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Traditional agro-forestry systems: Prospects for development

The role of trees in farming systems in the humid tropics

The role of trees in farming systems in the humid tropics

A. Getahun, G.F. Wilson, and B.T. Kang
International Institute of Tropical Agriculture, Ibadan, Nigeria


The bush fallow-food crop rotation system has been the most popular and stable arable cropping system in the humid tropics of Africa. The system's stability is attributed to the presence in the fallow of deep-rooted woody plant species that are essential to soil fertility restoration. Population increases and the associated pressures on land have been threatening the stability and productivity of the system. As more land is brought in to production, the fallow period is shortened and woody species are eliminated or become ineffective.

A recent survey in southern Nigeria confirmed that the bush fallow-food crop rotation is still the dominant land-use pattern. Other important patterns are permanent tree crops (including plantain and banana), taungya, and permanent compound farming, in which trees are major components.

The role of trees in nutrient recycling, soil organic matter buildup, and erosion control has been recognized by the traditional farmers, who have identified and have been encouraging the most effective tree species in the fallow. With these selected species, the fallow period can be effective/y shortened. To exploit the potential of selected tree species in land and soil management further, we have been perfecting a system called alley cropping. This system embodies the agro-forestry concept of combining crops and trees and ensures the dominance of effective tree species during the fallow period.


The tropics have about 50 per cent of the world's population and less than 40 per cent of the earth's land surface. It is estimated that by the Year 2000, the tropics will have nearly doubled their population as against a population increase of 20 - 30 per cent in the developed countries. BY the year 2000, 60 per cent more food will be required to feed the world population (FAO 1977). Increasing agricultural productivity to meet this demand poses a special problem, as the greater proportion of the population increase is expected in developing tropical countries where food production is relatively low and, in many cases, falls below the demands of the present population. Alternative solutions to this problem can be found by expanding the area of production, increasing the productivity of the area under production, or a combination of both.

Expanding the area under food production is possible only in areas where suitable lands are available. Unfortunately, many developing nations are already utilizing fully the area regarded as arable, and further expansion would bring into production lands of marginal productivity (under existing local practices).

Increasing productivity per unit area can be approached by:

  • Introduction of high-input management technologies based mainly on fossil fuel energy and inorganic fertilizers; the use of high-input technologies has been successful under certain soil, ecological, and management systems. These so-called modern farming methods have not generally been accepted in the humid tropics because of soil, climatic, and socioeconomic constraints. In many instances, these technologies have led to serious land and soil degradation (Uehara 19761; and
  • Development of more efficient low-input systems based on biological recycling of energy and chemical nutrients through use of fallow as already practiced by traditional farmers; this alternative may maintain naturally land and soil productivity in many areas of the humid tropics (Wilson and Kang 1980).

The bush fallow and related shifting cultivation system, which is still the dominant traditional food crop production system in many parts of the tropics, particularly humid tropical Africa, involves a few years of cultivation alternating with several years of bush following, with the main purpose of the latter being soil fertility regeneration ( Ruthenberg 1971). This system has often been criticized as being wasteful and inefficient, and the major reason for degradation of soil and rapid decline in soil fertility and crop yield (FAO 1957). However, while land has been abundant, the bush fallow system has provided the traditional farmers with an efficient, balanced, and stable system for maintaining soil productivity. Problems only arise when land becomes limited due to increasing population, as has already been observed in several countries in humid tropical Africa, where fallow periods have become progressively shorter and fertility restoration becomes correspondingly less effective (Steiner 1973). Grinnell (1975) mentioned: "shifting cultivation though apparently wasteful, if not pushed to excess, has given man his livelihood in the humid tropics for centuries and is significant even now, when after a quarter century of experiment in tropical Africa, we have failed to introduce to the forest regions any method of food production superior to the natural fallow system." Because of the importance of trees and shrubs in fallows or in association with food crop production systems in land and soil management (ICRAF 1979), and also because of their roles in providing fuel, staking material, and edible products (Bene et al. 1977; Brewbaker and Hutton 1979), attention has recently been given to improving the bush fallow system and to developing improved land-based production systems for the tropics (Wilson and Kang 1980).

FIG.1. Tropical Africa: Humid and Sub-humid Zones

Ecology of the Humid Tropics

The tropics are usually referred to as the region of the earth between 23.5 north and south of the equator. They cover 4.96 billion ha or 38 per cent of the world's land mass. Forty-three per cent of this area is in Africa (Dudal 1980). Among the agroecological zones in tropical Africa, the humid and sub-humid tropics make up over 44 per cent of the total area and extend between 8°S to 8° N latitude (Fig.1).

The upland soils of low-altitude humid and sub-humid tropical Africa are dominated by low activity clay soils characterized by low cation exchange capacity (CEC) and low moisture-holding capacity (Moormann and Kang 1978). The soils can be grouped into two groups. The first is Ultisols and Oxisols (Sols ferrallitiques by INRA classification or Acrisols by FAO World Soil legend) and associated soils. These are strongly acidic and leached upland soils occurring in the perudic to udic moisture areas (with rainfall > 1800 mm). Ultisols are dominant in coastal regions. They are mainly coarse-textured, kaolinitic Typic Paleudults. The Ultisols (and some Oxisols) derived from basement complex rocks are mainly coarse-textured Plinthudults and Tropudults. The second group is Alfisols (Sols ferrugineux tropicaux by INRA classification or Luvisols by FAO World Soil legend). These are slightly acidic and less leached soils from the humid and subhumid zones. Most of these soils are derived from basement complex rocks or sandstone. In the drier forest zone, Oxic paleustalfs are the dominant soil types.

The biological environment of the humid zone, which consists mainly of infertile and fragile or easily degradable soils combined with abundance of moisture and radiation, provides a suitable and continuous growing season for the trees, which can also accumulate the largest amount of biomass. The traditional bush fallow system and its related land and soil management system is a direct adaptation to the prevailing physical and biological environments. However, the traditional system, which relies heavily on forest or woody fallows, is undergoing significant changes as a consequence of increasing population, agricultural land-use pressure, and over-exploitation of forest resources. The result is a steady decrease in the number of trees and shrubs in fallows and a steady increase in grasses and weeds which are less effective in soil rejuvenation.

Dominant Farming Systems

A recent survey of the humid and subhumid zones of southern Nigeria (Getahun 1979a; IITA 1978 and 1979a) showed that the traditional agriculture is predominantly upland and consists mainly of: (1 I bush fallow-food crop rotation; (2) permanent tree crop farming; (3) taungya; and (4) permanent compound farming in the case of eastern Nigeria.

All are characterized and dominated by a tree component. In the bush fallow, the climax of the fallow is indicated by the presence and size of certain woody species. These woody species with their deep root systems play an important role in enriching the upper soil layers by depositing litter on the soil surface. The litter decomposes and releases nutrients brought up from lower soil depths. The importance of trees or woody species in the fallow cannot be over-emphasized. Wherever the fallow has been shortened to a period inimical to the development of trees, land productivity in terms of food crop yields has declined. Shifting cultivation, in the classical sense of the moving of entire villages, may still be observed in isolated cases.

The reasons for the shifts have not been made clear and may not be directly related to factors influencing land productivity.

Tree crops, including plantain and banana (Muse spp.), accounted for up to 67 per cent of the land under cultivation, whereas arable crops accounted for only 25 per cent. Combinations of tree and arable crops, in mixtures, were common but were usually associated with farmers operating on small areas.

The taungya system is found only where forestry departments are establishing tree plantations. Food crop production takes place during the period between land clearing and plantation establishment phase. The system is not attractive to farmers and persists only where there is population pressure or when the diversion of land to plantations reduces the area available for land rotation as practiced in the bush fallow system.

Permanent compound farming represents an intensive management system in which soil fertility is maintained by addition of crop residues and household refuse. Both trees and arable crops are usually found in mixtures in this system. Plantains and bananas are of special significance in the system, as the high organic matter and mulching effect of the refuse increase the yield and productive longevity of these crops (Wilson and Braide, 1978). Fruit trees are generally found in these gardens and are readily accessible to the farm dwellers.

The overall picture reveals that outside permanent compound farms each farmer operates an arable crop (multiple cropping) and a tree crop enterprise. The arable crops supply food, and the tree crop provides cash income. The cash returns to labour from tree crops such as cocoa are often more than twice those from the food crop (Grinnell 1975). Land and labour with cash/credit as an occasional modifier are the important production factors in traditional crop production. Shortage of land invariably leads to reduction in the fallow period and expansion of the area under arable crops. Shortage of labour increases the area under tree crops but reduces the area under arable crops. Thus shortage of land appears the most serious factor threatening the survival of trees and ultimately that of human beings in the humid tropics.

The productivity of arable crop farming in traditional agriculture is positively correlated with the duration of the bush fallow. Thus, as the fallow length declines, it becomes more and more difficult to produce the food necessary to sustain the population. Therefore, to reduce the role of woody species in soil fertility maintenance and erosion control is to reduce the food output of the traditional food production system (Grinnell 1975). Tree crop production systems are suited to the humid tropics, but food is essential for human survival. Thus, if self-sufficiency is deemed necessary, as in the subsistence systems common in the tropics, arable crops are essential in the farming systems.

The survey indicates that, under high population pressure, systems are evolved in which special woody species capable of restoring soil productivity with relatively shorter fallow periods are relatively encouraged to dominate the bush fallow (table 1). Farmers recognize the potential of these species, which can achieve in two to four years that which requires six to eight years under uncontrolled regeneration.

There are no clear indications that the farmers are deliberately planting special species as fallow (Benneh 1972; Okigbo and Lal 1979), but it is encouraging to know that their awareness of the effectiveness of these species may enhance their acceptance of using woody species to reduce fallow duration while increasing land productivity in the humid tropics.

The Natural Fallow

A natural fallow is regarded as one in which recolonization by plants occurs without the interference of humans. The normal sequence of fallow development is defined by soil and climatic factors, local plant species, the agricultural technology in use, and the duration of the fallow. The general fallow regeneration pattern in the humid regions of West Africa has herbaceous grasses and broadleaved species as dominant during the first two to three years, during which they are interspersed with seedlings, root shoots, or coppice regrowth of trees and tall shrubs. According to Okigbo and Lal (1979), where the fallow period exceeds 15 years the climax vegetation includes large trees such as Albizia gummifera, Anthocleista vogelli, Diospyros con fertifolia, Funtumia elastica, Nauclea (Sarcocephalus) diderrichii, Lophira alata, Brachystegia spp., Khaya ivorensis, Triplochiton scleroxylon, Ficus spp., Cola spp., Celtis spp., and Antiaris spp. Elaeis guineensis occurs frequently in the less-crowded spaces. This type of fallow occurs only in areas of low population density where the cropping period is short and the fallow period long.

TABLE 1. Vegetation Density and Botanical Composition of Three- and Seven-year-old Bush Fallows in Eastern Nigeria


Density/ha (%)

Density/ha (%)

3-yr. 7-yr. 3-yr. 7-yr.
Dialium guineense 48.4 41.0 0.8  
Anthonotha macrophylla 27.0 34.6 53.4 33.7
Pentaclethra macrophylla 2.4 - - -
Acioa barter) 12.7 23.9 - 3.6
Alchornea cordifolia 9.5 0.5 15.3 51.2
Napoleona imperialis - - - 3.6
MM (unknown) - - 30.5 7.8
Total 100.0 100.0 100.0 99.9
Total stems/ha 1,008 1,504 1,048 1,328

Source: Amaza, Akukwe, Getahun, Okafor, et al. (unpublished),

TABLE 2. Effects of Clearing Techniques on Maize Yield, Soil Erosion, and Water Runoff

Clearing Method Grain yield maize
Soil erosion
Water runoff (mm) Soil loss/ grain yield
Traditional (partial clearing of  
secondary forest) 0.5 0.01 2.64 0.02
Manual, complete clearing 1.6 4.64 54.30 2.90
Mechanical, complete clearing 1.8 19.57 250.33 10.87

Water runoff and soil erosion losses before forest clearing were minimal.
Source: IITA 1979 (b)

Where population density is high, the fallow is short, and a new set of species is dominant in what may appear as a climax vegetation. Obi and Tuley (1973) listed the dominant species as Alchornea cordifolia, Acioa barter), and Anthonotha macrophylla. Other abundant species include Harungana madagascariensis, Dialium guineense, and Crestis ferruginea. These are interspersed with many other species.

Among the many species that dominate natural fallows, farmers have recognized the superiority of certain species in restoring soil fertility and have encouraged these species.

The preference given to some of these plants results in almost pure stands in some fallows. Benneh (1972) and Okigbo and Lal (1979) have reported planted fallows of Acioa barter), Anthonotha macrophylla, and Alchornea cordifolia in eastern Nigeria. Observations by Kang (unpublished) at Onne in eastern Nigeria showed varying populations of Anthonotha ranging as high as 1,000 - 2,500 plants/ha. In Oyo State in south-western Nigeria Gliricidia septum dominates the fallow and could be regarded as an indirect planted fallow.

The effectiveness of trees in regenerating soil nutrients and land productivity is ascribed to their ability to absorb plant nutrients from the deep soil layers and contribute them to the upper layers through leaf litter (Lundgren 1978b; Nye and Greenland 1960). The conclusion drawn from these data is that tropical people have not yet devised systems of harnessing the nutrients derived from fallow without destroying or setting back the fallow.

The importance of trees in land management and particularly in soil-erosion control is clearly demonstrated by the results of a land clearing trial that was carried out at IITA (1979b) (Table 2). Complete removal of the tree cover and mechanical clearing greatly increased runoff and erosion.

The Planted Fallow

African farmers, renowned for mixed cropping, do not as a rule remove from their field any plants that are potentially useful. Thus a large number of the species seen in the field are not planted but are useful volunteers that are encouraged. This practice applies not only to food crop plants but also to plants that are known for their effectiveness in restoring soil fertility. The popularity of Acioa barter) and Anthonotha macrophylla in the bush fallow on acid Ultisols in eastern Nigeria does not result from direct planting but deliberate encouragement of volunteers. Farmers do not destroy the seedlings of these species, and this preference leads to their dominance in the plant population. In south-western Nigeria, especially around the city of Ibadan, farmers claim Gliricidia septum is an effective fallow species which restores land productivity for food crops after a fallow of only two years. Though the species was planted by farmers who have since accepted it as an effective soil-restoring plant, there is no evidence to suggest that it was ever deliberately planted for soil improvement. G. septum is usually established when green stems are used as yam stakes. These stakes grow, eventually providing the fallow that is maintained in a slash-and-burn system in which the base of the tree is never completely destroyed. Since G. septum readily coppices, it re-establishes itself once the pressure from cropping is removed.

Where planted forest becomes a part of the rotation, as in taungya systems in West Africa, farmers have reported their willingness to follow Gmelina arborea and Cassia siamea with food crops but have avoided lands that were planted to Tectona grandis. (See the paper by Kio, Bada, and Okali in this volume, pp. 108-110.)

Dilkman (1950) reported that prunings from the tree Leucaena leucocephah are traditionally laid among crops in Indonesia to provide nitrogen and that 1 ha of Leucaena provides nitrogen equivalent to that of 1 ton of sulphate of ammonia. Work in Hawaii (Guevarra 1976) has shown that 500 - 600 kg N/ha can be harvested from the foliage of L. leucocephala. Juo and Lal (1977) found that L. Ieucocephala was as effective as naturally regenerated fallow in restoring soil organic carbon and exchangeable cations. In addition to the nitrogen yield, the dry matter yield has an important role in preventing soil erosion when it is used as mulch. The nitrogen supplied by the leaves is the result of biological nitrogen fixation, as neither leaf nor nitrogen yield was affected by applied nitrogen (Kang et al. 1981). In a study of a single harvest at the start of the rains, the tree Gliricidia septum was shown to produce less leaf dry matter and nitrogen than the shrubs Cajanus cajan and Tephrosia candida (Wilson and Kang 1980). The low yield from G. septum resulted from its deciduous tendency, as the leaves are shed toward the end of the dry season.

Though there are many reports on the effectiveness of herbaceous fallow in the tropics (Webster and Wilson 1966), very little scientific information exists on the use of tree fallows. Jaiyebo and Moore (1964) have demonstrated that a bush fallow is more effective than legume or grass cover crops in nutrient recycling and in increasing soil organic matter.

Guevarra (1976) examined the possibility of intercropping L. Ieucocephah with maize and concluded that reasonable maize yields could be obtained when the L. Ieucocephala prunings were used as fertilizer. We (Wilson and Kang 1980) have developed the "alley cropping" concept in which food crops, usually cereals and legumes, are grown in narrow alleys formed by fallow species (usually shrub or tree legumes). During the cropping period, the fallow is suppressed by regular pruning. This system is regarded as an improved bush fallow in which the fallow is formed by selected species and arranged to facilitate easier planting and crop maintenance, especially with mechanization. Though maize yields have not been as high as they are when inorganic fertilizers are added, crop performance in alley cropping indicates that sustained yields are obtainable in what appears to be a relatively stable system.

Maize-leucaena alley cropping at I ITA has thus far proved to be successful on the Alfisols. On the acid Ultisols, where Leucaena has not grown well, other tree fallow species are being tested for inclusion in the alley-cropping system.

Though alley cropping appears feasible, there are fears that farmers accustomed to cleared land may not accept trees in their fields. In addition it may be some time before equipment is developed for the mechanization of the operations associated with alley cropping. To overcome these problems, IITA is looking into the development of a cut-and-carry form of fallow management. In this system the fallow species would be grown on land unsuitable for arable cropping. The leaves and other prunings would be harvested regularly and transported to arable lands where they would be used as mulch and nutrient sources.

The alternative concept of establishing forest trees among food crops and continuing to crop the interrow spaces between the trees until the tree canopy closes could be regarded as a form of alley cropping in which suppression of the tree species occurs only after certain periods, say five to ten years, and regular pruning is not done during cropping.

With the shear-blade method of clearing land under tree fallow and with minimum tillage planting techniques, it is now possible to recover land from tree fallow and to establish certain crops without disturbing the soil. With these innovations, trees in the rotation may no longer be regarded as serious limitations to mechanization and largescale crop production in the humid tropics.

Forest conservation strategies for tropical Africa

Forest conservation strategies for tropical Africa

P.R.O. Kio
University of Ibadan, Ibadan Nigeria


Recent interest in agro-forestry practices has been generated against a background of rapidly deteriorating problems of forest exploitation and conservation in all forest ecosystems in Africa The continent is faced with the possibility of timber and fuelwood scarcity towards the end of the century. Conventional methods of forest regeneration, such as improved natural regeneration, associated with less wasteful logging techniques, accelerated industrial plantation programmes under public and private ownership, and fuel plantations sited near urban centres, are ways of combating the problem of fuelwood and timber shortage. The best approach is through universal application of the agro-forestry system so that forest destruction is arrested at the source. Intensified agro-forestry research is required to anticipate the difficulties arising from the radical changes that the adoption of agro-forestry will induce in the life-styles of rural communities.


The 1980s may witness widespread disasters arising from the misuse and over-exploitation of forest resources in the African region. Yet, for thousands of years and until the middle of the nineteenth century, human beings had little or no impact on the environment. A rich and varied vegetation, dominated by trees and an equally heterogeneous fauna, developed and maintained itself within a complex ecosystem-a balance between plants, animals, and the physical environment. In particular, the diversity of the African tropical rainforests and the rich genetic pool they contained provided a resource of vast potential that the metropolitan powers were later to recognize and exploit with little or no regard for their conservation.

Currently, the timber-rich zones of West and Central Africa contrast sharply in utilization and conservation patterns with those of the wildlife-rich zone of East Africa. In North Africa, desert and sub-desert conditions predominate north and south of the Tropic of Cancer. All the regions are faced with diminishing resources because of forest degradation, human and animal population pressures, mismanagement, and other forms of exploitation. It has been predicted that within the next 30 years, unless adequate measures are taken, most of the humid tropical forests will be transformed into unproductive land, and the deterioration of the savanna into desert will be accelerated.

Forest Destruction

Traditional agriculture in most parts of Africa has been shifting cultivation. This involves clearing a small piece of land by felling and burning most of the vegetation in the natural forest, secondary forest, or savanna woodlands. The area cleared is farmed for a few years (two to four, depening on the soil and climate) and is then abandoned to bush fallow. The disused farm land is gradually invaded by trees -at first by short-lived pioneer species, springing up amidst a tangle of creepers and shrubs, and eventually by true forest trees. Many years later the same, or another, farmer clears the area of secondary forest and harvests good crops for a few years before moving to another piece of mature or secondary forest. Many agronomists and soil scientists claim that this farming system has proved well adapted to the environmental conditions of most of tropical Africa (Nye and Greenland 1960). However, once population density reaches and exceeds certain critical limits, the fallow periods diminish and the soil-microfaunawildlifevegetation matrix that protects sensitive ecosystems suffers, perhaps irreversibly.

Obviously, in the process of eking out a meagre subsistence, shifting cultivators lay waste vast natural resources. Valuable timber trees are cut without being properly utilized. Foresters have long argued that shifting cultivation ought to be replaced by a more sedentary system. For instance, it is estimated that in the last 25 years tropical Africa has lost 100 million ha of moist forest to shifting cultivators, and the current loss is of the order of 400,000 ha/year (UNEP 1980).

Forest degradation is sometimes the least of the consequences arising from shifting cultivation. On sensitive sites, over-intensive utilization can damage the soil for long times, as visitors to the Agulu gullies in Awka Division of Anambra State in Nigeria can readily verify. Effects are especially pronounced in dry environments where the vegetation tends to recover more slowly than in moist environments. Protracted cultivation keeps the ground bare and vulnerable to wind and water erosion.

Fire is an important element in the conversion of the natural forests into simpler ecosystems. It is used in the first instance as a means of releasing some of the nutrients locked up in the biomass, and for creating a clean environment for the agricultural crops. In a dry climate, frequent use of fire kills fire-sensitive species of trees and shrubs and creates favourable conditions for the invasion of grass species, particularly Imperata cylindrica. Dry savannas provide very important pastures, but over-grazing threatens the natural pastures in Africa and, indeed, in the entire tropical world (Persson 1977).

Fuelwood and charcoal account for more than 90 per cent of wood consumption in Africa. The cutting of trees for fuelwood occurs in all ecological zones and does not adversely effect the environment as long as natural regeneration is possible and the population density is low. In many areas, the present population is so large that the existing wood resources are over-exploited. In many parts of Africa misuse of the bush and over-exploitation have led to complete disappearance of the wooded vegetation. In and around urban centres, shortages of fuelwood occur even in humid zones.

The level of nutrition of a community is sometimes linked to fuelwood availability and costs. It is claimed that there are now places in the Sahel where fuel (petroleum products, firewood, and charcoal) has become so expensive that it absorbs about half the budget of some of the poorer families (Poulsen 1978). With extensive deforestation, villagers are forced to walk long distances to collect firewood and eventually are tempted to substitute dried cow dung and crop residues for firewood, with serious consequences for local agriculture. Even in oil-rich countries, such as Nigeria, rural households that have not invested in modern oil- or gas-burning stoves purchase firewood in preference to kerosene, which in some parts of the country is half the price.

Apart from the deterioration in the quality of life associated with forest degradation, there are other more insidious effects that endanger the future of human beings on this planet. For instance, climate is determined by physical factors near the earth's surface, set in motion by the sun's energy. Vegetation influences the earth's surface in two ways: by reducing wind velocity and by intercepting the sun's radiation (albedo). But climate is one of the main vegetation-forming factors, causing differences in the vegetation cover of the earth. This relationship suggests that a feedback mechanism exists and that changes in vegetation, including those induced by humans, may result in irreversible changes in climate.

The Forest Resources

Vegetation type is mainly determined by climate, soil, and anthropogenic factors. In Africa the moist forest at low and medium altitudes is concentrated in Central Africa. It extends from the Congo Basin to southern Nigeria. A gap occurs in Togo, Benin, and south-eastern Ghana, and it then continues westward to Sierra Leone. The extent of the moist forest is about 256 million ha, of which 76 per cent (194 million ha) is found in Central Africa (Persson 1977) and 19 per cent (48 million ha) in West Africa.

This forest type occurs where the monthly mean temperatures rarely fall below 25 C, the mean annual rainfall is always in excess of 1,500 mm, and there is at most a short dry season.

The forest-savanna mosaic forms a belt around the moist forest. The drier part of the moist forest is described as semideciduous, and, in West Africa, it tends to be richer in desirable timber species than the true moist or rain forest. Shifting cultivation has destroyed the major part of the dry forest. The intermediate stage in the final degradation of the original continuous belt of semi-deciduous forest is the formation of a patchwork of high forests and savanna woodlands.

The savannas, both moist and dry, cover a total of 988 million ha, or 42 percent of the land area in Africa. Many ecologists believe that the areas now occupied by moist savanna were once covered by semi-deciduous forests that have been transformed artificially into savanna by centuries of shifting cultivation and annual fires. The limit for fire-induced savanna is believed to coincide with those areas enjoying three dry months or, alternatively, with those areas receiving an annual rainfall of 1,250-1,500 mm. Some remnants of the original forest remain, for example, in the Casamance region in Senegal and the Mambilla Plateau in northern Nigeria.

The moist savannas in West Africa are known as Guinea savanna, and the drier ones are designated Sudan savanna. Miombo woodland is found south of the equator, particularly in Tanzania, Zambia, and Zimbabwe. When protected from fire, the Miombo woodlands develop the characteristics of tropical high forests, particularly by the presence of climbers and dense herbaceous and shrub layers. Kalahari woodland occurs as a broad belt in the western part of Zambia and continues into the kalahari sands of Angola. Mopane and Munga woodlands occur in the dry savanna south of the equator.

Wooded steppe with abundant Acacia and Commiphora is found between the dry savanna and semi-desert. It is characterized by the occurrence of widely scattered trees, and is typically known as Sahel vegetation in West Africa, where low thorny trees are the dominant woody plant. Unlike the savannas, over-grazing by animals is considered to be more a causal factor than is fire or shifting cultivation.

Grasslands occur as patches amidst moist and dry savannas and are predominant in steppes. Extensive grasslands occupy the central part of Madagascar, western Zambia, and eastern Angola.

The Mediterranean region has hot dry summers and cyclonic winter rains. Most of the vegetation in the region has been degraded over millennia. After being burned and over-grazed, particularly by goats, the forests disappear completely. Maquis scrub occurs both in dry and moist areas, and this is normally regarded as a degraded form of denser associations.

Management and Use

In terms of potential for forest management, only the moist forests, semi-deciduous forests, and the savannas are worthy of detailed consideration. Apart from about 2 million ha of natural softwood forests that occur in East Africa (mainly in the highlands of Kenya and Ethiopia), the natural forests of forestry importance can be grouped into closed hardwood and open hardwood (table 1). Each group can be subdivided on the basis of whether or not it can be intensively managed, that is, whether or not it is immediately operable.

Of the total productive forests of 466 million ha, 57 per cent, or 264 million ha, lie in Central Africa, whereas West Africa accounts for only 12 per cent (58 million ha) If the productive closed hardwood forests alone are considered, 115 million ha of a total 134 million ha are found in Central Africa. Central Africa, thus, has by far the most important forest resources in the continent, and West Africa now has relatively limited forest resources in relation to the present rate of exploitation.

Field studies undertaken in June 1980 have shown that timber production will rely increasingly on the reserved forest estate (Kio 1980). It is estimated that between 1990 and 2000 most of the timber outside the forest estate will have been extracted in Cameroon, Ghana, Kenya, and Nigeria.

The proportion of timber currently extracted from unreserved forest varies from less than 20 per cent in Nigeria to about 90 per cent in Cameroon. Of the six countries studied, only two (Cameroon and Ghana) exported more than half their total timber output. The others (Kenya, Nigeria, Tanzania, and Zambia) consumed virtually all their timber output internally.

The continent is faced with the possibility of timber and fuelwood scarcity toward the end of the century. What attempts are being made to alter the trends? By applying already available knowledge, by filling in crucial gaps in the understanding of the various ecosystems by well-directed research, and by recognizing the limitations imposed by the fragility of the African soils, this continent can arrest natural resource destruction and greatly increase production of natural raw materials.

Silvicultural treatment of the moist savannas of West Africa and Miombo woodland of East and Central Africa has consisted of protection from fire and thinning of mall-formed and over-mature trees. Harvesting is by clear-felling, and regeneration by coppice regrowth. This approach appears to be adequate, as the main products (pit props, particularly in Zambia, poles, fuelwood, and, in rare cases, sawn timber) can be more economically harvested through clear-cutting.

TABLE 1. Estimated Areas of Natural Forests in Africa in 1975 (in million ha)


Closed hardwood forests

Open hardwood forests

  Productive Inoperable (operable) Productive (operable) Inoperable  
Northern savanna 0.02 0.16 10.43 41.93 52.54
West Africa 12.13 1.95 45.94 2.65 62.67
Central Africa 115.36 55.29 148.43 6.17 325.25
East Africa 6.31 10.57 105.99 39.08 161.95
Tropical South Africa 0 0 21.72 21.29 43.01
Totals 133.82 67.97 332.51 111.12 645.42

Source: Data by Lanlv end Clement (1979)

Complex natural ecosystems, such as the moist tropical forest, with their many species and rich interaction structure, are in general dynamically fragile. Phenological changes tend to be distinctive for each species and occur over a very short time. Silvicultural and management treatments of the closed forests seem to alter the direction of the natural succession attributable to non-human phenomena. For these treatments to succeed, the largely unsolved problem of ensuring adequate regeneration following exploitation must be tackled. This requires detailed knowledge of flowering and fruiting sequences, of the processes and conditions of germination, establishment, and ensuing competition and growth of the desirable species.

The issue of natural regeneration of the moist closed forests is central to the problem of forest degradation and conservation in Africa. All silvicultural systems applied to tropical moist forests attempt to simplify the composition of the forest so that the stands are considerably richer in economic species after exploitation and treatment than before such operations. The methods include those of improving Aucoumea klaineana, Terminalia superba, Triplochiton scleroxylon, and similar forest stands in the Ivory Coast, the shelterwood system of Nigeria, and the selection system in Ghana. These techniques differ in their exploitation regimes. The Nigerian shelterwood system theoretically involves clearfelling with shelterwood regeneration to create a more or less uniform forest by a combination of intensive exploitation and clearance poisoning of shade-casting uneconomic trees in the middle and lower storeys. In reality, clear-felling as such has never taken place due to a highly restricted list of desirable species. Residual stands were so heavily wooded that higher volumes have been known to be removed in subsequent intensive exploitation than under the first exploitation.

As a result of the limited success and difficulties experienced with natural regeneration and the spectacular achievements of certain plantations such as Eucalyptus spp., Gmelina arborea, Tectona grandis, and Pinus caribaea, many foresters have proposed that natural forest should be replaced by predominantly monospecific plantations. This proposal gathered momentum after the World Forestry Congress at Buenos Aires in 1972 and is sustained by the readiness of international financial institutions to provide huge loans for plantation projects and their reluctance to finance natural regeneration programmes.

The consequences of the removal, modification, or transformation of substantial areas of moist forests in Africa are being publicized in national and international forestry conferences. An extensive bibliography is building up on the need to exercise caution and restraint in the exploitation and treatment of the tropical forests. It remains to be seen whether the traditional despoilers of the continent's natural resources will heed these warnings.


Various studies have shown that, with the possible exception of Zaire, Cameroon, and Congo, the natural forests of most countries in Africa will be unable to meet the domestic demand for wood-based products by the beginning of the 21st century. The establishment of plantations in all suitable vegetation types (not necessarily only moist closed forest) is one way of meeting this huge demand. The species chosen should be fast-growing and high-yielding, and the wood product should be homogeneous in both size and quality in order to meet the specifications of particular industries. However, the main disadvantages are the dangers of monoculture and the loss of rich natural forests if the plantations are not carefully sited. Every large-scale plantation project that neglects the need to diversify species and to conserve some natural forests, both in the untouched state and under intensive management, may in the long run prove disastrous.

It is often argued that the growth of world population, including that in Africa, is leading to a demand for food, space, and raw materials so great that it can only be met by exploiting the area now covered by forest for living space for people, for growing food and raw materials, and also for industry (Poore 1976). Uncritical acceptance of this view implies that the disappearance of most of the closed moist forests is inevitable. However, a careful evaluation of the circumstances of natural-resource utilization shows that the disappearance of natural forests is only unavoidable if no effort is made to change the factors and policies that have in the past led to the abuse of these resources.

Problems associated with forest degradation cut across national boundaries, and only internationally co-ordinated programmes of control and amelioration can stand a chance of some measure of success. First, forest policies that emphasize rational utilization of resources should be harmonized throughout the continent. Second, every country should improve the management of the forest estate, including legal protection of reserves against encroachment, make an inventory of all the forest resources, improve the training of personnel, and establish an effective administration supported by adequate and timely financial allocations to forest services. Third, the strategy for development of tropical forests should be based on a careful balancing of ecological and economic considerations. The major obstacles to good forest management are the lack of national and local institutions able to design and enforce proper strategies, and the disregard for the role of forestry in development.

Fourth, in spite of recent happenings in Chad, Niger, Senegal, and Gambia and in spite of the involvement of foreign elements in the recent Kano riots, regional economic groupings must be fostered for both economic and political reasons. Integration may become an important instrument for economic growth of subregions or the African continent as a whole. Removing barriers to the free movement of goods, labour, and capital within a region almost inevitably leads to the expansion of trade and, consequently, of incomes and employment.

Larger economic units, with their larger markets, permit economies of scale in production and justify the establishment of forest enterprises previously considered too costly. Resources and capital tend to move freely to the most productive areas with their larger markets and thereby stimulate further gains in production. Similarly, cheaper and more efficient transportation systems may result. The larger markets emanating from integration should attract more substantial foreign investment (Eken 1979). Especially in Africa, where forest resource endowments vary greatly from one country to another, the establishment of subregional economic groupings is the only way to strengthen collective self-reliance as an insurance against political subservience to metropolitan powers and against external subversion.

Finally, the practice of agro-forestry holds the key to the containment of shifting cultivation by replacing its destructive features with a system of land rotation that combines the simultaneous production of agricultural and tree crops. Much research into the various aspects of agro-forestry is in progress but is, at present, unfocused, and the role of the uneducated peasant farmer with little access to modern agricultural and forestry inputs is hardly defined in the schemes being suggested.

If socio-economic research is combined with the research strategy suggested by Lundgren (1979), greater progress is likely to be achieved: The suggested agro-forestry research strategy is:

  • Identification of interrelations between soils and crops, including the monitoring of the soil over at least one rotation, quantitatively monitoring the effects of different tree crops in terms of inputs and outputs of nutrients and organic matter in the system during the rotation, assessing the importance of catenary gradients on research methods, and finding more or less self-maintaining land-use systems (that is, research must have a strong resource-conservation base);
  • Identification of short- and long-term aims of soil management, including the importance of mulch cover and its duration; the maintenance of soil organic matter; the maintenance of dense and efficient top-soil feeder root systems; and the minimization of burning to prevent nitrogen and organic matter losses;
  • Synthesis of the state of knowledge of soil-crop relations relevant to agro-forestry; and - Identification of problems and bottlenecks particularly related to the study of soils in agro-forestry.

For greater effectiveness these research programmes have to be co-ordinated at subregional and regional levels by the establishment of appropriate machineries for consultation, collaboration, and dissemination of research information. Coordinated research throughout the African region, at least in so far as research into conservation and agro-forestry problems is concerned, will minimize wasteful duplications and produce results that truly reflect conditions in the ecosystems studied.

Impact of agricultural systems and rural development on Nigerian forests

Impact of agricultural systems and rural development on Nigerian forests

Bede N. Okigbo
International Institute of Tropical Agriculture, Ibadan, Nigeria


Agriculture is still the dominant means of livelihood in Nigeria, even though urban areas are growing rapidly in size and the rural-urban income and services gap is widening. The different types of traditional farms are discussed, with special emphasis on forest-farm interactions The sequence of agricultural intensification from shifting cultivation to sedentary agriculture in south-western Nigeria is defined, with special reference to the woody and perennial species of compound farms Possible alternatives, such as specialized horticulture and animal husbandry, are briefly reviewed with regard to their impact on the tropical rainforest Recommendations are then made regarding the future course of agricultural development


As three-dimensional units of the biosphere, forests constitute biomass in which the climax vegetation is dominated by trees. The tropical rainforest is the climax vegetation in areas of constantly high temperatures, humidity, and rainfall, precipitation usually exceeding evapotranspiration for more than half the Year (Bene et al. 1977). About 27 per cent of the world's tropical rainforest is located in Africa (Bene et al. 1977), and the tropical rainforest is estimated to amount to 31 per cent of the forested area of Nigeria (Redhead 19701. It usually consists of a plant formation of marked diversity of species-most of which are trees in association with shrubs and herbs- arranged in a number of strata within which there are mechanically dependent climbers, stranglers, and epiphytes in addition to heterotrophs (saprophytes and parasites], all of which under normal circumstances are in equilibrium with their environment through competition, interdependence, end complementarily (Richards 1952;Walter 19711. As a unit of vegetation, the zonal tropical rainforest, although closely related to the climate, soil, and rainfall of the region, may vary in species composition, extent of development, and physiographic features as a result of edaphic factors.

An agricultural farm or farming system consists of an enterprise or business in which sets of inputs and resources are uniquely orchestrated by the farmers in such a way as to achieve one or more desired objectives in a given environmental setting (Okigbo 1978). In the Nigerian context, the farm may be an enterprise or activity of one or more individuals-usually a family unit-with all or only some members participating for part or most of the time in farm work. In the complex traditional farming systems of tropical Africa, a specific farm system consists of one or more subsystems, each of which is differentiated from others in terms of the physiochemical (soils, water, climate, nutrients), biological (crops, plants, animals, pests), socioeconomic (labour, markets, preferences, religion), technological (tools, machines, practices) and managerial (knowledge, decisionmaking) elements involved. Consequently, a given agricultural system or subsystem is location specific in terms of sets of the elements that are involved in relation to the objectives to be satisfied.

Although the annual rate of urban population growth in West Africa is more than 5 per cent, the Nigerian population remains essentially rural, with only 12 per cent of the population estimated to be in towns of more than 20,000 (Unesco 1976). During the colonial era and, especially, since independence, pressures of modernization have resulted in high priority being given to industrialization and development of the non-agricultural sector of the economy. Agriculture, which is the dominant occupation and way of life of more than 80 per cent of Nigeria's population, has also undergone significant changes and development resulting from colonization, population pressure, introduction of new crops and techniques, and increasing commercialization. Changes in non-agricultural and agricultural activities involve interaction of environment, economy, and society that give rise to resource and environment issues (Knight and Newman 1976; Knight 1976). As a result of higher priorities being given to the industrial and non-agricultural sectors, higher incomes resulting therefrom, and problable greater complexity of the biological processes involved in agricultural production, much less progress has been made in agriculture. Consequently, the gap between rich and poor, and between rural and urban centres, is growing. Rural development is the process of redressing this imbalance by improving the quality of life and the rural environment through increased efficiency in management and utilization of resources. Development and modernization activities in agriculture and rural development vis-a-vis those in industrial and non-agricultural sectors may be competitive, complementary, or both. All the activities involved may have adverse effects on the forest ecosystem.

Farming Systems and the Forest Ecosystem in the Rainforest Areas of Nigeria

According to Okigbo and Greenland (19761, a simplistic model of traditional farming in the rainforest areas of Nigeria would regard each family farm as consisting of a more or less concentric pattern of fields on which are practiced various methods of fertility maintenance or fallows, clearance systems, production of various species of crops, and cropping patterns and sequences (fig. 11. Each field differs in the length of fallow, number of arable crop species grown, and distance from the compound farm. The farther the field from the compound farm the longer the period of fallow, the fewer the arable and other crops cultivated, and the more protected or useful wild plants are selectively left dotted about the field during clearing.

Unlike farms of developed temperate countries, farms of the humid tropics of West Africa are extremely complex. A typical farm family may operate a compound farm, several field systems of arable food or export crops, patches of tree crops and vegetable crops under peculiar topographic situations, and non-food crops intercropped with the food crops. The same farm family may carry out floodland agriculture close to a river or stream in addition to always having animal production in the compound farm and adjacent areas in association with crop production.

FIG. 1 Schematic Diagram of Compound Farms in Relation to Associated Fields in Traditional Farming Systems of the Humid Tropics of West Africa

Hunting and gathering continue to be associated with agricultural production in present-day Nigeria. However, the extent of dependence on hunting, fishing, and the gathering of wild plant products varies considerably from one location to another in relation to population pressure and resultant adverse effects on forests and wildlife.

Richards (19521, Adejuwon (1971), and Whyte (1974) have observed that initial degradation and disruption of forest ecosystems result from clearing and cultivation, but usually the forest vegetation regenerates itself during a prolonged period of fallow. This, according to Nye and Greenland (1960), may take more than five years. The extent to which the cleared forest develops into a savanna woodland with a high proportion of graminaceous species depends on how frequently fires are applied to the vegetation. Sometimes mining activities or sheet erosion may also produce similar effects to frequent fires.

Okigbo (1977) listed bush clearing, burning of vegetation, fallowing, preplanting cultivation, manuring and fertilization, weeding, cropping patterns, grazing, restriction of livestock, and harvesting practices as the human activities that are associated with different farming systems. These practices determine the extent of erosion hazard associated with the farming systems, nature and magnitude of modification of vegetation cover, land use and eventual cultural landscape of a region.

In general, regular cultivation of arable crops is detrimental to forest regrowth unless long periods of fallow are involved in the land-use cycle. The different practices associated with different farming systems determine the magnitude and type of erosion that will occur and the adverse effects of soil - plant - water relations that may result in soil degradation. The effects may not be limited to the farmland where the practices are used but may extend to adjacent non-farmlands.

In the humid tropics, where population density is low, long periods of fallow result in secondary forest vegetation that usually never matures due to continuous sequences of clearing and cultivation. Classical shifting cultivation in which homesteads periodically move with the fields and forests become easily re-established after each cropping phase is no longer found in the rainforest region of Nigeria because of prevailing relatively high population densities. Even when fallows are long, the introduction of mechanical clearing results in poor forest fallow establishment.

Shifting Cultivation and Compound Farms

The bush-fallow system is a modern version of shifting cultivation; it results in isolated patches of secondary bush at various stages of regeneration. The climax vegetation attained never reaches the same level of maturity as in the earlier version in which fallows are longer. However, since this is associated with sedentary culture, compound farms become more developed and approximate secondary bush conditions. Usually selected numbers and species of trees grow on both compounds and outlying fields, but the proportion of trees may be much less than 50 per cent of the plant species growing per unit area. This farming system results in gradual replacement of forest ecosystems with compound farms and more open fields at various stages of secondary bush regrowth.

In rudimentary sedentary cultures compound farms are usually well-developed, and, although the compound farm has a much lower diversity index, it approximates rainforest ecosystem conditions where rainfall, soil conditions, and farm practices permit. Crop production on field systems associated with the compound farm is usually more intense than in shifting cultivation and bush fallow, and protected trees and shrubs on outlying fields may be less in number per unit area. This also results in isolated compound farms with a mosaic of selected tree crops and arable crops inter-spersed with more open fields of arable crops, with the fields becoming completely devoid of trees and shrubs where more modern farming techiques and machinery are used.

In intensive sedentary agriculture or compound farming, the compound farm system is most highly developed, and fertility is maintained by the use of household and compound refuse and concentration of plant residues from surrounding farm and fallow land. In south-eastern Nigeria, the animal population increases with population density, with the animals also involved in nutrient recycling. Several compound farms and adjacent fields may coalesce to form oil palm or secondary bush ecosystems that cover large areas of land. This accounts for much of the oil palm bush in south-eastern Nigeria.

Terrace Farming and Flood Plain Agriculture

Terrace farms are farms that are built on defensive hillsides on Bauchi Plateau, Adamawa Highlands, and in the Maku area of Awgwu Division in Anambra State. Tree crops are abundant in the valleys, on some steep uncultivated slopes, and in compound gardens. The terraces are usually used for growing arable crops, high-value vegetable crops, and minimal tree crops. Usually, population density is very high and not much fallowing of more than two years is practiced.

Flood plain agriculture depends on alluvial deposits to maintain soil fertility. Farmers on banks of major rivers race against floods in harvesting their crops. Usually forests are unable to develop on the flood plains because of the periodic inundation.

Mixed Farming

Mixed farming involves the keeping of livestock in association with crop production. Classical mixed farms with large animals used for work and transportation are limited to the savanna. Most traditional farming systems are mixed farms involving various numbers of small animals. There is always danger of over-grazing, forest clearing, and fires, since no efficient system of growing browse trees and shrubs for regular and intense small livestock production has been developed. Some of the most eroded and gullied areas of Anambra State are areas where both dwarf cattle and small animals are kept on land with physiographic features favourable for serious erosion when there is inadequate vegetation cover.

Intensive Livestock Production

Intensive keeping of poultry, pigs, and dairy cattle is also practiced. Poultry do not pose a serious hazard to vegetation cover except insofar as forests may be cleared for arable crops, such as maize, for poultry feed. Intensive production systems for pigs and cattle involve the growing of arable crops for feed and maintenance of pastures. Since these crops are generally under continuous cultivation, forest cover is usually totally removed. However, efficient pasture and crop management is necessary to maintain high levels of productivity without continuous clearing of more forest land.

Large-Scale Plantations and Tree Crops

Large-scale plantations and tree crops result in the replacement of the high species diversity of the tropical rainforest with monocultures of tree crops or mixtures of two or more tree crops, such as in the growing of coffee or cocoa with shade trees. Unless soil fertility is low and fertilization is not practiced, vegetation approximating forest formations usually develops. Poor mechanical forest clearing prior to plantation establishment may result in irreversible degradation of soil, failure of the plantation, and take-over of sites by weeds such as Eupatorium odoratum.

Specialized Horticulture

Specialized horticulture may involve production of tree crops or ornamentals that may be trees or shrubs and are similar in physiognomy to plantations. Intensive vegetable production usually involves permanent cultivation and' initial removal of forest cover. Manuring and fertilization are usually practiced, but where adequate soil conservation measures are not taken, deterioration of farmland under permanent cultivation may threaten forests on land adjacent to the vegetable or ornamental plant gardens.

General Obsarvations on the Impact of Farming Systems and Rural Development on Rainforest Ecosystems

The impact of human activities on vegetation, of which the tropical rainforest is but a part, is dependent on the extent of intensification of agricultural production and economic activities including clearing, grazing, burning, forest exploitation, hunting, gathering, mining, etc. In the humid tropics, agricultural systems, as they become intensified and commercialized, involve permanent cultivation and continuing extension of areas under cultivation except to the extent that tree crops are grown in plantations and compound farms. With the exception of savanna-like woodlands and grasslands that are found within the climatic climax areas of the tropical rainforest as a result of certain physiographic and other factors (Adejuwon 1968-1971), only isolated forest reserves amounting to about 2 per cent of the land area of Nigeria approach the primary undisturbed forest ecosystem. Even these remnants are threatened by rapid exploitation without an assurance of effective reforestation. Consequently, along latitudes 6 - 7.5°N, and even below this zone, high population densities and agricultural activities have culminated in the rainforest being replaced by secondary bush. In most of southeastern Nigeria this consists of oil palm bush and natural or planted bush fallows at different stages of regeneration, depending on the number of years after the last cultivation phase.

Fully developed bush fallows, five to ten years old, in southeastern Nigeria consist of shrubs, young trees, some grasses, and herbs. The canopy height ranges from 2.5 to 5 m, with Alchornea cordifolia, Acioa barter), and Anthonotha macrophylla as the dominant species; abundant species include Harungana madagascariensis, Dialium guineense, and Crestis ferruginea, and some 60 other species (Obi and Tuley 1973). Occasionally fast-growing emergents and indicators of secondary forest regrowth such as Musanga cecroploides and Anthocleista spp. exceed the more or less uniform highs of around 3 - 5 m. Where over-cultivation and loss of soil fertility have occurred, a mixed grass and herbaceous dicot flora develop in which the dominant species may be Eupatorium odoratum, Panicum maximum, Andropogon tectorum, Mikanio cordata, legumes such as Centrosema and Pueraria, Imperata cylindrica; and successions involving Melinis minutiflora, Pennisetum pedicellatum, Axonopus compressus, Schizachyrium brevifolium, and Brachiaria spp., culminating later in the appearance of Pteridium aquilinum (Obi and Tuley 1973) in certain locations. Bush fallows are most highly developed outside the compound farms with an agro-ecosystem consisting of useful trees such as the oil palm, coconut, Cola spp., etc.

Usually the compound farm contains plants that, under natural circumstances, do not occur together-such as Pandanus candelabrum and Raphia spp. Some of the trees on compound farms provide support for useful woody climbers such as Landolphia owariensis, Tetracarpidium conophorum, and even Strophanthus spp. for medicinal purposes. The compound farm system in Bendel State resembles those of south-eastern Nigeria, but generally the oil palm and planted or bush fallows are replaced by thicker forest or secondary forest fallows. There are still large areas of secondary bush with trees of over 20 - 30 m. In Bendel State there are tree crop plantations of oil palms, rubber, and, to some extent, cocoa. In Ondo, Ogun, and Oyo states there are cocoa and cola nut plantations but urbanization is more pronounced and complex compound farm systems are not as elaborate as in south-eastern Nigeria. Some of the cocoa plantations carry shade trees such as Albizia spp. and Terminalia spp.; newly established cocoa plantations may have plantains intercropped with the cocoa. In the outskirts of urban centres and in rural areas, the compound farms involve complex tree crop intercropping systems in which cocoa, citrus fruits, coffee, cola, mangoes, and bananas are grown.

Thus, traditional production systems are being replaced by rotational bush fallows and semi-permanent and permanent cultivation systems. Therefore, the cultural landscape in most of the tropical rainforest area of Nigeria is one in which the zonal vegetation of evergreen and deciduous forest is fast disappearing as increased agricultural production is attained by increasing land area under cultivation at the expense of the forest ecosystem. In addition, the management of forests in Nigeria and their exploitation leave much to be desired.


Increased food production is vital to Nigeria's economic progress and the feeding of its rapidly increasing population cannot be effectively achieved and sustained on the basis of technology that is limited to increasing land area under cultivation. A suitable strategy should involve packages of improved agricultural production technology that increase productivity per unit area on small farms and enhance multiple land use. There is need also to develop permanent food production systems that effectively reduce the periods of fallow, thus releasing more land for agricultural production and other uses, including forest plantations. Moreover, agricultural development, industrialization, and rural development should, as a matter of policy, be planned and executed as an integrated whole with the objective of achieving efficient resource management and utilization with minimum adverse effects on the environment. One way of achieving this desired goal is through integrated land development, whereby watersheds are used as units in agricultural development in such a way that various crops, including tree crops, are grown in the different toposequences to which they are best adapted.

All the above would require that in education, training, and research, efforts are made to ensure that cultural practices which have adverse effects on the environment, such as the scraping away of vegetation from compounds, markets, and army camps, are eliminated, while ecologically sound traditional practices, such as certain aspects of intercropping on small farms, are retained and scientifically improved. The present cultural landscapes in many parts of Nigeria are culminations of interactions between humans and environment. Continuous monitoring and evaluation of effects of human activities on the forest ecosystem are necessary if timely and effective interventions are to be undertaken for maintaining favourable environmental quality while achieving rapid general economic and rural development.

Crop mixtures in traditional systems

Crop mixtures in traditional systems

Akinola A. Agboola
Professor of Soil Fertility and Farming Systems, Department of Agronomy, University of Ibadan, Ibadan, Nigeria


The traditional cropping system is stable because it is adapted to the farmers' level of technology and the soils' capability. It incorporates mixed cropping and bush fallow, and it gives a high total return per unit area of land. Furthermore, growing crops in mixtures is consistent with the farmers' goal of security. Their present systems have evolved naturally as an answer to the challenging environment in which they live.

Researchers have been hesitant to tackle multiple cropping experiments in general, and agro-forestry in particular, because of the infinite combinations possible, lack of knowledge about existing systems, and the traditional separation between agriculture and forestry. Also, multiple cropping is associated with unmechanized farming and low productivity; research in intercropping and multiple cropping should be geared to increasing the productivity and returns in both arable crops and forest products. The peasant farmers' system of agro-forestry should be improved upon, and researchers should evolve a combination of arable crops and fast-growing trees that can be easily adapted by smallholder farmers.

The traditional cropping systems will continue until an alternative is evolved that can fit into present technology, environmental constraints, and at the same time maintain high crop yield. My feeling is that agro-forestry research has the potential of offering an early and viable alternative.


Farming systems can be defined as the distribution of plants and animals in space and time and the combination of inputs believed to give maximum production in socioeconomic, political, and cultural contexts.

In Africa, a farmer or farm family usually operates a small, diversified agricultural enterprise. According to Okigbo (1978), farmers with a homestead in an upland, well-drained soil may operate a compound farm or garden close to their homestead and maintain two or more plots in cropping systems involving natural or planted fallow and in the flood plain of a nearby river or steam. They may also keep pigs, goats, sheep, and poultry for manure, meat, sales, etc.; they may be palm wine tappers, basket-makers, musicians, or priests in the traditional religion. The cropping mixtures on the farms often involve major staples, vegetables, and condiments in multiple, double, relay, and patch intercropping patterns of annuals, perennials, or both. The compound farm or homestead garden usually carries more species of cultivated plants than bush fallow farms.

The most common tradition in African cropping systems is the spatial arrangement of crops on the field. The crops are established haphazardly in mixed culture (Okigbo and Greenland 1975), the objectives being to take advantage of local topographic features and micro-relief; disperse species at wide enough spacings so that they do not compete for nutrients and light; ensure that crop cover is adequate to control soil erosion and weeds; and ensure that each species's requirements for sunlight are met. Where annual staples are uniformly planted among tree crops, heavy pruning of the tree crops is usually carried out to ensure that adequate light reaches the ground level. Whether crops are grown on mounds, beds, ridges, or the flat, their spatial arrangement and frequency in mixtures usually indicate their importance in the diet and sometimes their uses.

Intercropping and Multiple Cropping

The simultaneous cultivation of different crops on the same piece of land has been described interchangeably as mixed cropping or intercropping by Webster and Wilson (1966) and Norman (1971). Ruthenberg (1976), however, distinguishes between mixed cropping and intercropping on the basis of the pattern of the intermixture.

The term intercropping has been used rather generally in the literature as referring to the practice of growing two or more crops simultaneously in different but proximate stands (Okigbo 1978). Grimes (1963) defined a common practice in intercropping: the system of growing different crops in alternate rows, which he terms alternate row cropping. Row intercropping is common in filled areas, annuals often being planted under perennials. For instance, tall-growing crops such as cassava or bananas are planted in young coffee, cocoa, or rubber plantations (Sanchez 1979).

In multiple cropping, Herrera and Harwood (1973) indicated that each of the crop mixture patterns has different physiological characteristics and different advantages. For example, Norman (1974) showed that although there were at least 156 crop mixtures and many different spatial arrangements among Hausa farmers near Zaria (Nigeria), the most popular arrangement was a systematic spatial pattern on ridges. With intensification of cropping, interactions among plants become critical. The most widespread multiple cropping systems practiced in the humid tropics are mixed intercropping and relay intercropping.

Mixed intercropping is common when cereals, grain legumes, and root crops are grown together and when little or no tillage is practiced. For example, farmers in southern Nigeria plant simultaneously maize, cassava, vegetables, and cocoyam. In Abakaliki, Nigeria, mixed cropping is practiced in mounds or ridges of soil constructed with hoes. Several crops are planted on different parts of the mounds. For example, an Abakaliki farmer plants yams on the mound, rice in the furrow, and maize, okra, melon, and cassava on the lower parts of the mound. Mounding is beneficial because it increases the volume of soil available to root crops.

Relay intercropping is a practice where a second crop is planted after the first crop has entered the reproductive growth phase but prior to harvest. A common example is the maize-beans system used in most of Central America and much of tropical South America. Maize is planted in rows, usually at the beginning of the rainy season; when the ears are well formed, farmers break the stalks just below the ear and plant climbing bean varieties. Relay intercropping is also very common in rice-based systems in Taiwan. Up to five crops per year can be harvested by two relay successions, rice-melons followed by rice again relayed with cabbage and maize. At present, the maize-cassava relay is being developed at the University of Ibadan, with researchers studying the effects on soil nutrients.

Advantages and Disadvantages

Baker and Yusuf (1976) wrote that the almost universal practice of traditional cropping systems by subsistence farmers throughout the world is an indication that the system has evolved naturally as an answer to the challenging environment.

The rationales for crop mixtures are that they may be relatively more profitable than sole cropping (Chandra 1978), the difference between the marginal value product of resources and the opportunity cost of the resources being insignificant (Norman 1974); they are consistent with the goals of security and year-round subsistence needs (Andrew 1972); they may alleviate adverse conditions in the ecosystem; and they may maximize the space, water, and nutrients available. Some of these benefits can be further promoted by good tillage practices, based on the principle of minimizing disturbance of the ground and vegetative cover. The practice of minimum tillage, with ample crop residues left on the soil surface, has great potential.

Although monocropping tends to attract fewer diseases and insects, these are more likely to be highly prevalent and to cause considerable damage. Cropping mixtures may reduce the abilities of pests and diseases to spread. For instance, interplanting has been shown to reduce insect problems in groundnut-sorghum and cassava-maize mixtures and has reduced the incidence of bacterial blight.

The denser plant population usually found in crop mixtures may also help control weeds (FAO 1968). In addition, because crops mature at different times, mixtures may extend the period of the year during which the soil is protected by leaf cover and root systems (Igbozurike 1971).

The disadvantages of traditional systems are that there is reduced yield of the component crops (Chandra 1978; Webster and Wilson 1966; Agboola and Fayemi 1972); there may be competition for light, nutrients, and water (Dalal 1974; Willey 1979; Webster and Wilson 1966); there may be allelopathic effects due to excretion of toxic substances by one or more crops (Dalal 1974); the practice is not well suited to modern agriculture or mechanization and, thus, research on traditional systems has been inadequate (Ahmed and Gunasena 1979); and suitable methods for investigation are difficult to define (Haizel 1974).


Unfortunately, research workers appear to have been hesitant to tackle multiple cropping experiments because of the many crop combinations in use, and because multiple cropping by the peasant farmer is associated with non-mechanical farming and low levels of productivity. Doubts have been expressed as to whether any of the positive benefits of multiple cropping can be exploited at more advanced levels of farming. Attempts to improve production by the application of technology developed in temperate cropping systems have failed in Nigeria and in most other tropical countries, not because of farmers' conservatism but because the approach is inappropriate.

Farmers in the tropics have been noted to grow complex crop mixtures on compound farms, especially in the rainforest zones, where staples, vegetables, and perennial fruit trees are interplanted. As early as 45 years ago, Leakey (1934) observed that the relay and mixed cropping practices had many obvious advantages, and he recommended that those involved in agricultural development should give serious attention to research on traditional food production systems, especially those involving intercropping. This recommendation has largely been ignored, despite the fact that peasant farmers have repeatedly refused to adopt monocropping practices recommended by extension agents.

The main objectives of research into the productivity of mixtures might be to screen mixtures for high-yielding combinations; to test alleged advantages of traditionally grown mixtures; and to gain an understanding of the processes that lead to advantages so that, in a specific environment, a rational choice of components may lead to higher yields than are possible in monocultures.

Sturdy (1939) noted in East Africa that intercropping Crotalaria with millet, and groundnuts with sorghum, helped in the maintenance of soil fertility. Lambers (1940) reported that coffee intercropped with bananas in Kuri provided a mulch that improved the fertility of the soil. Results of experiments carried out by Agboola and Fayemi (1972) showed that legumes intercropped with early maize gave a maize yield equal to that obtainable with 55 kg/ha of nitrogen supplied as mineral fertilizer.

Much work still has to be done to quantify the nutrient level of soils under traditional crop combinations. In a study conducted in 1981 composite soil samples were taken from eight farms and their adjoining fallows, and in only one case was the fallow land significantly higher in nutrient status than the adjacent cultivated land. P, K, Fe, Zn, and Ca levels in the top 0-15 cm layer were higher in the cultivated fields than in the adjoining fallows, and this was attributed to the effect of burning after clearing. These data support the view that the length of the fallow has been drastically reduced, thereby reducing also the nutrient build-up. They imply that most farmers are actually cropping infertile lands and that the nutrient status of the field does not influence the farmers" choice of crop combinations. The choice of crop combinations seems instead to be influenced by the food staples usually planted in the area, and the inclusion of vegetables is related to the economic value of the crops and food preferences. No definite effect of the crop mixtures on the soil nutrient status could be established.

Summary and Conclusions

The best cropping system in the tropics, once the soil is considered as the main factor sustaining crop production, is one that will not expose the soil to erosion hazards Therefore, more research is needed to identify better combinations, including agro-forestry schemes, so that the best type of rotation can be developed for each ecological zone. Although zero tillage has been advocated by IITA, this cannot be practiced ail over the humid tropics because it is dependent on the soil, particularly the clay content, and the prevailing weather conditions. In some areas, the temperature is low during the harmattan, and the Fadama soils cake, necessitating extra soil preparation in the following rainy season. Thus at the University of If e zero tillage has proved to be unsatisfactory.

Besides protecting against erosion, an appropriate cropping system must guard against the breakdown of the soil structure and nutrients. A good system needs to take advantage of the tonnes of human, plant, and animal refuse being produced. It should be emphasized, however, that traditional farmers will continue with their existing system until an alternative is found that will maintain higher yields, conserve the soil, control weeds, and generally fit into their present technology.


The author appreciates the contributions from J.M.A. Tocunana and C.F. Yamoah, both postgraduate students of the University of Ibadan's Department of Agronomy.

Agricultural tree crops as a no-tillage system

Agricultural tree crops as a no-tillage system

R.D. Bowers
International Institute of Tropical Agriculture, Ibadan, Nigeria


The crisis in tropical agriculture is demonstrated by falling food production and migration to the towns It is argued that this is an inevitable process resulting from the inability of tropical agriculture to compete with the industrialized agriculture of the temperate zones. Industrial agriculture is a high-input agriculture, and success or failure depends on the input:output ratio. In the humid tropics, the input: output ratio is unfavourable, and industrial agriculture therefore impossible; hence the only viable form of production is subsistence farming. The obvious alternative to subsistence farming is mixed tree cropping, in which the characteristics of the natural forest cover are copied as closely as possible. Only in this way can the productive potential of the environment be realized and the fertility of the soil maintained. Crop mixtures may be selected from oil palm, coconut palm, breadfruit, plantains, coffee, cocoa, cola, citrus, and other trees. A plea is made for a research programme to be devoted to mixed tree cropping as one of the possible ways to improve the agriculture of the region lying between 10°N and 10°S.


The growth of temperate agriculture over many centuries has involved the destruction of forests and the planting of annual crops in their place. Land clearing and progress are seen to be linked. When developers come to tropical Africa, they assume that clearing the forest is progress; likewise, African people, anxious of emulating progress seen in other countries, follow the same course.

As an agricultural engineer, I suppose that I should be in the camp of forest destroyers, and I certainly would be if I thought that this policy could be successful in economic terms and acceptable ecologically. But all the evidence indicates that the widespread clearing of tropical forest and the large-scale planting of annual crops leads to financial and ecological disaster. The worst possible combination of circumstances for Nigeria would be for the fertility of the soil to run out at the same time as the oil runs out-a possibility which could well arise unless great care is exercised. A new type of agriculture, such as that based on mixed tree cropping, must be developed with all urgency, as it offers, perhaps, the only hope for the future.


I propose that there is a crisis in the agriculture of the region Iying between 10°N and 10°S and that there must be a reason for it.

The evidence for this crisis is falling food production and an increase in food imports. Further evidence is the mass migration from the rural areas to the towns. For those who stay in the country, the standard of living remains low, and there is little hope of improvement. The great majority of the people in the countryside are still subsistence farmers, just as they were before and during the period of colonialism, depending for the most part on the unaided strength of their bodies to wrest a living from the soil. They would seem to live in a world with which Western technology is unable to communicate.

Over the past 30 years, there has been no lack of attempts to improve agriculture in the humid tropics. That none of these efforts has significantly changed the methods of production, even in a limited area, cannot reasonably be held to be a result of bad luck or bad management. There must be fundamental economic reasons to explain why these attempts have failed so catastrophically. The competitiveness of tropical agriculture has seriously declined in relation to temperate agriculture; the reasons for this decline include:

  • The development of bigger and more effective machines. Just as it is no longer possible for a person with a headpan to shift earth competitively against one with a Caterpillar D9, so it is no longer possible for a person with a sickle to compete against one with a combine harvester; 30 years ago, however, when machines were smaller and less efficient, it was still possible for hand labour to compete;
  • All major crops have now been mechanized; 30 years ago, machines had not been perfected for the harvesting of cotton, groundnuts, or sugar cane. Production of these crops can now only be competitive (and provide the producer with a reasonable standard of living) if they are mechanized; and
  • Temperate region substitutes have been found for tropical crops. Soybean, sunflower, and oilseed rape have greatly reduced the demand for groundnut oil. Cotton has been displaced to a considerable extent by artificial fibres. Cane sugar has been threatened by sugar beet and, more recently, by high-fructose corn syrup.

Agriculture has gone through three phases: subsistence farming, commercial farming, and industrial farming. This last phase is still in full evolution and is rapidly displacing all forms of small-scale production because it is economically more efficient. Never in the history of human beings have the main food items been produced so cheaply in real terms as they are now in the temperate countries.

Industrial agriculture is, of necessity, a high-input agriculture because it depends on inputs of machinery, fertilizers, herbicides, insecticides, etc. Because labour forms a small part of production costs, the system cannot be made to work by a substitution of labour and land for capital.

Success or failure of industrial agriculture depends on the input:output ratio expressed as the cost of the various inputs that are needed to produce a given value of produce. By using this ratio, one can compare the efficiency of production at different places (table 1).

A profit of $0.05 is made on every dollar of produce in the USA, whereas a loss of $1.20 per dollar of produce occurs in the tropics. The loss has to be covered, for example by subsidizing inputs to subsidize the price, or by introducing import restrictions that keep the price artificially high. Support for the reliability of such input:output ratios is provided by the comparative farm gate prices of maize- approximately $1 50/t in the USA vs. $450/t in Nigeria.

Generally, profitability increases as expenditures on machinery and chemical inputs increase, up to a limit of about $0.55 per dollar. If the inputs cost more than about $0.65, commercial production is no longer possible. Production becomes economically absurd if the foreign exchange cost of the inputs exceeds the foreign exchange cost of the product.

TABLE 1. Indicative Input:Output Ratio of Maize Production in the USA and Nigeria (cents input to produce $1 output)

  USA Nigeria
Land 20 cents 30 cents
Infrastructure and machinery 15 cents 50 cents
Seed and agric. chemicals 35 cents 110 cents
Management and labour 10 cents 30 cents
Finance and taxes 15 cents -
Total cost of production 95 cents 220 cents

Input:output ratios are generally unfavourable in the humid tropics. Low yields are a result of leached soils, heavy runoff, loss of nutrients, and weed competition. Drying and storage in a hot, humid environment present further problems. Generally, unfavourable input:output ratios are found where yields are low. Approximately the same inputs per hectare will produce about 2.5 tonnes of maize in the humid tropics as against 7 tonnes in the USA. In other words, only 0.15 ha of land in the US, as compared with 0.4 ha in the humid tropics, is required to produce 1 tonne of maize. All land, machinery, herbicide and insecticide costs are directly related to area. Thus, they are all three times more expensive in the humid tropics per tonne of maize produced.

Increasing energy costs make the possibility of high-input agriculture recede even further. When inputs are expensive they can only be used where the return per unit used is high; only when inputs are cheap can they be used extensively. Since the oil price rise of 1973, hopes of using expensive inputs in marginal areas have declined.

Subsistence farming is the inevitable consequence of the unfavourable input:output ratios associated with the production of annual crops in the humid tropics. All other forms of annual crop production are economically impossible until such time as the agricultural scientists develop varieties that give input:output ratios comparable with those of similar crops grown in more favourable climates. This conclusion accords with the observable fact that subsistence agriculture is the universal form of annual crop production in West Africa.

But subsistence farming has been shown to have already failed: it cannot produce sufficient surplus to feed the large towns; it cannot supply cheap basic foodstuffs; and it cannot retain the young people on the land. The impasse appears total-the only system that is economically viable is incapable of supporting the modern economy for which developing countries are striving.

The Tree Crop Alternative

The tree crop alternative offers some hope. It is logical in both economic and ecological terms. The climax vegetation of the humid tropics is high forest, which produces the greatest sustainable rate of biomass formation. It captures all solar radiation year-round by virtue of the different layers of foliage. The layers of leaves, twigs, and branches absorb the incoming energy of tropical rainstorms, thus protecting the soil. Organic matter on the forest floor is protected from the direct sun. Runoff is reduced so that more water is available for plant growth, and extensive root systems explore the whole soil profile for nutrients. If society demands that the high forest be removed, it must be replaced by economic crops that copy as closely as possible the characteristics of the natural forest, and that afford equal protection to the environment. If mixed tree cropping is to be freely chosen in preference to annual crops it must show economic advantages.

There are reasons to think mixed tree cropping will significantly outperform annual crops as the cost of highenergy inputs rises because of its low labour requirements; low fertilizer, herbicide, and insecticide requirements; the prospects for an ideal no-tillage system; and rediced weed competition.


Tree crops appear to be so well-suited to the environment and have so many economic advantages that a research programme of tree crop development is urgently required. The potential for tree crops exists and in many cases is already being realized. The oil palm, for example, is by far the most efficient and cheapest source of vegetable oil. Under good conditions it will produce up to 6 tonnes oil/ha. It will, therefore, always hold a competitive advantage over the annual oilseed crops. It may be expected to constitute an important part in any mixed tree crop system. The coconut palm produces a good yield of both oil and protein. Further, the open canopy makes it very suitable for mixed cropping with plantains or bananas. The breadfruit tree (Artocarpus altilus) appears to produce up to 8 tons carbohydrates/ha. Accurate yields are not available because the tree has not been seriously studied. The best cultivars should be assembled to determine its productive capacity under a range of environmental conditions. The shea butter tree (Butyrospermum parkii) should be studied and improved so that it may replace groundnuts in the drier areas.

For the wet tropics, it is suggested that mixed tree cropping is likely to be most effective, as it copies as closely as possible the natural forest. Oil palm or coconut palm would be interplanted with breadfruit to form the top gallery. Beneath this would be planted plantains, cocoa, and coffee, and, in places, as a bottom layer of vegetation, small plots of maize, sweet potato, and cocoyams. The aim would be not to get the maximum yield of one particular crop per unit area but, rather, to maximize total production.

The objective must be to give the people of the wet tropics crops that will outyield and undersell the main food crops grown in the temperate zones. Oil from palm oil already does this; it is to be hoped that carbohydrate from breadfruit would become cheaper than maize as the cost of high energy inputs increases. If the people of the wet tropics attempt to grow temperate crops competitively, they will always be losers, and, if they cannot produce cheap food, industrialization may well be impeded.

Long-term tree research is a most urgent requirement, It is a field that has been totally neglected except in the plantation context. Trees have all the right characteristics for smallholder farmer production in an energy-hungry world, although in some cases breeding programmes must be undertaken to combine desired properties.

It is essential that one get away from the idea that trees only grow in forests or in plantations. This concept has meant that the people of the wet tropics have been (and still are) denied the help of modern research. Economic trees grow just as well on smallholdings as on plantations, and there is little loss of economic efficiency. On has only to think of the struggle of the Chagga people in Tanzania before they were allowed to grow coffee to realize how obstructive the plantation mentality can be.

One cannot know what the future holds but surely one must plan for several different possibilities. One of these is a world of increasing energy shortage, where energy-related products become more and more expensive. In such a situation low energy-input tree crops have a potential that is unmatched. Prudent people do not put all their money on one horse, and scientific researchers and government policymakers should likewise spread their bets. Mixed tree cropping may be a favourite for some, or an outsider to others, but it looks to be so well-suited for the next 20 years that it would be unwise not to put some money on it.

Traditional agro-forestry systems in the central African republic

Traditional agro-forestry systems in the central African republic

Etienne Yandji
Head, Forest Management Service, National Forestry Bureau, Bangui, Central African Republic


The Central African Republic is a land of forests, and yet its agrosilvicultural balance is being jeopardized by the lack of an afforestation policy. This paper contains a detailed description of the seven types of trees cultivated on many types of plantations and combined with food and other crops. The report also describes the traditional systems in use and proposes a series of measures aimed at improving their productivity. Finally, it is recommended that multidisciplinary research on soil protection end restoration be conducted, with the understandiny that human end social factors are of paramount importance in the restoration of tropical forests.


The Central African Republic is located between latitude 2° 16' end 11°20' N and longitude 14 20' end 27 45' E In the extreme north, between Sudan and Chad, is the Birao region, with which this report is mostly concerned. Here the climate is Sudano-Sahelian to the north and Sudano-Guinean to the south, and nowhere does the yearly rainfall exceed 1,000 mm.

Despite various botanical explorations, the vegetation of the area is still not very well known. The following divisions for the Sudanian forest were proposed by Sillons in 1950.

  • District XI, between the Chari and Logone rivers, north of a line running north of Batangafo and south of Ndélé and Ouadda. This is characterized by the alternation of wooded savanna with Uapaca sp., Isoberlinia sp., and Monotes sp. (Oxytenanthera abyssinica may also be present) and shrub savanna with Terminalia laxiflora, Grewia mollis, and Combretum hypopilinum.
  • District XII, along the Upper Aouk River, between 9° and 10 N. This is characterized by the alternation of parkland savanna populated with rachitic trees (with Piliostigma [Baubinia] reticulate, Combretum glutinosum, and various acacias dominating! and easily flooded grass savanna with Andropogon grasses etc
  • District XIII, north of Birao, betwen 10° and 11 N. Thornbush tropical steppe covers this entire region, with acacia shrubs, jujubes, and various mimosas dominating.

All of these formations may be grouped together in three regions: the first being that of the Bahr Aouk River (west of 21 E); the second that of the plains of Chad between the Koumbala River and Birao; and the third that of the areas of rocky relief south of Birao, around Ouanda Djallé and the Ouandjia Mines and along the Sudanese border. In the Bahr Aouk Zone, on quartzitic crests of the Old Precambrian period (sometimes with surface induration) grows woody vegetation composed of Daniellis oliveri, Anogeissus sp., Butyrospermum parkii, Parkia filicoidea, and Pterocarpus lucens.

In the Aluk-Aoukale zone one finds tree savannas where the most widespread woody plants are Terrninalia laxiflora, Hymenocardia acida, Prosopis africana, and Anogeissus. Actually, this is not a homogeneous zone, as there are also the main types of graminaceous pastures and dry termite forests with a tree layer of Khaya sp., Tamarindus indica, and Anogeissus and a shrub layer of Combretum spp., Cacia sp., and Bascia sp. Around the grassy plain of Lake Manoun, one may observe Borassus aethiopium, and Hyphaene thebaica, with Anogeissus, Butyrospermum, Tamarindus, Balanites, and Isoberlinia dominating. In the villages, alongside planted Ceiba pentandra, Moringa oleifera is found, which indicates a former Chadian occupation of the area. Between Dahal Hadjer and Tissi, Combretum savanna grows on the gaz (ancient aeolian sand fields).

Traditional Associations between Crops, Fodder Species, and Trees

Forest Zone

The Central African Republic is a land of forests, and thus its inhabitants have no difficulty in obtaining wood. The Republic's forest belt covers the prefectures of Sangha, Sangha Economique, Lobaye, and the southern part of Ombella-Mpoko. Bananas, cassava, coffee, taro, some groundnuts, and some sesame are grown in these regions. The cultivation of all these crops entails the destruction of forests. All trees are cut down, with the largest trees being killed either by burning or girdling. After the forest has been cleared and all the plant material burned, the plot is ready for sowing. For all except two or three of the above-mentioned crops, the soil must be turned before seeds are planted. Since the crops must have full sunlight, not a single tree is left standing and the forest is irreversibly destroyed.

Moreover, since the tropical forest is rich in wood products, the people do not spare any trees when cultivating their fields. Coffee is one of the country's main cash crops, and a modern system of cultivation is followed. If, in this type of cultivation, one finds trees still standing here and there, especially on plantations belonging to the village people, it is because they feel that allowing the trees to remain will protect the coffee plants from over-exposure to the sun, thus increasing production. Generally speaking, no trees are left standing on large-scale coffee plantations. In cocoa cultivation, trees are preserved for their shade. This type of cultivation is not widespread in the Central African Republic because of the relatively unfavourable growing conditions for cocoa . Other crops are raised on land that has been cleared and burned, although sesame is often cultivated in pockets of savanna in the midst of the forest. Production per hectare is superior to that found in typical savanna regions.

Intermediate Zone

The intermediate zone is located between the forest zone and the Vakaga zone. Its climate permits the cultivation of different types of crops. In this zone, where the majority of the population lives, cotton, sesame, groundnuts, and many other subsistence crops are cultivated. In Basse-Kotto and Mbomou, even coffee is grown. The crops are raised on Sudanian savanna where tree density per hectare is considerable. This means that the forest must be completely destroyed except where trees are of some use because they provide edible fruit, shade, or some other byproduct for which the farmer feels there is a need.

Vakaga Zone

The trees are carefully preserved in Birao (which is roughly in the middle of Vakaga prefecture) as wood is the primary fuel for cooking and lighting. As the rainy season approaches, inhabitants lay in a supply of firewood to tide them over until the next dry season. Inhabitants of this region traditionally protect "useful" trees that grow in their fields -useful because they provide fruit, oil, medications, and fodder for livestock.

There is a noticeable lack of industrial-scale cultivation in the Vakaga region. The population depends primarily on subsistence agriculture, sheep-herding, hunting, and gathering. There are approximately 15,000 inhabitants of the Vakaga prefecture, with a population density of 2 people/km². The Vakaga prefecture is divided into two subprefectures, Birao and Ouanda Djalle. The region's chief town is Birao. All Ministry of Rural Development services are represented there: agriculture, animal husbandry, and forestry. The latter is further divided into three sections (Birao Centre, Gordil, and Ouanda Djallé) with ranger stations and patrol areas.

The Vakaga region differs from other regions of the Central African Republic in that cassava has been introduced there fairly recently. Millet is grown in light, sandy soils and its abundant foliage is favoured by horses and cattle. Two varieties of Sorghum candatum are found, as well as Sorghum vulgatum, an intermediate variety, and red and white berbere (the term is used to describe heavy, compact, clayey soil and also for several varieties of Suorghum durra). Groundnuts are cultivated, but maize is not very widespread since it is simply planted around huts as a back-up cereal.

The population of the Vakaga region consumes vast quantities of roselle (Hibiscus sabdariffa), whose calyx and early fruit are used as ingredients in couscous and whose flower is used in herbal teas. This malvaceous plant is almost always planted in millet fields and around huts. Hibiscus esculentus (okra or gumbo) is one of the most common field and garden vegetables. Sesamum indicum (sesame) is planted in sandy soil, especially in fine sand, where its yield is excellent. Cucumis sativus (cucumber, or fagouss) is one of the most widely cultivated vegetables, and this is often cultivated together with squash.

Trees Recognized as Useful

Vegetation in the Vakaga region, as in most Central African regions, has been greatly affected by human intervention. Over-grazing has sometimes caused the almost total disappearance of woody vegetation in some areas. Vast stretches of desert can be seen around Birao, even though climatic conditions warrant the growth of abundant thorny vegetation. Nevertheless, six trees are recognized as being particularly useful: Balanites aegyptiaca, Butyrospermum parkii, Parkia biglobosa, Borassus aethiopium, Adansonia digitata, and Tamarindus indica. This is proof that, even when the inhabitants do not try to protect trees in their fields and incorporate them into their farming system, a certain equilibrium between agriculture and silviculture is sometimes established.

Throughout the Birao region, Balanites aegyptiaca is carefully cultivated because of its many uses. Its fruit provides an oil that is often used in cooking and some old people will eat only sauces made with Balanites oil. The sulphur-yellow flesh around the pit is eaten in much the same way as chocolate. The tree is often stripped by livestock, which favour its foliage, and also by herders, who cut off branches to build shelters for their calves. Treated in this way, the tree acquires a straight trunk. Village people use it as the main member in the frames for their huts, because the hard wood resists attacks by termites. The wood is also used to make handles for spears, axes, and other tools. Villagers are fond of eating fried beef liver on Balanites aegyptiaca leaves, which are reputed to cure liver ailments. Sometimes there are clashes between stock breeders and village people, not because livestock have destroyed millet fields but because a herder has cut branches from a tree to make a bed. This species more or less covers the northern part of the area, and three or four of these trees can be found in even the smallest fields. Its many uses cause it to be cultivated also in Bangui, the capital of the Central African Republic.

Butyrospermum parkii .(karite, or shea tree) is characteristic of the region. It provides a fleshy fruit and a stone whose oil extract is valued as a preservative. Farmers gather the bark to make beehives; this usually kills the tree. In some villages, this practice is forbidden by tradition, except for trees that have been declared unproductive.

Parkia biglobosa (nitta) is a leguminous mimosa producing pedunculate fruit and a yellow powder eaten by the local inhabitants. The seeds are boiled, fermented, and used to make a tasty sauce for eating with Hibiscus esculentus (okra). Village people often set their beehives in this tree.

Borassus aethiopium (palmyral is widely used in this region. All huts constructed by the government are made from planks from this tree, rough-hewn locally. Since the palmyra resists termites, it is also used locally in the frames of huts. The flesh of its fruit is eaten by village people; elephants are also fond of it and can sometimes even be seen in an inebriated state near large stands of palmyra. Young shoots are gathered and marketed as in other regions.

Adansonia digitata (baobab) figures in African mythology and is greatly revered. The local inhabitants make sacrifices under this tree. Shoots are eaten in a smoked fish sauce. The tree is found throughout the area but is practically non-existent in places where elephants have come to rest, for they strip the tree of its bark. The white powder around the seeds is eaten in the same way as chocolate.

There are several varieties of Tamarindus indica in Birao. Some do not sprout leaves until the start of the dry season; their fruit is picked toward the end of this season to feed livestock (sheep and kids). Others, however, have year-round foliage. It is this second kind that is usually found in fields and villages. It produces a very sour fruit thought to be a good cure for colds because it is rich in vitamin C. The branches are gathered, boiled, and used as a medicine for fevers, rheumatism, and fatigue.

Oxytenanthera abyssinica (bamboo) must be added to the six described above because of the role it plays in local construction. It is used for roofing and especially for fences, for the region is Moslem and each hut must have a fence around it.

Agrisilvicultural Equilibrium

The theory that some sort of balance must be established between agriculture and silviculture presupposes the maintenance of an ecosystem. The ecosystem is greatly influenced by climatic, biotic, human, and soil-related factors, but must be continuously maintained by agronomists, veterinarians, and foresters. Such multidisciplinary activity is difficult. When farmers in the Vakaga region allow trees to remain standing, the reason is that they derive some products or service from the trees. This explains why, although there is indeed a certain traditional agro-forestry system, its aim is not just to preserve trees or to ensure a certain equilibrium between agriculture and silviculture. Thus an information programme should be set up to teach agro-forestry methods in the areas concerned.

An information campaign presupposes an established plan ready for execution. Consideration should perhaps be given to the application, in this region, of all silvicultural methods used to date in wet forest zones and savanna: the taungya method, the Malayan uniform system, the tropical shelterwood system, the semi-selective management system, the cross-ride method, full-capacity planting, and restricted grazing Some of these methods can be applied only in forest zones, but taungya, full-capacity planting, and restricted grazing (which is the most economic and most important method), could be widespread. Initially, farmers in central Birao should be organized into three groups, according to the kinds of crops that suit each system. The first group would adopt the taungya method; the second and third groups would practice full-capacity planting and restricted grazing, respectively. Later, all three systems could be applied in every village of the Vakaga region, depending on the crops grown and the environment, the main factor being the dominant species of tree. A five- or six-year rotation would suffice to allow the rural population to grow crops on land enriched by fallowing to improve its yield.

The taungya method may be practiced in conjunction with full-capacity planting and restricted grazing. In heavily treed areas where the dominant species of trees are those that farmers are in the habit of preserving and growing in their fields, the taungya method will be applied. In Birao Centre, Ouanda Djalle, and the rural areas in these two subprefectures, the same method will be used but the kinds of crops will vary depending on the farmers' means of livelihood. This will give rise to a wide diversity of crops being raised in conjunction with Balanites aegyptiaca, Parkia biglobosa, Butyrospermum parkii, and Tamarindus indica, which are the only local trees suitable for the taungya method and restricted grazing. Even if the taungya method and fullcapacity planting fail, restricted grazing (which is the least costly method) will undoubtedly be successful if brush fires and human factors can be contained.

From the example of other African countries, it can be seen that farmers automatically preserve useful trees in their fields. However, it should be noted that this still does not provide the level of forestation necessary to maintain a favourable climate and soil fertility.

Other solutions may be considered, such as:

  • Prolonging fallow periods;
  • Planting a large number of useful trees in the fields;
  • Planting useful trees (fastgrowing exotic species) alongside paths leading to fields and around the boundaries of these fields; and
  • Planting fast-growing species and fruit trees along cattle and goat paths through farm areas and around water holes.


The immediate result of this activity will be to check deforestation around the city of Birao and the villages in that region, and to create an environment favourable to reforestation. Over the medium term, the main objectives will be to combat soil erosion and to make local inhabitants aware of the forest's usefulness and of the adverse effects of systematic deforestation on agriculture. Over the long term, the forest cover will be re-established and city-dwellers will be supplied with firewood through cuttings on a rotational basis.

This work will involve considerable multidisciplinary research on soil protection and restoration in each ecological zone, keeping in mind agriculture, animal husbandry, and forestry -without neglecting the human and social aspect. Customs are so important that nothing can be accomplished without a great information, popularization, and organizational campaign. The future of our tropical forests depends on it.

Prospects for agro-forestry in Benin

Prospects for agro-forestry in Benin

A.G. Agbahungba
Department of Agronomic Research, Cotonou, Benin


Benin's forest resources have been impoverished by 25 years of sawmill operations, bush fires, clearing by state farms and corporations, insufficient fallowing periods, and the encroachment of the Sahel in the north of the country and the savanna in the south. The country must depend on imports to make up a growing deficit in firewood, timber, and lumber. This report describes the objectives for an agro-forestry research programme aimed at improving Benin's forest economy.


Situated on the Bight of Benin between Togo, Nigeria, Niger, and Upper Volta, the People's Republic of Benin - with a surface area of 112,000 km² - is a country with limited forest resources.

A brief outline of the ecological factors affecting Benin helps explain the country's forest situation. The southern and coastal regions correspond to the terminal continental shelf and have soil of variable quality derived from long-shore drift materials, alluvial deposits of silicon clay, and cretaceous formations that have developed into Vertisols. Further north, in central Benin, thre is crystallized rock, granite jutting out of the Precambrian substratum, with ferruginous types of tropical soils, occasionally with lateritic concretions.

According to surveys by the Food and Agriculture Organization (FAO) and the United Nations Development Programme (UNDP), 60 per cent of the country's surface is covered by natural, uncultivated vegetation, which is threatened every year by bush fires. Most of Benin's classified forests are located in the country's northern and central regions. For a full appreciation of Benin's forest situation and the problems that have arisen, other factors must be added to these ecological data; these include the extent to which state farms and corporations have been clearing the land, the inadequate natural fallow periods on most traditional farms, the encroachment of the Sahel in the northern areas and the savanna in the southern areas, and the development of urban areas.

Benin's national forests cover a total of 2 million ha, or 19 per cent of the country's territory. However, commerically valuable forests represent a mere 2 per cent of the land area. Classified forests account for 1,580,028 ha and plantations (mostly teak) cover 10,000 ha. These plantations, between 14 and 30 years old, are mainly located in the country's southern region and are intended for timber production. In teak farming, both short-term (45-55 years) and long-term rotations are used. To these teak plantations must be added the existence of a natural reserve in the Djougou-Bante-Beterou triangle; in the immediate future, however, this reserve's annual timber production will not exceed about 35,000 m³ of Khaya grandifoliola and K. senegalensis, and 40,000 m³ of Antiaris sp. and Triplochiton sp. Corrent production is low as a result of 25 years of overexploitation by local sawmills.

In addition to the 10,000 ha of plantations already mentioned, there must be added 6,000 ha of cashew trees, which supply a small shelling plant in Parakou (annual capacity: 1,500 tons). Furthermore, although lumbering in Benin is not sufficient to keep a foreign trade going, other forest products such as Karite (Vitellaria paradoxa) and cashew nuts have made possible a considerable influx of foreign exchange-about 542 million CFA francs. in 19771978. Production rose sharply in 1979-1980. National parks and wildlife preserves cover a total of 578,000 ha.

Shortage of Wood

The problems that arise from a scarcity of forest products can be expressed in terms of needs. Wood is the leading domestic fuel and is used for cooking in Benin. It comes to people's homes in the form of firewood or charcoal. Wood is currently in chronically short supply in all urban centres and even in rural areas. The rural district of Ouake in Atacora Province, where millet stalks and cow dung are used for cooking fuel, is a good example of the problem.

In the south, this shortage is aggravated by the progressive shortening of natural fallow periods. According to Huart (1976) of the FAO/UNDP forest industries advisory group for Africa, an increase of 15 per cent in the total area sown to crops would cause a deficit for cities such as Cotonou and Porto-Novo of 57 per cent (table 1).

TABLE 1. Fuel Requirements, Present and Predicted

  Firewood equivalent (in m³)
Present requirements Estimated requirements in 1990
Cotonou-Porto-Novo 360,000 1,015,000
Parakou and Djougou 180,000 315,000
Rural areas and other localities 2,640,000 3,470,000
Totals 3,180,000 4,800,000

However, the country's wood shortage affects more than the supply of fuel; there is also a widespread shortage of timber that is felt at every level of society. To the figures for annual timber consumption must be added 1,500 m³ of plywood and fibreboard, most of which is at present imported. This analysis indicates an annual deficit of 6,000 m³ of saw timber and plywood and 1,000 m³ of roundwood.

Prospects for Agro-forestry Solutions

Attempts have been made to combine and integrate farming, forestry, and animal husbandry methods for improved farm management with a view to continually increasing production without causing major deforestation and yet obtaining a substantial yield from marginal land.

In concrete terms:

  • Structures have been established to provide guidance and support for rural production;
  • Experience has been acquired in agro-forestry; and
  • An agro-forestry research programme has been developed.

Agriculture, forestry, and animal husbandry are not rigidly compartmentalized in Benin. Maize is sown, trees are planted, and animals are raised by the same labourer on the same farm. Rural development structures devised and implemented by the government of Benin take into account the concern for integrating these systems. Specifically, regional rural development action centres (CARDERs) bring together all government aid services in rural areas.

The involvement of rural populations in forest development is a proven technique in Benin. The taungya planting method is one agro-forestry production system in which farmers take part in setting up state plantations. This practice has made it possible to plant 6,000 ha of teak in southern Benin.

There have been many variations in the practice of taungya. In the south, maize is cultivated in combination with the establishment of teak plantations. In North Zou, maize or groundnuts are grown on cashew plantations. Mixed cultivation of cotton and cashew has not proved as successful because of the high risk of attacks by parasites, notably Heliotis, a cotton parasite that causes a great deal of damage. In the north, millet and cashew have been successfully combined; cashews and yams can also be cultivated together if the yam's twining stalks are kept from winding themselves around the young trees.

Generally speaking, agro-forestry experience to date in Benin has been based on the taungya method.

Agro-forestry Research Objectives

The shortened fallow periods currently noted in southern Benin, and the resulting problems-decreased soil fertility, decreased firewood production, and reduced natural fallow areas-motivated the Department of Agronomic Research to start a research programme in 1980 with a view to including timber trees in traditional crop rotations.

The objective of this programme is to upgrade soil fertility and obtain substantial forest production over a relatively short fallow (three to four years). Acacia auriculiformis and Leucaena leucocephala are being grown as fallow species and being observed for their positive contribution to soil fertility and firewood production. If successful, this programme will enable agro-forestry to play an important role in improving Benin's forest economy.

Summary of discussion: Traditional agro-forestry systems

Summary of discussion: Traditional agro-forestry systems

In the discussions on traditional agro-forestry systems and their prospects for development, the first major point which emerged was that insufficient attention had been paid to the improvement of traditional cropping systems, in short, to make them economically viable as well as to meet subsistence needs. To continue to divorce agriculture from forestry was to be moving in the wrong direction, and this was especially true in the humid tropics. One participant observed that the value of mixed cropping systems was being demonstrated all around us, but that we have been blinded by the success of monocultures in the temperate zone. A "farming systems" approach was strongly advocated, although it was recognized that such an approach was relatively rare and demanded large inputs of scarce, trained personnel to be effective.

It was pointed out that the rapidly increasing population density was leading to smaller farms, yet these had to meet the basic food needs as well as provide cash income. Stable systems must be developed, and research must be carried out to determine whether agro-forestry will indeed provide greater benefits to the small farmer. The claim that higher diversity will increase stability (i.e., lessen risk) was questioned, as the data were still ambiguous. Certainly from a management viewpoint a higher diversity of crops makes it difficult to maximize the yield of the individual components. The problem of crop compatibility was also raised, and it was noted that there was great variability in the demands of annual crops for light, nutrients, water, etc. Similarly, crops vary greatly in their response to different management practices such as weeding. This means that each component within a given system will have to be tested independently and in situ in order to fully evaluate the potential of the system in question. Because of this inherent complexity we must use existing systems as guideposts, and only test systems which could fit in the existing socioeconomic milieu.

The question of tree root architecture was brought up, and the trade-off in the humid tropics between trapping nutrients with a dense, shallow root system vs. increased root competition was recognized. In this case further complications arise because the tree root system is also affected by the herbaceous component, and one would expect the balance to vary in accordance with rainfall, soil type, management practices, etc.

Several speakers felt that insufficient attention had been paid in the past to the development and management of the tree crop component. In this context the point was again made that one has to work within the context of the existing system by looking at the farmers' needs and then providing new plant material or other inputs which are demonstrably better. Improved coconut varieties and the Crop Diversification Project in Sri Lanka were cited as examples from outside Africa. It was also suggested that a type of planted fallow might be developed which would hasten the fertility recovery rate and provide a crop which could be harvested at the end of the fallow.