Linking biodiversity and sustainability in agroecosystems : The case of agroforestry systems in the humid tropics

Most agrosystems strongly modify and affect biodiversity and, as a consequence, ecosystem functioning in a variety of domains such as biological control of pests and diseases, nutrient cycling, erosion control, sediment retention and water regulation. Agroforestry systems in the humid tropics are traditional agrosystems that both provide essential productions for poor local populations (including food, habitat, energy, medicine, etc.) and ensure significant part of coffee, cocoa, rubber, oil palm or coprah world production. These systems are characterized by a high complexity that can be related to the number and the type (annual vs perennial, cultivated vs spontaneous or sub-spontaneous, herbal vs ligneous, etc.) of species that are combined simultaneously. This vegetation structure, due to human management, constitutes a specific habitat for numerous vegetal and animal species, hence increasing the global biodiversity and the useful products of these systems. By this way, they are susceptible to play an essential buffer role in the ecological functioning of often fragile and menaced ecosystems and constitute a potential sustainable alternative to intensive monoculture of perennial crops. Facing the ecological complexity of these systems and in the aim of understanding their functioning and performances, it became imperative to develop original approaches that combine concepts and tools from both Agronomy and Ecology. This paper proposes and discusses such approaches from local situations studied in Africa (coffee based systems in forest Guinea), Central America (cocoa based systems in Costa Rica) and Oceania (coconut based systems in Vanuatu). It focuses on characterisation and evaluation of the multiple functions of the planned biodiversity managed by the grower with a specific attention paid on its impact on the global biodiversity. Such studies require i) to work at different spatial (from field plot to landscape) and temporal scales and ii) to take into account the structural and functional attributes of the planned biodiversity. Thus, the concept of spatio-temporal dynamics and the adequate definition and analyzis of functional plant traits and groups represent key steps for understanding the link between planned biodiversity and productivity, stability or global biodiversity of these complex agroecosystems . (Texte intégral)