Indiana State University Newsroom

Reading history - one ring at a time

September 2, 2011

Kristen de Graauw balanced on a ladder as she pressed the drill-powered borer above her into the dusty log that framed a Virginia barn's feed room for at least a century.

"I wanted something fresh and new and dendroarcheology sounded fun," said the Indiana State University graduate student during a break from boring samples from the wood. "This gives us the hands-on experience of applying dendrochronology in different ways."

By attending the International North American Dendroecological Fieldweek, which was held in Virginia this year, de Graauw expanded her skills in the study of tree rings.

On this early August day in the barn, the smell of sawdust replaced the barn's age-old mustiness of hay and dust. The occasional passing car competed with the hum of a generator and the whir of drills as de Graauw and eight other scientists bore dowel-sized cores of wood from the old logs. The barn's builders chose the rough hewn logs, wider than a spread hand, to stand the test of time, and they have. But the question remains for the current owners of how much time they have withstood. The scientists, all students at NADEF, climbed inside stalls, in hay lofts and under the barn in an effort to read its history.

"Dendrochronology, if you break the word down, dendro means tree and chronology is the study of time, so it's using the annual production of rings in a tree as a chronometer, as a time keeper," said Jim Speer, fieldweek director and Indiana State University professor of geography and geology.

The fieldweek, in its 21st year and run by ISU since 2003, gives the participants a nine-day intensive, introduction to the science and techniques of dendrochronology. This year, Indiana State received more than $330,000 dispersed through five years for the fieldweek from the National Science Foundation. The money goes to aid undergraduate and graduate students to attend the fieldweek, as well as equipment and stipends for graduate students to polish papers on the projects and submit them to peer-reviewed journals.


The week aids students and professionals with unlocking the history buried in trees' cores. As trees grow, they collect the stories of their lives in their rings. The fieldweek trains the scientists to read it. In the trees' stories, scientists can find the climate of an area or if the tree withstood fire and insect outbreaks. All of which helps scientists unravel the past for which humans has no data.


"The participants work with research projects from start to finish," Speer said. "They go out and sample for the first day, take all the samples that they need to analyze. The rest of the week, they're analyzing the samples, and at the end of the nine days, they present their research. They also write up a short paper about the work that they've done here. So, we're contributing to the scientific data bases and the students are learning about the research."

The barn's owners, Jack and Mary McDonald, wanted to know the cantilevered barn's true age and a team from NADEF hoped to help her find out. Tax records, Mary McDonald said, shows a barn on the property in 1814. Initials carved in the wood along with the date of 1830 could be early graffiti or a tantalizing clue to the barn's age. The dendroarcheology group converged on the barn, a cabin and smokehouse on the McDonalds' property to take cores of the white oak that may have been cut in the early 1800s and by rough estimates could have been 200 years old when it was cut down to build the barn.

By counting the rings from the core samples taken from the rough hewn logs, the one-time tree's age can be determined by comparing the sample's rings to previously dated samples contained in reference chronologies. When the samples' rings line up with corresponding rings, team members can determine how long ago the builders felled the oaks.

"Our goal is to find out when all three of those historic structures were built by dating the tree ring samples inside the logs inside the historic structures," said Henri Grissino-Mayer, professor of geography at the University of Tennessee-Knoxville and director of the Laboratory of Tree Ring Science who led the dendroarcheology group during fieldweek.

Through all of this the students learned about dendroarcheology, which allows the telling of age of barns, cabins, musical instruments and more. Such learning and contributing back to communities is a central part of NADEF's annual field week. This year 52 individuals from across the world attended the fieldweek to learn about how to use tree rings to date building, discover the area's ecology or climate as well as dating the age fish and mussels through techniques similar to dendrochronology.

"I really like history and I find that when I read written history and books it becomes so artificial in one way," said Anna Maria Rutio, a doctoral student at the Swedish University of Agriculture in Bumio, Sweden. "But when I go to the forest with my CMT's (culturally modified trees), it feels like you live the history. You're in the same place where people like my ancestors lived several hundred years ago and you can tell something about how they lived from the trees. I find that very interesting."

De Graauw agreed.

"I like the fact that trees hold history for us," said the student who studies dendroecology at ISU. "I think that that's a really neat idea. They have something to tell us. It takes a little bit of extracting but it's there."


Indiana State graduate student Ross Alexander learned about wood anatomy during the fieldweek, and he hopes it will aid him in his thesis research.


"I was looking at mostly just wood anatomy from an identification perspective, which features we can look at: yes, this is a white oak; yes, this is a maple," he said. "For my own research project, I've been using wood anatomy to indentify woody debris in the forest. There are limited characteristics that can be identified in the field, so we take them back and look at thin sections under a microscope to really identify the species so I don't group things in wrong categories and such."

Sam Wood, a post-doctoral student at the University of Tasmania in Australia, used dendrochronology while working on his graduate research, but he wanted to know more and signed up to learn about fire scars during the fieldweek.

"I thought this was a good way to work out what else you can do with tree rings and work out the next part of the story," he said. "I'm interested in dendroecology work, looking at fire scars and looking at frequency of fires, and trees can give good clues to that. There's not a lot of people in Australia working on that, so the obvious choice is to come over here and there is a long history of looking at fire ecology through tree rings and it was a really good opportunity. I think Margo (Kaye, a professor at Pennsylvania State University), Henry (Grissino-Mayer) and Jim (Speer) have looked at this sort of stuff in the past and it's better to learn from the experts."

This year's fieldweek also included a group studying sclerochronology, which applies dendrochronology techniques to the ear bones of fish and bivalve shells.

"It turns out there is quite a wide variety of species and variety of organisms that live a really long time," said Bryan Black, associate professor of forest ecosystems and society at Oregon State University. We can measure the growth increment width just like dendrochronologists measure the widths in tree rings and those widths reflect the growth rate of these marine and fresh water organisms so that we can reconstruct or establish growth patterns that these organisms have experienced over time."


From that, Black said, scientists can then establish climate and environmental variables associated with that growth. "Those organisms that live a really long time, those that predate instrumental records, you can use to tell what the climate and environmental variability were" prior to human's record keeping, he said.


While the sclerochronologists worked with shells and bones from fish ears brought to the fieldweek, other participants went to the woods to gather their samples. All participants studied their samples in the lab, seeking answers in the science, before presenting their findings. For the McDonalds, that's when they would learn the dates of the structures on their farm.

"Tree rings have a little bit of forensics in it," Grissino-Mayer said about the dendroarcheology project. "Tree rings add that historical accuracy that is not possible by the other means. We're able to date the logs in this historic structure to the exact years when the trees were cut down, not plus or minus five years, to the exact year and even the season when the trees were cut down."

The group found that the logs used to build the barn were cut in 1830 and 1831 while pioneers felled the logs used in the cabin from 1838 to 1840. The logs used in the smokehouse dated to 1838-1839.

"It's good to know," Mary McDonald said after the group's presentation on her farm, which is in the National Register of Historic Places, and thanked the group for its work.

"It's reading history and often rewriting history," Grissino-Mayer said, adding that family tales get changed over time with repeated telling. "What I found with my historic structures that we've dated is one to two generations younger than what was originally thought. We like old things. We want things to be old. It's the same thing for historic structures. Sometimes we're not helping history, we're helping reinterpret history and often we have to rewrite history."

While, the McDonalds received an answer to their structures' ages, the group members learned through following the scientific process.

De Graauw said she learned how to use an automatic drill with a borer bit.

"I've really never known anything about coring barns or cabins or anything of that nature," she said. "So, that's been a learning experience too. I'm really glad I chose a totally different group because I think I'm learning a lot of things I wouldn't have had the opportunity to learn otherwise."

Photo: de Graauw, ISU graduate student, bores a core out of a log during the International North American Dendroecological Fieldweek. ISU Photo/Jennifer Sicking Maria Rutio, a doctoral student at the Swedish University of Agriculture, holds a core removed from a log in the barn. ISU Photo/Andrea Kelley Speer, ISU professor, and Ross Alexander, ISU graduate student, hike through woods looking for trees with fire scars to sample during the fieldweek. ISU Photo/Jennifer Sicking Butler from the University of North Wales discusses the shell of an arctica islandica, also known as a ocean quahog, and how to date their shells. ISU Photo/Andrea Kelley

Contact: Jim Speer, professor of geography and geology, 812 237-3011,

Writer: Jennifer Sicking, associate director of media relations, at 812-237-7972 or



Story Highlights

The International North American Dendroecological Fieldweek, in its 21st year and run by ISU since 2003, gives the participants a nine-day intensive, introduction to the science and techniques of dendrochronology.

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