UF, UT researchers join forces to bring tree-ring dating technology to heart of Southeast

June 2, 2010

GAINESVILLE, Fla. — In the history of the world, 20 or 30 years is but an eye blink. But for those in the historical accuracy business, that kind of difference is vast and can mean an inaccurate textbook or museum display.

University of Florida and University of Tennessee researchers recently joined forces to settle such a time question for historians working to renovate one of St. Augustine’s oldest historic properties, the Ximénez-Fatio house.

In the current issue of the journal Tree-Ring Research, Henri Grissino-Mayer, an associate professor in geography at UT, and Leda Kobziar, an assistant professor with UF’s School of Forest Resources and Conservation, describe their use of dendrochronology to help verify the home’s original age and to pinpoint when it was expanded to include a second-story wing.

They were able to verify the age of the original building to 1798 and that the second-story wing was built in the late 1850s — at least two decades later than historians had believed.

While dendrochronology, or tree-ring dating, has been used extensively in some parts of the U.S., it has been used far less in southeastern states such as Virginia, Tennessee and North Carolina, and only rarely in the southernmost states, such as Georgia and Florida. Because the region’s rainy, hot climate causes wood to decay more quickly, the technique had not been attempted as often as in other regions.

But the UF-UT study proves it can be done accurately in the southernmost parts of the U.S., said Kobziar, a member of UF’s Institute of Food and Agricultural Sciences, and researchers expect to be asked to use the technique more in the future.
Dendrochronology works like this: Trees from a particular geographic area tend to respond similarly to climate changes, such as rainy seasons or drought. Those changes cause differences in the width of growth rings inside the tree.

Researchers create a master chronology by visiting a living forest and collecting many growth-ring samples from living and long-dead trees. In this case, UT researchers had created a massive chronology based on longleaf pine stumps in the Lake Louise, Ga., area.

The pines were full of resin, which kept the stumps extremely well-preserved, and some samples from that area dated to the 1400s, said Grissino-Mayer.

Once researchers have a baseline chronology of growth rings, they can extract samples from the building or wooden artifact whose date is in question and cross-check using a computer program that compares the relationship between tree rings to find matches.

For the researchers in the Ximénez-Fatio study, however, it took a lot of elbow grease — and a little paint thinner — to finally unravel the mystery of the home’s age.

Unlike less-resinous tree species, the longleaf pine beams in the home were much tougher to extract samples from, Kobziar said. The researchers’ drills gummed up repeatedly because of the pine resin, until Grissino-Mayer found an engineering colleague who suggested dipping the hollow drill bits in paint thinner.

“I wish we had thought of it beforehand, because I can tell you I gained some bicep muscles doing all that work,” Kobziar said.

Grissino-Mayer, a national leader in modern-day dendrochronology, predicts a growing market for those wishing to ensure historical accuracy for buildings and artifacts — everything from ship timbers to violins.

For Julia Gatlin, executive director of the Ximénez-Fatio historic house and museum, solving the mystery of the home’s timeline, “totally changed the story as we knew it.”

By knowing the correct dates, she said Ximénez-Fatio officials can now tell visitors that it was the third colonial woman to run the home as a boarding house, Louisa Fatio, who undertook the renovation — not the first, Margaret Cook, as was thought. And they know the wing was built between 1856 and 1858, not between 1830 and 1842.

Gatlin has been speaking to history groups from St. Augustine to Mount Vernon, encouraging them to use dendrochonology to pin down questionable dates.

“The story we had was wrong and now we know our facts are right,” she said. “I am so excited about this.”