The occurrence of bark beetles on cut Norway spruce branches left in managed stands relative to the foliage and bark area of the branch

Abstract

This study addresses the relationships between the foliage and bark area of Norway spruce (Picea abies) branches left in the forest after managing large timber: the densities of infestation by Pityogenes chalcographus, Pityophthorus pityographus and Dryocoetes autographus; and the reproductive efficiency of P. chalcographus. Based on the models developed in this study, a positive correlation was found between the foliage area of spruce branches and the densities infested by P. chalcographus and D. autographus, though a higher negative correlation was found in relation to the size of the branch bark area (BA) and the infestation densities. A negative correlation for the branch BA was also found on P. pityographus. This result shows that the desiccation of branches affects the infestation densities of bark beetles. In contrast, the size of the branch BA was positively correlated with the reproductive efficiency of P. chalcographus, with higher reproductive efficiency on the branches from the outer layer of the pile than on disorderly scattered branches on the ground.