Commission hears about Resistograph, sonic tomography and veteran-tree assessment tools

The commission heard a technical overview of tools used to assess internal decay and shell-wall thickness in trees, including the Resistograph drill and sonic tomography approaches. The chair explained how these instruments generate graphs that help arborists decide whether a tree has sound wood or requires mitigation.

"The Resistograph is a device, that actually drills with a very small needle into, tree parts, you know, tree trunks, tree flares," the chair said, explaining that the tool prints a graph of wood resistance used to assess decay and inform mitigation such as pruning or load reduction.

The chair noted the technology comes with costs (the chair said they believed units cost about $11,500) and emphasized that interpretation requires arboricultural expertise because results can be misread. The chair also said Frank Wren — identified as the inventor of the modern Resistograph — will keynote the New England ISA conference and give a veteran-tree workshop prior to the conference.

Commissioners asked whether Northampton owns such equipment and about time and expense for field use; the chair said the device is not inexpensive and that reading outputs requires knowledge of tree biology. The commission discussed the value of these tools for preserving mature or veteran trees and for tailoring mitigation rather than assuming removal based on external appearance alone.