Genotypic differences in biomass production during three rotations of short-rotation coppice

Short-rotation coppice (SRC) will play a major role in meeting the predicted demands for woody biomass, but data on genotype-specific biomass productivity and growth parameters are still largely missing. These data are, however, important for assessing the expected revenue, but also for predicting the choice of harvester. Therefore, an operational SRC with 12 Populus genotypes was yearly monitored over its first seven years (three rotations). Inventories of shoot diameters at 22 cm above the ground, of number of shoots per stump and stump mortality were converted to above-ground woody biomass (AGWB) with allometric relations. The dataset was based on 23,656 sampled stumps for determining the number of shoots per stump, while 36,792 shoots were measured to determine their diameter. An AGWB productivity of 3.43, 11.13, and 16.49 Mg ha−1 y−1 was reached in the first (two-year), second (two-year), and third (three-year) rotation, respectively. Within each rotation, the AGWB productivity increased yearly, while rotations (after the establishment rotation) reached comparable AGWB productivities over the same (two-year) duration. Significant genotypic and spatial variation in shoot diameters, number of shoots per stump and AGWB were found within and among the seven sampled years. Additionally, repeated sampling at breast height in the second and third year of the third rotation was comparable to sampling at 22 cm above the soil. Lastly, a shoot diameter measurement accuracy of 0.01 mm proved exagerrated for biomass assessments and could be limited to an accuracy of 1 mm.