A country whose lands are overgrazed by cattle
We shall try to prove in this write up that Nigeria is a country whose lands are very much overgrazed by cattle. It is obvious that if this proof can be validated, then how to tackle the problem will depend less on speculations and political considerations. It will depend on the overall interest of Nigeria.
Nigeria experiences the influence of the North – east (N/E) trade wind and South- West (S/W) prevailing wind direction systems. It has been found that the North- East (N/E) tropical trade wind cloud layer system is usually contained in a square area whose side ranges between 120 and 130 of latitude. That is between about 1334km and 1445Km. The equatorial trough extends from the equatorial centre up to 100 to 150 of latitude. This range of size is about the same as the range of size for the distance, which the north East trade wind occupies. It has also been estimated that a convective cloud layer system extends for a minimum of about 1500km .All the above, suggests that both the North- East trade wind belts and the South- west cloud layer belts cover the same absolute distances of about 1400km.
Fluctuation is an inherent property of nature. Apart from the daily ebb and rise of tides, the oceans are also subjected to other natural fluctuations. In some years they over flow their banks causing floods. In some other years they retain smallest possible volume of water. Yet in some other years they have the bank full status. However, there is always the long-term mean position. These represent positions of stable equilibrium. Streams and Rivers undergo similar fluctuations and so also the incidences of temperature and rainfall etc.
There cannot be anything higher or greater then the maximum positions. Also there cannot be anything lower than the minimum positions. The laws of mother Earth precisely fix the minimum, the mean and the maximum.
The concept of Desert encroachment or Desertification must therefore be in terms of the above Definitions of natural fluctuations. This implies that a desert cannot go beyond the boundaries fixed for it by nature, in the same way that the Ocean cannot go beyond the boundaries fixed for by nature.
Let us take for example boundaries of the Sahara Desert, the largest and one of the hottest deserts of the world. The above implies that Sahara Desert and the North- East trade wind belt occupy the area bounded by about latitude 260N and 130N latitude. Thus Sahara Desert and North- East trade wind belt fall within an area dominated by anti Cyclonic atmospheric circulatory patterns or depressions. Such circulatory patterns or systems leave an area with practically no or very little rainfall. However, when rains do fall, they come in torrents which give rise to flash floods. Such flash floods follow any available depressions and result in serious erosions, silting and clogging of lakes, rivers and reservoirs.
Evidences, which have been given to show that there occurs desertification or desert encroachment include silting and drying up of water curses, lakes, reservoirs, rivers and streams and extension of sand dunes and other desert conditions to lands beyond the confines of the desert, so called desert encroachment or desertification. The Sambisa Forest Reserve in the North Eastern region of Nigeria is situated South of latitude 130 N.
Since the equatorial trough extends from about 130N latitude to the equatorial centre, therefore, this forest reserve possibly represents the Northern or Polar sector of the equatorial rain forest region. The thickness of this rain forest region increases Southward from about 130N to the equatorial centre. Patches of this kind of forest are still found along water curses in Sokoto, Kebbi, Zanfara and Niger states.
It is, therefore, most probable that the absence of these kind of forest in what is presently called Savannah Grassland region of Nigeria is due to overgrazing by cattle and that the so called Sahel savanna, which is situated North of latitude 130N actually belongs with the portion of Nigeria occupied by the North- East prevailing wind belt region where the Sahara desert is located.
•Prof. A.I. Agwu is of the Department of Physics, Abia State University