Comparing hybrid Populus clones for SRF across northern Italy after two biennial rotations: Survival, growth and yield

Short rotation forest (SRF) plantations of hybrid poplars are attractive for Italian farmers due to the availability of public grants and the potential for producing wood chips for energy production. Growth and dendromass yield of new clones for SRF were evaluated after two biennial rotations within a network of experimental fields established in 2003 on three sites of low (Bigarello), medium (Vinovo) and high soil quality (Mira), across northern Italy. Soil preparation, planting density (5900 trees ha⁻¹), weed control, tree water status and mechanical harvesting were homogeneous across the sites. Nitrogen fertilization was applied only in Mira (300 kg N ha⁻¹).In all sites, survival was high for almost all clones, and stem density increased dramatically, with a decrease of stem dimensions, after the first coppicing. In Bigarello, with limiting soil conditions, there was no significant difference among clone biennial yields, which varied from 10.3 (first rotation) to 14.2 (second rotation) Mg ha⁻¹ in dry matter (dm). In the medium and high quality sites of Vinovo and Mira, there was a significant difference in clone yields, with the new clones performing better than control clones (I-214 and Lux). In Mira, mean biennial yield increased from 30.2 to 40.3 Mg dm ha⁻¹ from the first to second cycle.Preliminary results of new clones on medium and high soil quality need to be further confirmed throughout further coppicing cycles; on a marginal soil, even by using the new clones, poplar SRF is not an advisable option.