The walnut plantations (Juglans spp.) in Italy and Spain: Main factors affecting growth

Walnut tree species (Juglans spp.) are commonly used for high-quality wood production in plantation forestry. In this paper, the most relevant walnut plantations in Italy and Spain have been reviewed and analysed under a geographic and technician management point of view. Between 2016 and 2019 a total of 96 plantations (15 - 25 years old) were visited distributed in the North-western part of the Mediterranean basin. A statistical analysis (linear model no interaction and PCA) was then performed to evaluate the relative importance of some environmental and management variables for walnut trees in analysed plantations. Results highlighted a variable situation with many different adopted planting schemes across the regions as well as a not standardised spatial layout and management type (thinning). Lower densities and smaller trees were adopted in Italy with about 200 trees ha versus 330 trees ha in Spain. In addition to the age of the plantation as one of the most influencing parameters also the plantation density and the average crown diameter were highly statistically significant. Overall, the interesting potentiality of walnut for timber production with active management in suitable areas was detected as the focal point for a successful timber production from walnut trees.