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Promising trees for agro-forestry in southern Nigeria
Forestry Development and Investigation Branch, Forestry Commission, Enugu, Nigeria
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.
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:
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.
Food crop yield under teak and cassia siamea in south-western Nigeria
P.R.O. Kio, S.O. Bada, and D.U.U. Okali
Department of Forest Resources Management, University of Ibadan, Ibadan, Nigeria
Maize yields on land that had borne plantations of teak and Cassia siamea of varying ages in south- western Nigeria were evaluated. Soils and standing crop biomass of the experimental plots differed between and within sites. Without the application of fertilizer, maize yields from the more humid sites with clayey soils tended to be higher than from other sites There was indication that yields were greater on soils that had borne Cassia than on those that had carried teak. Fertilizer application has been recommended for successful agro-forestry practice on marginal soils. Improved maize yields were obtained in seasons after fertilizer application, with particularly heavy harvests in the season immediately following that in which fertilizers were applied. Management problems encountered in the study and the possible significance of the results are discussed.
Existing forest plantations provide several advantages for investigation of problems that are likely to arise from the widespread adoption of agro-forestry. First, they give an indication of site productivity, as their ages are usually known and the standing crop biomass can be determined. Second, because their history is usually known, they provide an immediate means of assessing the effects of tree species, tree density, cultural practices, plantation age, and tree harvesting practices on sites. Third, they are available for investigation of methods of coppice-shoot management for successful intercropping with various food crop species. Many nearby communities have participated in their establishment and would welcome the opportunity to farm the plantation land again. Such communities can readily serve as a setting for undertaking studies of farmers' attitudes to the intercropping of trees with food crops on a long-term basis.
Besides these advantages for investigating problems of agro-forestry, forest plantations, together with plantations of cash crops such as cocoa, cola, citrus, oil palm, and rubber, cover a sizeable area of land in southern Nigeria (Allen 1981). This land is potentially available for the practice of agro-forestry, particularly as the plantations become due for felling and replanting. Although the major impact of agro-forestry is ultimately expected to be made through widespread adoption by smallholder farmers, the potential contribution of food from these larger plantations cannot be ignored.
Recognition of the contribution that can be made by studying existing plantations prompted us to undertake a pilot research project in 1977 on agro-forestry sponsored by the International Development Research Centre (IDRC). The plantations investigated were teak (Tectona grandis) and Cassia siamea.
The project sites were located in Gambari Forest Reserve, Alalubosa, and Eleiyele plantations, and Iwo and Ede forest areas. These study sites spanned the three major ecological zones of Oyo State but were restricted to an area within about 50 km of Ibadan. The main reason that the project was restricted to this area was the ease of accessibility from the University of Ibadan and, hence, the potential for adequate supervision. Gambari Forest Reserve is at the southernmost end of the area studied, and Iwo marks the northern end. Ede is on the north-eastern tip, Eleiyele plantations are a little northwest, and Alalubosa lies a little to the south-west. The part of Oyo State in which the sites are located is of uniform relief (though with some scattered inselbergs), consisting of a gently undulating plain on basement complex rocks.
Two plots in both Ede and Alalubosa carried stands of Cassia siamea while the remaining plots in Ede and Alalubosa, as well as all the plots in the other three study sites, carried only teak. The Cassia stands in Ede were established in 1935, whereas the teak plantations were established in 1960. In Alalubosa, the teak stands were planted in 1913 and 1925, and the Cassia in 1925. Much younger farms were examined in Gambari Forest Reserve and Iwo forest areas. The two farms in Gambari were Busogboro, established in 1967, and Onipe, established in 1968. At Iwo, one of the two plantations examined was established in 1960 and the other in 1963. All the tree crops were planted at an initial spacing of 1.83 m.
In each study area, a boundary survey of each plantation was carried out from which an area map was produced. Sample plots were selected from a table of random numbers. Usually plots that fell on marshy areas, hilltops, or rocks were rejected. Each experimental plot was 30 x 30 m with a 3 m border to protect against shading. The plots were clear-feiled, burned, and planted with maize at 30 cm along the row and 1.83 m between the rows. At Iwo, some of the plots were artificially fertilized because of the poor initial performance of the crops.
Soil sampling was undertaken early in each plot at 0-15 cm, 15-30 cm, and 30-45 cm. The samples were mixtures from a minimum of 16 auger points per plot. After soil analysis, the trees in the plots were tallied and measured for diameter at breast height (1.3 m) before being felled. Stems were burned, the larger ones being removed. Weeding and other tending operations were regularly carried out in all plots after the sowing of maize. The agronomic data collected included periodic maize plant height up to tasselling, leaf area, weight of maize cobs with and without sheath, grain yield, and plant dry weight at harvest. Maize grains were subsampled for nutrient analyses.
Results of soil analyses have been published elsewhere (Kio and Bada 1981), as have figures on biomass accumulation and maize yield (Kio and Bada 1981). Briefly, lwo soils are loamy sand with the percentage of sand in the topsoil (0-15 cm) often greater than 80 per cent. In contrast, Gambari soils are sandy loam, with relatively high clay values (10.8-18.8 per cent) in the top 0-15 cm; the silt values for the same depth range between 17.6 and 23.6 per cent. Alalubosa soils vary from sandy loam to loamy sand, although the soils in this area may have been sandy loam at the time of conversion from natural forest to plantations (between 1913 and 1925); because the Cassia plantations have been coppiced several times, the soil texture has tended towards loamy sand as a result of exposure, erosion, and disturbance (compaction) during past coppice extractions. Clay values generally increased with depth in all sites whereas sand decreased. in addition to receiving a higher annual rainfall with a relatively longer rainy season, Gambari soils had higher water-holding capacities.
Though variations in soil acidity between the three sites are not significant, lwo soils were generally more acidic (pH 6.57.6) than Gambari soils (pH 7.2-7.6) in the top 0-15 cm. Significant pH differences between Cassia and teak soils were not observed in Alalubosa.
Organic carbon and total nitrogen in the top 0-15 cm varied markedly between and within sites. For example, in the Gambari forest area, organic carbon for the 1967 plantation ranged from 0.95 per cent, whereas values of 1.39 and 1.50 per cent were obtained for the same depth (0-15 cm) in the 1968 plots. Equally large within-site variations were observed in plots of the same age at Iwo. The variations in organic carbon have resulted in similar differences in the carbonnitrogen (C:N) ratios for most plots. According to Kadeba (1976), a high C:N ratio is an indication of soil impoverishment often associated with grass cover. Higher C:N ratios were obtained for two plots in Gambari forest that were burned more regularly than two others in the same forest. In the Alalubosa forest area, the mean organic carbon in the Cassia plot was 1.0 per cent, and values of 1.50 and 2.41 per cent were obtained for the plots that carried teak. The mean C:N ratio for the teak plots was 6.9, whereas the value for Cassia was 6.0 (0-15 cm).
Like organic carbon, available macronutrients varied greatly within and between plantations as a result of past cultural practices, the tree species, and soil properties. In Alalubosa, teak soils had a mean value of 3.69,ug/g of available phosphorus with a range of 2.58-4.80,ug/g; calcium was 1,050-1,545,ug/g; and potassium was between 105 and 210,ug/g. Cassia soils had the lowest mean values of available phosphorus (3.30 ug/g) and calcium (660 ug/g). Generally, low values of available phosphorus and manganese were observed in Gambari soils, though a clear pattern of nutrient variability according to age could not be established. The highest values of the extractable cations were in a single plot; these values were Ca (1,800 ug/g), Mg (122 ug/g), Mg (122, ug/g), Mg (122,ug/g), and K (90 ug/g)
In Iwo, the mean available P was 5.10,ug/g (3.6-6.6,ug/g); Ca was 1,648,ug/g (1,455-1,830,ug/g). Higher K values were recorded in Iwo soils because the shallow, less-weathered soils have higher total exchangeable potassium ratios than deeper, more-weathered soils such as those in Gambari. Better tree growth could still occur in Gambari than in Iwo because the high ratio of total potassium may be an indication of potassium reserves within the soil and not an indication of the amount of potassium available for plant growth (Akin 1979).
The biomass estimated for the young (1968) teak plantation was greater than that for the older plantations at Gambari. Whereas the two plots in the 1968 farm had mean standing crop values of 213 t/ha and 219 t/ha, plots planted in 1967 had values of 131 t/ha and 204 t/ha respectively. Similarly, in Iwo forest area, the highest biomass value per hectare was recorded in one of the young (1963) plots, although the situation was not as clear-cut as in Gambari.
The two Iwo plots planted in 1963 had mean biomass values of 162 t/ha and 52 t/ha, whereas those planted in 1960 had values of 95 t/ha and 50 t/ha. Biomass mean annual increments also varied between the plantations and may be a reflection of soil differences and previous cultural practices.
The maize yields that can be most meaningfully compared are those for 1979 before fertilizer was applied to plots in Iwo and Ede. During this season, maize yield was generally higher in the moister Gambari plots (520-1,217 kg/ha). The maize in Cassia plots in Ede showed some initial promise but was subsequently destroyed in particular by livestock and also by rodents. One plot under teak in Ede failed completely as a result of soil impoverishment as well as severe rodent attacks. Pest attacks occurred in all the plantations. The crops in Gambari were destroyed by antelope and primates, whereas those in Iwo were attacked by grasscutters and other wildlife. No direct and consistent relationship could be established between plantation age and maize yield, though some of the older plots gave greater yield than others. For example, in Gambari one plot planted in 1967 gave the highest yield (1,217 kg/ha), whereas another plot with similar history and the same soil type produced the lowest yield (520 kg/ha). Maize yields in Iwo and Ede areas were tremendously increased by fertilizer application. Though fertilizers were applied only once (during the 1979 late maize season), the residual effects on maize yield in the cropping season that immediately followed were very great. Of all the sites, the 1935 Cassia plot in Ede produced the highest maize yield of 4,279 kg/ha. Furthermore, the Cassia plots consistently performed better than teak plots in Ede forest area. In Gambari forest, where fertilizers were not applied, there was a general decline in maize yield from one crop to the next.
Some Management Problems
During the course of the studies, a number of problems were encountered. One was the timing of the planting of maize Late planting can result in losses of almost 50 per cent. There was also the problem of pests: maize plants were attacked by pests of various types. In some sites, rodents such as grasscutters and rabbits constantly cut back the maize shoots, and others were attacked by antelope and other game. In Ede (Cassia plots) in particular, the plots were heavily damaged by livestock that regularly fed on the green maize plants. In Gambari Forest Reserve, various primates not only attacked the green plants but constantly fed on the ears before they matured. Climatic cycles posed equally serious problems to maize production. Crop yield was greatly reduced by delayed or unsteady rainfall because the plots were not irrigated, In addition, excessive rainfall (as occurred in September 1980 around Ibadan), destroyed many farms by washing away the maize plants.
The findings suggest some basic conclusions:
Agro-forestry possibilities in oil palm plantations in the Ivory coast
Laboratoire de Botanique Agricole, Ecole Nationaie Superieure Agronomique d'Abidjan, Abidjan, Ivory Coast
Cocoa, coffee, banana, Hevea, coconut palm, and oil palm are important industrial crops in the Ivory Coast, and, although they are usually monocultures, some of these are traditionally grown together in a taungya system. In tropical forest zones the need for food crops, on the one hand, and the shortage of protein, on the other, have tended to encourage consideration of complementary uses of large forest plantations. In particular, use of the adventitious vegetation in oil palm plantations as forage for cattle is being considered as well as the introduction of food and cash crops among the trees. Palatable species have been identified in the vegetation, and some crops, such as cocoa, offer promise as intercrops.
The oil palm (Elaeis guineensis Jacq.) is an African tree native to the Gulf of Guinea. Its distribution in West Africa extends from Senegal to Angola, where the natural populations have always been exploited by the native people for many purposes, including food, handicrafts, pharmaceuticals, and religious uses.
In the Ivory Coast, palm groves establish themselves naturally in the traditional plantations of cocoa (Theabroma cacao L.) or coffee (Coffee spp.) and constitute a very valuable by-product. They also grow among food crops as a result of the exploitation and development work of humans and dissemination by numerous animals partial to the palm's fruits and seeds (monkeys, rodents, and birds).
Industrial plantations of oil palm were first developed in 19201926 by the Union Tropicale des Plantations (UTP) and the Societe des Plantations et Hulleries de Bingerville (SPHB). Cultivation of the oil palm, however, experienced its greatest growth in the Ivory Coast after the Institut de Recherche pour les Huiles et Oleagineux (lRHO) developed a very productive hybrid form-the tenera-by crossing aura and pisifera. In fact, until 1964, before the creation of the Societe d'Etat pour le Developpement du Palmier a Huile (SODEPALM), industrial palm groves occupied only 10,000 ha. By the end of 1966, SODEPALM had planted almost 19,000 ha, and oil palm plantations occupied a total of nearly 30,000 ha. By 1970 this area had increased to 76,000 ha, and in 1980 it reached 100,000 ha.
In view of such growth, optimal use of the land occupied by these palm groves has attracted considerable interest. Economically feasible ways of intensifying the use of these areas could occur either by grouping the palms with other crops (industrial crops such as coffee and cocoa, or food crops such as cassava and maize), or by growing feed for cattle. Two stations were selected to study the adventitious vegetation; one, belonging to the Societe des Plantations et Huileries de Bingerville (SPHB), is located on sandy soil in the Bingerville region, and the other, belonging to the Institut de Recherche pour les Huiles et Oleagineux (I RHO), is located on clayey soil in the La Me region.
The forests of the Ivory Coast belong to the humid, tropical region of Africa, and the climate can be classified as subequatorial; from the viewpoint of plant geography, they belong to the Guinea-Congo forest massif. The original vegetation is a dense, ombrophilous, evergreen forest, which contains a number of tree savannas and grassy lagoon savannas: the Adiake, Moossou, Bingerville, Dabou, and Grand-Lahou savannas. The industrial palm groves are found on three types of soil: sandy; more compact clayey-sandy; and compact, essentially clayey (which retains a great deal of water).
The two stations selected for study were originally covered by very distinct types of vegetation. The Bingerville station is situated in the heart of the dense, psammohygrophilous evergreen forest dominated by Turraeanthus africanus and Heisteria parvifolia (Mangenot 1954). In addition, one sees here and there some expanses of savanna consisting of Brachiaria brachylopha and Anadelphia africana (Adjanohoun 1962). The La Me region belongs to the dense, pelohygrophilous evergreen forest consisting of Mapania spp. and Diospyros spp. (Mangenot 1954).
The adventitious vegetation consists of various plants distributed in the following proportions: phanerophytes (56.5 per cent), therophytes (17.9 per cent), and chamaephytes (14.5 per cent). Hemicryptophytes are rare 17.4 per cent), and geophytes are negligible (3.7 per cent).
The vegetation beneath the palms is varied. Its most striking aspects are: its vitality-phanerophyte and chamaephyte vegetation that is always green; flowering and fruiting limited to a few herbaceous plants; its floristic composition, both heterogeneous and uniform depending on whether one considers isolated plots or the whole plantation area; and its gregariousness, which frequently allows local enrichment of the flora with a particular species-this is a characteristic that is most marked for cetain herbaceous and ligneous species that propagate by means of suckers. Clusters of the following species have been observed: Dissotis rotundifolia; Aspilia africana; Melanthera scandens; Eupatorium odoratum; Thaumatococcus daniellii; Axonopus compressus; Commelina nudiflora, C. forskalasi, C africana, and C. condensate; Imperata cylindrica; Rottboellia exaltata; Nephrolepis biserrata; Pteridium aquilinum; Anchomanes diffomis; Acroceras zizanioides; Paspalum scrobiculatum var. commersonii and P. conjugatum; Panicum repens and P. brevifolium; Sporobolus pyramidalis; Borreria latifolia; Diodia rubricosa and D. scandens; Eleusine indica; Mariscus umbellatus and M. flabelliformis, often mixed with Cyperus sphacelatus; Palisota hirsute; Asystasia gangetica; Selaginella myosurus; Scleria barter) and S. naumanniana; and Setaria megaphylla and S. chevalieri.
The distribution of these numerous clusters is related to farming operations-clearing the land, ploughing, and so forth-that cause either abnormal concentrations of a given species at certain points, or their dispersion over the whole cultivated area. Local ecological conditions may also come into play and favour the growth of certain plants.
Possibilities for Agro-forestry
Oil Palm with Cattle
Phytosociological, floristic, and agrostological studies were conducted to assess the suitability of palm groves for cattle raising. These led to the identification of species having a high forage value by virtue of their palatability, biomass, and position in stable and profitable associations. The most important species are:
From attempts to assess the biomass and regeneration of the vegetation within various associations, it appears that for young plantations (one to seven years old) the often large amount of vegetable matter per unit area (nearly 100 tons/ha in certain cases) diminishes considerably with increasing age. Likewise, the regrowth of the vegetation, vigorous at first, becomes practically nil when the canopy closes. The vegetation within palm groves that are from eight to eighteen years old is increasingly sparse and poor (photograph no. 6). It grows back progressively with the clearing of the woodland vault after the eighteenth year.
Many factors other than age affect the composition and physiognomy of the vegetation under oil palms; among these are human activities, climate, and the degree and type of herbivory.
Oil Palm with Crops
In the Ivory Coast it is possible to consider cultivation of the oil palm in association with other industrial crops such as Hevea, coffee, and cocoa. Many studies have already been undertaken of the palm-cocoa association. There are two main reasons for favouring this combination:
In the traditional village plantations the oil palm-cocoa association constitutes a viable system, as the oil palms are not being planted by the farmer but simply maintained at a certain density. However, experience has shown that the same is not true of industrial plantations, where the density is calculated for maximum yield and becomes an obstacle to the proper development of the cocoa. In fact, the hybrid cocoa plants that are now common are more heliophilous than sciaphilous. In addition, the size of the palm roots in the soil is such that, despite the differences between the two root systems, the cocoa grows poorly and may perish (photographs 8 and 10).
Any food crop can be grown in the spaces between the rows of a young plantation (photograph no. 1 1). None can be grown in the palm groves when the crowns meet. The only precaution to be taken is to ensure adequate control of species whose remains after the harvest can develop into quickly spreading weeds and inhibit, to a considerable extent and for a long time, the young palms. This is the case, for example, with cassava (Manihot utilissima) (photograph no. 9). Once the canopy closes, the only spaces that can be developed for food crops are those that have been cleared by natural decay or where, for some particular reason, there is an absence of palms.
Cattle raising in the palm groves, although possible in terms of available palatable plant species, is worthwhile only on a large scale, and, even then, it would require bringing in a substantial quantity of additional feed. This is especially true for the older plantations, where regeneration of the vegetation is very slow and difficult. With regard to associated crops, only species whose lifetime is at most seven to ten years can be cultivated without special measures in existing plantations. In existing industrial palm groves profitable associations with other perennial crops are not possible for purely ecological reasons.
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