|Agro-forestry in the African Humid Tropics (UNU, 1982, 162 pages)|
|Current agro-forestry activities|
Laboratoire de Botanique Agricole, Ecole Nationaie Superieure Agronomique d'Abidjan, Abidjan, Ivory Coast
Cocoa, coffee, banana, Hevea, coconut palm, and oil palm are important industrial crops in the Ivory Coast, and, although they are usually monocultures, some of these are traditionally grown together in a taungya system. In tropical forest zones the need for food crops, on the one hand, and the shortage of protein, on the other, have tended to encourage consideration of complementary uses of large forest plantations. In particular, use of the adventitious vegetation in oil palm plantations as forage for cattle is being considered as well as the introduction of food and cash crops among the trees. Palatable species have been identified in the vegetation, and some crops, such as cocoa, offer promise as intercrops.
The oil palm (Elaeis guineensis Jacq.) is an African tree native to the Gulf of Guinea. Its distribution in West Africa extends from Senegal to Angola, where the natural populations have always been exploited by the native people for many purposes, including food, handicrafts, pharmaceuticals, and religious uses.
In the Ivory Coast, palm groves establish themselves naturally in the traditional plantations of cocoa (Theabroma cacao L.) or coffee (Coffee spp.) and constitute a very valuable by-product. They also grow among food crops as a result of the exploitation and development work of humans and dissemination by numerous animals partial to the palm's fruits and seeds (monkeys, rodents, and birds).
Industrial plantations of oil palm were first developed in 19201926 by the Union Tropicale des Plantations (UTP) and the Societe des Plantations et Hulleries de Bingerville (SPHB). Cultivation of the oil palm, however, experienced its greatest growth in the Ivory Coast after the Institut de Recherche pour les Huiles et Oleagineux (lRHO) developed a very productive hybrid form-the tenera-by crossing aura and pisifera. In fact, until 1964, before the creation of the Societe d'Etat pour le Developpement du Palmier a Huile (SODEPALM), industrial palm groves occupied only 10,000 ha. By the end of 1966, SODEPALM had planted almost 19,000 ha, and oil palm plantations occupied a total of nearly 30,000 ha. By 1970 this area had increased to 76,000 ha, and in 1980 it reached 100,000 ha.
In view of such growth, optimal use of the land occupied by these palm groves has attracted considerable interest. Economically feasible ways of intensifying the use of these areas could occur either by grouping the palms with other crops (industrial crops such as coffee and cocoa, or food crops such as cassava and maize), or by growing feed for cattle. Two stations were selected to study the adventitious vegetation; one, belonging to the Societe des Plantations et Huileries de Bingerville (SPHB), is located on sandy soil in the Bingerville region, and the other, belonging to the Institut de Recherche pour les Huiles et Oleagineux (I RHO), is located on clayey soil in the La Me region.
The forests of the Ivory Coast belong to the humid, tropical region of Africa, and the climate can be classified as subequatorial; from the viewpoint of plant geography, they belong to the Guinea-Congo forest massif. The original vegetation is a dense, ombrophilous, evergreen forest, which contains a number of tree savannas and grassy lagoon savannas: the Adiake, Moossou, Bingerville, Dabou, and Grand-Lahou savannas. The industrial palm groves are found on three types of soil: sandy; more compact clayey-sandy; and compact, essentially clayey (which retains a great deal of water).
The two stations selected for study were originally covered by very distinct types of vegetation. The Bingerville station is situated in the heart of the dense, psammohygrophilous evergreen forest dominated by Turraeanthus africanus and Heisteria parvifolia (Mangenot 1954). In addition, one sees here and there some expanses of savanna consisting of Brachiaria brachylopha and Anadelphia africana (Adjanohoun 1962). The La Me region belongs to the dense, pelohygrophilous evergreen forest consisting of Mapania spp. and Diospyros spp. (Mangenot 1954).
The adventitious vegetation consists of various plants distributed in the following proportions: phanerophytes (56.5 per cent), therophytes (17.9 per cent), and chamaephytes (14.5 per cent). Hemicryptophytes are rare 17.4 per cent), and geophytes are negligible (3.7 per cent).
The vegetation beneath the palms is varied. Its most striking aspects are: its vitality-phanerophyte and chamaephyte vegetation that is always green; flowering and fruiting limited to a few herbaceous plants; its floristic composition, both heterogeneous and uniform depending on whether one considers isolated plots or the whole plantation area; and its gregariousness, which frequently allows local enrichment of the flora with a particular species-this is a characteristic that is most marked for cetain herbaceous and ligneous species that propagate by means of suckers. Clusters of the following species have been observed: Dissotis rotundifolia; Aspilia africana; Melanthera scandens; Eupatorium odoratum; Thaumatococcus daniellii; Axonopus compressus; Commelina nudiflora, C. forskalasi, C africana, and C. condensate; Imperata cylindrica; Rottboellia exaltata; Nephrolepis biserrata; Pteridium aquilinum; Anchomanes diffomis; Acroceras zizanioides; Paspalum scrobiculatum var. commersonii and P. conjugatum; Panicum repens and P. brevifolium; Sporobolus pyramidalis; Borreria latifolia; Diodia rubricosa and D. scandens; Eleusine indica; Mariscus umbellatus and M. flabelliformis, often mixed with Cyperus sphacelatus; Palisota hirsute; Asystasia gangetica; Selaginella myosurus; Scleria barter) and S. naumanniana; and Setaria megaphylla and S. chevalieri.
The distribution of these numerous clusters is related to farming operations-clearing the land, ploughing, and so forth-that cause either abnormal concentrations of a given species at certain points, or their dispersion over the whole cultivated area. Local ecological conditions may also come into play and favour the growth of certain plants.
Possibilities for Agro-forestry
Oil Palm with Cattle
Phytosociological, floristic, and agrostological studies were conducted to assess the suitability of palm groves for cattle raising. These led to the identification of species having a high forage value by virtue of their palatability, biomass, and position in stable and profitable associations. The most important species are:
From attempts to assess the biomass and regeneration of the vegetation within various associations, it appears that for young plantations (one to seven years old) the often large amount of vegetable matter per unit area (nearly 100 tons/ha in certain cases) diminishes considerably with increasing age. Likewise, the regrowth of the vegetation, vigorous at first, becomes practically nil when the canopy closes. The vegetation within palm groves that are from eight to eighteen years old is increasingly sparse and poor (photograph no. 6). It grows back progressively with the clearing of the woodland vault after the eighteenth year.
Many factors other than age affect the composition and physiognomy of the vegetation under oil palms; among these are human activities, climate, and the degree and type of herbivory.
Oil Palm with Crops
In the Ivory Coast it is possible to consider cultivation of the oil palm in association with other industrial crops such as Hevea, coffee, and cocoa. Many studies have already been undertaken of the palm-cocoa association. There are two main reasons for favouring this combination:
In the traditional village plantations the oil palm-cocoa association constitutes a viable system, as the oil palms are not being planted by the farmer but simply maintained at a certain density. However, experience has shown that the same is not true of industrial plantations, where the density is calculated for maximum yield and becomes an obstacle to the proper development of the cocoa. In fact, the hybrid cocoa plants that are now common are more heliophilous than sciaphilous. In addition, the size of the palm roots in the soil is such that, despite the differences between the two root systems, the cocoa grows poorly and may perish (photographs 8 and 10).
Any food crop can be grown in the spaces between the rows of a young plantation (photograph no. 1 1). None can be grown in the palm groves when the crowns meet. The only precaution to be taken is to ensure adequate control of species whose remains after the harvest can develop into quickly spreading weeds and inhibit, to a considerable extent and for a long time, the young palms. This is the case, for example, with cassava (Manihot utilissima) (photograph no. 9). Once the canopy closes, the only spaces that can be developed for food crops are those that have been cleared by natural decay or where, for some particular reason, there is an absence of palms.
Cattle raising in the palm groves, although possible in terms of available palatable plant species, is worthwhile only on a large scale, and, even then, it would require bringing in a substantial quantity of additional feed. This is especially true for the older plantations, where regeneration of the vegetation is very slow and difficult. With regard to associated crops, only species whose lifetime is at most seven to ten years can be cultivated without special measures in existing plantations. In existing industrial palm groves profitable associations with other perennial crops are not possible for purely ecological reasons.