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Forest conservation strategies for tropical Africa

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

Abstract

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.

Introduction

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)

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.

Outlook

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

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

Abstract

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

Introduction

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.

Recommendations

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.

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