A Technical Report from The Bartlett Tree Research Laboratories 384
Years ago, filling tree cavities with concrete, bricks, or mortar was common practice, following the dental practice of removing decay and filling teeth. However, aggressive decay removal was found to actually interfere with trees’ natural defenses and wound compartmentalization and so has been largely abandoned. Trees with cavities need to receive a tree risk assessment to determine the extent of the cavities and their contribution to likelihood of failure. In trees of low risk, cavities can be covered or filled to keep wildlife out, to stop the accumulation of water and debris in the cavity, or for aesthetic reasons. If a cavity is to be filled, a coated, expanding foam should be used.