University of Florida

Home > Tree structure basics > Structural defects > Hollows and cavities > Evaluating decay

Evaluating decay

decayed wood at base of treeDecayed wood reduces its strength. Visible decay at the base of the trunk reduces reduces the trees ability to stand up. A thorough evaluation by trained personnel of the extent of decay using appropriate tools and techniques such as visible tree evaluation, mallets, drills, resistograph, and others is the best method of evaluating risk for failure. A resistograph (shown below) is a tool that uses a drill bit to measure the force required to drill through wood. Decayed regions and hollows can be seen on the printout generated by the device as it drills through the wood.

resistograph shown with drill bit
Resistograph shown with a drill bit through the sound wood and into the decayed hollow.
failed oak tree wiht larged decayed cavity
Huge oak failed due to a large decayed cavity.