Biology student analyzes tree rings to establish history of Shullsburg’s Gratiot House
PLATTEVILLE, Wis. – Jamie Jefferson, a University of Wisconsin-Platteville senior biology major with an emphasis in ecology as well as a double minor in geography and Spanish from Watertown, Wis., is analyzing tree rings in the wood beams of the Gratiot House near Shullsburg, Wis., to gain insight into the home’s history. She is mentored by Dr. Evan Larson, UW-Platteville assistant professor of geography and co-director of the Tree-Ring, Earth, and Environmental Sciences Laboratory.
The research project, funded by UW-Platteville Pioneer Academic Center for Community Engagement and a private donation, began when the Gratiot House’s current owners, Chris and Heather Price, spoke with Larson to see if the university’s geography department could help them find out more about the home’s history to determine if it is one of the oldest settlements in Southwest Wisconsin.
The couple is renovating the home, which was added to the National Register of Historic Places in 1980, into a bed and breakfast. The Gratiot House is a large, stone, Georgian style home built in the late 1820s by pioneer lead miner and farmer Colonel Henry Gratiot in what was then Gratiot’s Grove. He settled in this location in 1824 with his brother John and set up a mine and smelting operation. Construction on the home began in August of 1827.
“I am very excited to have the opportunity to study the interior of the Gratiot House in order to determine when the home was built,” Jefferson stated. “This project involves an interesting combination of research and the study of people and history. In my research, I have the chance to use computers and microscopes, but also have the chance to use power tools such as drills. It’s exciting.”
In her research, Jefferson is using dendroarchaeology, a scientific method of dating wood found in old buildings, furniture and artifacts, based on the analysis of patterns of tree rings, also known as growth rings. This form of dating is very accurate because the last complete ring that grows, closest to the bark, is the year the tree was cut. It is also very likely the year the wood was used in an archeological structure because at the time, trees were used within a few years of the cut date because they were easier to work with when slightly green. In some places in the world, it is possible to date wood back a few thousand years or even many thousands of years.
Jefferson has spent much of her time researching the Gratiot family in UW-Platteville’s Southwest Wisconsin Room, trying to discover when and why the family built the home.
“While doing research, I found a speech that Henry Gratiot’s son-in-law, Elihu Benjamin Washbourne, had given in which he noted that the Gratiot House had burned down in 1853,” Jefferson said. “This was an interesting clue into the home’s history. Using tree-ring analysis, we are looking for evidence that the house burned down so we can see if it is one of the oldest settlements in the area.”
Jefferson examines the timbers used to construct the windows and doors in the home. Then, using a large-diameter, hollow drill bit and a power drill, she drills into the wood and removes a core sample about half an inch long. The tree’s rings are visible on this core and, after sanding the core to a high polish, she examines it under a microscope to mark out the years that the tree lived. She then uses special equipment to create a high-resolution digital image that is imported into the computer.
Using WinDENDRO, an image analysis system designed specifically for tree-ring research, Jefferson is able to precisely and efficiently measure annual tree-ring widths from the scanned image on the computer. Using her computer mouse, she indicates where the rings in the image should be measured by tracing straight-line paths that extend perpendicular to the rings. Each ring represents one year’s growth of the tree. By counting the tree rings, Jefferson can get 40 to 70 years of chronology for most of her samples, which enables her to determine the age of the beam.
“Trees grow in two phases marked by light and dark sections of the wood,” Jefferson explained. “I put a marker on every year and a line at the separation point. That information is then turned into a text file that can be viewed on a graph, which is similar to the fingerprint of the tree. As additional cores are analyzed from other beams in the home, that data are entered into the system, creating a collection of fingerprints. At that point, I look on the International Tree-Ring Data Bank and compare my data to other people’s data, trying to match my tree’s fingerprint with other trees’ fingerprints from the local area.”
The data bank contains measurements and tree-ring chronologies from more than 1,500 sites around the world from more than 100 tree species.
Through the research process, Jefferson has identified that all of the beams she sampled from the Gratiot House were cut in 1849, which does not match the suspected date of construction or the purported date of the fire.
“The beams should date to the original construction date,” said Jefferson. “Because the trees that the beams were built from were cut in 1848 and 1849, we know they could not have been used in the original construction of the house. We know that something happened to the house and right now, we are speculating about what happened. Historical evidence suggests a fire, but we don’t see a coinciding of the dates given.”
“There could be three explanations for this,” Jefferson continued. “Either the beam was replaced, the original beam was lost in a fire, or the house is not as old as it is thought. I am working on dating other beams and rafters in the home that will help provide more clues as to the home’s age.”
“This research is so exciting because it helps create a more accurate picture of the past,” said Jefferson. “It’s also giving me hands-on experience that will help make me more marketable in my field.”
If you have a historical structure with at least some wood construction and are curious about its history, contact Larson at the TREES Lab at email@example.com or (608) 342-6139.
Written by: Laurie A. Hamer, communications specialist, College of Liberal Arts and Education, (608) 342-6191, firstname.lastname@example.org