Field performance of poplar for bioenergy in southern Europe after two coppicing rotations: effects of clone and planting density

Short Rotation Forestry (SRF) plantations are estimated around 7 000 hectares in Italy, mostly established in northern regions. Recently thousands hectares of SRF were established in central and southern regions of Italy also (especially in Latium and Molise) due to the promising introduction of new clones resistant to summer water limiting and pest attacks. A poplar SRF plantation was established in central Italy in order to investigate the influence of site conditions and planting densities/spacings on the growth and yield production of three hybrid poplar clones (AF2, AF6 and Monviso). Cuttings of each clone were planted at two different densities/spacings and planting design as: (a) low density = 7 140 cuttings ha-1 in a single-row design (SR); (b) high density= 10 360 cuttings ha-1 in a twin-rows design (TR). Growth (both diameter and height) and yield were evaluated after biennial (2006-2007) and triennial (2008-2010) rotation. Relationships between fresh weight and diameter were determined to calculate the yield of each clone expressed in MgDM ha-1 years-1. At the end of the triennial rotation (2010) all poplar clones showed very high stump survival rates with higher values in SR (89.9%) compared to TR (85.6%). AF2 clone can be advisable thanks to the higher yield production than both AF6 and Monviso. Considering planting densities/spacings, SR seems to be more advisable than TR in order to obtain a good biomass production and a low planting costs. Considering the coppicing cycles, triennial rotation allows higher annual yield production (average value of 13.0 MgDM ha-1) than biennial rotation (average: 10.1 MgDM ha-1).