Sonar technology determining health of West Campus trees

September 03, 2010 By Bryan Roth, Office of Communication Services


David McDowell, a horticulture technician with Facilities, uses sonar to check for
the possibility of decay in Willow Oak trees on the West Campus quad.

Facilities staff are using hi-tech gear this week to determine the health of White and Willow oak trees on West Campus.

Working with Bartlett Tree Experts, a Raleigh-based tree-care company, Facilities Management has been using sonar to send sound waves through the wood of each tree to determine the level of decay. The trees on the West Campus quad are more than 70 years old and have been around since the campus was being built in the 1930s. More than 20 trees are being tested.

“We’re doing a proactive investigation of the trees because they’re in an urban-style environment, which means they have to compete with factors like pollution, buildings and sidewalks,” said Roger Conner, Duke Grounds superintendent. “All these things will naturally reduce the life of a tree because it’s not in its natural, woodland environment.”
Despite those factors, Conner said almost all the trees on the quad should end up having a normal lifespan between 80 and 100 years. He added that at this point in Facilities’ study, normal decay has been found in some trees. The full results of the study haven’t yet been compiled, so it hasn’t been determined if any trees will need to be removed and replaced. Facilities previously pruned trees throughout West Campus in May and June to improve tree health and reduce the risk of branch failure.

The sonar system works by placing 10 regular-sized aluminum nails into the tree which are long enough to pass through a layer of bark and into wood. By tapping an area around each nail with a hammer wired to a monitor, sound waves are passed through the wood and intercepted by 10 transmitters attached to each nail. Information is fed to a laptop that graphs the sonar to show if wood is damaged. Portions of each graph will show up in different colors to display the health of the tree.

“Instead of drilling into each tree with a bit, the nails offer a very non-invasive way to check each tree,” Conner said. “These trees are icons of Duke that were ordered to be planted by the Duke family.”