Environmental factors

There are four key environmental elements that help to define different types of swamps.   Each of these environmental elements affects the plant and animal community of a swamp. All must be considered when defining what type of swamp is being studied.

Hydroperiod

 The first element is called the hydroperiod, or length of time that the land is flooded.  Swamps are defined as fresh water, woody communities with water throughout most or all of the growing season.  As transitional habitats between upland areas and aquatic systems, there is much variation among presence of water. Some stay wet most of the year while others have more frequent dry periods.   A swamp’s source of water affects its nutrient supply, hydroperiod, and flow rate.  Swamps, which are fed entirely by rainfall, fluctuate with wet and dry seasons and have relatively short hydroperiods. A cypress dome is a good example of this type of swamp.  Swamps that are flooded most of the year, such as those with groundwater supply have a long hydroperiod. Swamps with long hydroperiods generally have fewer plant species and less vegetation than short hydroperiod swamps.

Swamps fed mainly by rainwater have short hydroperiods and dry down during dry weather.

Water slows the decay of fallen plant material and thus most swamps have a dark organic soil layer.

Type of accumulated organic matter and soils

The type of accumulated organic matter is the second environmental element to consider. A cypress swamp will have different companion plants than a hardwood swamp. Each type of swamp represents a community of plants that grow well together and provide habitat for certain wildlife. As the plant community’s change so do the insects and animals that will live there. Swamp soils are generally a poorly drained mixture of sand, organic matter, and clay that forms layers and slows down the seepage of water. Rainwater may collect and be held in place by pockets of clay in the substrate. The water will slowly leach down to the water table over a period of weeks or months.

Water Quality

The third key element in defining swamps is water quality. The quality of water may be affected by the source of the water, the rate of flow, nutrient and pH levels, and a number of other factors. Swamp water is more acidic in some types of swamps than in others depending on the vegetation and the soils and geology that the water comes in contact with. For example, swamp water from sandy soils in pine flatwoods will be almost 10,000 times more acidic than swamp water that has been in contact with limestone. Swamps fed by deeper ground water, like springs and seeps, have clearer water than swamps fed with shallow groundwater or surface runoff.   Bacteria that decay leafs and other plant parts that fall into swamps remove oxygen from swamp water. The shade from swamp trees hinders algae from putting back the oxygen; so swamps especially stagnate swamps, have low oxygen levels that limit the types of fish that can survive in them. 

Swamps feed by deeper sources of groundwater have clearer water.

Swamps fed by shallow ground water or surface water have dark tea-stained water and are sometimes call black-water swamps.

Fire

The fourth element is the frequency of fire. Fire helps to define a swamp by controlling build-up of vegetation and affecting the type of plants and trees that will grow there. Many species, such as pond pine and titi, depend on occasional fires to regenerate. These species have developed adaptations to protect them from fire damage. Pond pine trees have a layer of thick, shaggy outer bark that protects the inner bark. After a burn both kinds of trees are quick to resprout from adventitious roots or shoots.

Slow burning fires in peat expose roots and kill wetland trees. Photo courtesy of Charlie Houder. 

How often a swamp burns is largely determined by the type of fuel that is present and the length of the hydroperiod.