Organisation spatiale et dynamiques des systèmes de culture à base de cocotier (Cocos nucifera L.) dans une île mélanésienne: le cas de Malo (Vanuatu).

Copra production has represented a major income source for Vanuatu’s rural population since at least the mid-nineteenth century. European plantations and then smallholder coconut plantations made a significant and rapidly increasing contribution to Vanuatucopra production, particularly in the Northern islands of the Archipelago. The extension of the plantation system substantially modified the traditional smallholder farming and cropping systems. Since the late 1990s, world copra prices and farmer’s net incomes have declined significantly. Consequently, farmers and agricultural extension services are investigating new cropping systems in which ecological sustainability and economical profitability can both be realized. After forest or bush fallow clearing, food gardens and coconut trees are frequently associated in a complex annual-perennial system involving intercropping and other agricultural enterprises, such as livestock production. In such cases, established coconut stands are associated with various crops and enterprises, e.g., fruit trees, cocoa, pineapples, vanilla, cattle pasture and sometimes new coconut plantings. Our objective was to evaluate the performance, evolution and sustainability of this type of mixed cropping system, and the capacity to integrate food gardens in these systems. Due to the difficulty in analysing the long term effects on long duration perennial crops, we chose to study a variety of cultural situations at a given time (plots with coconut trees of various ages and in different types of association) in order to understand the temporal dynamics of the mixed cropping systems. The main steps of this approach are presented in this paper. The study was undertaken on Malo island, Vanuatu. Firstly, a historical analysis of the coconut population of the island was carried out using “zonal mapping through key human resource” methodology. The results have been analysed and used to identify and locate representative target areas for field work. Next, we then characterised coconut plantations in the target locations in order to represent the greatest diversification of cultural situations possible. The two main cropping systems were then identified enabling us to understand their temporal dynamics. Two main systems were identified: (i) agropastoral systems, and (ii) agroforestry systems. These two systems differ from each other when coconut trees begin to produce. The transitional cultural situations between the two systems have been identified, showing their flexibility. The importance of the two main cropping systems varies according to locality. The most dominant system is the agropastoral, which appears more frequently in coastal areas. The agroforestry system appears more frequently on the plateau, where the foreign origin of the farmers may explain their wish to achieve the optimal use and enhanced value of their limited available land resources. The multiple generations system is observed only on the West Coast where the plantations are comparatively older and where the area for cultivation has become limited. The agroforestry coconut-based system may appear as the most profitable in a context of current poor copra profitability. The agronomical and economic evaluation of these systems will permit us to test the validity of this hypothesis. The results show that the association between food gardens and coconut plantations has to be in moderation, at least under the conditions of our study. Both systems appear to be evolving in close association. The integration of food gardens with coconut plantations might be possible both at the beginning of the coconut cycle and also on senile coconut-tree plantations where there is increased light filtering through the canopy. The characterisation of the different cropping systems has been the first step before their evaluation. On a pilot plot scale, the temporal evolution of soil fertility, light availability under the coconut canopy and root colonisation, which are key factors in mixed systems, will be explored. On a regional scale, the spatial location of different cropping systems will be studied using remote sensing data.Dans les îles du nord du Vanuatu, le coprah constitue la première source de revenu. L’extension des cocoteraies, initiée au début du siècle, a profondément modifié les systèmes de culture mélanésiens. Le déclin actuel de la rentabilité du coprah et l’augmentation de la pression démographique motivent maintenant la recherche de nouveaux équilibres agricoles. Les plantations de cocotiers constituent en réalité des systèmes de culture complexes, objet de multiples associations végétales et/ou animales. Les cocotiers en phase juvénile sont fréquemment associés à des jardins vivriers, puis en phase productive à des pâturages pour bovins ainsi qu’à diverses cultures (fruitiers ligneux, cacao, tubercules, etc.). L’évaluation des performances productives et environnementales de ces systèmes nécessite la compréhension de leurs dynamiques temporelles, et notamment du positionnement spatial et temporel des différentes associations (jardins, pâtures, fruitiers) au sein de ces cocoteraies. Une démarche spécifique, utilisant la diversité des situations culturales (en termes de stade de développement des cocotiers et de type d’association) existant sur la zone d’étude, a été mise au point et appliquée sur l’île de Malo (Vanuatu : 15°40’S ;167°10’E). Deux systèmes de culture principaux, l’un de type agropastoral et l’autre de type agroforestier ont ainsi pu être identifiés. Leur localisation géographique est discutée