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Promising trees for agro-forestry in southern Nigeria

J.C. Okafor
Forestry Development and Investigation Branch, Forestry Commission, Enugu, Nigeria

Abstract

In Nigeria, several tropical trees are suitable for agro-forestry because of their multiple uses as sources of food, animal feed, timber, firewood, stakes, chewing sticks, and soil fertility restorers. Adequate information on the suitability of different species, however, is lacking or is not readily available. The scope of work, results, and achievements obtained at the Forestry Development and Investigation Branch, Enugu, where substantial tree crop improvements have been carried out during the past ten years, are noteworthy. The work reported here is a basis for selecting some tree species that are promising for agro-forestry. The selected species are given in two broad categories of fruit/food trees and non-food trees. Suitable species are suggested for each category, for both compound and outlying farm types, within the tropical forests and derived savanna. An ongoing study of natural fallows to elucidate their efficiency in restoration of soil fertility in southeastern Nigeria is briefly mentioned.

Introduction

The importance of indigenous trees as direct sources of food in Nigeria, such as leafy vegetables, fruit, alcoholic drinks, edible fats and oils, is being increasingly, though not adequately, recognized and documented (Anakwenze and Ettah 1974; Okafor and Okolo 1974; Okafor 1975b, 1978, 1980 a, b; Okigbo 1975; Roche 19741. The important roles and applications of trees in the agriculture-cum-forestry production systems for food and wood production have also been amply recorded in the literature (Ball 1977; King 1968; Okon 1973; Okafor 1975c, 1980c; Okigbo 1976; Iyamabo 1979). The roles range (in addition to food production) from supply of timber, firewood, pulp and fibre through fodder, gum, drugs, and dyes to restoration of soil fertility.

Despite the general acknowledgement of the roles of trees in agro-forestry systems, there is as yet limited precise information on how these roles are fulfilled or on the suitability of the species involved. Recently, Nair 11980) has discussed in general terms the characteristics of species suited for agro-forestry. According to Nair the species should give economic yields in a relatively short time; they should tolerate partial shade when intercropped; they should be easy to manage; they should withstand adverse climatic and managerial conditions; and they should yield marketable and locally used produce. Nair 11980) presented "crop sheets" of plant materials that can be used in agro-forestry covering major economic groups; namely, cereals, pulses, roots and tubers, fruits, oils and fats, beverages, fibres, spices, nuts, condiments, stimulants, medicines, and aromatic plants. Detailed information was provided for each species with respect to its uses and economic importance, origin, distribution, characteristics, ecology, physiology, composition, agronomy, yield, pests and diseases, and agro-forestry potential. Although some trees were included, such as cocoa, cashew, rubber, coconut, oil palm, breadfruit, shea butter, etc., the crop sheets dealt mostly with herbaceous and shrubby plants rather than trees and fodder species.

This paper will, therefore, focus attention on tree species with agro-forestry potential. The basis of selection was their importance in traditional farming and diets, extent of geographic and ecological distribution, adaptability, and ease of propagation and regeneration.

The Forestry Development and Investigation Branch

The objectives and scope of the work being carried out at the Forestry Development and Investigation Branch (FDIB), Forestry Commission, Ministry of Agriculture and Food Production, Enugu, are noteworthy in the selection of promising trees for agro-forestry. The main areas of research are production of food from wild and semi-wild fruit and food trees; production of wood and wood products from fast-growing exotic and indigenous species; biological aspects of soil-erosion control; and the components of the Nigerian flora, including the establishment and maintenance of the Enugu Forest Herbarium (EFH).

Within the first area of research, FDIB is executing a project on indigenous fruit-tree production (Okafor 1975b). The aim of the project is to increase and diversify available food supply in the country through the selection, multiplication, domestication, improvement, and conservation of edible wild and semi-wild woody plants. The scope of this project includes the identification of wild woody plants in the Nigerian forest zone of nutritional importance; the adaptation and conservation of edible wild and semi-wild woody plants; and large-scale production of improved seedlings for sale to farmers throughout the country. Research is under way on the development of suitable propagation methods and techniques for the fruit- and food-producing woody plants; taxonomy of principal species, with the collection, preservation and documentation of herbarium specimens; ecology of the species, with surveys to determine the occurrence, abundance, and distribution; seasonality and economics of the species (through market surveys); phenological records and estimates of yield of various edible plants; food values by proximate analysis (carried out in co operation with the Project Development Institute [PRODA], Enugu); the industrial potential of the edible parts (carried out in cooperation with PRODA and the Food Investigation Project, Enugu); and the wood value and other socio-economic roles of the woody plants, especially in the traditional farming systems, by means of laboratory and questionnaire assessments.

The results and achievements so far have been previously reported (Okafor 1975a, b, 1978, 1980a, b; Okafor and Okolo 1974). The results that are relevant to this paper can be summarized as follows:

  • Suitable techniques of vegetative propagation with buds and stem cuttings have been developed for about 30 species of indigenous woody food plants including Irvingia gabonensis (wild mango, "ugiri/ogbono"); Treculia africana (African breadfruit, "ukwa"); Pentaclethra macrophylla (oil bean tree, "ugba/ ukpaka"); Chrysophyllum albidum [local star apple, "udala"); Dacryodes ecu/is (African pear, "ube"); Par*ia clappertoniana (locust bean tree, "dorowa"); Afzelia africana ("akpalata"); Ceiba pentandra (silk cotton tree); Dialium guineense (velvet tamarind); Myrianthus arboreus ("ujuju"); and Precarpus spp. ("ora");
  • The fruiting age and fruiting height of some fruit trees, such as Irvingia gabonensis, Treculia africana, pentaclethra macrophylla, Chrysophyllum albidum, and Dacryodes edulis, have been drastically reduced, fruiting being as early as two to four years and at breast height or less;
  • Researchers have been able to produce, within three years, viable fruits at ground level from stem cuttings of T. africana
  • New varieties have been described in some principal species (I. gabonensis, T. africana, D. ecu/is); this information will facilitate identification and enhance complete collection and conservation of germ plasm (and utilization) of the economic trees;
  • Pilot seed orchards and conservation plantations of about 60 ha have been established in various parts of Anambra State;
  • J. africana has been shown to be promising for pulp and paper making;
  • A total of 150 edible wild and semi-wild woody plants have been identified within the Nigerian forest zone through a national survey recently concluded with the financial support of the Federal Ministry of Science and Technology; and
  • Determination of nutritional values has also been carried out for a large number of wild fruits and vegetables.

Selected Agro-forestry Species

Based on extensive field observations made during the ecological survey of woody plants of nutritional importance (in which non-food plants were also noted) within the traditional farming systems of the lowland humid tropics in Nigeria, FDIB personnel consider several indigenous species to be promising for agro-forestry. The selected species have been classified into fruit and food trees, and non-food trees. Both categories are further divided by ecological zone-forest and derived savanna vegetation subtypes. Within each subtype, the species suited to compound farms and outlying farms are indicated, making a total of eight categories. Each of these is considered in depth in the following section.

Fruit and Food Tree Species for Compound Farms in the Forest Area

The species in this group are either cultivated or semi-wild and protected (Okigbo 1975; Okafor 1975b, 1980a, b, c). They are planted or retained as farm trees and interplanted with arable crops, in close proximity to the homestead where they are protected.

The fruits of Treculia africana are an important food item that is cooked and eaten in many parts of southern Nigeria. The roasted nuts are also eaten in conjunction with palm kernel or coconut. The wood is very popular as fuel. The fruit mesocarp is commonly fed to domestic animals such as goats and sheep. The tree is amenable to pruning, which is often necessary for the control of shade; the pruned branchlets and leaves are palatable browse for domestic animals. Propagation is easy from both seed and buds. The latter results in fruiting within four years at reduced height. The species (variety inverse) has great prospects for plantation development as a source of pulp (Okafor 1980a). Because it coppices readily and vigorously, it does not have to be replanted from seed after the first rotation. Thus, it is promising as a planted, productive fallow, with great potential for the restoration of soil fertility.

Two varieties of Irvingia gabonensis have been described- gabonensis and excelsa (Okafor 1975a)-and are considered noteworthy. The kernel of excelsa is important economically and is used in soup as well as a complement to fufu, cocoyam, and gari. The pulp of gabonensis is sweet and edible, suitable for jams and fruit juice. The wood is durable and is used for farm tool handles. The species can be propagated from seeds and buds, with viable fruiting within three years for gabonensis and five years for excelsa.

Dacryodes edulis produces fruits that are softened in hot water or hot ash and eaten in conjunction with boiled or roasted maize, especially during the "hungry season" when the staples, such as yam and cocoyams, have been exhausted. The kernels and leaves are fed to domestic live. stock. The species is easily propagated from seeds. If the leading shoots of planted trees are pruned, the crown will spread. Pruned trees have fruited within 2.5 years.

Chrysophyllum albidum fruits are widely eaten in southern Nigeria, being especially popular with children and women. The fruit pulp is suitable for jams. The wood is suitable for domestic utensils and tools. It can be propagated from seeds and buds, though the latter is not easy.

Cola acuminate (cola) is highly important economically on account of its edible seeds, which also fulfil cultural roles throughout Nigeria. Pruned leaves are fed to domestic livestock. The trees can tolerate partial shade and are, therefore, suitable for agro-forestry.

Elaeis guineensis (oil palm) is the most widely planted and protected tree as well as the most economic and useful tree within the traditional farming system in south-eastern Nigeria. The wide range of useful products-palm oil, kernel, palm wine, palm fronds (structural material!, brooms, etc.-and the possibility of pruning leaves to reduce shading make this species especially appropriate for agro-forestry practices. Most of the farmers' needs are obtained from their own trees. Improved varieties are now available from many sources, including the Ministry of Agriculture and agricultural institutes.

Pterocarpus soyauxii, P. mildbredii, and P. santalinoides are important sources of leafy vegetables, especially during the dry season when conventional vegetables are scarce. They yield the cam wood of commerce. Propagation from stem cuttings is easy, and plants can be established on relatively poor sites with good growth.

The importance of some species of Ficus (fig trees) in agro-forestry derives from their usefulness as leafy vegetables (F. capensis) and browse. They are also used as roosts by bats which are hunted or trapped.

Spondias mombin (local hog plum) produces edible fruits that are popular with children. The leaves serve as good browse. The trees are used for fencing and in the construction of yam storage barns. Propagation is from seeds and buds.

Garcinia kola (bitter cola) is the source of edible seeds that serve as cola. The wood is used for chewing sticks, utensils, and tools. Propagation is easy from seeds.

Fruit and Food Trees for Outlying Farms in the Forest Zone

The recommended species of trees for use in outlying farms in the forest area include Pentaclethra macrophylla, Canarium schweinfurthii, Myrianthus arboreus, Afzelia belle, Dialium guineense, Napoleona imperialis, Blighia sapida, and Raphia spp.

Although these species have edible fruits and vegetables, they are generally less important economically than are those suggested for compound farms and do not require as close protection. Some of them require tedious processing and fermentation (e.g., seeds of Pentaclethra macrophylla) before they can be eaten as food supplements. Perhaps their more significant role in agro-forestry is the supply of wood, farming materials such as stakes and mulch, and as natural fallow species for fertility restoration. For example, Dialium guineense and Napoleona imperialis are predominant in natural fallows in most parts of south-eastern Nigeria. They supply edible fruits as well as stakes, chewing sticks, and browse. P. macrophylla is a good source of firewood, stakes, and mulch. Leafy vegetables are obtained from Myrianthus arboreus and Afzelia belle variety belle (used after fermentation). Edible fruits are also obtained from Canarium schweinfurthii (eaten after being softened in hot water) and Blighia sapida, both of which are good sources of timber. Raphia spp. are of high economic importance, being a source of palm wine, stakes (poles), piassava, raffia, and mats for construction of farm huts. P. macrophylla and D. guineense are easy to germinate, and both can be propagated vegetatively from buds, with viable fruiting in 3.5 years. C schweinfurthli grows well over a wide range of sites, including poor ones.

Fruit and Food Trees for Compound Farms in Derived Savanna Zone

Few species suitable for agro-forestry are commonly observed around compound farms in the derived savanna: Adansonia digitata, Ceiba pentandra, Moringa oleifera, and Tamarindus indica are noteworthy. Edible vegetables are obtained from A. digitata, C. pentandra, and M. oleifera; the flowers end young pods of M. oleifera are also used as vegetables. Fruits of T. indica and A. digitata are edible and are used in the preparation of local drinks. The wood of M. oleifera is very useful on the farm as stakes and fence material. C. pentandra is a source of lumber, and its kapok is extensively used for stuffing of pillows and mattresses. Live C. pentandra fences commonly surround farms and compounds in the derived savanna. Leaves of all these species are extensively used as browse for domestic livestock. C pentandra and A. digitata can be planted from cuttings (Okafor 1980b).

Fruit and Food Trees for Outlying Farms in the Derived Savanna Zone

Most of the fruit and food trees suitable for outlying farms in the derived savanna fall into the categories of semi-wild and protected species in cultivated farmland. Few are cultivated. The selected species are Borassus aethiopium, Afzelia africana, Butyrospermum paradoxum, Parkia clappertoniana, Prosopis africana, Detarium microcarpum, Brachystegia eurycoma, Nauclea latifolia, Vitex doniana, and Ficus spp.

All these species are important sources of food (Okafor 1980b), ranging from staple items (e.g., moulded fruit pulp of P. clappertoniana), condiments (e.g., see P. clappertoniana, A. africana, P. africana, D. microcarpum, B. evrycoma), leafy vegetables (V. doniana, F. capensis), and edible fruits (B. paradoxum, B. aethiopium, and, marginally, M latifolia and F. capensis). Oil is extracted from the kernel of B. aethiopum and from B. paradoxum. In terms of supplying wood and wood products, such as timber and stakes, B. aethiopium is the most important. Browse material is obtained from P. clappertoniana and F. polite.

As reported by Okafor (1980a, b), it is possible to propagate vegetatively, from buds, A. africana, P. clappertoniana, P. africana, D. microcarpum, and V. doniana Most of the species, especially the legumes, enrich the soil with nitrogen through the bacterial root nodules as well as serving as "nutrient pumps," bringing up nutrients that have been leached to soil horizons deeper than the topsoil, and eventually releasing them in the form of leaf litter and decaying organic plant residues. Apart from their role in restoring soil fertility, the trees also provide much-needed shade. For instance, some farmers report that the performance of several crops is better around and under the shade of P. clappertoniana.

Non-food Trees for Compound Farms in the Forest Zone

Few non-food trees are retained in compound farms, but there are some that have widespread distribution for production of browse and supports for yam vines (Ricinodendron heudelotii and Newbouldia laevis). N. Iaevis is also used in yam storage barns, in boundaries and fences, and for religious purposes; leaves of Hymemodictyon pachyantha are used as wrappers and for water collection in some areas.

Non-food Trees for Outlying Farms in the Forest Zone

The non-food species considered suitable in outlying farms within the forest vegetation are Chlorophora excelsa, Berlinia grandiflora, Anthonotha macrophylla, Acioa barter), and Alchornea cordifolia.

Their suitability for agro-forestry is based on their production of timber and structural materials (C. excelsa, B. grandiflora, A. barter)), stakes (A. barter), A. cordifolia), wrapping leaves (A. macrophylla, A. cordifolia, B. grandiflora), utensils (C excelsa and A. barter)), tool handles (A. barter)), and browse (C. excelsa). Apart from C excelsa, the species are predominant in natural fallow where they fulfil the important role of restoration of soil fertility. A. barter) and A. macrophylla are sometimes planted for this purpose.

Non-food Trees in Compounds and Outlying Farms in the Derived Savanna

The species that happen to be dominant in an area of the derived savanna and that satisfy the farmers' needs for wood, stakes, browse, wrapping leaves, provision of shade, and restoration of soil fertility include Anogeissus lelocarpus, Daniellia oliveri, Albizia spp.-all of which yield fodder Erythrophleum suaveolens for utensils, and Uapaca spp. for firewood and supply of wrapping leaves.

Discussion and Conclusions

Trees are an integral part of the traditional farming system and the combined forestry and agricultural multiple land use in southern Nigeria. Food production has been combined (at least for the first two years) with the raising of timber trees, such as Gmelina, teak, and Terminalia, in taungya and agrisilvicultural systems in many part of southern Nigeria. Emphasis in such systems has been on wood production. The present concept of agro-forestry attempts to place equal emphasis on food production over the same piece of land, especially in fragile ecosystems (King 1979).

The use of fruit and food trees in providing both food and wood has been suggested by Okafor (1980c). Suitability of various species of fruit, food, and non-food species for agro-forestry depends not only on their isolated roles as sources of food and other useful products but also on their compatibility in mixtures with other crops, ability to withstand pruning and shade, and efficiency in restoring soil fertility. This last consideration calls for a detailed study of natural fallows, which have remained the dominant feature and tool in fertility recovery in the traditional farming system. Such a study has recently been jointly initiated by FDIB and the International Institute of Tropical Agriculture (IITA) over a transect in south-eastern Nigeria; it aims at elucidating, among other things, the structure and specific composition of natural fallows of

different ages and cropping history, their soil fertility status, and relative efficiency of the dominant species in nutrient recycling and restoration of soil fertility. A comparative study of the effectiveness of different types and ages of fallow natural and planted-with respect to the restoration of soil fertility within the traditional farming system is also envisaged.