Non-destructive assessment of internal decay in three hardwood species of northeastern North America using sonic and electrical impedance tomography

Sonic tomography and electrical impedance tomography (EIT) were used to detect and quantify internal decay in living trees. Twenty-two cross-sectional images, representing variations in sonic velocity and electrical impedance, were captured from nine trees (four Acer rubrum L., three Betula lenta L., and two Fagus grandifolia Ehrh.) in two forests in Connecticut. Following acquisition of tomographic data, 8 trees were felled, from which 19 stem disks were cut for comparison to the tomographic results. For one black birch, with extensive trunk rot and an internal cavity, sonic tomography (SoT) and EIT were very accurate in depicting both the area of the cavity as well as the area of fungal colonization and incipient decay. The use of both SoT and EIT to estimate area of decay resulted in a level of accuracy that far exceeded that produced from either method alone. Specific gravity values obtained from clear and decayed wood from three trees corroborated tomographic assessments, and permitted an estimation of the amount of carbon lost through decay. The implications of internal decay on carbon sequestration rates in temperate forests are also addressed.