Fire Effects in Shrub Bogs
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).
Encyclopedia ID: p241
