Logging operation damage to roots of clear-felled Picea abies and subsequent spore infection by Heterobasidion annosum

Two studies were carried out to examine the effects of clear-felling operat ions on stump roots of Norway spruce (Picea abias (L.) Karat.). In study I, the number of cases and the degree of damage to stump roots of Norway spru ce were investigated on three clear-felled sites in northern and southern S weden respectively. The cutting was done in winter or spring. A mean of 37 % of the stumps had signs of root damage caused by clear-felling operations . Study II was carried out on two sites in southern and two sites in northe rn Sweden. The trees were clear-felled in June or July. The frequency of na tural infection by Heterobasidion annosum (Fr.) Bref. through damaged roots was compared to infection through stump surfaces. The total area of damage on roots was 88 % of the stump surface area. On average, 54 % of the stump s were infected through the stump surface and 19 % through locations of roo t damage. The root infections, however, were generally small in size as com pared to stump surface infections. The study shows that damage to roots at clear-felling may be extensive, but this probably is not of great importanc e for the efficacy of stump treatment against H. annosum.