Shigometer and electrical resistance studies of paper birch

Abstract

The Shigometer was evaluated as an instrument for detecting red heart of paper birch. The Shigometer accurately detected the presence of red heart at a 50% decrease from the maximum reading rule but sometimes failed to precisely define its outer limits. Although it did not always correctly detect the presence or precise location of discoloured wood, it was able to correctly detect the presence of discoloured wood within a few centimetres in approximately 85% of attempts. There was a general increase in ion concentrations in the red heart as compared to the clear wood. The ions appear to accumulate in vessels along the clear wood to discoloured wood transition zone, in the ray parenchyma in the transition zone and in the discoloured wood. Following wounding there was an increase in soluble and insoluble potassium. The Shigometer readings were found to be correlated with mobile ion concentrations of potassium and magnesium. Because few microorganisms were found in association with the red heart, it is felt that the initial accumulation of ions may be a wound response by the tree.