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Forestry aspects of agro-forestry practice in Nigeria
F A. Akinsanmi
Department of Forest Resources Management, University of Ibadan, Ibadan, Nigeria
There is an increasing demand for land for various uses, all of which have to be satisfied. Agro-forestry, which is defined as the integration of agriculture, forestry, and animal husbandry on the same land, appears to offer a solution to the problem of land shortage. It is also a potential solution to the demandsupply crisis for forest products. Analysis indicates that the remaining pockets of high forest in Nigeria will be exhausted by 1995, but demand will keep rising. The demand for more land for farming can be met by further encouraging the taungya system in areas earmarked for plantation establishment The use of a plantation fallow as part of the shifting cultivation cycle is recommended, as it considerably increases the area of land available for planting tree crops and discourages dereservation.
The concept of multiple use of the land is becoming more widely accepted because of the increasing demands on the land for agriculture, forestry, industrial development, urban settlement, and recreation. This is especially true of countries that depend heavily on the produce from the land to support their economy. The land area is fixed in relation to the increasing demand on it. The tendency, therefore, is to seek ways of utilizing the available land area efficiently to the benefit of various land users.
Land constantly put under crops loses its fertility. The fertility is, however, restored if the land is left fallow from five to ten years. As a result of increasing pressure on the land due to the rising population, the fallow period has been reduced to three or four years or even less. The land, therefore, does not always have enough time to replenish its fertility. Lands under forest cover are fertile and have become targets by farmers for farming. Foresters are reluctant to release forest lands for farming because the land available for forestry activities is equally limited. This is the general picture in most countries in Africa.
Agro-forestry is a land management technique which, according to Combe and Budowski (1979), implies the combination of forest trees with crops or with domestic animals, or both. The aim of agro-forestry with respect to agriculture is to increase crop yields; with respect to silviculture (forestry), to give emphasis to the forest; with respect to pasture land, to manage grazing (Dosne 1979). It appears, therefore, that agro-forestry offers a solution to the problem posed by the high demand on the land. The object of this paper is to examine the whole issue of agro-forestry practice vis-a-vis the extent to which it has satisfied the forestry component, particularly in Nigeria. Furthermore, suggestions are made on how to achieve maximum results in the forestry sector by taking advantage of the opportunities offered by agro-forestry.
A comprehensive review of agro-forestry systems is provided by Combe and Budowski (1979). The review provides a classification scheme by types of agricultural output, functions of the forestry component, and distribution in time and space. The first covers the type of agricultural products combined with forest, namely farm crops, animals, or both crops and animals. The second indicates the principal objectives of the tree component in a non-forest environment-production, protection, or services. The third relates to the rotation of both the agricultural and forestry crops as well as the spatial distribution of the species.
Agro-forestry may be practiced either within or outside forest reserves. Within forest reserves, the object is to establish plantations of selected species to replace the natural understorey. The emphasis here is on the production of tree crops while satisfying the demand of farmers for fertile land, i.e., the taungya system. According to King (1968), the taungya system results in the establishment of plantations that do not demand heavy investments. It offers a solution to the problem of shifting cultivation and reconciles the often conflicting interests of the tropical foresters and farmers.
When agro-forestry is practiced in agricultural lands outside forest reserves, the principal object is food crop production. Tree crops play only a secondary, though important, role.
If the trees used are legumes or other species able to fix nitrogen, there is an increase in soil fertility. Forest crops may be raised with both food crops and farm animals. Trees are planted for fodder, shade, or as live fences.
Nigeria's Forest Resource
At the beginning of this century, the high forest in Nigeria was very extensive and rich in large trees. With the increase in human population, the area of the high forest started to diminish as a result of demand on forest land for farming and other forms of land use. Gradually, all the forests disappeared except those in reserved areas. In 1978, the total area of reserved forest was 20,443 kmē, excluding both the freshwater swamp and mangrove forest, which amounted to a total of 778 kmē (FAO 1979). The bulk of usable timber for industrial purposes comes from the reserves of the moist tropical forest. In a study carried out on the silviculture and management of the high forest zone of Nigeria, and using the results of the indicative inventory of the reserve high forests, FAO (1976b) reported that the total area of forest reserves in Ogun, Oyo, Ondo, Bendel, Kwara, Anambra, Imo, Cross River and Rivers states was 2,549,523 ha. Of these, 128,053 ha were plantations, 608,545 ha were unproductive, and 1,766,290 ha were potentially available for production. Later (FAO 1979), this information was supplemented by a study of the overall production system of the Nigerian forestry sector. The findings were that felling of existing natural forest over a 20-year period ranged from 436,000 ha to 1.4 million ha and the rate of plantation establishment in the moist lowland forest zone was 15,000 ha/year between 1975 and 1980, with a projected increase to 20,000 ha/year by 19901995. Together, these data indicate that the remaining natural forests of Nigeria will be exhausted by 1995 if demand follows the high forecast.
Nigeria is committed to supplying the raw material for two pulp mills, each requiring 100,000 tons annually. Only the large-scale establishment of pulpwood plantations will ensure the constant supply of this raw material.
Accompanying this mounting pressure to increase productivity from the forest areas is the competing demand for forest lands by agriculture, industrialization, urban development, etc. Quite often the political climate and the desires of politicians determine the success of resistance to dereservation. Most government functionaries favour agriculture over forestry because of the faster rate of returns (not necessarily higher rate of returns) from planted stock.
On the other hand, FAO (1978b) states that no country should completely liquidate that part of its natural heritage represented by the flora of the high forest and the habitat provided for indigenous fauna. It has, therefore, recommended that an area of 1 per cent of the high forest be reserved in perpetuity. At present, Nigeria has no such reserve, and the high forest is being clear-felled at a staggering rate.
The current practice of plantation establishment by taungya should continue, as it reduces the dangers to monoculture at the early stage of plantation establishment. FAO (1979) has, for instance, recommended that combinations of agriculture with plantation establishment should be encouraged and expanded, and, in particular, that the traditional taungya scheme be encouraged while other forms of agrisilviculture are being developed. More emphasis should be given to the production of food and trees in forest reserves.
The area of land available to forestry could be considerably increased if fallow areas-as part of the shifting cultivation cycle-were used for tree plantations. It is estimated that 3 million ha of such land is readily available in the moist forest zone (FAO 1979). The amount of plantation trees available could also be increased if incentives were provided for private and commercial forestry operations in areas outside forest reserves.
Summary of discussion: Current agro-forestry activities
Since the papers presented covered a wide variety of ideas and techniques, the discussion also touched on a number of topics, many of which had been discussed previously but in a different context. In particular, a number of comments on plant-plant interactions were made, and these again served to emphasize the need for further research and observations. Great care must be taken when interpreting results, and an example was cited where the tending had had a greater effect on the maize yield than the presence or absence of a tree crop. In another example the growth of Gmelina arborea was found to vary according to the annual crop, but this could have been due to the different weeding practices for maize and cassava rather than the type of crop. Cassava, in particular, was noted to be weed-tolerant and to have a negative effect on tree crops when planted too close. In short, management provides yet another set of variables that must be examined when evaluating agro-forestry practices.
Experience with intercropping Terminalia superba with cocoa, coffee, and banana was found to be relatively similar in Gabon, Congo, and Sierra Leone. Cocoa performance under T. superba in the Congo was particularly poor after 20 years because of excessive shading. As in Sierra Leone, both the overstorey timber crop and the understorey tree crop will be clear-felled after 40 years.
The better performance of food crops under former teak (Tectona grandis) plantations as compared to Cassia siamea stimulated much discussion. A number of factors were mentioned which could have caused this result, and these included the nitrogen-fixing ability of Cassia, the faster breakdown of Cassia leaves as compared to teak leaves, the relative abundance of ground fires in teak plantations, and the fact that the Cassia had been coppiced several times, a management operation which leads to more herbaceous growth, higher levels of soil organic matter, and greater soil aeration.
The successful introduction of improved varieties in southern Nigeria was further expounded upon. The basic technique used was to graft adult buds of fruiting trees on to young stock, and this led to early fruiting at reduced heights. At present the work is concentrating on native species, and the demand from the local people for improved material exceeds supply. Since the new varieties are intended for use in combination with other food crops, there is no substitution of fruit products for essential food crops. It was noted that relatively few crops have been successfully introduced, but since agro-forestry aims at sustainability rather than high, short-term yields, it may prove to be a more successful vehicle for introducing new crops or varieties. In the case of Rwanda, the dissemination of agro-forestry techniques to the local farmers was simplified by the fact that they were required to work on demonstration plots in each community. In this way they were exposed to new techniques and new crops, and over time many of the farmers adopted these.
In response to questions on the role of animals and forage species in agro-forestry systems in the humid tropics, one speaker noted that pasture and browse species could play an important role in reducing erosion and fires, but this depended on proper management and species selection. In the case of erosion one must maintain a sufficiently dense groundcover under the forest canopy and control grazing accordingly. The possibility of competition between browse and forage species was raised, but at least in the case of Gliricidia septum this was not felt to be a problem, probably because of its relatively deep rooting habits. The use of leguminous species for browse was also discussed, with particular attention to the question of toxicity. In general it was felt that the problem could be avoided by including the protein-rich legume with a variety of other feeds; specific tolerance levels had to be set for each animal with regard to each leguminous species. Toxicity can also be reduced by processing and plant breeding, and location is still another important variable.
In noting the high loss through volatilization of certain nutrients, particularly nitrogen when Leucaena cuttings are used as mulch, it was suggested that crop residues and other plant material might best be fed to ruminants. This would allow more efficient use of nitrogen and perhaps the organic matter as well.
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