by Sydney Widell – When Brian Schlaff and I park our car on Birch Tree Lane, a quiet road that meanders past rows of tidy, mid-century homes and well manicured trees, I have a surreal feeling that we could be anywhere in America.
In fact, we are in Fond du Lac, Wisconsin — where researchers from the U.S. Geological Survey and the Environmental Protection Agency, as well as UW-Madison, have converged on this block to monitor a neighborhood tree removal project slated for next summer. The removal has given them a unique opportunity to study the role different species of trees play in managing stormwater.
Brian is an undergraduate working for PhD candidate Dom Ciruzzi at Trout Lake Station, 200 miles to the north. Dom is interested in the relationship between trees and groundwater, and how that relationship changes during times of drought.
Most of the research they are doing this summer has taken place in the Northern Highland State Forest, which encompasses Trout Lake. The Fond du Lac project takes advantage of an idea Dom has been developing over the last three years of his research.
The concept applies an engineer’s solution to an arborist’s dillema: Finding the most efficient way to monitor a tree for water stress – whether it’s growing on a suburban park strip or in a remote corner of a state forest.
Like any tall building or bridge, trees sway in regular patterns. Dom is finding that trees experiencing drought sway differently than trees with dependable water access.
Tree sway is a function of the mass and the stiffness of the tree. Both of those things are related to the amount of water moving through a tree at any time — the more water stress a tree experiences, the less massive and stiff it is. Kind of like a flower in a vase, Dom explains.
“What we think is that when these trees are water stressed, they actually exhibit different swaying motions,” Dom said. “If we continuously track trees’ swaying motions, and also get some understanding of their water status from tracking the water in the soil, the leaves and the sap, we can start making a story that says trees sway like this under these conditions.”
Dom uses a tree’s acceleration to measure its sway with the same technology your iPhone uses to measure your step. The device is called an accelerometer, and it’s what Brian is installing at the six Fond du Lac field sites today.
“When you take a step, the accelerometer understands that you’re taking a step and counts it. When you’re in a roller coaster, the accelerometer can quantify the acceleration you’re feeling, that sense that your heart is dropping,” Dom explained. “We’re bridging that understanding of what acceleration can be used for to not necessarily track the steps of trees, but to track their movement.”
To put the wallet-sized accelerometers onto the trees, Brian has to physically climb them.
Luckily for Brian, the trees in these park strips are not that tall, and he never has to climb more than 10 feet in the air. At Trout Lake, Dom would sometimes have to scale 30 feet up a trunk to mount an accelerometer even though, in his words, he’s “totally horrified” of heights.
Now, Dom’s team uses high powered slingshots to rig pulleys in the taller trees, and they deploy the accelerometers that way.
“This project has really tested my ability to come up with a truly unique method,” Dom said. “If there was a space for Macgyver in science, I feel like this project would fit in that space. The methods we’re using are just so bizarre.”
But Dom also said he thinks that the innovative, cross-disciplinary ways of thinking about drought that make this project bizarre are what make it important as well.
“Traditionally, hydrologists and ecologists think about drought a little differently from each other,” Dom said. “What a grad student before me started… is bridging the hydrological and ecological responses of ecosystems to drought together.”
Where Dom said hydrologists tend to focus on the physical implications of drought — like rainfail or streamflow, ecologists may think about it in more biological terms.
And drought is a problem that is only expected to get worse across the state in the next century. Climate models show that Wisconsin should expect more intense and frequent droughts that last for longer periods of time in the coming decades.
For the state’s forests, Dom said that trend may mean declining production, groundwater depletion and reduced biodiversity.
“A goal of studying drought now is to understand how we can better face forest and ecosystem challenges in the 21st century,” Dom says. “If we are to expect drought to increase in frequency, duration and intensity, then we need to prepare.”
Back in Fond du Lac, Brian and I wind our way out of the neighborhood, leaving the trees outfitted in their new scientific garb, swaying imperceptibly as we begin to better understand their patterns and what those movements mean.