Blue Mountains News

Picus Sonic Tomography measures the time sound moves through the woody tissue of a tree via 12 to 24 sensors attached to the bark.

“Soundwaves travel around the sensor points and the resulting image shows the proportion and location of healthy and decayed wood, wood chemically altered by fungi, and hollows inside trunks and branches,” Elizabeth Begg, BMCC Public Lands Tree Officer, explained.

“It’s like being able to cut a tree open at a particular location, take a look inside, and put it back with no ill effects to the tree. It’s less invasive than the alternative resistograph, which drills far into the tissue of the tree to investigate its structural integrity.”

In the past, BMCC engaged a local Consulting Arborist to provide this specialist service but has now bought its own technology and trained staff to conduct the testing in-house.

The results of these tests have assisted not only with regular tree assessments, but helped determine the risk of failure through understanding the rate decay might be spreading through a tree.

“One good news story is a pre-settlementEucalyptus sclerophylla – or Scribbly Gum – tree located in Glenbrook Park,” Ms Begg said.

“Tests conducted more than a decade ago showed there was a problem at the base of the tree, and removal was recommended. However, follow-up Picus testing 10 years later has revealed the tree outgrew that defect after a fence was placed around the base, preventing the soil from being compacted.”

The technology is currently being employed to investigate the health of a 22-metreAngophoria costata – or Sydney Red Gum – located near the Great Western Highway at Buttenshaw Park in Faulconbridge.

The tree is what’s known as “co-dominant”, meaning two main trunks grow from the same base, and Picus testing has shown decay at the base.

“The issue for the tree is its location. It’s surrounded by infrastructure like footpaths, a toilet block, the highway, overhead wires, a car park, and seating areas,” Ms Begg explained. “This presents numerous targets with little opportunity for soil remediation to improve the health of the tree.

“We will be using the Picus tomograph to determine the rate of decay to see if the tree is in decline, or whether retention is a viable option.”

Initial and follow-up Picus testing can identify rates of decay, helping Council officers make the difficult decision to either significantly reduce the crown of the tree or remove it completely, Ms Begg said.

“In other cases, that information helps to support remediation work. While it is not the only factor in tree assessment, it does take some of the guess work out understanding the internal structure of trees.

“It has been especially useful in locations where there has been a high degree of concern, or where a failure would have very serious consequences and on trees that are very prominent and generally much loved by the community.

“Council now has the technology to do this work in-house, which is a great support for tree management officers to help make these difficult determinations.”