amount of water entering the bog. Some pollutants, such as herbicides, can damage or kill bog plants directly, and others do so by changing the acidity or nutrient levels in the bog. If fertilizer or lime used to treat lawns reaches the bog, increased nutrient levels and reduced acidity may allow vigorous growth of more common wetland plants that can out compete bog species.
The maintenance of an adequate forested buffer on the slopes surrounding bogs is the best insurance against changes in their chemical composition and the water flow into them. Forested buffers also reduce the spread of non-native, weedy plants that can crowd out rarer bog species. Monitoring programs can measure water pollution and vegetation changes to help alert as to problems.
The loss of fire as a natural disturbance will eventually threaten our remaining Coastal Plain bogs by allowing natural succession to proceed and woody plants to encroach on the bog vegetation. At some sites, manual removal of woody vegetation may be required if the rare bog species are to survive.
The collection of unusual and attractive bog wildflowers by naturalists and plant growers has hastened the decline of rare species. To reduce collection, the Wildlife and Heritage Service of DNR does not publish the exact locations of Maryland's bogs. Even people with good intentions can "love to death" the fragile bog surface by trampling it. Human impact was lessened at Suitland Bog, located in an urban park, by the construction of a boardwalk through the bog and a fence around the most sensitive area. Visitors can look at unusual bog plants without disturbing them.
The Wildlife and Heritage Service of DNR is working to protect our Coastal Plain bogs as part of its effort to preserve biodiversity --- the natural variety of living things --- in Maryland. A few of our state's Coastal Plain bogs are already owned by government agencies or private conservation organizations. However, funding is available to purchase only a very few of the most significant natural areas statewide. Protection of Coastal Plain bogs will depend on the voluntary commitment of private landowners who recognize the value of these rare habitats.
For more information, please contact:
Maryland Department of Natural Resources
Wildlife and Heritage Service
Tawes State Office Building, E-1
Annapolis MD 21401
Toll-free in Maryland: 1-877-620-8DNR
Text by Judith R. Modlin with assistance from other staff
of the Wildlife and Heritage Service and local naturalists.
Illustration by Josephine Thoms, DNR Land Planning Services.
Funded by the DNR Coastal Resources Division through a
grant from OCRM, National Oceanic and Atmospheric Administration.
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