PHYSICAL SETTING

Posted by on 2/6/2003 10:20:15 AM
Post Comment PHYSICAL SETTING Nigeria

Geology: There are two distinct geological regions in Ondo State. First, is the region of sedi mentary rocks in the south, and

Okikikpukpa Oil Palm Industries, Okikikpukpa
Okikikpukpa Oil Palm Industries, Okikikpukpa

secondly, the region of PreCambrian Basement Complex rocks in the north. Some few kilometres north of Aaye occurs the basement complex sedimentary rocks boundary.

The sedimentary rocks are mainly of the postCretaceous sediments and the Cretaceous Abeokuta Formation. The basement complex is mainly of the medium grained gneisses. These are strongly foliated rocks frequently occurring as out crops. On the surface of these outcrops, severely contorted, alternating bands of dark and light coloured minerals can be seen.

These bands of light coloured minerals are essentially feldspar and quartz, while the darkcoloured bands contain abundant biotic mica. A small proportion of the state, especially to the northeast, overlies the coarse grained granites and gneisses, which are poor in dark ferromagnesian minerals (A. J. Smyth, 1962).

Relief and Drainage: Ondo State is composed of lowlands and rugged hills with granitic outcrops in several places. In general, the land rises from the coastal part of llaje/EseOdo (less than fifteen metres above sea level) in the south, to the rugged hills of the north eastern portion in Akoko area.

Adeyemi College of Education, Ondo
Adeyemi College of Education, Ondo

Some of the more prominent hills found at Idanre and Akoko rise above 250 metres above sea level. The geomorphological units of the creek and river ine areas include sand ridges, lagoons, swamp flats, creeks and the anatomising distributaries of the western Niger Delta. Numerous rivers flowing southwards to the Atlantic Ocean drain the state.

These rivers include the Owena, Oluwa, Oni, Ogbese and Ose. The most outstanding characteristics of the drainage systems over the areas of Basement Complex rocks is the proliferation of many small river channels. The channels of the smaller streams are dry for many months, especially from November to May.

The major rivers flow through sedimentary rocks in deeply incised valleys aligned in a northsouth direction, into the coastal lagoons. The lagoons flow in a westeast direction, parallel to the coast. Another aspect of the relief of Ondo State is the prevalence of many erosion gullies along hill slopes.

The gullies are very common and rather devastating in Owo and Akoko areas. Gullies also occur in areas of sedimentary rocks in Okitipupa and Araromi Rubber Estate. Along the Creeks, there are no sandy beaches since the entire area is swampy.

Oluwa Glass Industries, Igbokoda
Oluwa Glass Industries, Igbokoda

Climate: The climate of Ondo State is of the Lowland Tropical Rain Forest type, with distinct wet and dry seasons. In the south, the mean monthly temperature is 27C, with a mean monthly range of 2C, while mean relative humidity is over seventy five percent.

However, in the northern part of the state, the mean monthly temperature and its range are about 30C and 6C respectively. The mean monthly relative humidity is less than seventy percent. In the south, rain falls throughout the year, but the three months of November, December and January may be relatively dry.

The mean annual total rainfall exceeds 2000 millimetres. However, in the north, there is marked dry season from November to March when little or no rain falls. The total annual rainfall in the north, therefore, drops considerably to about 1800 millimetres.

Vegetation: The natural vegetation is the high forest, composed of many varieties of hardwood timber such as Melicia excelsa, Antaris africana, Terminalia superba, Lophira procera and Symphonia globulifera. In the northern districts, the vegetation consists of woody savanna featuring such tree species as Blighia sapida and Parkia biglobosa.

Museum Building, Akure
Museum Building, Akure

The swamp flats are the domain of the fresh water swamp forests in the interior and the units of mangrove vegetation near the coast. The sand ridges are characterised by savanna and stunted rain forests.

Over most of the state, the natural vegetation has been very much degraded as a result of human activities, the chief of which is based on the rotation of bush fallow system. As a result, the original forest is now restricted to forest reserves.

An important aspect of the vegetation of the state is the prevalence of tree crops. The major tree crops include cocoa, kola, coffee, rubber, oil palms and citrus, cocoa being the most prevalent.

It is also important to note that rubber and oil palms have been cultivated in large plantations in Odigbo, Okitipupa and Irele Local Government Areas. Trees that are not native, have also been intro duced as forest plantations. These exotics have been used to revegetate large portions of harvested old forest reserves in Omo and Owo. They include mainly Tectona grandis (teak) and Gmelina arborea (pulp wood).

Owena Motels, Akure
Owena Motels, Akure

Soil: The soils derived from the Basement complex rocks are mostly welldrained, with a medium texture. The soils, classified as Ondo Association, are of high agricultural value for both tree and arable crops. But to the northeast, is found a soil series under two Association. The soils here are skeletal in nature and are of comparatively recent origin.

In the southern part, the older sand ridge complexes develop brown and orange sandy soils, while the most recent ones near the coast have light grey sandy soils. The swamp flats are characterised by swampy organic and flooded organic soils, while the major part consists of decomposed and partly decomposed organic matter; whereas areas affected by tide bear saline soils. The latter soils are mostly useless for agricultural practices.

The Federal University of Technology, Akure
The Federal University of Technology, Akure

Ecological Problems: The creeks and the riverine areas of Ondo State are a region with ecological problems. Penetration of the area is hampered by mangrove swamps. In addition, the infestation of the creeks and water bodies in Ondo State by the hyacinth weed is probably the most menacing ecological problem in the state.

A lot has been done, though, to curb the menace of hyacinth weed thereby making the island waterways navigable by boats and trawlers. Another menacing ecological problem is the accelerated soil erosion. This is common in EfonAlaaye, Irele, Odigbo, Okitipupa and Owo LGAs.




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Janet Adeyemi(Missiouri, Texas, US)says...

we need clarity on the vegetation of the coastal belt of Ondo state