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Science and Technology

Exploradio: A tree falls in the woods
Scientists from around the world come to Davey Tree's research farm to gather data on the biomechanics of falling trees
This story is part of a special series.

Reporter / Host
Jeff St. Clair
Lothar Goecke, right, leads a team of German researchers measuring the amount of force needed to pull down a young pin oak. The data gathered at Davey Tree's research farm in Northeast Ohio is used to determine critical strain models for tree safety worldwide.
Courtesy of Jeff St.Clair
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In The Region:

Trees are an integral part of our Northeast Ohio landscape. But trees felled by storms cause hundreds of millions of dollars in damage each year.  Likewise, keeping trees healthy and upright can be challenging.  

In this week’s Exploradio, WKSU’s Jeff St.Clair takes us to an international gathering of scientists studying the biomechanics of how trees topple, tilt, and heal.

LISTEN: Exploradio: A tree falls in the woods

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The sound of one tree falling
A trio of German tree scientists cranks away on a mechanical winch. They’re tightening a cable anchored to a young pin oak, apparently trying to discover whether a tree falling in the woods makes a sound. The answer arrives like a gun shot, as the oak begins to snap under nearly three tons of pressure.

Researcher Steffen Rust says the crowd watching the demonstration at Davey Tree’s Portage County research farm was betting against the Germans. He says the locals laughed, saying, "'You will never break a pin oak.’”

Finally the young tree gives way, bent double in splintered submission. Scattered applause celebrates the effort.

It wasn’t to test the metaphysics of a tree falling in the woods that drew Rust and arborists from around the world to the 40-acre tract in Shalersville. They came for a week of field research and symposia on the biomechanics of falling, toppling  and tilting trees.

Rust says they are toppling trees, “to find thresholds of safety for trees to estimate the load when a tree will break in the wind." But he acknowledges it would take a very strong wind indeed to flatten pin oaks.

Root damage in urban landscapes
In another part of the Davey research farm, workers use air knives to strip away soil from the roots of a London plane tree.

Andreas Detter, a tree consultant from Bavaria, is excavating the roots, "looking for cracks, deformations, failures in the root zone – so we can correlate them with a specific degree of inclination.”

Detter and his team tilt the trees and then scour the roots to gather data to build their computer model. His goal is to predict the likelihood of root-damaged trees toppling in the urban landscape where roots are often severed when repairing pavement, or constructing a house. He says the field tests allow him, "to analyze whether that tree is still stable enough so we can give it time to recover from damages that have been done.”

The biomechanics of 'system hardening'
Washington state tree expert John Goodfellow uses a digital scale to weigh a leafy branch that dangles from the end of a crane. Goodfellow and engineers with the Electric Power Research Institute are measuring what happens when a falling branch hits a substitute power line.

“We’re looking at the strike force of tree failure as it might affect the power system and subsequently outages and all that kind of thing…”

Goodfellow was one of the experts brought in 10 years ago to review the causes of the 2003 blackout, when overloaded power lines dipping onto unpruned trees began a cascade of failures that spread from Ohio -- blackening half of New England and parts of Canada and Chicago.

He calls it a watershed event in the study of how trees affect infrastructure, and the regulatory environment that exists today.

His experiment ready, Goodfellow counts-down…“3,2,1...” as a tree branch crashes onto a steel pipe.  Both are outfitted with accelerometers.

Goodfellow determines the impact force by measuring the rate of deceleration. He says, “it’s not how fast it’s going - it’s how fast it stops," that causes damage. Goodfellow says these types of experiments provide data for utility engineers working on what he calls ‘system hardening.’

He says utilities want to make the overhead power system more durable with upgrades to cross arms and poles, but have very little field data on which to base the redesigns. 

Tending champion trees
The crane used in the testing is owned by Mark Hoenigman of Busy Bee tree service in Novelty, Ohio. Rather than testing the biomechanics of trees falling, he specializes in keeping his favorite ones healthy and upright.

“I have a number of customers who have some big red oaks that are just gorgeous.  One of them is state champion northern red oak.”

Hoenigman looks at how soil chemistry, root health and nutrient flow act as preventatives.

He says, “if you can increase the health of the soil and get it in a good balance, the tree will take care of itself.”

The tree laboratory
The Davey Tree research farm is littered with the remains of trees sacrificed in the name of biomechanics research.  But resource manager Ward Peterson says that’s part of the plan, “Davey planted these trees in the early 1960s.”

About a dozen species - maple, ash, oak, pine, London plane trees and others - grow in neat plots. Peterson says most are genetically identical clones that allow for reproducible experiments, “So it gives the researcher just the perfect laboratory.” 

At Davey’s research farm, when a tree falls in the woods and a scientist is there to hear it, the sound is data.

(Click image for larger view.)

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