Growing agroforestry systems with apple in Montpellier-Mediterranean – preliminary results on the influence of adult walnut trees on growth and branching of two-year-old apple trees

International audience; Apple cultivation has evolved tremendously in the past decades to increase tree productivity and fruit quality. However, this was achieved at the cost of an increasing dependence on external inputs such as water, fertilizers and pesticides. This dependence is now questioned because of the generated environmental pollution and health issues. Different solutions have been considered to reduce this dependence including more efficient practices that improve resilience of agricultural systems to external pressures (climatic disturbances, new diseases, economic crises). To reduce pest and disease pressure, to improve resources use and to buffer extreme climatic events, agroforestry systems (AFS), i.e., the association, in one field, of tailored perennial and annual crops and possibly animals, are proposed as a way to use positive interactions between various plants. In temperate climate, AFS associate a tree stratum and a (or several) crop stratum, e.g., fruit trees and vegetables. An original AFS located in southeastern France, characterized by a Mediterranean climate and composed of mature walnut grown for timber, apple trees in an intermediate vertical stratum, and alfalfa at the lowest stratum, is being used to study the impact of an AFS on apple trees. Comparing apple trees in the AFS and in full sun, we first showed a significant effect of walnuts on the below-canopy microclimate reducing incoming global radiation and acting as a buffer on temperatures surrounding the apple trees. Secondly, AFS significantly altered the apple tree stem geometry (lesser tapering), growth dynamics (more growth cessation) and morphology (higher individual leaf area and specific leaf area). Results will be discussed with regard to the putative long-term effects of agroforestry conditions on the apple tree architecture and fruiting.