Mountain bog

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Distinguishing Features

Mountain bogs are small, isolated wetlands with a wide range of herb-, shrub-and tree-dominated areas and significant amounts of peat moss (sphagnum).

Introduction

Mountain bogs are isolated wetlands surrounded by terrestrial communities. Bogs are inherently rare because flat or gently sloping wet sites are scarce in the southern Appalachians. Drainage, changes in grazing or mowing, and development have further reduced the number and extent of mountain bogs. Despite their small size and rarity, bogs have high species diversity and harbor a large number of rare and endangered species, including swamp pink (Helonias bullata), Gray's lily (Liliumgrayi), and monkey face orchid (Platanthera integrilabia).

Vegetation

Species composition varies from bog to bog, reflecting differences in elevation, topography, hydrology, underlying rock, and recent land-use history. Three distinct types of bog are described: southern Appalachian bog, the swamp forest-bog complex, and cataract bogs. Bogs are technically known as fens, though they are commonly called bogs, a term that is retained here.

SOUTHERN APPALACHIAN BOG

These bogs occur on relatively flat areas along valley bottomlands as well as on gentle slopes along the margins of mountain streams. Rainwater and a high water table keep bottomland sites moist, whereas gentle slopes receive moisture from seepage flow. Soils are generally acidic and nutrient-poor, but rich in organic matter. The vegetation consists of a mosaic of low-growing shrub thickets and herbdominated areas with scattered trees. Common trees include red maple (Acer ru-brum), eastern white pine (Pinus strobus), and pitch pine (Pinus rigida) along with shrubs such as winterberry (Ilex verticillata), wild raisin (Viburnum cassinoides), cranberry (Vaccinium macrocarpon), and swamp azalea (Rhododendron viscosum). The herbaceous layer is relatively sparse under shrub thickets but is dense and species-rich in more open areas. Sedges (Carex and Rhynchospora spp.) are often abundant, along with thick mats of peat moss (Sphagnum spp.), kidneyleaf grass of parnassus (Parnassia asarifolia), scattered ferns, and showy orchids. Introduced pasture species such as Timothy grass (Phleumpratense), velvet grass (Holcus la-natus), and fescue (Festuca arundinacea) also commonly occur in southern Appalachian bogs.

SWAMP FOREST-BOG COMPLEX

This forested wetland community is associated with small streams that have level or gently sloping areas whose soils are often water-saturated and strongly acidic. The vegetation is characterized by a broken canopy with an open to dense shrub layer and small boggy openings less than an acre in size. Sites vary in the relative amount of closed forest, shrub thickets, and boggy openings they contain. At lower elevations, red maple, tulip tree (Liriodendron tulipifera), and black gum (Nyssa sylvatica) are dominant, while on poorly drained sites at higher elevations, red spruce (Picea rubens) can dominate. Once common at higher elevations, Canada hemlock (Tsuga canadensis) is increasingly rare due to an infestation of hemlock woolly adelgid. The shallow roots of red maple and other canopy trees result in frequent tree-falls, which create openings (gaps in the canopy) that provide habitat for species that require high light levels.

Dominant shrubs include rosebay (Rhododendron maximum) and mountain laurel (Kalmia latifolia) as well as more typical wetland species such as tag alder (Alnus serrulata) and winterberry. Both red and black chokeberry (Aronia arbuti-folia, A. melanocarpa) also occur. Boggy openings in small depressions typically have dense mats of peat moss along with herbaceous plants such as sedges, false hellebore (Veratrum viride), arrowhead (Sagittaria latifolia), and cinnamon fern (Osmunda cinnamomea). Rare species include swamp pink and marsh marigold (Caltha palustris).

In Virginia and northern North Carolina, this community is called a "skunk cabbage bog" because of abundant skunk cabbage (Symplocarpus foetidus), which has large cabbage-like leaves and unpleasantly pungent (to the human nose) winter-blooming flowers.

CATARACT BOG

This rare and unusual community occurs alongside streams that flow over the rock surface of granite domes. Here water slides, rather than falls, over the rock surface, providing a nearly constant source of moisture for small mats of vegetation that form along the water's edge. In this narrow linear community, conditions are ideal for bog plants because light levels are high, moisture is readily available, and the miniature pockets of soil that collect on the smooth rock substrate inhibit succession to a shrub- or tree-dominated vegetation. Be careful when exploring this community as algae growing on the wet rocks make the substrate extremely slippery.

Among the rich array of typical bog plants are insectivorous plants such as pitcher plants (e.g., Sarracenia purpurea and S. jonesii), roundleaf sundew (Drosera rotundifolia), and horned bladderwort (Utricularia cornuta). Other notable plants include orchids such as the common grass pink (Calopogon tuberosus). Shrubs such as tag alder, witch alder (Fothergilla major), and yellowroot (Xanthorhiza sim-plicissima) occur on deeper soils.

When streams dry up due to prolonged drought, margins of vegetation mats curl up. In subsequent storms, entire mats may be washed away and the process of soil accumulation and plant colonization starts anew. Steeper slopes have sparser vegetation because soil pockets are less likely to form and vegetation mats are more frequently carried downslope.

Seasonal Aspects

Spring-flowering species include swamp pink, purple pitcher plant, and swamp azalea. Striking clusters of pink flowers with conspicuous blue anthers at the tips of largely leafless stalks distinguish swamp pink, a federally listed species. The purple-streaked leaves of purple pitcher plant (Sarracenia purpurea) are modified into keeled, pitcher-shaped containers that attract and capture insects. Its solitary, purple, nodding flowers (on leafless stalks well above the leaves) depend on bumblebees for pollination while insects captured in the leaves provide an important source of nutrients for the plant. Swamp azalea's long, slender white to pinkish tubular flowers in dense clusters bloom from late spring through early summer. The flowers are particularly fragrant in the evening, when its primary pollinators (moths) are most active.

Other summer-blooming plants include Gray's lily, a rare species whose dark red, bell-shaped flowers are pollinated by hummingbirds (fritillary butterflies also visit the flowers for nectar but apparently aren't effective pollinators of this plant). Roundleaf sundew has small white flowers on short upright stalks that are pollinated by mosquitoes, gnats, and midges. An insectivorous plant, its small round prostrate leaves are covered by reddish sticky hairs that capture and digest insects. False hellebore, a plant highly toxic to humans (if ingested), has stout leafy stems with dense clusters of yellow-green flowers. Arrowhead derives its name from its large arrowhead-shaped basal leaves; the 3-petalled white flowers on the lower portion of the upright stalk are usually female, the upper ones male.

Three of the showier plants of late summer and fall are kidneyleaf grass of parnassus, nodding ladies' tresses (Spiranthes cernua), and soapwort gentian (Genti-ana saponaria). Kidneyleaf grass of parnassus has kidney-shaped basal leaves and showy white flowers with conspicuous green veins that radiate from the center of the flower, guiding insect pollinators to the nectar. Nodding ladies' tresses is an orchid whose small, white, spirally arranged flowers on an upright stalk usually bloom through the first heavy frost. The bluish purple tubular flowers of soapwort gentian also persist well into fall—look for bumblebees pushing their way into the closed flowers to access nectar.

Winterberry produces dense clusters of bright red berries in autumn that persist on the plant well into winter. When other foods are scarce, birds and small mammals eat the fruits and disperse the seeds. Similarly, the red berries of cranberry and wintergreen (Gaultheria procumbens) ripen in fall but persist on the plant into winter. The large basal leaves of skunk cabbage emerge in spring and die back in fall, but its tiny flowers enclosed in a hood-like brownish purple spathe bloom in winter.

Distribution

Bogs are more common in the northern Appalachians than the southern Appalachians, largely because receding glaciers scoured out basins favorable for bog development in the north but not in the south. The swamp forest-bog complex is scattered throughout the Appalachians from Pennsylvania to Georgia, but the Southern Appalachian bog type is largely restricted to Virginia and North Carolina, mostly at mid- to high elevations. Cataract bogs are rare, known only from South Carolina; other locations are likely but have yet to be documented.

Dynamics

Factors responsible for creating and maintaining mountain bogs are poorly understood. Some mountain bogs are of relatively recent origin, but others are known to be at least 10,000-12,000 years old. Beavers, large grazers, and fires play important roles in bog dynamics.

BEAVERS

By building dams and flooding stream and river valleys, beavers create boggy habitats that are subsequently colonized by peat moss and other typical bog plants. Beavers also help keep boggy habitats open by cutting down trees and shrubs. Over time, abandoned beaver ponds typically undergo succession from being herb-dominated communities to shrubby bogs to complex mosaics of forest, shrubland, and herbaceous cover. By the early 1900 s, overhunting led to the extinction of beavers in our region, which probably reduced the acreage covered by bogs. Beavers have made a comeback due to a successful reintroduction program. Their effect on mountain bogs has been somewhat mixed: new bogs have been created, but flooding has damaged some previously established bogs that supported rare species.

LARGE GRAZERS

Bison, elk, and other large grazers likely played an important role in keeping bogs and other wetland habitats open (much like the role they played in grassy balds). The grasses, sedges, and other herbaceous plants found in bogs would have attracted large grazers. By also foraging on woody plants, large grazers helped prevent bogs from undergoing succession to shrub thickets or forested landscapes. Following their extinction, domestic animals (such as cows) played a similar ecological role in many bogs.

FIRE

The role of fire in maintaining mountain bogs is unclear. Both lightning-induced fires and the burning of bogs by Native Americans likely occurred, but we don't know how frequently bogs burned. The presence of numerous species whose distributions are centered in fire-maintained coastal plain bogs suggests that fire played a role in maintaining some mountain bogs. In the Blue Ridge Escarpment region and other relatively low-elevation sites, fires probably occurred frequently enough to keep bogs open, but fires were probably less frequent and important in maintaining bogs in the cool, moist air at higher elevations.

Biogeography of bogs. About one-third of the more than 600 species of vascular plants found in "boggy" wetlands of the southern Appalachians are widely distributed in eastern North America, including red maple, tag alder, and swamp rose (Rosapalustris). Species distributed primarily in the northeastern United States and adjacent areas in Canada make up another third of the total number of species, including many species at or near the southern limit of their range in Georgia, the Carolinas, and Tennessee. Examples include cranberry, dragon's mouth (Arethusa bulbosa), and cotton grass (Eriophorum virginicum). A third group of species is comprised mostly of coastal plain species that have disjunct populations in mountain bogs, including Carolina sheeplaurel (Kalmia carolina), netted chain fern (Woodwardia areolata), and purple pitcher plant. Very few species are restricted (endemic) to southern Appalachian "boggy" wetlands.

Conservation Aspects

Bogs in the southern Appalachians are inherently rare because flat, wet sites are scarce. Habitat degradation and destruction (e.g., drainage, logging, conversion to agriculture, and clearing for resort and residential development) have substantially reduced the number and extent of mountain wetlands. Most remaining bogs are small (less than 5 acres) and have an altered hydrology that threatens their long-term persistence. In the absence of grazing and hay mowing, shrubs and trees are invading many bogs, which, if left unchecked, could eliminate many of the herbaceous species that characterize bog vegetation. Some mountain bogs have persisted for thousands of years, so this recent change from relatively open, boggy habitat to shrub thicket or forest is cause for concern.

The ecology of mountain bogs is poorly understood. Nevertheless, it's clear that slight changes in the surrounding landscape can have major effects. For example, many bogs formerly surrounded by forest now occur adjacent to agricultural fields, pastures, or Christmas tree farms. Since forested slopes release water more slowly and constantly than unforested slopes, bogs adjacent to cultivated land are more likely to dry out. Similarly, the channeling of an adjacent stream can lower the local water table, causing substantial drying and thereby allowing woody plants to invade when an unaltered water table would have prevented their establishment. Once established, shrubs and trees take up huge amounts of water, further drying up bogs and accelerating their succession to shrub thicket or forest. Other threats include changes in water quality due to increased sediment load from soil erosion and soil chemistry altered by nearby agriculture. For example, excess nutrient input causes a decline in peat moss abundance, which subsequently promotes succession to woody plants. Collectors of commercially valuable species such as rare orchids, insectivorous plants, and bog turtles (a threatened species) also degrade bogs.

SUGGESTED READING

Moorhead, K. K., and I. M. Rossell. 1998. Southern Mountain Fens. In M. G. Messina, and W. H. Conner, eds., Southern Forested Wetlands: Ecology and Management, 379-403. Boca Raton, Fla.: Lewis Publishers. Murdock, N. A. 1994. Rare and Endangered Plants and Animals of Southern Appalachian

Wetlands. Water, Air and Soil Pollution 77:385-405. Pittillo, J. D. 1994. Vegetation of Three High Elevation Southern Appalachian Bogs and Implications of Their Vegetational History. Water, Air and Soil Pollution 77:333-48.

MOUNTAIN BOG: CHARACTERISTIC PLANTS

Trees

OCCASIONAL TO LOCALLY ABUNDANT SPECIES

Acer rubrum Betula alleghaniensis Nyssa sylvatica Picea rubens Pinus rigida Pinus strobus Tsuga canadensis

Shrubs

Red maple Yellow birch Black gum Red spruce Pitch pine Eastern white pine Canada hemlock, Eastern hemlock p. 222 pp. 226-27 pp. 245-46 p. 248 p. 250 p. 251 pp. 264-65

ABUNDANT SPECIES

Alnus serrulata Ilex verticillata Kalmia latifolia Leucothoe fontanesiana Rhododendron maximum 'Rosa palustris Vaccinium corymbosum

OCCASIONAL TO LOCALLY

Aronia melanocarpa Menziesia pilosa Rhododendron viscosum

Salix nigra tSalix sericea fSpiraea tomentosa fToxicodendron vernix Vaccinium macrocarpon Viburnum cassinoides Xanthorhiza simplicissima

Tag alder Winterberry Mountain laurel Mountain doghobble Rosebay Swamp rose Highbush blueberry

ABUNDANT SPECIES Black chokeberry Minniebush Swamp azalea,

Clammy azalea Black willow Silky willow Steeplebush Poison sumac Cranberry Wild raisin Yellowroot pp. 269-70 p. 289 pp. 291-92 p. 292 pp. 302-3

pp. 311-12

Herbs

OCCASIONAL TO LOCALLY ABUNDANT SPECIES

Drosera rotundifolia

Roundleaf sundew

pp. 365-66

Eutrochium fistulosum

Joe Pye weed

p. 373

Gaultheria procumbens

Wintergreen

PP. 376-77

Onoclea sensibilis

Sensitive fern

P. 411

Osmunda cinnamomea

Cinnamon fern

pp. 412-13

Osmunda claytoniana

Interrupted fern

pp. 413-14

Phleum pratense

Timothy grass

pp. 421-22

Platanthera ciliaris

Yellow fringed orchid

p. 424

Sagittaria latifolia

Arrowhead, Duck potato

p. 434

Sphagnum species

Sphagnum

p. 445

Spiranthes cernua

Nodding ladies' tresses

pp. 446-47

Veratrum viride

False hellebore

pp. 463-64

Rare Plants

tCaltha palustris

Marsh marigold

Helonias bullata

Swamp pink

pp. 383-84

Lilium grayi

Gray's lily

pp. 396-97

Parnassia asarifolia

Kidneyleaf grass

pp. 417-18

of parnassus

Platanthera integrilabia

Monkey face orchid

p. 425

tSarracenia jonesii

Mountain sweet

pitcher plant

Sarracenia purpurea

Purple pitcher plant

pp. 435-36

Symplocarpus foetidus

Skunk cabbage

p. 448

f = plant not included in the species profiles (Part IV)

Low-Elevation Dry Communities

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