Report dissects decay in street maples

PHOTOGRAPHER: Sara Foss

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Every year trees fall.

In the best-case scenario, no one is hurt and no property is damaged.

But that isn’t always the case.

Christopher Luley, a pathologist with the Naples-based Urban Forestry LLC, is trying to develop a better system for determining when a tree is so decayed it needs to be cut down. In a recent report for the state Department of Environmental Conservation, he studied wood decay in street maple trees in four upstate cities: Albany, Buffalo, Rochester and Syracuse.

The goal, Luley said, is to develop better methods for determining the frequency and severity of decay in street maple trees, and create a protocol that towns and cities can use to determine whether trees are so decayed they need to be removed. Smaller communities cannot afford to employ a full-time arborist, and a protocol would make it easier for them to locate and remove hazardous trees.

Mary Kramarchyk, community forestry coordinator for the DEC’s Urban Forestry Section, said the agency’s foresters train municipalities to identify problem trees. Luley’s research, she said, will help make the process more accurate and precise.

Luley studied a random selection of street maple trees — Norway, silver and sugar — because there are so many in upstate New York. Too many, in fact; maple trees comprise more than 54 percent of the tree population. Luley said a greater diversity of tree species is healthier. The Norway maple alone accounts for more than 36 percent of the total tree population. “Many of these trees,” the report states, “are mature to over-mature as they have served as replacements for trees killed by Dutch elm disease.”

Overall, Luley evaluated 1,849 trees.

On average, the trees were in fair or worse condition, according to the report, with large-diameter trees in the worst condition of all.

The incidence of decay in these trees, Luley said, was “high — over 50 percent.” But the frequency of serious decay — a level of decay that would necessitate a tree coming down — was much lower, around 2.5 percent.

“A lot of trees have decay, but you don’t want to remove them,” he said. “You don’t want knee-jerk removal of trees.”

In his report, Luley wrote that larger-diameter maples — maples greater than 25 inches in diameter — of all species require increased levels of inspection, removal and replacement because of their poor condition and increased amounts of decay.

Luley also looked at a random selection of other species of tree, and found that they were in better condition and had lower severity of decay, “suggesting the diversity is a buffer against decay.”

He found that more than half the Norway maples were in poor condition.

Trees in Albany, Buffalo and Syracuse were rated in slightly lower than fair condition, while trees in Rochester were rated in slightly better than fair condition.

Rochester, Luley wrote, has the longest standing tree maintenance and inspection programs in the state and the northeast. Of Albany, he wrote, “Forestry operations in Albany have been understaffed and funded in recent history.”

In his research, Luley used three methods, of increasing sophistication, to check for decay. First, he did a visual test. Then he did a visual and sound test, where he looked at the tree and hit it with a 6-ounce Sears Craftsman hammer with a hard plastic head to see if it was hollow.

He also tested the trees with a device, called the Resistograph F400, that uses a drill bit to record mechanical resistance to the drill bit on chart paper. The Resistograph provides a measurement of the thickness of the outer shell of wood in a tree.

“Most people look visually, or they look and sound,” Luley said. “Visually, you can’t tell a whole lot, but if you sound and use a mallet, that’s pretty good.”

“You can look at a tree until you’re blue in the face, but that won’t tell you what’s inside of it,” Luley said.

In his report, Luley wrote that the “decay incidence was surprisingly high.”

Resistograph testing revealed a decay incidence of over 57 percent, compared to decay incidence of 12 percent in New Jersey and 16 percent in New York City’s Central Park.

Indicators of decay included external cavities, wounds such as missing bark and cankers and bulges and cracks.

Although foresters have been using sounding for a while, they have not been using it to assess decay, Kramarchyk said.

Now, “they can pinpoint where the bulk of the decay is located and if the decay is substantial enough the tree should come down,” she said. “If they’re not sure through sounding, they can use the Resistograph to clarify what they think they heard.”

Luley plans to keep working. Next, he will determine the volume of wood decayed in urban trees and the impact of decay on carbon storage.

“This report is only the tip of the iceberg,” he said.