even nearer to the surface, this rainforest merges into seasonal and then permanent swamp forest.
However, the islands and ridges all vary; ridges may be wide enough to support a relatively wide plain of broad-leaved rainforest, or so narrow that the palm forests of the FAM on either side almost meet.
8.3.2 FRESH-WATER ECOSYSTEMS OF THE TROUGHS
Similarly, troughs between ridges may be wide enough to carry a permanent or seasonal lake. However if the trough is very narrow, the broad-leaved rainforest of the ridges either side may make it too dark for any palms to become established.
8.3.3 BRACKISH-WATER ECOSYSTEMS
To the North of the model island illustrated in Fig. 3A, mangrove forest has colonised the brackish-water and sheltered fringe of the island, inland. Mangrove forests are also thriving on the East and Southeast edges of the island, where they are protected from the prevailing south-westerly winds and waves by the sand spit that has developed as a result of long-shore drift. The West side of the island is exposed to stronger winds and currents; nonetheless, a salt-water creek exploring a wider than normal trough has attracted an Avicennia mangrove forest to the protected interior.
8.4 THE BEACH STRAND SUB-ECOZONES
Within the Niger Delta, the Beach Strand ecosystems are unique to the Sand Barrier Islands. The beach strand sub-ecozone can be broken down into three bands: the beach that is exposed at low tide, the beach ridge that has risen above the high tide mark; and littoral forest inland.
8.4.1 THE BEACH
The beach itself, about which very little is known, is obviously it is constantly being changed by the sea. Crabs and Polychate worms live under its surface.
8.4.2 THE BEACH RIDGE
The beach-ridge is a pioneer ecosystem containing a narrow range of plants that can withstand the salty winds blowing off the Atlantic. These include the convolvulus, Ipomea pes-carpea, and the shrubs Hibiscus tiliaceus and Conocarpus erectus, all of which have thick waxy leaves. The soils are inceptisols (see 4.5.5); young, but nonetheless exhibiting a surface horizon which enables larger plants to establish themselves.
8.4.3 THE LITTORAL FOREST
The Littoral Forest is a development of the Beach Ridge ecosystem. The same types of thick waxy leafed plants are present, but more as a dense scrub forest which graduates into small trees that protect plant species more characteristic of the interior. This forest in turn forms a protective barrier against windborne salt for the interior tropical rainforest beyond.
