| Agro-forestry in the African Humid Tropics (1982) |
|Traditional agro-forestry systems: Prospects for development|
Forest conservation strategies for tropical Africa
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.
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|
|Tropical South Africa||0||0||21.72||21.29||43.01|
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:
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.