Distribution and Composition of Shrub Bogs

Though some types of shrub bogs are referred to as pocosins, the shrub bogs discussed here differ from pocosins in several ways. Pocosins tend to be larger in extent, occur in different topographic settings, occur on extensive peatlands, are poorer in nutrients, can have a different hydrology, and experience less frequent fire than the small shrub bogs discussed here.

Shrub bogs are distributed throughout the Gulf and Atlantic Coastal Plain. They range as far west as eastern Texas (Brooks et al. 1993), and south into northern Florida (FNAI 1990) and as far north as southeast Virginia (Robertson et al. 1998).

Small shrub bogs are often associated with two topographical settings: 1- headwaters of stream systems within sandy uplands and 2- within small depressions such as lime sinks, Carolina bays, small swales or other depressions (Weakley and Schafale 1991). These topographical settings are often embedded within uplands that experience frequent fires such as sandhills, flatwoods or savannahs (FNAI 1990, Weakley and Schafale 1991). Depression shrub bogs are surrounded by these communities, whereas headwaters shrub bogs grade downslope into bay forests or streamside swamps. The upslope ecotone between shrub bogs and upland communities is often herb dominated. These upslope areas of headwater shrub bogs are often referred to as seepage slopes, pitcher plant bogs or herb bogs.

Rainfall patterns in the southeast are seasonal. Throughout the Coastal Plain the wettest period is in the middle of the growing season. Along the Gulf Coastal Plain there are two wet seasons, one in winter associated with passing cold fronts, and another in summer due to convective storms (Chen and Gerber 1990). Farther north and west in the costal plain, rainfall tends to be more evenly distributed throughout the year (Kirkman et al. 2000).

The hydrology of shrub bogs is characterized by a long hydroperiod, and nutrient poor waters, but water inputs and outflows differ among shrub bogs of different topographical settings. The hydroperiod of basin shrub bogs (6 –9 months) is typically somewhat shorter than headwater shrub bogs, but both are at least seasonally flooded with streamhead pocosins being semi-permanently flooded (Weakley and Schafale 1991, Sutter and Kral 1994). Wetland drying and low water events depend on soils, connections to shallow groundwater, local climate and periods of high transpiration. Water inputs in basin shrub bogs are dominated by rainfall and runoff from surrounding uplands, whereas streamhead shrub bogs receive water from rainfall, runoff and from shallow groundwater in the form of seepage. Opposite processes maintain high water levels in the two types of shrub bogs. In streamhead shrub bogs, water seeping downward from uplands maintains saturated soils, while in depression shrub bogs, capillary action draws water upwards (FNAI 1990). Basin shrub bogs typically have no outflows, where streamhead shrub bogs drain into streams (Weakley and Schafale 1991, Richardson and Gibbons 1993).

Soils are generally wet and acidic. Streamhead shrub bogs have sandy soils underlain with clay or can have organic surface horizons underlain by or interbedded with sand or clay (Schafale and Weakley 1990, Wolfe et al. 1988). Basin pocosins have soils that can range from peaty sands to thicker organic accumulations. Underlying hardpans contribute to perched water tables (Richardson and Gibbons 1993, Schafale and Weakley 1990).

Vegetation:

A dense shrub layer dominates vegetation of basin and streamhead shrub bogs. Dominant shrub species include fetterbush (Lyonia lucida), titi (Cyrilla racemiflora), black titi (Cliftonia monophylla), gallberry (Ilex glabra), sweet pepperbush (Clethra alnifolia), and blueberry (Vaccinium corymbosum). Other less dominant species vary geographically and with topographic setting, but can include hurrah-bush (Leucothoe racemosa), giant gallberry (Ilex coriacea), myrtle-leaved holly (Ilex myrtifolia), Carolina sheeplaurel (Kalmia caroliniana), zenobia (Zenobia pulverulenta) and wax myrtle (Myrica cerifera) among others. Shrub diversity is higher in basin and streamhead shrub bogs than in pocosins. The higher diversity is likely due to the greater nutrient availability because of inputs from surrounding communities and because of greater root contact with mineral soils (Schafale and Weakley 1990, Wolfe et al. 1988, FNAI 1990).

A sparse to relatively dense canopy may be present. Tree canopy species can include pond pine (Pinus serotina), red maple (Acer rubrum), loblolly bay (Gordonia lasianthus), swamp tupelo (Nyssa sylvatica var. biflora), sweetbay (Magnolia virginiana), red bay (Persea borbonia) and other species shared with bay forests. (Weakley and Schafale 1991, FNAI 1990, Sharitz and Gresham 1998). Tulip poplar (Liriodendron tulipifera) is an important component in streamhead shrub bogs (Schafale and Weakley 1990).

Herbs are sparse but can include ferns (Osmunda cinnamomea, Woodwardia virginica, Woodwardia areolata), and sedges (Carex spp.) (Weakley and Schafale 1991). Streamhead shrub bogs are reported to have a less dense shrub layer than other types of shrub bogs and a more well-developed herb layer (Robertson et al. 1998) at least when frequently burned. Sphagnum moss is common in shrub bogs (FNAI 1990).

Where these communities grade into surrounding uplands there is often an herbaceous ecotone, however, in some cases the grassy ecotone is not present. Where the herbaceous ecotone exists, it is often quite species rich, and it is often classified as a seepage slope or herbaceous bog. Several listed species are known from these ecotones that utilize the shrub bog edge rather than being more characteristic of herbaceous bogs.

Animals

Little information is available on the fauna that occupies shrub bogs. Shrub bogs, with their dense, often evergreen vegetation, provide good cover and refuge for wildlife. The prevalence of plant species that produce “soft mast” such as holly fruits or greenbrier fruits are likewise thought to provide food sources for certain animals (Hart and Newman 1995). Colonial wading birds are known to utilize shrub bog canopy trees for roosting and nesting (Hart and Newman 1995).

Amphibians and reptiles are perhaps the best studied group that is known to use shrub bogs. In a recent study that was admittedly not comprehensive, thirteen amphibian and 19 reptile species were captured within shrub bogs. Although most species were more common in the herbaceous portion of the bogs than in the shrubby portion, several species of salamanders were only captured in shrub portions of bogs (Enge 2002). The pine barrens treefrog (Rana andersonii), a formerly federally listed species, utilizes both herb and shrub bogs. Shrub bogs are utilized by adults for foraging and larvae develop in pools in herb bogs (Means 1992). The Florida bog frog (Rana okaloosae) is another species with a very limited range in the panhandle of Florida that is known from shrub bogs (Moler 1992).