European Hazelnut: Plant Training, Planting Layouts and Pruning Innovations

European hazelnut is a suckering woody species traditionally cultivated as a multi-stemmed shrub, even though its structure is usually modified to enhance orchard management efficiency. The present review analyzed the main changes in hazelnut cultivation over the last few decades, with a special focus on the transition from a multi-stemmed shrub to single-trunk system, influencing plant light interception, promoting some mechanized operations and more in general the whole orchard management. Pruning practice is an essential agronomic operation, covering a relevant role in ensuring the healthy status of the plant and maintaining satisfactory levels of production. Traditional approaches and the current direction toward a mechanical pruning operation as a cheap alternative were evaluated. Furthermore, recent trends in orchard layout, characterized by the reduction in planting distances to enhance orchard performance, were investigated. Furthermore, emerging approaches for precision agriculture were reported, such as those related to automated plant canopy management. Overall, this review aims to highlight the strengths and limitations of different plant training and shaping adopted for the species, as well as to identify future research directions in the field of hazelnut canopy management aimed at ensuring consistent crop productivity over the years.