Use of the tree ring data vs. precipitation to discuss how trees respond to drought
I utilized part of the activity What do trees know about the rain in a lecture on drought effects on plant communities in my Earth System Science course, an upper division course for environmental science and biological sciences majors. This lecture predominantly focused on the current widespread dieback of trees in the Sierra Nevada and how scientists study drought effects on both a landscape level and an individual plant level. The lecture can be given in ~50 minutes, depending on times for discussion.
I introduced tree ring chronologies as a method to investigate how trees have responded to past widespread drought events. I then showed students the data table displaying the year, ring width and actual or extrapolated precipitation amount. We had a discussion on how our instrument record does not extend as far back as tree ring chronologies can go. I then asked the students how the researchers were able to estimate the precipitation that occurred in years when we have no record. Students discussed amongst themselves for a few minutes and we reconvened to discuss their ideas. I then showed a scatter plot of the data with a trend line and associated equation.
Some students in this course have taken an upper level statistics course, while many have not. Given this, students had questions about why some of the data points were above and some below, so I talked briefly about pros of best fit/trend lines and their limitations.
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