Tropical shelterwood system of forest regeneration its development and application in the Benin Division of Southern Nigeria and a consideration of factors affecting its success

Abstract

It is the purpose of this paper to give a description of the development of a system of natural regeneration for the Benin forests, to measure the success of the work, and to set out some of the factors which appear to limit or to assist the regeneration. Between the latitudes 6 and 7 degrees north and the longitudes 5 and 6 degrees east in Western Provinces, Kigeria,is situated Benin Division, the most southern and western of the four political Divisions which together form Benin Province. The area of Benin Division is approximately 4,000 square miles, and in 1931 (the latest census figures available) the population was taken to be 111,000, although there is no doubt that during the last two decades this latter figure has greatly increased due to a rising birth -rate and an influx of labour, mainly from the south and east, to the prosperous rubber estates and expanding timber industry. The provincial and divisional capital, Benin City, lies in the centre of the Division. With a population of over 20,000 it is the hub from which radiate the several roads which serve the many small and few large villages of the area and which link the capital with neighbouring Provinces. GEOLOGY: Crystalline rocks (the "undifferentiated basement complex" of gneisses and granites) occur in the extreme north-west of the Division, but the remainder is entirely sedimentary, being part of the extensive Benin Sand Series. In parts this formation consists of a homogeneous layer of quartz sand several hundred feet thick, but the Benin Sands may be part of the Lignite Series, in which unevenly distributed strata of sandstone, shales and clays occur in the red sands. RAINFALL AND DRAINAGE: The average rainfall of the whole Division is probably about 75 inches per annum, distributed in the typical two-peak fashion of the coast of West Africa. The rainfall in the south averages 110 inches per annum (probably higher in the extreme southwest) but that in the extreme north may be as low as 60 inches. The figures for Benin City show that the months of November, Decembers January and February have precipitation below 3 inches per month, but the relative humidity (especially in the forest) remains fairly high throughout the year, and the effect of the dry Harmattan wind from the north is weak and is obvious on only very few, isolated days. The table (t ore p. 3 shows average rainfall, temperature and relative humidity figures for Benin City which is not itself in the forest. Within the forest the mean relative humidity, particularly at 3 p.m., is higher and probably without such large fluctuations between months. The area of the Benin Sands is characterised by a scarcity of streams and the rain water appears to drain to considerable depth, the rivers flowing in deep trenches cut below the general level of the almost flat plain. Except on land which has been completely cleared of vegetation there is little run-off, and the streams, fed by underground drainage, generally hold deep and very clear water. Chukwuogo and other writers have stressed the severe water shortage which exists in the country districts, in the dry season, away from the limited number of streaa. FARMING: The local food farming technique involves the practice of a bush fallow system; the number of years for which a farm is cropped is small, usually two, or possibly three years if the land proves to be of high qw l ity, and this is an index of the rapidity at which the Benin Sands lose their fertility after the removal of the forest vegetation. The farmer cuts, heaps and burns almost every tree on the new farm, and this practice of leaving no high shade has important ecological and economic repercussions. There is a sharp contrast with the practice in other parts of West Africa where the largest trees remain as a high shade, an important reservoir of timber, a source of seed and a skeleton of forest structure. There are practically no cattle in the Division owing to the susceptibility of all but a few strains to trypanosomiasis. The most common domestic animal is the goat, which is here a village or compound animal, living by scavenging and seldom, if, ever, found either it forest or farm. An important plantation crop of the Division is rubber and considerable areas have been planted with Heavea brasil,iensis. During the 1939 - 45 war the plantations prospered, and were largely extended Owing to the inflated price of rubber following the Japanese occupation of Malaya, but the present prices are subject to large fluctuations. TIMBER. By far the most important industry, apart from food farming for local use, is timber working. On this trade, whether for the export market or the Nigerian market, the prosperity of Benin largely depends. A result of the rising standard of living of many Nigerian people, and the growing needs of industry in West Africa and abroad, is that the demand for Nigerian timber has increased. At the same time the area of non reserved forest (forest land not included in Forest Reserves) has been greatly reduced in the last fifteen years owing to the destructive work of farmers and the planting of permanent cash crops. The supply of timber outside the gazetted Reserves dwindled rapidly, particularly because of the clear-felling technique of the farmers, and the Forest Department was faced some years ago with the need to allow the exploitation of Forest Reserves to begin; such exploitation had to be accompanied by regeneration, either artificial or natural. Artificial regeneration, while important in certain limited areas and for special purposes, could not be attempted on the scale necessary to ensure the future of the forests and thus natural regeneration had to be attempted on an enormous scale. The intention in this paper is to describe briefly the technique of natural regeneration adopted and to examine in some detail the success obtained in different forest associations in a single compartment with the object of assessing the suitability of the technique for the maintenance of the forest