Above-ground biomass characteristics of young hybrid aspen (Populus tremula L. x P. tremuloides Michx.) plantations on former agricultural land in Estonia

Fifty biomass production model trees were analysed in 7-yr-old commercial hybrid aspen plantations established on abandoned agricultural land in Estonia. Above-ground leafless biomass (ALB) of the model trees varied from 0.1 to 9.8 kg DM. The ALB of plantations with a density of 880-1340 trees ha−1 growing on former field soils was between 2.18 and 8.54 t DM ha−1. The amount of nitrogen accumulated in the ALB varied between 14.4 and 48.5 kg ha−1, the amount of phosphorus, between 1.7 and 5.9 kg ha−1, and the amount of potassium, between 6.5 and 21.9 kg ha−1. The removal of major mineral nutrients from the site with the removal of woody biomass in 7-yr-old plantations would be relatively small, constituting 0.5-3.4% of the nutrient pool in the humus layer of the previously fertilized field soils. The stembark content decreases rapidly until the DBH reaches 4 cm, which can be considered a target diameter for the hybrid aspen coppicing system.