The science of tree stability analysis uses both biological and engineering principles in attempting to rate a tree's structural soundness and make reasonable predictions of potential for failure. In such analysis, arborists are often challenged by internal structural defects hidden from view within the trunks. This paper reports the results of an investigation using acoustic tomography to detect internal decay in park trees. Two century-old red oak (Quercus rubra) trees located at the Capitol Park in Madison, Wisconsin, were nondestructively evaluated using an acoustic tomography technique. The trees were subsequently felled, and a disk at each test location was obtained and examined. We found that the light-colored zones in the tomograms were larger than the true decay present in the disks. The oversized light-colored areas were the composite effects of both decay and large internal cracks. The results of this study demonstrated that acoustic tomograhy cannot distinguish between large internal cracks and heartwood decay. To make a better assessment of internal condition for urban trees, resistance microdrilling should also be used prior to tree removal.

Arborists are often challenged to identify internal structural defects hidden from view within tree trunks. This article reports the results of a study using a trunk inspection protocol combining visual observation, single-path stress wave testing, acoustic tomography, and resistance microdrilling to detect internal defects. Two century-old red oak (Quercus rubra) trees located in Capitol Park, Madison, Wisconsin, U.S., were visually inspected and then evaluated using a single-path stress wave timer, an acoustic tomography, and a resistance measuring drill. The trees were subsequently felled, and a disk at each test location was obtained and examined. It was found that the visual inspection and single-path stress wave tests correctly identified a general problem but without specificity; the tomograph accurately revealed the general location and magnitude of the defect within the cross-sections tested but required resistance microdrilling to precisely locate defects and differentiate between decay and crack-induced acoustic shadows.

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Researchers have developed various methods and tools for nondestructively testing urban trees for decay and stability. A general review of these methods includes simple visual inspection, acoustic measuring devices, microdrills, pull testing, ground penetrating radar, x-ray scanning, remote sensing, electrical resistivity tomography and infra-red thermography. Along with these testing methods have come support literature to interpret the data.

This report summarizes a state-of-the-art review conducted on the topic of field measurement of the quality of wood in trees. The foundation science of micro-resistance drilling and acoustic-based techniques for use with woody materials is presented, and use of these techniques for the detection of biodeterioration in wood is discussed. Quantification of the physical and mechanical properties of wood, in standing timber, is reviewed. Studies designed to examine the use of these techniques with trees are summarized, and a list of commercially available technologies that use these techniques is presented.