Designing a sustainable orchard – plant diversity as a key and ways to implement it

International audienceConventional fruit-tree farming systems are highly productive and strongly dependent on external inputs, including pesticides, fertilisers, and water. To reduce this dependence, various initiatives have been developed in past decades, such as Integrated Fruit Production, Organic Farming, and more recently, Agroecology which is strongly inspired by research in ecology. These initiatives include plant diversity as the main driver to improve the sustainability of the orchard. Plant diversity can either be planned (choice of productive and not productive species) or associated (unintentional) and at different scales (within the cultivated plot and/or the surrounding landscape). To increase plant biodiversity, companion, i.e., mostly non-productive, plants can be either herbaceous, bushes, or trees. The interest of plant diversity to improve the sustainability of agrosystems is documented from three points of view: composition, structure, and function. First, companion plants have to fulfil precise functions within the system, such as sustaining nitrogen provisioning (e.g., herbaceous legumes between fruit-tree rows), hosting natural enemies of main pests, or attracting herbivore insects outside the orchard. Recent works on agroecology analyze fruit-tree based agrosystems documenting fruit production and the various “services” (e.g., mitigation of CO2 emission, soil nitrogen availability) companion plants can provide. Second, to optimise plant functioning, it is necessary to define rules of plant assemblage at spatial (e.g., distance between plants) and temporal (e.g., plantation at the same time period or not) levels. Based on a literature survey and current experiments, we will show that agrosystems that combine trees grown for fruit and possibly for timber or firewood and agricultural crops, i.e., fruit-tree based agroforestry systems (FT-AFS), provide promising results in the temperate climate context, including the Mediterranean zones. Further, the introduction of plants providing pest regulation services opens to challenging perspectives toward friendly fruit-tree-based agrosystems