Mangrove

(botany) A tropical tree or shrub of the genus Rhizophora characterized by an extensive, impenetrable system of prop roots which contribute to land building.
(materials) Liquid derived from the mangrove tree Rhizophora mucronata and used in the leather tanning industry.

A taxonomically diverse assemblage of trees and shrubs that form the dominant plant communities in tidal, saline wetlands along sheltered tropical and subtropical coasts. The development and composition of mangrove communities depend largely on temperature, soil type and salinity, duration and frequency of inundation, accretion of silt, tidal and wave energy, and cyclone or flood frequencies. Extensive mangrove communities seem to correlate with areas in which the water temperature of the warmest month exceeds 75°F (24°C), and they are absent from waters that never exceed 75°F (24°C) during the year. Intertidal, sheltered, low-energy, muddy sediments are the most suitable habitats for mangrove communities, and under optimal conditions, forests up to 148 ft (45 m) in height can develop. Where less favorable conditions are found, mangrove communities may reach maturity at heights of only 3 ft (1 m). See also Ecosystem.

Plants of the mangrove community belong to many different genera and families, many of which are not closely related to one another phylogenetically. However, they do share a variety of morphological, physiological, and reproductive adaptations that enable them to grow in an unstable, harsh, and salty environment. Approximately 80 species of plants belonging to about 30 genera in over 20 families are recognized throughout the world as being indigenous to mangroves. About 60 species occur on the east coasts of Africa and Australasia, whereas about 20 species are found in the Western Hemisphere. At the generic level, Avicennia and Rhizophora are the dominant plants of mangrove communities throughout the world, with each genus having several closely related species in both hemispheres. At the species level, however, only a few species, such as the portia tree (Thespesia populnea), the mangrove fern (Acrostichum aureum), and the swamp hibiscus (Hibiscus tiliaceus), occur in both hemispheres.

The mangrove community is often strikingly zoned parallel to the shoreline, with a sequence of different species dominating from open water to the landward margins. These zones are the response of individual species to gradients of inundation frequency, waterlogging, nutrient availability, and soil salt concentrations across the intertidal area, rather than a reflection of ecological succession, as earlier studies had suggested. See also Ecological succession.

Most plants of the mangrove community are halophytes, well adapted to salt water and fluctuations of tide level. Many species show modified root structures such as stilt or prop roots, which offer support on the semiliquid or shifting sediments, whereas others have erect root structures (pneumatophores) that facilitate oxygen penetration to the roots in a hypoxic environment. Salt glands, which allow excess salt to be extruded through the leaves, occur in several species; others show a range of physiological mechanisms that either exclude salt from the plants or minimize the damage excess salts can cause by separating the salt from the sensitive enzyme systems of the plant. Several species have well-developed vivipary of their seeds, whereby the hypocotyl develops while the fruit is still attached to the tree. The seedlings are generally buoyant, able to float over long distances in the sea and rapidly establish themselves once stranded in a suitable habitat.

A mangrove may be considered either a sheltered, muddy, intertidal habitat or a forest community. The sediment surface of mangrove communities abounds with species that have marine affinities, including brightly colored fiddler crabs, mound-building mud lobsters, and a variety of mollusks and worms, as well as specialized gobiid fish (mudskippers). The waterways among the mangroves are important feeding and nursery areas for a variety of juvenile finfish as well as crustaceans. Animals with forest affinities that are associated with mangroves include snakes, lizards, deer, tigers, crab-eating monkeys, bats, and many species of birds.

Economically, mangroves are a major source of timber, poles, thatch, and fuel. The bark of some trees is used for tanning materials, whereas other species have food or medicinal value. See also Ecological communities; Forest management.