Researchers use cores from oaks to study climate

June 2, 2014

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PLATTEVILLE, Wis. — Two students and a post-baccalaureate fellow from the University of Wisconsin-Platteville are studying tree rings in core samples they have taken from 200 old growth oak trees throughout Wisconsin's Driftless Region to gain insight about the area's past environmental conditions.

The researchers include Sara Allen, a research technician in the Tree-Ring, Earth, and Environmental Sciences Laboratory at UW-Platteville from Platteville; Jaime Teutschmann, a junior biology major at UW-Platteville from Shullsburg, Wis.; and Cassie Jorgenson, a senior geography and history major from South Wayne, Wis. All three are completing the research under the mentorship of Dr. Evan Larson, associate professor of geography at UW-Platteville.

The research is being conducted as part of the “Establishing the Long-Term Range of Variability in Drought Conditions for Southwest Wisconsin” research project. The two-year project, which began in June 2013, is funded by a $162,953 grant from the U.S. Geological Survey through the UW Water Resources Institute, which coordinates research programs that are involved in solving present and emerging water resource problems.

Allen and undergraduate research assistants spent the 2013-14 fall, winter and spring collecting tree-ring samples from about 200 living white oak and burr oak trees in 12 counties across the Driftless Area of Southwest Wisconsin. Allen said that many of the trees pre-date European settlement, making them excellent recorders of past environmental conditions.

The researchers are using dendrochronology, a scientific method of assigning exact calendar dates to the annual growth rings of trees and analyzing patterns of tree-ring width to provide information about climate variation going back 300 to 400 years. Using an increment borer that contains a bit with a hollow tube inside, a thin core of wood is extracted from each tree, on which the tree rings are visible. Once the oak tree cores have been brought to the TREES lab, Teutschmann and Jorgenson glue them onto pieces of wood, sand them, assign calendar dates to each growth ring through a process called crossdating, scan them into a computer using a high-resolution scanner and finally, use a special program to measure the width of every tree ring in the sample.

Once measured, the growth patterns of each tree are examined individually and eventually combined with the growth patterns of the other trees sampled for the study to create site-specific and regional chronologies of mean tree growth. At these scales, wide rings generally indicate wetter, cooler years resulting in good growth while narrow rings indicate warmer, drier years and represent stressful times. Therefore, the patterns in growth rings give a representation of how the trees' growing environment changes from year to year.

“This climate history can help us better understand current climate and the impact it has on our environment,” said Allen. “Southwest Wisconsin has had a variety of extreme weather events over the last few years, such as the flooding in 2008, severe drought in summer 2012 and heavy rainfalls that drenched much of the region in 2013. Because the area is agricultural, these extreme weather fluctuations have had a negative impact on farmers' crop production.”

Allen explained that data from tree-ring measurements helps explain the frequency of weather fluctuations and allows for people to better prepare for extreme events in the future so they can effectively manage natural ecosystems, agricultural ecosystems and water resources.

“This research helps us reconstruct drought patterns for the Driftless Region and can also help us date historical structures, such as barns and homes,” said Teutschmann. “Trees can tell us so much about the past and the present. It is interesting to see how far back some of the trees date.”

“Having the opportunity to participate in undergraduate research has been amazing,” said Jorgenson. “I never realized what could be learned from tree rings until I got connected with the TREES lab.”

To date, Allen, Teutschmann, and Jorgenson have presented the preliminary results of their research at three conferences, including the University of Wisconsin Posters in the Rotunda Symposium, held each spring at the Capitol in Madison, and the national meeting of the Association of American Geographers in Tampa, Florida, this past April. The research has also been featured in a short news piece on Wisconsin Public Radio and a newly released video produced by the Wisconsin Sea Grant Program and Water Resources Institute. An article about the project is forthcoming in the Wisconsin Natural Resources Magazine.

“It has been so much fun to see Sara, Jaime, and Cassie grow through this project,” said Larson. “They have developed into a highly productive team that is producing extremely interesting results for a project with local and regional implications. Whether it is speaking with their fellow students, giving their presentations, or talking with a film crew, all three show impressive confidence and comfort with the work they are doing. It is these types of experiences that capture the motivation behind the research we are conducting through the TREES Lab.”

The research is one of several on-going projects in UW-Platteville's TREES Lab focusing on understanding the past to inform actions in the future. The lab conducts federally- and locally-funded research across Wisconsin, the Great Lakes Region, the United States, Canada and Sweden.

UW-Platteville is committed to providing its students with high impact, hands-on, experiential learning opportunities such as those provided by undergraduate research to ensure that students are prepared to enter the workforce and pursue their career endeavors.

Anyone living in southwest Wisconsin who would like an old oak tree considered for this research study may contact Allen at (608) 342-6149. For more information on the research study, view the following videos: "Ancient Oaks Tell Climate Stories" and "Got Oaks?"

Written by: Laurie A. Hamer, College of Liberal Arts and Education, (608) 342-6191, hamerl@uwplatt.edu

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