A giant Norway maple on South Higgins Avenue saw a tree doctor of sorts Wednesday for an assessment of its condition.
“The tree has a full canopy, but it clearly has a defect at the base,” said Christopher Gray, an arborist with the Urban Forestry Division of the Missoula Parks and Recreation Department. “Is this a high-risk tree? Low-risk tree?”
To determine the future of the maple, one of some 32,000 trees the program manages, the city used for the first time a device called a sonic tomograph. The Urban Forestry Division has catalogued an estimated 74 percent of municipal street and boulevard trees, and most of them are, to a trained eye, obviously healthy or obviously hazards in need of removal.
The maple just south of Hellgate High School, though, fell into a questionable category. Its green leaves shade the sidewalk, but it leans over the parking lane on Higgins Avenue, and its trunk is mottled and misshapen near the ground.
To ascertain its health, the city hired Jim Flott of Community Forestry Consultants in Spokane to bring the sonic tomograph to Missoula. On Wednesday morning, Flott, a certified arborist, had inserted probes with sensors around the trunk of the tree.
“We use this all over the world, actually,” Flott said of the machine.
The device measures the time it takes for sound to travel through the tree, and a program maps the results. The waves will travel more quickly through a healthy tree, and they will move more slowly if the wood has hollows or decay.
“When I tap on the sensor, the signal is picked up by all the other sensors,” Flott said.
After assessing the image of the tree as well as its surroundings and the possible risks it poses, Flott will make a recommendation about its future to the city forester. He anticipates releasing his report early next week.
On Wednesday, Jim Cook of Able Tree Service showed up to the site to observe the device in action. It’s a $14,000 gadget, and he said the city would do well to purchase one of its own; some models are cheaper, but they damage the trees in their assessments, he said.
Measuring the health of the single tree cost $2,600, according to the city. If the city had its own tool, it could assess other trees in the future, and it would have a way to show people the interiors and help them understand the reasons arborists sometimes remove trees, Cook said.
“People are tree huggers. They will not want it cut down,” he said.
The city plants trees, too, some 180 in the past couple of weeks. Urban foresters plan to finish cataloguing the remaining 26 percent of trees along city streets, and they also will document the ones in municipal parks.
City forester Chris Boza said his division is crunching data and collecting input for a document that will map out the plan for the urban forest for the next 30 years. Once the plan is adopted, he will have a guide for how to put resources toward planting, maintaining, pruning and generally caring for the urban forest so it’s healthy in years to come.
“All of the trees around town have value, and what we are doing is identifying that value,” Boza said.