Does increment coring enhance tree decay? New insights from tomography assessments

Increment coring is a standard method to obtain growth history information stored in trees. Although the method is invasive, the long-term effects on tree decay are largely unknown. Here we assess a possible side-effect of scientific research, i.e., coring-induced stemwood decay, using the high-resolution imaging technique of sonic and electric resistivity tomography. To this end, we use data from a Norway spruce (Picea abies (L.) Karst.) forest in the Swiss Alps (forest reserve Scatlè) containing a large number of trees cored in 1965-1966. In 2011, in-situ tomography was applied to 22 pairs of cored and uncored trees to assess their stemwood decay status. Each pair was characterised by similar tree diameter at breast height, vitality, forest layer class, micro-site, and competition status. Samples from a subset of 10 trees were checked for common heart rot fungi. We found no significant difference between the decay status of cored and uncored trees. Few trees of both groups showed distinct signs of decay, most of them growing in a cluster containing three cored and seven uncored trees. Heterobasidion annosum s.l. was identified in seven trees, and Armillaria sp. was identified in one tree only. Heterobasidion annosum was found in two trees without distinct decay signs, showing the latent presence of this pathogen in unmanaged forests. Our findings suggest that increment coring of P. abies does not cause a significant increase of tree decay frequency in undisturbed high-elevation forest stands.