Ecological dynamics

The Saline Firm Marsh ecological site is a broad, nearly level coastal flat that are subject to tidal activity. This is a dynamic ecosystem which changes constantly and sometimes rapidly as a result of natural environmental conditions and climatic events. An overriding site requirement is accessibility of tidal exchange by salt water. Characteristically, saline marshes occur at or near sea level, usually between mean high tide and low tide.

The Saline Firm Marsh ecological site is typically a wet grassland inhabited by salt-tolerant species. The vegetation consists almost entirely of grasses and grass-like plants. Portions of the site may have dense vegetation, but there are frequently areas where plant density is sparse. The micro-relief on saline sites may restrict plant density. Areas which have a shallow depth of water at high tide frequently have a crust of salt crystals at low tide. This concentration of salt restricts the number of species that can persist on this site (e.g. saltworts and glassworts). Likewise, areas which remain wet at low tide frequently have more dense stands of vegetation adapted to higher moisture regimes (e.g. seashore saltgrass). Smooth cordgrass and black needlerush are the dominant plants on the site. Both species need alternating water regimes (i.e. tidal activity) for optimum production and stand persistence. This site has the least plant species diversity of all the marsh sites due to the high concentrations of salt. Site transitions to other vegetative communities can occur with prolonged fresher influences and adequate seed source.

The marsh serves as a natural filtration system for the adjacent coastal waters. It captures sediments, waste, pollutants, and nutrients deposited from agricultural, urban, and industrial areas above the marsh. As upstream waters move through the marsh ecosystem, the continuous filtering action releases cleaner water into the Gulf of Mexico. Marsh sites function as nitrogen and phosphorous sinks, resulting in the improvement in the quality of water that passes through the site. It can serve as a buffer to modify the effects of storms. Marsh vegetation also stabilizes the shoreline and reduces erosion caused by tides, wave action, storms, and flooding.

The proximity to the Gulf of Mexico makes this site susceptible to degradation by several natural and human induced actions. Hurricanes and tropical storms can cause entire plant communities to be destroyed in a very short period of time. Constant wind action and low topographic relief make shoreline erosion a constant threat. Those areas with a long fetch of open water are especially vulnerable to wave action.

Subsidence is the process of the soil surface sinking to a lower level. It may occur naturally or be influenced by human activities such as pumping water from wells or creation of navigation channels. As subsidence progresses, vegetation is submerged and may eventually weaken and die. Deepening of existing water bodies and/or dredging new access to canals can cause changes in water depth and increase salinity levels, which may affect marsh vegetation. The loss of anchoring vegetation and the subsequent subaqueous erosion of surface sediment and organic detritus as the result of current or wave action, may lead to permanent loss of vegetation and eventually result in regression to an open water state.
Grazing by cattle, furbearers, and geese can adversely affect vegetation on this site if not properly managed. Cattle grazing can be managed with proper stocking rates and manipulation of the time, frequency, intensity, and duration of grazing. Wildlife grazing pressure presents a management challenge because it is not possible to consistently control the numbers and movements of most wildlife species.

Fire is primary tool for management of saline marsh ecosystems. In order for fire to play a beneficial role in marsh management, burning must be done in a prescribed manner. Burning should be done when there is at least six (6) inches of water covering the marsh. This cushion of water protects the vegetative reproduction tissues of marsh plants. Fire is an excellent tool for removal of old growth to encourage vigorous high quality growth. Fire is effectively used to enhance wildlife habitat and aid in cattle management. A fresh burn will attract cattle, deer, furbearers, and geese to the lush new growth. Burns should be sufficient in size to prevent destructive grazing (eatouts) by furbearers and geese. Timing of Prescribed fire to reduce impacts by tropical storms or Hurricanes must be part of the planning process, untimely burns and subsequent tidal or storm action can degrade the site.