The association of various food and cash crops with coconut is a key issue for the sustainability of coconut-based agroforestry systems in the humid tropics. Crops can be associated at various coconut development stages, but the effects of above-ground competition for light and below-ground competition for water and nutrients throughout the coconut cycle, which lasts several decades, must be taken into full consideration to optimise such associations. New modelling tools are used here to simulate light distribution under coconut stands and root-free soil volume for food and cash crops. Modelling of light transmission through coconut stands is based on three-dimensional coconut models and a numerical light model which simulates the shade cast by these 3D models on underlying crops. This approach was validated in Vanuatu on standard coconut plantations against in situ hemispherical photographs and was extended to evaluate smallholder situations. Root-free soil volume is assessed with a 3D coconut root system model. The light quantity and distribution as well as root-free soil volumes available for food and cash crops were analyzed for 6, 20 and 40 year old coconut trees in smallholder plantations. The possibility of using open places created as a result of coconut mortality was then assessed for different planting patterns and tree densities. Realistic predictions were achieved using a very simple data collection strategy. This approach is useful for drawing up recommendations about tree patterns and planting densities as well as associated crop management in most sunlit areas with minimal root competition. (Texte intégral)