Agro-forestry research for the humid tropics

A.G. Seif el Din
International Development Research Centre, Nairobi, Kenya

Abstract

If the principal aim of agro-forestry is to meet the needs of human communities, then research should be directed towards preservation or modification of the undisturbed habitats, rehabilitation of the disturbed ones, and rational use of the improved ecosystems. The goals of agro-forestry should be food production, forest production, and environmental conservation. Within the forest ecosystem, taungya offers particular scope for research, especially the determination of how long the forest land can sustain food crops before complete canopy closure, and the identification of optimal spacings that maximize food production without interfering with the form and the rate of tree growth. Within the agricultural production system, research should be devoted to the introduction of trees that rejuvenate soil fertility by nutrient recycling within the shortest possible time and that produce forest products to increase the farmers' income or satisfy their needs.

Introduction

This presentation does not undertake the definition of agro-forestry practices and systems, because much has already been written and said in this regard. The term agro-forestry is used here as defined by King and Chandler (1978), i.e., a sustainable land management system that increases the overall yield of land. There seem to be two main reasons for the growing interest in a sustainable land management system: the first is that there is a serious degradation of the ecosystem as a result of deforestation; the second, which is a consequence of the first, is that the global forest resources and arable land areas are diminishing at an alarming rate. The environmental aspect of agro-forestry necessitates planting trees in such a way as to bring about conservation and improvement of the ecological factors that influence the production systems. In addition, the trees should provide one or more of the forest products, such as wood, fodder, and food, that are needed for the improvement of the living conditions in the rural areas.

The term agro-forestry should thus imply land management systems in which forest management, food production, and conservation form integrated components, i.e., a multidisciplinary exercise.

Some of the recognized agro-forestry practices have been in use for centuries in many parts of the world (King 1968). They were evolved in the rural areas when demands for specific tree products were not easily met from the natural forest or when a tree species proved useful and important to food crops. Gum arabic production in the Sudan and the cultivation of crops under Acacia a/bide in West Africa are two of the known examples of agro-forestry practices today two of the better-known examples of agro-forestry practices today (Self el Din 1980). The continuation of these practices is threatened by the problems caused by the growing human populations, for example, over-cultivation of the land and, hence, the gradual elimination of the tree component from the system. The task of agro-forestry research is, therefore, to find the best system within physical and biological limitations and communal or individual socio-economic requirements.

One of the important tasks of agro-forestry research workers should be to find ways to maintain stability in ecosystems that have not yet been seriously interfered with, to render them more productive of human needs. The painful reality is, unfortunately, that there is very little left of the natural forest to maintain. Consequently, agro-forestry research programmes should be directed towards tackling the immensely difficult task of rehabilitating degraded lands and devising land management systems that will fulfil the objectives of agro-forestry.

The gravity of the problem is apparent in the rapid disappearance of the tropical moist forests. Myers (1980) has given the global rate of conversion of these forests into other forms of land use as being 40 ha/minute. He states that up to the mid-1950s, about 1 million km² of tropical forests were lost in Africa alone, and that 40,000 km² of forest are annually disappearing on this continent. The Ivory Coast is estimated to have lost nearly 40 per cent of its forests between 1966 and 1974, and in Nigeria it is reported that only about 25,000 km² of forest exist today, representing less than 3 per cent of the total area of the country. Addo-Ashong (1980) states that of the original 82,000 km² of tropical rainforest in Ghana, only 20,500 km² or one-quarter, remain today.

Research Proposals

If the principal objective of agro-forestry is to meet the immediate and future requirements of the human communities living in the region concerned, then the approach should be directed towards the preservation or modification of undisturbed habitats; the rehabilitation of disturbed ones; and rational utilization of the improved ecosystems.

In other words, agro-forestry should be viewed in the context of food production, forest production, and environmental conservation, which is similar to what has been suggested by Combe (1979) as being economic, ecological, and silvicultural. The result of an agro-forestry approach should be a new environment, dissimilar but strongly related to the natural one in its basic features, so that it is reasonably stable and productive enough to satisfy human requirements. It should offer, as stated by Wassink (1977), "a reasonable and acceptable permanent way of life to the people that dwell therein."

Several workers have suggested the essential elements of an agro-forestry system (Greenland 1977; Grinnell 1975; Combe and Budowski 1979; and Reategui 1979). Most people agree that an agro-forestry system should cater to:

• diversification of species per unit area;
• permanent soil protection;
• continuous restoration of soil fertility; and
• control of weeds, pests, and diseases.

The next step is to consider the type of land and the combinations of plants and animals that constitute an agro-forestry system. There are considerable differences of opinion in this regard, for the simple reason that most of the ideas advocated in agro-forestry have not yet been subjected to systematic investigation.

In the Philippines, Kuo (1977) proposed three classes of land: forest land, agro-forestry land, and agricultural land. He places the forests on the steepest slopes with the shallowest soils, agriculture on the deepest soils with gentle slopes, and agro-forestry in the middle occupying a relatively small portion of the area. He points out, however, that the latter can be practiced on either side of the classification depending on land-use policy and soil characteristics.

In the example cited by Kuo, some of the forest lands are so steep that any cropping or grazing would endanger the entire landscape, whereas some areas are suitable for continuous cultivation of agricultural crops that can only be economically produced when cultivated in monocultures. The implication is that not all crops and not all lands can be included in agro-forestry systems. Consequently, there should be areas solely managed for crops, pastures, or pure forest stands. For the agro-forestry combinations, the broad classification of the systems proposed by Budowski (1977) and also by Torres (1979) are thought to be adequate, i.e., trees combined with farm crops; trees combined with farm crops and animals; and trees combined with animals. In order to arrive at the desired agro-forestry system, one must tackle research from both the agricultural and the forestry perspective. These two disciplines have, for a long time, had conflicting interests over land use, whereas livestock was, in most cases, completely neglected. Forestry and crop production systems should therefore be gradually modified independently toward a common end where both meet at a stage called agro forestry. Livestock production should be accommodated in both systems in such a way that optimum yields are obtained without adversely affecting the system, and even improving it. This, simply stated, means production of crops and livestock within forest land and production of forest products and livestock on agricultural land.

Some agricultural research scientists view the subject of agro-forestry as merely involving the use of short-lived, fast growing tree species to improve soil fertility for food production and not as a source for forestry production. Still others view it as an introduction of new tree crops into farming systems to increase and diversify the food supplies of the rural people. The last point of view is similar to that of domestication of new animals as a form of agrosilvopastoral system. The danger of this approach to agro forestry is that very little is known about the biology and the environmental implications of the new crops and animals.

Some of the forest research scientists look upon agro-forestry as another name for the taungya system, in which a certain amount of food is produced at the treeplanting stages of forestry plantations. This group does not take into consideration the need for the use of the space available for food production at the time of tree establishment in even-aged plantations, at the stage of opening up the canopy for natural regeneration in what is known in West Africa as the Tropical Shelterwood System (TSS), and, finally, at the various stages of stand treatments such as thinning. With this understanding of agro forestry, the taungya system then forms only one step of the comprehensive system that calls for the use of appropriate combinations of plants and animals and the best spatial and temporal distribution for food and wood production as well as for the preservation of the ecosystem. Agro-forestry research on the taungya system should be devoted to the determination of how long the forest land can sustain cropping before complete canopy closure or the decline of soil fertility, and to the identification of optimal spacings that maximize food production without interfering with the form and the rate of tree growth as required in traditional forest management.

Food Production within the Forest Ecosystem

Various silvicultural systems were developed to regenerate the natural forests in the humid tropics of West Africa, but the most popular one at present is the TSS. This involves gradually opening up the forest canopy by killing and clearing the trees so that sufficient light is available for the growth of the natural seedlings of the desirable species. The degree of clearance depends on the forest type (density and composition by species), the available resources, and the status of the naturally occurring seedlings.

The agro-forestry research approach here should aim at food production by increasing the intensity of clearance and by the use of shade-tolerant food crops that do not endanger the tree species. Even though little experience is available to show the interactions between food crops and trees, it is possible that the latter would benefit from cropping because most of the undergrowth (bush) would be removed to provide space for the food crops and, hence, competition from weeds would be reduced.

It is desirable to test different crops at different stages of tree growth that entail changes in the environment, especially the amount of leaf litter and the sunlight reaching the ground surface.

Once forest stands pass the seedling stage, they are treated at different intervals by processes known as cleaning and thinning to create the best possible stand of managed forest. The intensity of these operations, especially thinning, depends again on the tree species concerned and the objectives set out for each plantation. Because the need for more food producing space is universally recognized, thinning itself can be modified to provide room for crops and livestock without jeopardizing the objectives of forest management. Appropriate avenues for research are the planting of food crops at different intensities of thinning, and fodder production at the various stages of thinning from both the planted trees and the natural undergrowth.

The main points to be considered when planning the research experiments are: ( 1 ) the types of food crops that will favourably respond to the newly created environment in the forest without endangering the trees; and (2) the potential for the introduction of browse shrubs and grasses to enrich the natural pastures for optimum livestock production.

Forestry Production on Farm Plots

Forestry production on farm plots is feasible only if there is demand for the forest products grown on the farm plots; otherwise there will be little incentive to the farmers to plant trees. However, if the gains in soil fertility are clearly demonstrated, farmers may be willing to introduce and maintain trees. This possibility is the basis for present efforts by researchers to adapt and optimize the traditional system of land rotation or shifting cultivation, where soil fertility is regained through the regrowth of the natural bush during the fallow period. The suggestion is that trees be planted on abandoned farm plots to rejuvenate soil fertility by nutrient recycling within the shortest possible time and also produce forest products to increase the farmers' income or satisfy their own requirements.

The tree species used in these efforts must be fast-growing to produce marketable products in a short time, i.e., the farmer does not lose time when he again requires the land for food production. At the same time, the tree plantation should be at least as good as - and preferably better than-the natural bush in restoring soil fertility.

Tree planting in conjunction with food crops entails producing forest products and food crops simultaneously on the same piece of land. In addition to their principal role, the trees should improve the soil. In this way the farming system can be prolonged beyond the current one to three years and perhaps lead to the development of a combination that will sustain permanent cropping. The combination aimed at is an extension of that occurring in certain dry tropical areas where food crops are cultivated under Acacia albida, but, in addition, the trees will be managed in such a way as to produce marketable products continuously or at regular intervals. The correct tree species and their spatial arrangements should be adequately investigated in research trials.

Some crops, like cocoa, coffee, etc., are known to tolerate a certain amount of overhead shading. A number of forest tree species have been successfully used to provide shade as well as produce wood. One example in South America cited by Fuentes Flores (1979) is what he calls "stratified tropical agriculture" to produce coffee, citrus fruits, plantain, beehives, and vegetables under scattered trees of Cedrela sp. In India, coconut plantations are intensively intercropped in ways that maximize the use of both aerial and subterranean space (Nair 1979). Okigbo (1977b) and Getahun (1980b) have compiled comprehensive lists of woody plants, including forest trees, which are of nutritional importance in the traditional farming systems of Africa.

It should be pointed out that neither the use of shrubs solely for soil improvement nor the introduction of new tree crops on the farm as additional food sources serves the purpose of agro-forestry. instead, the research should be directed towards finding the tree species that create favourable environmental conditions for optimal production of crops and livestock in addition to wood production.

The research topics outlined are by no means exhaustive. Instead, they should be considered as a basis for discus signs leading to a comprehensive agro forestry programme with long- and short-term objectives. Some of these proposals are likely to apply to the drier tropics where agro-forestry is just as important, in fact even more so, especially when livestock production becomes a more prominent landuse factor.

Before an agro-forestry research programme is worked out, sufficient basic information must be obtained. There should be a survey of the existing land-use practices in the region in a manner similar to that carried out by Getahun (1979a) in southern Nigeria. This will enable researchers to understand the way in which the rural people operate so that they can aim at improving the existing land-use systems rather than designing entirely new ones that would not be easy to implement. The survey should include evaluation of the soil characteristics, the existing vegetation and its effect on soil protection! and the needs of the local communities in terms of food and forest products. The next step is to identify the crops that grow best under trees and the forest trees that will provide protection and soil improvement on farm plots. The research activities should be designed in such a way to find the optimum combinations of trees, crops, and animals to ensure maximum productivity and improvement of the environmental conditions. Finally, a strategy for agro-forestry research should be outlined and methods for its implementation be developed. One such strategy has been proposed by Steppler and Raintree (1981 ) and provides the basis from which to start (see paper by Steppler in this volume, pp. 1 - 5).