Caractérisation et évaluation agroécologique de systèmes de culture agroforestiers : une démarche appliquée aux systèmes de culture à base de cocotiers (Cocos nucifera L.) sur l'île de Malo, Vanuatu

Coconut palms play a major role in the culture and economy of Pacific islands. The extension of coconut plantations, which currently occupy the majority of the arable land, has gradually changed the traditional cropping systems of the Northern Island of Vanuatu. With a growing population and a downward trend in copra market prices, farmers and extension services are now looking how to improve the profitability and sustainability of the cropping systems. The length of the coconut biological cycle and the diversity of intercrops in farmers’ plots raise specific difficulties for characterising and evaluating coconut-based cropping systems. The aim of this study was to propose an approach for characterising and evaluating the agroecological performance of such systems. The approach focused on Malo Island (Vanuatu: 167°10’S, 15°40’E), highlighting a typical context of smallholder copra production. Coconut-based cropping systems and their temporal dynamics were identified using the diversity of situations existing in smallholder plots in the study area. The diverse situations were described and classified according the structure of the vegetation in the plots. They were then considered on a temporal basis in relation to coconut palm development. Five coconutbased cropping systems were characterised, along with their key situations. Once the systems had been characterised, a plot network was established that was representative of coconut palm development in different systems. An agroecological evaluation of the coconut-based cropping systems was then carried out based on this plot network, applying a “space for time substitution”. The agroecological evaluation corresponded to an evaluation o f the production and biophysical limiting factors of those systems. The different uses of the species identified in smallholder plots were characterised and production in the plot was quantified as the production of the different types of species in the plot (coconut palms, food species, fruit trees, etc.). The dynamics of light transmission, soil occupation by palm root systems and soil organic content were evaluated in the coconut-based cropping systems due to their biophysical relevance in agroforestry systems. Specific tools (indicators of production and simulations of light transmission and coconut palm root development using 3D models) were developed for the agroecological evaluation of these systems. The agroecological sustainability of coconut-based cropping systems was ultimately considered on a plot scale according to the performance and biophysical functioning of these systems. Proposals are made for their development. (Résumé d’auteur)