Decreased volume growth of Picea abies in response to Heterobasidion annosum infection

Comparisons of growth between paired healthy Picea abies (L.) Karst. trees and those infected by Heterobasidion annosum (Fr.) Bref. were made within two stands on previous arable land in southern Sweden. Diameter growth at breast height, 3 m, and 5 m, and height and volume growth were reconstructed in the two stands over 12 and 20 years, respectively. In the first stand, where the fungus had been present for 8 years, no growth reduction was detected. In the second stand, where H. annosum was probably introduced at the first thinning 17 years ago, infected trees lost 9.9 mm (5%) of diameter growth at breast height and 10% of volume growth during the 20-year period. Fitted orthogonal polynomials showed that growth reductions of the infected trees increased with time. Over the last 5 years, diameter growth losses at breast height averaged 20%, while growth of height, diameter at 5 m, and volume was reduced by 25%, 20%, and 23%, respectively. The impact of the extent of decay on tree growth was investigated, but no significant differences were found. Tree position in the stand was mapped for the healthy trees, and the possible differential effect of whether neighboring trees were healthy or infected was investigated. The neighboring trees' health status seemed to have no effect on growth of healthy trees.