University of Washington Botanic Gardens

The University of Washington Botanic Gardens would like to thank Tree Solutions, Inc. for bringing the latest technology in tree risk assessment to the Washington Park Arboretum.  Tree Solutions assessed a large western hemlock (Tsuga heterophylla) using sonic tomography, a device which measures sound waves to detect decay and other abnormalities in wood.

Assessing the risk associated with trees is a vital component to maintaining the urban forest.  Visually assessing a tree can often give more than enough information.  However, what cannot be seen can yield valuable information to the risk assessor or manager.

It is normal for trees that appear healthy to have decay inside the trunk and limbs.  It is the extent of this decay, along with the overall vitality of the tree that determines management (pruning, cabling, removal).  Traditional methods of assessing internal decay include sounding the tree with a mallet, increment borer, and drilling.  A more sophisticated method is the resistograph, which determines the decay extent using a very fine drill bit and produces a printed record.

Among the very latest technology is the minimally invasive procedure (i.e. no drilling!), sonic tomography.  Sound waves sent through the tree are measured by sensors placed around the assessed part, which feed into a computer.   The computer analyzes the input producing a color image which accurately shows healthy wood and decayed wood.  This detailed information greatly helps in determining management of the Arboretum main attraction…the trees!