Production and role of epicormic shoots in pruned hybrid poplar: effects of clone, pruning season and intensity

Pruning one third of crown length in summer produced the least number of epicormic branches after two growing seasons. Epicormic branches can be removed without compromising tree growth. The formation of epicormic shoots is often observed following pruning treatments, but their role in the overall tree growth is unknown. The objectives of this study were to examine how pruning intensity and season affect the production of epicormic branches and how their presence (or removal) affects tree growth and total non-structural carbohydrate reserves in the roots. Trees from four hybrid poplar clones were pruned in fall, spring, and summer at two intensities 1/3 and 2/3 of the crown length and an unpruned control. Produced epicormic branches were removed from half the trees. Pruning intensity and season were the most important factors affecting the number and biomass of epicormic shoots while clone was not. Pruning 1/3 crown length in summer reduced the emergence of epicormic shoots compared to 2/3 and spring or fall pruning. Two years after pruning, the removal of epicormic shoots did not affect height or diameter at breast height of trees, and their presence did not restore root total non-structural carbohydrates reserves to unpruned levels. We concluded that pruning should be done in summer at 1/3 of the crown length to reduce epicormic shoot formation and to avoid decreases in stem growth. If epicormic shoots appear, they can be removed without compromising tree growth.