The impact of stumps’ height on secondary spread of Heterobasidion parviporum in precommercial thinning stands of Norway spruce (Picea abies)

Abstract: The economic losses caused by Heterobasidion spp. infection is an important issue in the Swedish forestry sector where Scots pine and Norway spruce make up to 80% of the standing volume. Both of the fungi species naturally existing in Sweden: H. annosum and H. parviporum cause decay of the wood and decrease quality of the timber. In spruce dominated stands the risk of primary infection occurred even in small sized (2-14 cm at stump height) percommercial thinning stumps. Therefore, there is a need to develop useful methods of preventing the primary infection and secondary spread the in young spruce stands. The paper investigates the impact of stump’s height created during precommercial thinning operations on transferring H. parviporum infection into adjacent trees due to root contact. Ninety Norway spruce trees were cut down in three precommercial thinning spruce dominated stands in southern Sweden to create two types of donor stump high- (100 cm above the ground) and low stumps (15 cm above the ground). Four years after artificial inoculation of H. parviporum sample discs were collected from donor stumps and the four the biggest trees within 2 m radius in order to examine the secondary spread of the infection. The infection frequency has reached 16,2%. In most cases it was naturally occurred contamination, the artificially inoculated strain of H. parviporum was found only on four out of 51 infected discs (0,7 % infection frequency). Trees surrounding low stumps were infected more frequent than those adjacent to high stumps, 31 and 18 infected trees respectively. It means that 63% of the infection was found in the trees adjacent to low stump and 37% of infected trees occurred next to high stumps. However, the differences of infection frequency occurred in the blocks with high and low stumps is too slightly to be significantly important (p-value equal 0,0691) when all investigated strains of Heterobasidion are taken into account.