Check-ups for Old Trees

Are trees getting MRI scans? Not quite, but arborists and biologists are now determining tree health by using a new technology -- tomography -- to “scan” the insides of trees.

Until now, a comprehensive review of a tree’s health involved drilling holes into the tree’s core and examining the samples for decay; a process called resistographing. But drilling through the trunk is slow, damages the tree, and the results are not always accurate. .

Tomography, on the other hand, involves sending sound vibrations through the tree without cutting into the wood; a process that is quick, non-invasive, and accurate.

“It’s like x-ray vision in a forest,” says Nicholas Whittaker Dankers, an arborist at Tree Solutions in Seattle, who has been using tomography for the past three years.

Here’s how the technology works: Dankers drives pins and microphones into the bark. Hitting a pin sends sound waves through the tree that are received by microphones on the other side. Sound travels slower through hollow wood, which is a sign of degraded tree health. By analyzing the time it takes the sound vibrations to travel through the tree, Dankers can determine the tree’s level of hollowness, or decomposition. Based on this data, a computer is then used to create a digital, color-coded image of the inside of the tree. Multiple scans up a trunk can create a 3-D model of a column of decay.

"Generally, [after a tomography scan] we recommend to promote root development and - when needed - thin trees by focusing primarily on the outermost branches," says Dankers. Advocating a scientifically-informed approach to tree care allows for appropriate actions from the root tips to the leaf ends.

Scans like these are becoming more common as more residents understand the importance and value of large, mature trees in their neighborhoods. Besides offering psychological benefits to people and ecological functions such as purifying the air and preventing soil erosion, these trees also add value to property. A majestic oak or maple tree on your lawn can increase the real estate value by thousands of dollars. As Dankers notes, an old tree can be the equivalent in price of the cost of a new car. Unless old trees are properly maintained and examined, they could become sick, rot, and fall onto surrounding property.

Technologies like tomography help urban and suburban trees stay healthy as they grow in an ecosystem that is much more disturbed than the one in which their ancestors once grew. Preserving the health of large trees, wherever they stand, is an investment in the future - especially in cities, where trees can live for hundreds of years. With help, they can survive beyond the lives of their caretakers and the buildings surrounding them and be enjoyed by generations to come.