Human Ecosystems: Anyama District
fossil levees, or a lot more water, eroding a young flood plain. Settlements are confined to the levees which are the only areas that are entirely safe from the wet-season flooding. Travelling by boat through the area gives the impression of a drier landscape than really exists because the levees disguise the flood plains and swamps behind them.
The local Anyama landscape is typical: an "island" confined by rivers in the East, North and West, and in the South by mangrove swamps and creeks. The island is shovel shaped: the levees of the three rivers forming a discontinuous rim of higher ground around an interior flood-plain containing lakes and swamps, that is inundated from June to August, when Anyama's dry land shrinks to a narrow strip from Ologi to Okodi.
18.3 SOILS
As the topography suggests there are three main soil types in the district: levee soils; flood-plain soils; and swamp soils.
The levee soils are deeper than the Okoroba levee soils but have similarly developed on the sand and silt deposited by floods. Thus they are sandy loams, fine sandy loams and silty loams with a low permeability so that if they are not flooded in the wet season there may be, nonetheless, standing water at times. Some of these soils may be quite deep, as seen at the Anyama waterfront in the dry-season, when the village is 3-4m above water level, but generally they are shallow because of the permanently high water table. When they are cleared for agriculture and without the addition of humus, such soils rapidly lose fertility.
The flood plain soils are like those at Okoroba also. Typically, they are high water-table silty clay and clay gley (seasonally reduced) soils criss-crossed with flood streams which work their way around the buttresses, stilt and knee roots that are typical of the trees that grow on them.
Similarly, the swamp soils are like those found at Okoroba: permanently wet and sometimes submerged having a higher clay content than the flood-plain soils because they are the final sink for the alluvial deposits and because their is no downward leaching at all. Also because of reduced conditions and the accumulation of organic matter in depressions there are deposits of peaty soil.
18.4 THE NATURAL ECOSYSTEMS
As stated, Anyama lies within the Freshwater Alluvial Monsoon (FAM) ecozone, which, in its natural state would have been youthful in relation to the natural lowland tropical rainforest beyond the Delta. FAM ecosystems are defined by the drainage regime, thus: on the levee soils, comparatively good drainage with standing water in the wet season; on the flood-plain soils, high water tables with some seasonal flooding; and on the swamp soils permanent flooding. Intermediate conditions exist, for instance on natural or man-made ridges (log canals) running through the back swamps and in swamps which dry out for short periods.
The vegetation of the natural ecosystem corresponds to the soils. The forest on the levees is most like the lowland tropical rainforest beyond the Niger Delta, but with a lower species diversity because of its relative youth. The trees are tall, with large buttresses to support them in the shallow soil, straight and without branches almost up to the thirty metre canopy. So dark is the under-story, that undergrowth is confined to young trees growing in a slash of light created by the fall of a dead tree. Beside the wider rivers, lighter conditions encourage oil palms, shrubby trees and woody climbers.
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