Community Types

Several major types of mangrove communities are described which result from differences in geological and hydrological processes. Generally, mangroves grow best in depositional environments with low wave energy. Extreme wave conditions: prevent establishment of propagules, destroy relatively shallow root systems, and prevent accumulation of fine sediments. The best sediment conditions are fine-grained muds of silt/clay with lots of organic matter. Primarily, these conditions exist along deltaic coasts or estuarine shorelines. However, all local species can grow on a variety of substrates: sand, mud, rock, and peat. When found on rock surfaces, it appears that they are growing in sediment trapped in cracks rather than directly on the rocky surface.

Riverine forests are tall flood plain forests along flowing waters such as tidal rivers and creeks. Conditions are favorable for extensive growth due to flushing by daily tides. In addition, freshwater runoff and terrestrial nutrient influx enhance this type of mangrove community. Maximum heights of trees in this community are 66 feet (20 m).

Fringing forests exist as a relatively thin fringe along waterways. These forests appear to be flushed daily by tides, but do not receive then amount of terrestrial runoff as the riverine forests. Typically, the classic mangrove zonation pattern of seaward Red-Black-landward White scheme is exhibited in this forest. Maximum heights of trees in this community are slightly over 30 feet (l0 m).

Overwash forests exist as islands frequently washed over by tides. All species are present with the Red mangrove the dominant species. Typically, these islands develop as a Red mangrove propagule strands in a shallow flat. As more and more propagules strand and grow, the “island” begins as a tangle of prop roots. As the island develops the roots eventually trap sediment. Often, bare sand flats are found in the center of these islandsThe maximum height of the community is between 2&emdash;25 feet (7 m).

Scrub or Dwarf forests are common in the flat coastal fringe of southern Florida and the Keys. All 3 species are present, but height is limited to less than 7 feet (l.5-2 m) except in depressions of mangrove peat. Nutrients appear to be the limiting factors affecting growth, although substrate (marl) is also important.

Two similar forests are the Basin and Hammock communities. Basin forests are inland in depressions channeling terrestrial runoff toward the coast. Trees in this community have maximum heights of almost 50 feet (l5 m). Hammock forests are in depressions but exist on slightly elevated ground. In Florida, these communities exist in the sawgrass communities of the Everglades. Trees rarely growth height in excess of 17 feet (5 m). Tidal flushing of both of the communities is infrequent.

A newer simplified system of mangrove community types is now in use among researchers. It retains the riverine and fringing forest types and omits the overwash forest. Additionally, the scrub or dwarf, hammock, and basin forests are lumped into the category of basin forest. This scheme seems focus on hydrological processes as the dominant influence affecting community types. The fringing forest is along waterways and bays. The riverine forests are along tidal rivers and creeks. Inland of both of these communities are the basin forests.

Riverine Forests

Fringing Forest

Overwash Forest

Scrub or Dwarf Forest

Basin Forests

Hammock Forest