Effects of clear-cutting, thinning, and wood moisture content on the susceptibility of Norway spruce stumps to Heterobasidion annosum

Abstract

The effects of clear-cutting and thinning as well as heartwood and sapwood moisture content on spore infection by Heterobasidion annosum (Fr.) Bref. were investigated in summer cuttings in southern and central Sweden. At five sites, 20-100 stumps in clear-cut, thinned, and precommercially thinned stands of Norway spruce (Picea abies (L.) Karst.) were created and left for natural spore infection. An additional 20 stumps per stump type and site were artificially inoculated with conidiospores of H. annosum. The probability of natural infection was 0.73 and 0.53 for stumps in thinned and clear-cut stands, respectively. Almost all (95%) of the artificially inoculated stumps in thinned and clear-cut stands became colonized, and no differences due to stump type were found. The probability of infection of stumps in precommercially thinned stands was lower than for the other stump types of both naturally and artificially inoculated stumps. The proportion of colonized sapwood was reduced with increasing moisture content. Stump colonization seemed unaffected by temperature, even though stump temperatures exceeded 40°C for 2 h at one site.