| Agro-forestry in the African Humid Tropics (1982) |
|Traditional agro-forestry systems: Prospects for development|
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.
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 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 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.