First vs. second rotation of a poplar short rotation coppice: Above-ground biomass productivity and shoot dynamics

Within the global search for renewable energy sources, woody biomass from short rotation coppice (SRC) cultures is a valuable option. So far there is a shortage of large-scale field yield data to support stakeholders. We investigated an operational-scale SRC plantation (POPFULL) with 12 poplar genotypes in Flanders during its first two biennial rotations. By inventorying shoot numbers and diameters, combined with allometric relationships, productivity related data were derived after each growing season. We observed significant variation in biomass yield and productivity-related characteristics among the 12 poplar genotypes, of which two recently selected. Genotype Hees (Populus deltoides × Populus nigra) and Skado (Populus trichocarpa × Populus maximowiczii, selected in 2005) reached the highest productivity among genotypes, i.e. 16 Mg ha−1 y−1 of dry matter (DM) yield in the second rotation, which was more than double than the poorest performing genotype Brandaris (a pure P. nigra). However, with many small shoots genotype Hees had a different growth strategy than Skado that resprouted with few, thicker and higher shoots. Biomass production increased from a plantation average of 4.04 Mg ha−1 y−1 of DM in the first (establishment) rotation to 12.24 Mg ha−1 y−1 in the second rotation. Mean height growth raised from 2.08 m y−1 during the first rotation to 2.99 m y−1 during the second rotation. The influence of the first coppicing on tree mortality was negligible. Monitoring of subsequent rotations over the plantations' lifetime - which counts for SRC bioenergy cultures in general - is essential to evaluate productivity in the long term.