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Sensitive and Rare Communities

Extent of Threatened Communities

Several authors have described and identified the threatened and sensitive communities in the South (Boyce and Martin 1993; Grossman and others 1994; Noss and others 1995; White and others 1998). The South supports a diversity of communities; a high proportion of them are considered imperiled to some degree (Walker 2001).

Noss and others (1995) listed numerous threatened and endangered communities that have experienced losses in the South (Table 9). The amount of areal loss relative to the estimated presettlement area was used as an indicator of vulnerability. The 14 communities listed as critically endangered have estimated losses of over 98 percent of their area since European settlement. These include old-growth deciduous forest, spruce-fir forests, longleaf pine savannas, bottomland forest, and several types of prairies. Twenty-five endangered communities have experienced losses between 85-98 percent. These communities include coastal plain hardwoods, pocosins, mountain bogs, ultramafic glades, and Louisiana prairies.

Having experienced over 70 percent losses compared to estimated presettlement area, 11 communities are regarded as threatened. These include tropical hardwood hammocks, sandhill woodlands, and saline prairies.

In addition to the list in Table 9, Noss and others (1995) reported 24 communities that have lost at least 50 percent of their area. These include pocosins (Coastal Plain), sand pine (Florida), baldcypress-tupelo (Mississippi, Tennessee), flatwoods-swale habitats (Florida), herbaceous marsh (Florida), calcareous forest (Louisiana), scrub-shrub swamp (Louisiana), cove hardwood forest (Tennessee), and others.

Boyce and Martin (1993) also recognized several sensitive communities that are under pressure from a variety of factors. Such factors included urban growth, land-use conversion, water diversion, exotic species, and pesticide runoff. Everglades, mangroves, bottomland hardwood forests, pocosins, mountain bogs, and Carolina bays were classified as threatened. They classified longleaf pine, spruce-fir and other high-elevation forests, heath balds, maritime communities, rock outcrops, glades, grasslands, and sand-pine scrub as vulnerable.

Grossman and others (1994) listed 57 rare communities in the South (Table 10). Community types were ranked on a global scale based on the number of occurrences, areal extent, condition, threats, and fragility. These 57 communities had global ranks of G1 (found in 1-5 occurrences globally) or G2 (found in 6-10 occurrences globally). Twenty-one types occur in the Coastal Plain, 5 in South Florida, 17 in the Southern Appalachians, and 11 in the Continental Interior.

Communities can decline in areal extent or have their structures impoverished or compromised. Communities covering smaller areas tend to maintain smaller populations that are more vulnerable to extinction than larger populations (Soulé 1987). Communities also can lose vigor because of change in their structure, function, or composition. For example, intense livestock grazing entails replacement of native perennial grasses with exotic annuals. The factors contributing to community imperilment that are listed in Table 10 are further discussed in the following section.

Profiles of Selected Rare Communities

This section reviews some selected communities of concern. Each general community type can include multiple associations. Each account includes distribution, composition, threats, and potential management. Where available, steps toward restoration are presented. The accounts were developed from White and others (1998), Boyce and Martin (1993), Noss and others (1995), and Walker (2001). The discussion of communities follows White and others (1998).

Old-Growth Forests. Although forests predominate in the South, less than 585,790 acres of old-growth forest exist (White and others 1998). The remaining old-growth forests tend to be on steeper, rockier, or mesic sites difficult to farm or harvest. Old-growth forest composition varies with forest type, but characteristics generally associated with old-growth forests include large, old trees; accumulations of woody debris; and multi-layered canopies.

Many vertebrate species occur in patches of old-growth forest. These include the Jefferson salamander, the Peaks of Otter salamander, the oak toad, and the scarlet kingsnake (Wilson 1995). Public lands such as the Great Smoky Mountain National Park and several national forests protect some of the largest tracts in the South. With the exception of these areas, old-growth remnants are often smaller than 250 acres.

Threats to old-growth remnants include invasions by nonindigenous species, interruption of natural disturbance regimes, outbreaks of forest pests, and timber harvest (Walker 2001).

Management options vary by forest type, but controlling nonindigenous species and herbivores, and choosing benign methods to accomplish these objectives are factors to consider. Management actions that mimic natural disturbances are particularly important because natural disturbance regimes are unlikely to be intact. Management emphasis may also include the provision of forested buffers around existing old-growth remnants.

Spruce-Fir Forests. The spruce-fir community is confined to the highest peaks of Virginia, Tennessee, and North Carolina. Red spruce communities occur at an approximate elevation of 4,500 feet. In the northern limit of its range, Fraser fir is replaced with balsam fir. This community is characterized by relatively high moisture levels, short growing seasons, acidic soils, and extreme weather conditions. The flora is distinctive. The community reproduces in small-scale patches resulting from wind disturbance.

The presettlement extent of the Southern Appalachian spruce-fir community has been estimated as 30,000-35,000 acres (White and others 1998). These remote forests remained relatively undisturbed until the widespread harvests of the late 1800's (White and others 1998). In 1934, the majority of the remaining spruce-fir forest went into public protection with the establishment of the Great Smoky Mountains National Park.

Spruce-fir communities are threatened by infestations of balsam woolly adelgids. The stresses induced by insect attack are exacerbated by additional stresses of acid precipitation, which influence soil and stream chemistry. Air pollution and the deposition of heavy metals, such as lead, copper, zinc, nickel, and manganese, also contribute to the decline of this community (refer to Chapter HLTH-3). They inhibit regeneration and contaminate the understory. Airborne pollution is carried with prevailing winds originating from industrial areas of southern Ohio and Indiana.

In addition, recreation activities compact soil and damage young trees. As the southern population centers expand, continued recreational pressure may further adversely affect the spruce-fir community.

Spruce-fir communities support several terrestrial species that are uncommon elsewhere. Examples include the endangered subspecies of northern flying squirrel, Weller's salamander, the endangered spruce-fir moss spider, mountain ash, and the threatened rock gnome lichen. The northern saw-whet owl, black-capped chickadee, and red crossbill also inhabit the community.

Restoration centers on enhancing the stocking of red spruce trees and increasing stand structural complexity. Appropriate silvicultural treatments include the release of spruce saplings from the understory and the removal of competing stems. In some areas, restoration may involve conversion of open areas to forests by planting seedlings.

Wetlands, Bog Complexes, Pocosins. In the last two centuries, the nation has lost approximately 30 percent of its wetlands. Substantial losses have occurred along the Southern Coastal Plain and along the lower reaches of the Mississippi River. In addition, Florida has lost 46 percent (9 million acres) of its wetlands (Stein and others 2000). Wetland loss is of special concern, because these habitats provide critical waterfowl and fish habitat.

Small wetlands occur in depressions embedded in forested areas. Soils are saturated for extended periods from rainfall and groundwater seepage. Among the most vulnerable areas are small (<2 acres), isolated bogs that retain characteristic species. Bogs require distinct hydrological conditions to function ecologically. Intermittent fires and beaver activities may contribute to the origin and maintenance of this complex.

The exact number of remaining bogs is difficult to determine but is most certainly fewer than 150 in the entire South. Over half of the existing bogs occur on private land, and are threatened by development, grazing, off-road-vehicle use, agricultural practices, and hydrological alteration.

Pocosins are freshwater wetlands dominated by a dense cover of broad-leaved evergreen shrubs or low-growing trees. They have highly organic soils that developed in areas of poor drainage. This community occurs in upland interstream areas. Peat layers are thick and vegetation is shrubby.

The bog complex provides habitat for a diversity of herpetofauna. Wilson (1995) lists 37 species of reptiles and amphibians associated with Carolina bays, pocosins, and bogs in the South; 41 are associated with swamp habitat. These species include the bullfrog, green frog, eastern tiger salamander, four-toed salamander, mountain chorus frog, and snapping turtle. The bog turtle, threatened in the northern portion of its range, also inhabits these areas. This turtle is collected illegally, as are rare orchids and carnivorous plants. Opportunities for species to recolonize are minimal, and the community is permanently diminished.

Avian species occurring in these communities include cedar waxwing, Nashville warbler, northern waterthrush, purple finch, white-eyed vireo, and wood duck. Characteristic mammals include the long-tailed shrew, marsh rice rat, mink, muskrat, river otter, southern bog lemming, southern short-tailed shrew, and the star-nosed mole. Butterflies include the Atlantis fritillary and silver-bordered fritillary.

No vertebrates are endemic to pocosins, but the community provides habitat and refuge from adjacent landscape development. In North Carolina, 41 species of mammals inhabit pocosin and Carolina bay sites (White and others 1998).

Conservation activities include protection from heavy equipment, off-road vehicles, and foot traffic; controlling changes in site hydrology by providing buffers between adjacent sites, filling ditches and blocking drains; and restricting livestock grazing. The retention of woody debris provides valuable microhabitat for many species. Adjacent land management activities that alter the surrounding watershed degrade these sensitive communities. Restoration includes maintenance of site hydrology and woody plant control. Periodic prescribed burns adjusted to maintain vegetative conditions help to maintain the community. Species reintroduction into selected sites also may be required.

Bottomland and Floodplain Forests. The forested wetlands of the Coastal Plain, Piedmont, and Continental Interior provinces include bottomland hardwood forests and deepwater alluvial swamps. Bottomland hardwoods are located along waterways and in low-lying areas such as the Mississippi Delta region. Common tree species include ash, sycamore, water tupelo, cypress, willow, cottonwood, elm, oaks, river birch, silver maple, sweetgum, black walnut, and pine. Vegetative composition and structure vary with flooding duration. Trees are vulnerable to prolonged changes in hydrology and are characterized by rapid growth. Bottomland hardwoods are found almost exclusively on alluvial soils that are associated with old riverbeds, existing streams, and impoundments and their terraces. Soils are saturated year-round or nearly so; the understory is sparse with vines and shrubby vegetation.

Beneficial characteristics of this community for wildlife include hard mast production, cavity tree provision, and production of abundant invertebrate biomass. In agricultural landscapes, bottomland forests serve as refuges for many species. Species associated with this community include wood stork, prothonotory warbler, marbled salamander, and the swamp rabbit. The loss of bottomland hardwood forests to agricultural conversion contributed to the decline of the Carolina parakeet and the ivory-billed woodpecker (Dickson 2001).

Many bottomland sites are productive and have been in agricultural production for long periods. Several cypress-oak reforestation projects in the Mississippi Alluvial Valley have been successful in areas where frequent flooding precludes agricultural development. Restoration of this community occurs primarily on public land.

Glades, Barrens, and Prairies. Scattered throughout the South are naturally treeless areas referred to as prairies, glades, and barrens. Historical accounts suggest that these open communities were once widespread (Delcourt and others 1993), but estimates of original extent are uncertain. These grass-dominated communities occurred in the Piedmont, Interior Plateau, Ridge and Valley, and Coastal Plain provinces.

Lightning fires, Native American burning, grazing by elk and bison, and soil conditions historically maintained these areas. Today, these communities occupy only a fraction of their original extent due to agricultural conversion, recreation use, exotic species invasions, fire exclusion, and the loss of large herbivores.

Forbs and grasses occurring on rocky or shallow soil dominate glades; composition varies with geology, soil type, and soil depth (Walker 2001). The limestone glades of the Ozarks, dominated by perennial grasses, have a more open nature than glades of the Interior Low Plateau. Eastern redcedar woodlands are commonly associated with glades of various types. Threats to glade communities include construction, quarrying, agriculture (pasture), fire suppression, and nonindigenous species invasion.

The barren and prairie communities contain the majority of the region's native grasslands. In the South, they include the Black, Jackson, and Grand Prairies. In these communities, grasses are dominant, and shrubs and trees are generally absent. The sites are highly productive because they retain nutrients. As a result, they support a vast array of animal and plant life. Species composition varies with site moisture. Characteristic species include little bluestem, Indian grass, and big bluestem. Composition varies depending upon specific soil and geologic types.

The size and isolation of these open areas preclude support of endemic vertebrates. Many rare species of birds, reptiles, and arthropods use these communities. Vertebrate species that have been extirpated from these communities include the greater prairie chicken, bison, and elk.

Restoration centers on the control of woody species from adjacent forest habitats and the use of prescribed burning to maintain the diversity of the grassland communities. The retention of characteristic species relies upon site-specific management.

Longleaf Pine and Southern Pinelands. Longleaf pine historically dominated Coastal Plain sites from southern Virginia to eastern Texas. It also occurred on sites in the Piedmont, Southern Ridge and Valley, and Southern Blue Ridge provinces (Figure 22). This community once covered over 40 percent of the entire region, but it has declined by more than 98 percent (Noss and others 1995).

The community came under pressure during the mid-seventeenth century. Demand began for naval stores and then turned to timber needs. By the 1960s, extensive areas were harvested and converted to commercial plantations of loblolly and slash pine. Fire suppression and the introduction of livestock further restricted the longleaf community to a few isolated locations comprising about 5 million acres. At present, the majority occurs on private land. Much of what remains is largely degraded due to lack of proper management.

Community composition varies with soil moisture and geography. Wiregrass and bluestem dominate the herbaceous layer. This herb layer is diverse and includes grasses, wildflowers, and carnivorous plants. In mature communities, the trees are thinly distributed, and flat-topped, and have limbless lower trunks.

The community harbors several vertebrate species. The fox squirrel is a long-lived-species with low reproductive rates. It depends on longleaf pine for late-summer forage. The decline in longleaf communities has limited its range and reduced population levels. The red-cockaded woodpecker occurs in the open pinewoods, using fairly mature trees with minimal understory (Hamel 1992). Trees also must have proper heartwood conditions for nest cavities. This species has also declined, but active management has stabilized several populations. The sensitive Bachman's sparrow breeds in dense, grassy places where scattered pine trees and saplings are present.

Dodd (1995) reported that 74 amphibians and 96 reptiles occur in the range of the longleaf pine community. These include the flatwoods salamander, Red Hills salamander, striped newt, Carolina gopher frog, eastern indigo snake, gopher tortoise, eastern diamondback rattlesnake, Florida pine snake, and Florida scrub lizard.

Although the influence of longleaf reduction on the herpetofaunal community has not been assessed directly, several species may have been affected. The gopher tortoise, a keystone species in longleaf pine savanna, has declined by 80 percent over the last century (White and others 1998). Amphibians breeding in temporary ponds have been particularly affected by habitat alteration. The flatwoods salamander has disappeared from its eastern range; gopher frogs are nearly extirpated in North Carolina, Alabama, and Mississippi; and dusky salamanders appear to have declined in coastal South Carolina and peninsular Florida.

Conversion of longleaf pine forests to agriculture, slash or loblolly pine plantations, and urban development threatens the continued existence of several herpetofauna species in Georgia and Florida (Ware and others 1993). Hardwood encroachment stemming from fire suppression also has contributed to the loss of longleaf pine communities. Historically, frequent low-intensity fires reduced litter accumulation, controlled competing woody species, and improved herbaceous vigor (Walker 2001). Recent awareness of the importance of this sensitive community has encouraged restoration efforts.

Atlantic White Cedar Swamps. Atlantic white cedar once was distributed from southern Virginia to interior Georgia and from the Florida Panhandle along the Gulf of Mexico to Mississippi. Drainage, development, and harvest without regeneration have reduced Atlantic white cedar to 10 percent of its original extent.

Much of the original community was destroyed by European settlers who cleared land for agriculture. Today, white-cedar swamps are restricted to inaccessible freshwater wetlands in small, isolated stands. Road construction and the damming of waterways continue to diminish this habitat, as does suburban encroachment, industrial runoff, and pollution.

Atlantic white-cedar swamps are unique communities adapted to variable hydrological regimes, fire, and peat soils. This community type often represents some of the only forest in regions of intense agricultural and urban development. Atlantic white-cedar areas provide habitat for many species, including black bear, deer, rabbits, and other fauna. The diversity of bird species is relatively high in Atlantic white-cedar swamps, compared to adjacent areas. The Hessel's hairstreak is a butterfly that feeds exclusively on Atlantic white cedar.

During restoration, these stands require frequent, light fires in the dry season. Fire removes competitive vegetation and clears the seedbed for regeneration.