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).
Rochner uses a chainsaw to collect a cross section from a remnant log on an avalanche chute outside Red Lodge, Montana.
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.