Fire Ecology and Management of Isolated Herbaceous Wetlands
Isolated herbaceous wetlands include both seepage wetlands with outflows and depression wetlands typically lacking outflows. These communities can all be found embedded in upland fire type communities such as pine savanna, pine flatwoods, sandhill or other upland types throughout the Southeastern Coastal Plain. Rainfall, runoff and shallow groundwater provide nutrient poor water to these wetlands. Underlying soils, topographic positions, rainfall, and evapotranspiration rates influences hydrologic patterns. Seepage wetlands tend to be permanently to semi-permanently saturated, whereas depression wetlands are often seasonally flooded with unpredictable, widely fluctuating water levels. Soils are typically acid sands overlying impermeable layers. Organic accumulations are variable. Depression wetlands can have organic accumulations towards their centers.
Vegetation of these wetlands varies geographically. Many seepage wetlands are particularly diverse and known for their carnivorous flora. Shrubs may also be present and their dominance is strongly influenced by fire regime. Vegetation in depression communities often shows strong zonation relating to water level fluctuations. Herbaceous plants dominate with sparse to dense coverage. Shrubs will ring wetlands in some instances or will occur as scattered individuals. Seed banks within herbaceous depressional wetlands have higher densities and richness than that reported for most other freshwater wetlands.
Animal inhabitants of herbaceous isolated wetlands include invertebrates such as crustaceans and aquatic insects. The ephemeral nature of depression wetlands often prohibits the development of extensive fish fauna. The absence of fish provides ideal breeding locations for many amphibians including frogs and various salamanders. Reptiles, particularly turtles also use isolated wetlands. Wood storks, sandhill cranes, and various ducks are examples of wetland birds that utilize isolated herbaceous wetlands. No mammals are wholly dependent on isolated herbaceous wetlands, but opportunistic predators such as opossum, and raccoon will utilize these habitats.
The fire regime of isolated herbaceous wetlands is highly influenced by fire regime of uplands in which they are embedded. Hydrologic patterns also influence fire regimes: wetlands flooded for shorter periods are more likely to burn than those with long hydroperiods. Because depression ponds are more likely to dry in summer months, they are also more likely to carry fire in summer months.
Overall, vegetation of isolated wetlands tends to recover rapidly from fire. Many species resprout, while others re-colonize from seed. Fire may be particularly important for maintaining diversity in wetlands by exposing soil that allows germination of infrequently occurring annual plants whose seeds exist in the seed bank. Fire followed by flooding may change species response to fire. It is generally thought that a combination of fire and flooding prevent the establishment woody plants in herbaceous wetlands. Though little is known of animal response to fire in isolated herbaceous wetlands, it is probably the lack of fire and resulting changes in vegetation structure that most affect animal use of wetlands.
Isolated wetlands tend to be burned by prescribed fire because they are inclusions within larger systems that are being actively managed with fire. Fire, however, plays a role in maintenance of these wetlands. Variable moisture regimes, variable accumulations of organic matter, altered hydrology, and possible presence of listed species are all topics of concern for land managers practicing prescribed burns in lands including these wetlands.
This section is currently in review and will be available Spring 2005.
Encyclopedia ID: p155
