Preface; D. Auclair, C. Dupraz. A review of belowground interactions in agroforestry, focusing on mechanisms and management options; G. Schroth. Adequate design of control treatments in long term agroforestry experiments with multiple objectives; C. Dupraz. Nutrient cycling in an agroforestry system with runoff irrigation in Northern Kenya; L. Lehmann, et al. Growth and nitrogen status of young walnuts as affected by intercropped legumes in a Mediterranean climate; D. Dupraz, et al. Testing the safety-net role of hedgerow tree roots by 15N placement at different soil depths. Temperature and water-use efficiency by lucerne (Medicago sativa) sheltered by a tree windbreak in Tunisia; J. Benzarti. Developing a canopy closure model to predict overstorey/understorey relationships in Pinus radiata silvopastoral systems; R.L. Knowles, et al. A simplified description of the three-dimensional structure of agroforestry trees for use with a radiative transfer model; S. Meloni. Competition for light, water and nitrogen in an association of hazel (Corylus avellana L.) and cocksfoot (Dactylis glomerata L.); F.X. de Montard, et al. Growth of widely spaced trees. A case study from young agroforestry plantations in France; P. Balandier, C. Dupraz. Diameter and height growth curves for widely-spaced trees in European agroforestry; A. Cabanettes, et al. A model of tree-crop competition for windbreak systems in the Sahel: description and evaluation; M. Mayus, et al. Analysis for dry and wet years with the WIMISA model of tree-crop competition for windbreak systems in the Sahel; M. Mayus, et al. WaNuLCAS, a model of water, nutrient and light capture in agroforestry systems; M. van Noordwijk, B. Lusiana. Incorporating agroforestry practices in the management of walnut plantations in Dauphine, France: an analysis of farmers' motivations; F. Mary, et al. Simulating integration of agroforestry into livestock farmers' projects in France; M. Etienne, H. Rapey. Volume contents. Author index. Instructions to authors.