A study case on polycyclic plantations (PP) as innovative models for sustainable combined production of noble hardwood and biomass

Aim of study: To verify the short rotation coppices (SRC) aboveground biomass production; to define the best planting intra-row spacing for walnut and poplar growth and wood production, with the last goal to assess the possibility of obtaining competitive yields in comparison to those produced by traditional monocultures. Area of study: Po Valley, municipality of Meleti (Northern Italy). Material and methods: A randomized block design with three replications was applied for the experimental design. The growth-monitoring activities started in 2009 and have continued for 5 years on the SRC, 10 years on poplar clone ‘I-214’, whereas on common walnut they are still going on but only data concerning the twelfth year are reported in this work. The normality of distribution was evaluated for growth and yield data of species in the SRC model; all data were analysed with ANOVA; growth data were included in a linear mixed model analysis to evaluate the effect of age, spacing and their interaction, and the effect of SRC rows on growth and yield of poplar and walnut. Main results: After 5 years of cultivation under SRC system, biomass yields obtained from the poplar clone ‘AF2’ were 39.9 Mg ha-1, from the elm 31.9 Mg ha-1 and from the plane 14.8 Mg ha-1. After 10 years high timber production was obtained from poplar clone ‘I-214’ (average volume 98.2 m3 ha-1). After 12 years, walnut trees reached a diameter at breast height (DBH) of 17.8±0.2, 18.9±0.2 and 18.7±0.3 cm, respectively, for planting distances of 6, 7 and 8 m, and showed diameter increments of 1.5-2.0 cm yr-1. With these growth rates, walnut can reach a merchantable dimension within 25-30-years. Research highlights: Polycyclic wood plantations are a recent arboriculture model able to produce, on the same site, different assortments using various crop trees characterized by different growth rates and turnovers. This new type of mixed plantation is more environmentally sustainable compared to monoculture and allows diversification of production, obtaining continuous wood yields over the years (5, 10, 20, 30 years).