This field trial was set up in March 2011 in central Catalonia (Solsona, Lleida province, Spain) as part of the POCTEFA Pirinoble project. Initially, the trial consisted of a 1.5-hectare plantation of hybrid walnut (Juglans × intermedia) and some pear (Pyrus sylvestris) and narrow-leaved ash (Fraxinus angustifolia) trees, all of which were grown for their valuable timber. The trees were planted in a 4 x 4 m frame and we assessed the performance of various planting techniques, such as the use of mulches and tree shelters. In late 2025, it was deemed necessary to conduct a thinning intervention and transform the plantation into an alley-cropping system. This involved carrying out systematic, high-intensity thinning and turning the planting frame to 12x8 m to provide enough area for intercropping. Wheat was planted in the alleys in early 2026. The aim of this conversion is to generate annual revenue, with the area being eligible for CAP payments as long as the tree density stays below 100 trees per hectare. During the SCALARE project, we plan to monitor cereal phenology, physiology and microclimate monthly from late winter until early summer, as well as yield at harvest time. This will be done at various distances from the tree row (2.5 and 4.5 m) and in open areas in nearby fields. Some parts of the field will be kept unsown for use as a tree control treatment.
