Above: At UAF’s Fairbanks Experiment Farm in March 2020, Jessie Young-Robertson ’20 stands by a stack of firewood that she and a small research team are monitoring for moisture content. UAF photos by JR Ancheta and Sam Bishop.
Metal bands tightly wrapped around birch trees gave Jessie Young-Robertson a problem one freezing cold April day several years ago when she hiked out to her research site north of Fairbanks.
The bands, used to measure trunk circumference, had slipped down the trees. Without the bands in place, she had no data.
Young-Robertson, a UAF research associate professor, suspected what had happened.
Today, her research has not only confirmed her suspicions but also inspired a project that could help clean up Alaska’s wood stove smoke by identifying the best times to cut firewood.
The trees in the research site off the Steese Highway, it turned out, shrank so dramatically that cold April day because they’d pumped much of the water out of their trunks and back into the ground.
The water loss was so great that the sensor bands, which had previously expanded as the tree swelled with spring meltwater, could not keep up with the shrinkage and simply slid down the trunks.
“I had gone out the week before and they were expanding. It would be a couple millimeters at a time,” Young-Robertson recalled. “Then we had a big drop in the temperature. It dropped way below zero. It was annoying, because the tree shrank by like half a centimeter, and the bands just dropped off the tree.”
Young-Robertson has since switched to better sensors. With those and other tools, she has made some interesting discoveries that could help firewood cutters who seek the most efficient way to produce dry wood.
That, in turn, could help improve Fairbanks’ notoriously foul air.
Addressing air troubles
With a sharp whack from an axe, Stefan Milkowski split a birch log at the six-acre plot southwest of Fairbanks that he leases from the state for commercial firewood cutting.
Milkowski had already split the log once late last winter to allow it to dry. The chunk of birch, with its outer bark layer impermeable to water, would otherwise have retained nearly all its moisture over the summer.
After the second splitting, in late August, Milkowski stabbed the log’s freshly exposed surface with a moisture meter. The result: 14.5 percent.
Photo caption: At top, a spring-loaded sensor detects expansions and contractions in a birch tree near Milkowski’s woodlot in August 2021. Below that, covered by the small white box labeled “3,” probes in the trunk record the wood’s moisture content.
Young-Robertson and her husband Matt Robertson, a field technician at UAF’s Forest Soils Laboratory, set up a variety of sensors in the woods just off Milkowski’s sale site.
The state-of-the-art tree sensors — not the old drop-prone metal bands — are bolted to birch trees near Milkowski’s firewood stacks. Each sensor has a spring-loaded metal rod that rests against the exterior bark and moves with expansion and contraction. That movement is recorded electronically.
Nearby, a white plastic box, just a few inches long, clings to the bark. Covered by the box, three metal rods fit tightly into holes drilled deep into the trunk. They record water content.