Production of hybrid aspen on agricultural land during one rotation in southern Sweden

High potential productivity together with short rotation periods have made hybrid aspen an interesting option for wood production on former arable land in Nordic countries.In this study,some of the oldest active experimental plots with hybrid aspen in Sweden were remeasured at 23–30 years of age.A main aim was to assess age and productivity at the time of maximum mean annual volume increment.In addition,the infl uence of commercial thinning on stand development and diff erences in genetic gain among clones were investigated.Data from fi ve experiments in southern Sweden were used,including three genetic trials,one demonstration stand with a clone mixture and one stand regenerated from root suckers.The three genetic trials were treated as single plot experiments,subject to a standard thinning program.In the remaining experiments,diff erent thinning strategies were tested in a balanced block design.Volume growth had culminated or was close to maximum at age 25–30 years.Mean annual stem volume increment at culmination was 20–22 m 3 ha^−1 a^−1.Dominant height reached 30–35 m at 28–30 years of age.Mean diameter at breast height was 27–29 cm after 29–30 years in the genetic trials.Clonal ranking based on diameter at age 7–9 years was positively correlated with the ranking at the fi nal measurement in the genetic trials,20 years later.This indicates that clones can be selected for superior growth based on results from young trials.More intense thinning programs increased the mean diameter compared to light thinning.The study indicates that one or two early and relatively heavy thinnings can promote the development of crop trees,without jeopardizing total volume production during a rotation of 25–30 years.