Published on: 12/8/2020 4:24:29 AM

In contract to the high energy conditions experienced by many beaches, sand dune areas and exposed cliffs, much quieter conditions exist with in estuaries, behind spits and bars and in deep embayment’s. Here finer sediments settle out forming mud flats, allowing salt loving plants to colonise much of the area. In such environments, three zones related to tidal activity may be recognised.

The SUB-TIDAL ZONE is made up of permanently occupied creeks and channels. These channels are often intricately meandering and exhibit many of the features of a dendritic drainage system. The Intertidal Slopes, covered by every high tide, compose the muddy flanks of the channels. These are normally bare of vegetation. except near their upper parts. Just above the mean high-water mark, the High-Tide Flat is, as its name suggests, a level surface built up at the extreme limit of deposition.

These three units can be recognised in a wide variety of climatic and vegetational environments. In temperate areas, the high tide flat is colonised by salt marsh, usually dominated by cord grass (spartina) and marsh samphire (Salicornia). In tropical areas the high-tide flat is characterised by mangrove swamps.

Marshes in low-energy zones are very much dependent on protection, and if this is removed for any reason, such as with the migration of a spit or bar, then erosion is usually rapid.

Coral reefs are uniquely different, they are composed entirely of matter accumulated through organic processes. The reef is built by the corals secreting lime in forming their skeletons. coral reef shorelines are essentially tropical and virtually confined to within 30° of the equators. They are not found in Muddy water and corals will not grow in water any deeper than about 50M.

Fringing reefs are built as platforms attached to the shore, and ae widest around headlands, where corals receive clean, fresh water with abundant food supply. Barrier reefs lie offshore, separated from land by a lagoon. Large barrier reefs may be some distance offshore from the mainland, broken by occasional passes. Atolls are more or less circular reefs enclosing a lagoon which has no land inside it.

Biological Desert

Very few areas of the world, apart from ice sheets, are absolute deserts, devoid of any form of life. On the other hand, there are extensive regions where biomass and organic productivity are very low. The largest areas where this is the case are climatically conditioned, either by a lack of water as in hot desert, or by extreme cold as in tundra regions.

Despite the obvious climatic and geomorphological differences between arid and cold deserts, they have certain basic ecological characteristics in common. In both, the environment is harsh, requiring a high degree of tolerance or adaptation in the organism present. Plants and animals of biological deserts tend to show less species variety than other ecosystems, but more specialisation. The physical conditions’ often unstable because of high rates of wind deflation, frost heave and other processes, exert a greater ecological influence on the composition and form of the vegetation in biological deserts than elsewhere. As a result, the diversity of physical habitats in these regions is reflected in the mosaic of small communities, especially in the more hilly regions.

The virtual absence of trees is a marked visual feature of biological deserts. with the exception of giant cacti, they are characterised by plants of low growth of which much of the organism is below ground. The communities form only a discontinuous ground cover. Inevitably, the lack of plant food restricts the number of heterotrophs that can be supported. The close inter-relationship between the lack of vegetation cover and the unstable geomorphological environment gives biological deserts a character of delicate instability in which they are particularly susceptible to disruption by man.