Shrub bogs are distributed throughout the Gulf and Atlantic Coastal Plain. They occur in headwaters of stream systems within sandy uplands and within small depressions. These systems typically have long hydroperiods and may be fed by rainfall, runoff and seepage. Soils are generally wet and acidic and can be sandy or have organic accumulations. Vegetation is dominated by a dense shrub layer and a sparse to relatively dense canopy may be present. Herbs are generally sparse, but where these communities grade into surrounding, fire maintained uplands there is often an herbaceous ecotone. Amphibians and reptiles are known to use shrub bogs, otherwise, relatively little is known about animal use of shrub bogs.

The natural fire regime of shrub bogs was influenced by the fire regime of the surrounding communities. There is agreement that the edges of shrub bogs were burned relatively frequently, however, there is little agreement on the natural fire return interval for shrub bogs. This may be due to the variability of vegetation and situation in which shrub bogs occur. When entire shrub bogs burn, fires are intense. Many shrub bog plants are adapted to fire and can resprout following fires.

Alterations of fire regimes of communities that surround shrub bogs, namely decreases in frequency and changes from lightning to dormant season have lead to an increase in shrub cover and density. Shrubs recover from fires and fires have been shown to cause very little mortality in shrubs killing only the smallest individuals. Increases in shrub cover and densities affect herbaceous plant communities, and potentially hydrology. The maintenance of herbaceous portions of bogs, and early successional shrub bogs is important for the perpetuation of rare amphibian habitat.

Shrub bogs have not typically been the primary target of prescribed fire programs and were even routinely ?protected? from fires by the construction of firebreaks. The practice of protecting shrub bogs from fire is now less prevalent than historically partly in recognition that shrub bog ecotones are important habitats for rare plant and animals. The frequency with which entire bogs are burned as opposed to edges depends on management goals for the bog community.

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).

Shrub bogs are embedded within upland communities that historically burned frequently. Frequent fires that swept through surrounding uplands are thought to have affected at least the outer portions of shrub bogs regularly (Weakley and Schafale 1991, Robertson et al. 1998). A large range of values has been reported in the literature for fire return intervals for shrub bogs. Basin shrub bogs may have burned as often as every 3 to 8 years (FNAI 1990) or every 15 to 30 years (Sutter and Kral 1994). For titi swamps values range from 5-10 years and 20 – 50 years (citations in Wolfe 1988). Variable fire frequencies are also reported for streamhead shrub bogs ranging from 20 to 50 years (FNAI 1990) to 1 to 5 years with fire frequencies decreasing toward the center with an increasing moisture gradient (Robertson et al. 1998). Vegetation stature is likely related to time since last fire (Robertson et al. 1998). In the absence of fires, bogs are thought to become bay forests.

Fires are thought to have periodically swept through shrub bogs during prolonged summer droughts when water tables dropped. Under conditions when entire shrub bogs ignite, fires are intense. Most above ground fuel is consumed and peat is sometimes consumed (Wolfe et al. 1988). Fuel loads are high. Depending on burn history, fuel loads in small shrub bogs are likely similar to those found in pocosins (6 – 12 or more tons/acre) (Wade and Ward 1973).

(See Shrubs of Pocosins and Shrub Bogs: Adaptations to Fire)

Human Alteration of Fire Regimes

Like other systems in the southeast the natural fire regime of shrub bogs has been altered. Like most wetlands in the southeast, the fire frequency of shrub bogs has decreased since presettlement times. Shrub bogs have not typically been the primary focus of historical prescribed fire programs so when they do burn it is a consequence of the surrounding communities burning and fire sweeping downhill into shrub bogs. Thus, any changes in the frequency and season of surrounding communities would be reflected in the fire regime of shrub bogs. Further, many shrub bogs have purposely been “protected” from fire by the construction of firebreaks.

As a consequence of decreased fire frequency, shrub bogs vegetation may be of a larger stature than under the natural fire regime or may have succeeded toward bay forest. Decreases in fire frequency and shifts from growing season to dormant season have lead to an expansion of shrub bogs into areas formerly dominated by herbs (Bridges and Orzell 1989). This process has negatively affected numerous rare herb species including carnivorous plants (Harper et al. 1998).

Vegetation

Similar to patterns in other habitats, an anthropogenic change in fire regime (i.e., decreases in frequency and shifts from growing season burns to dormant season burns) has resulted in greater densities, and coverage of woody plants in streamhead shrub bogs and upslope communities (Drewa et al. 2002a, 2002b). Observational data suggests that lack of fire allows shrubs to expand upslope into herb dominated, species rich ecotones, whereas frequent fires confine shrubs to the lower parts of slopes. (Schafale and Weakley 1990). In experimental work, fires have been found to cause very little mortality of shrubs in streamhead shrub bogs. Only the very smallest individuals died from fires (Olsen and Platt 1995). Thus, to prevent colonization of new areas such as herbaceous ecotones, fires must occur at a frequency that prevents shrub recruits from reaching a non-fire-susceptible stage. In addition, dormant season burns have been found to increase the density of shrubs, and growing season burns did not change shrub densities in streamhead shrub bogs (Drewa et al. 2002a).

More evidence suggests that fire regime controls shrub distributions. In a study to determine if environmental gradients control plant distributions, shrubs grew over a wider range of environmental variables such as moisture and soil properties than did herb species (Drewa et al. 2002b). The sites studied had been winter burned and had experienced some fire suppression, i.e., had not experienced the historical fire regime. This body of information suggests that, shrub distributions and densities are likely controlled by fire regime (Drewa et al. 2002a, 2002b). In addition, once the fire regime is altered, and vegetation patterns become altered, reintroduction of the natural fire regime may be insufficient to restore the distribution and density of shrubs.

Similar to upland systems, the abundance of herbaceous species is likely positively related to fire frequency (Martin 1992 cited in Robertson et al. 1998). Fire is particularly important for the perpetuation of many rare plant species that utilize shrub bog ecotones (Chafin 2000, Robertson et al.1998). Fires that burn holes in peat within basin shrub bogs may be important for the perpetuation of the listed white wicky and rough-leaved loosetrife.

As a result of frequent fires in surrounding uplands, shrub bogs may receive nutrient pulses in runoff water following fires. These nutrient inputs may be partially responsible for the higher diversity of shrubs within shrub bogs compared to pocosins, which are extremely nutrient poor and have fewer species of shrubs (Weakley and Schafale 1991).

A result of an altered fire regime, shrubs in many streamhead shrub bogs have expanded upslope, and have purportedly caused a change in hydrology. Transpiration by evergreen shrubs is higher than that of herbs and forbs, thus water is intercepted upslope by evergreen shrubs thus decreasing sheet flow (Wolfe et al. 1988).

Animals

Fire is important for the maintenance of habitat for some amphibian species that utilize shrub bogs. Frequent fires maintain herbaceous portions of bogs utilized for breeding and development of pine barrens treefrogs (Means 1992). The Florida bog frog is only found in early successional habitats suggesting that fire is instrumental in maintenance of habitat (Moler 1992).

Shrub bogs have not typically been the primary target of prescribed fire programs and were even routinely “protected” from fires by the construction of firebreaks. This practice of protecting shrub bogs from fire stems from the misconception that forested wetlands should not burn and from practical concerns with fire control and smoke management. Recently, land stewards and ecologists have recognized that fire in shrub bogs is ecologically important and that past practices of fire suppression have had detrimental effects on plant species and on the maintenance of natural communities. Of particular importance is the ecotone of streamhead shrub bogs where concentrations of rare plants are known to occur and where firebreaks are often constructed.

In implementing a prescribed fire program with the goals of managing shrub bogs several considerations emerge:

1. It is important to let fires burn downslope from upland communities into shrub bogs in order to

• Discourage shrub encroachment into herbaceous plant communities thus maintaining rare plant habitat in ecotones.
• Maintain amphibian habitat.
• Burn holes in peat within basin shrub bogs to maintain diversity and habitat for rare plants.
• Mimic natural processes and maintain early successional plant communities.

2. Land stewards should monitor fire behavior in shrub bogs to ensure that goals are being met. Due to operational concerns, prescribed fires are often set under moderate environmental conditions when fires can be controlled. Under these conditions, fires may be less likely to sweep through wetlands such as shrub bogs. Thus, setting fires under more extreme conditions may be necessary for fires to sufficiently burn shrub bogs or for fires to burn holes in peat.

3. Using prescribed fires under conditions when shrub bogs will burn creates operational concerns such as:

• Fire control due to more extreme fire behavior in communities with high fuel loads.
• Igniting unplanned ground fires that produce excessive smoke when burning in shrub bogs with organic soils.

Depending on management goals, the frequency with which prescribed fire is applied to any community may vary. It has been recommended that streamhead shrub bogs be burned every 3-5 years and that the natural moisture gradient will limit fire spread downslope (Robertson et al. 1998). Basin shrub bogs can be managed to have vegetation structure similar to high or low pocosin. Longer fire return intervals would be employed to manage for a structure similar to high pocosin (5-8 year intervals) and shorter intervals for low pocosin (Robertson et al. 1998). The presence or absence of rare plants or animals may influence desired fire frequencies or season (Robertson et al. 1998). Life history information on the particular taxa should be referenced where available when planning a burn program.