The Incidence of Rot in Norway Spruce and its Influence on the Value of Trees in Slovenia

Nacrtak Rot is one of the most important defects in timber assortments of Norway spruce (Picea abies). With the aim to investigate this phenomenon, we analyzed 1,334 spruce trees from 65 locations across Slovenia. The study showed that the incidence of rot was higher in even-aged stands compared to uneven-aged stands. Lower-trunk rot (for the purpose of this study, lower-trunk rot is rot that affects the stem up to 5 m above ground) is significantly connected with the diameter of the tree, whereas rot in the upper part of the trunk, i.e. upper-trunk rot, does not show such dependence. Rot is most commonly associated with dolomite bedrock. Its incidence increases with tree age, site productivity, and site altitude. Mechanical stem injury is another contributing factor. On the other hand, slender trees, sun-exposed sites, and uneven-aged stands carry a lower risk for the studied defect. The incidence of rot may decrease the value of usable timber by as much as 19 €/m, with the decrease being highest in 50 to 70 cm tree diameter.