ABSTRACT
A wide range of methods and tools are available to aid in the process of tree risk assessment. The vast majority of trees can be assessed visually, but when the likelihood of failure remains uncertain after a visual inspection, a number of tools can be used to measure the extent of decay, loss of strength, or anchorage. The most common way to assess the strength of a tree part is on the basis of the distribution of sound wood. A visual inspection and a mallet are often used to detect areas of weakness for further assessment. Currently, there are two types of tomographs widely used in tree assessment, either based on the time of flight of stress waves or on the electrical resistivity of wood. Electrical resistivity tomograms (ERT) display the distribution of resistivity across the stem cross-section. ERT has been applied to find discoloured wood, ring shake and decay in trees, and even to detect roots in the soil.
