Maegen Rochner, a graduate student specializing in dendrochronology in the Department of Geography, is recreating a millennia of climate history one tree at a time. Armed with a chainsaw, a face shield, and hiking boots, she climbs the landslides and avalanches of the Beartooth Mountains in Montana and Wyoming searching for her next potential sample.
Tree-ring science, or dendrochronology, is a fundamental tool in understanding climatological and ecological histories of a location.
At the most basic level, tree rings show the amount of precipitation a region experiences in a year. When moisture is plentiful in the spring, a tree’s cells expand quickly, forming a light band. As the year progresses and the ground becomes more dry, the cells shrink, forming a thinner, darker band. One light and one dark band together constitute a year, with the variation in ring widths marking the different amount of moisture absorbed year to year.
Tree rings are also very dependent on temperature. The earlywood (light band) reflects the early growing season (spring and summer), and the latewood (dark band) reflects the later growing season (late summer and early fall) into dormancy (late fall, winter).
Wildfires, insect outbreaks, floods, droughts, and avalanches can alter the pattern, creating a unique “fingerprint” of that period that is present within all the trees of that location. Matching up the overlapping patterns from a sample with a known age to an older log of unknown age allows us to date that older sample. Continuing the process with older and older samples allows us to go back tens of thousands of years while giving us a more complete climatic picture of the area.
Decoding ring patterns and recreating the history of an area is what drew Rochner to dendrochronology in the first place.
“The science has such a broad applicability to many of the biggest problems we face today, such as climate change and natural hazards,” she said.
Rochner got involved in tree-ring science during her master’s program at UT.
“With my bachelor’s degree in geology, I was looking for a way to combine both geology and tree-ring science. That’s when I discovered dendrogeomorphology,” a method of using tree-ring data to study changes in the Earth’s surface.
Rochner’s master’s thesis used tree rings to reconstruct the history of a debris slide on nearby Mount Le Conte in the Great Smoky Mountains National Park. While her master’s thesis field work kept her in the Smokies, her dissertation required her to travel to a mountain range a little farther out than East Tennessee.
Rochner samples dead logs and stumps using a chainsaw and takes core samples from living trees using an increment borer for her dissertation research project, “Tree-Ring Evidence of Climate and Disturbance History in the Beartooth Mountains of Wyoming and Montana, U.S.A.” Back in the lab, she measures tree ring widths from these samples to a 0.001 millimeter precision, using patterns in the widths to notate how the overall climate of the location differentiated from year to year. She also notes disturbances that would have reduced growth, such as fires or avalanches. The patterns found in one sample are matched up to another from the same location, and a more complete history of the area starts to take shape.
Ultimately, Rochner will develop two millennial-length tree-ring chronologies for the site. With each sample as a guide, she can determine how past climate affected the landscape, reconstruct the wildfire patterns dating back to the late Holocene period, and develop an avalanche history for the Rock Creek Valley of Montana.
“I hope to not only improve knowledge on the impacts of climate change on an important threatened ecosystem, but also on how patterns of disturbance have changed—and may change in the future—in a dynamic climate.”
Rochner has had some unique experiences due to her research. She’s ridden in a sea plane towards Isle Royale National Park on Lake Superior, climbed up steep landslides in Wyoming and Montana, and used a chainsaw as an academic tool.
“I want to teach, to be a professor, continue tree-ring research, and hopefully start a new tree-ring lab,” she said.
Rochner received her bachelor’s degrees in geology and English from Indiana University Southeast and conducts her research at the Department of Geography’s Laboratory of Tree-Ring Science in the Burchfiel Geography Building.
Raphael Rosalin (865-974-2152, firstname.lastname@example.org)