A professor’s quest to understand history through the study of trees

Thomas Jefferson spent most of his life designing and building — and then redesigning and rebuilding — his main residence, Monticello, in Charlottesville, Va. The house, along with its grounds, survives as one of the most iconic homes in the United States, but later in life, Jefferson adopted a private retreat called Poplar Forest about 80 miles south of Monticello. A few times a year, he traveled there to find relief from the bustling activity of Monticello and, once he completed his presidency, he built an octagonal brick home on the property where he could read, study and observe the world from a distance.

A meticulous record-keeper, Jefferson documented meteorological details day in and day out, noting in his diaries the temperature, precipitation and the direction of the wind. One day, he recorded the unusual appearance of frost during the warm-weather growing season. More than 200 years later, Dr. Dan Druckenbrod, an associate professor of Rider University’s Geological, Environmental & Marine Sciences Department, led a pair of students on two separate research trips to Poplar Forest to unravel the climate history of Jefferson’s landscape. That work would ultimately lead Druckenbrod and his students back to the observation recorded in Jefferson’s diary.

The team visited Poplar Forest once in January and again in May of 2015. Their work consisted of identifying most trees over four centimeters in diameter and drilling into their trunks to retrieve core samples — essentially long, skinny cylinders of wood.

“This allowed us to look at tree rings and see how old the trees were,” says Jessica Munyan ’16, an environmental science major on the trip. The concept of counting tree rings — known scientifically as dendrochronology — is familiar to most children. But because the width between rings measures a tree’s growth rate over time, scientists like Druckenbrod and his students can also use them make inferences about past events.

By looking deeper into the meaning of the rings, they can deduce factors like how much light trees received during certain moments in time or if they ever suffered drought or freeze damage. The trees surrounding the homes of the Founding Fathers contain information that can even reveal how land use like slave-based agriculture impacted forests in ways that are still felt today in the long-term changes of tree species through forest succession.

“The tree rings can tell us about historical events,” Munyan says, “and what we were trying to find in Poplar Forest were the past events that had occurred there.”

Such work is emblematic of Druckenbrod’s decade-plus investigation into the history of the forests of the Eastern United States. He began working on major sites related to Colonial history, such as Monticello, Montpelier, the home of James Madison, and Mount Vernon, the home of George Washington, while a student at the University of Virginia, where he earned a doctorate in environmental science in 2003. 

From that foundation, Druckenbrod has been steadily amassing a master chronology of the history of trees on the east coast. He also works closely with forest ecologists at Harvard University in Massachusetts and can often be found with his students in the forested environs surrounding Rider’s Lawrenceville campus.

“I’ve always had an interest in long-term environmental change — from regional to global change,” Druckenbrod says. “Making connections with early American history is also exciting.”

After the multi-day rounds of fieldwork at Poplar Forest and subsequent lab work back at Rider, Druckenbrod and his students discerned that the trees had experienced two major frost events during Jefferson’s lifetime. Narrowing down the approximate time of the frost, the team went back to Jefferson’s diary and found that their discovery matched Jefferson’s observation, confirming the unusual pattern of weather. 

“Most people traditionally focus on the presidential houses, but the houses are really part of a larger landscape,” Druckenbrod says. “The long legacy of land use gives us a better appreciation of the historical context.”

Coring a tree to obtain a sample is not as tidy as it sounds. “Samples are messy,” Munyan says, “and sometimes they come out in multiple pieces.” Brought back to the Rider’s tree-ring lab from the field, the samples must be dried, power-sanded and labeled. They are then examined under the microscope and cross-dated using a statistical analysis program that matches the pattern of ring widths in each core to the expected regional pattern resulting from the underlying variation in annual climate.

The hands-on work, in addition to the environmental angle, attracts students like Munyan, who will enter a master’s program in environmental science at UVA in the fall of 2016, following in the footsteps of “Dr. D,” as she, like most of his students, calls Druckenbrod. “I like figuring things out, explaining why things happen and then telling people about it,” she says.

Munyan, who is from West Deptford, N.J., and Druckenbrod have known each other since her freshman year, and she worked in his lab all four years at Rider. “He definitely provided me with a lot of guidance,” says Munyan, who hopes to earn her doctorate and become a professor. “When I told him I wanted to go to grad school, he helped me in every way, from writing a recommendation to helping me contact people. I don’t think I could have done it without him.”

Being able to help students in this way is “one of the reasons we get into this profession,” Druckenbrod says. “You want to conduct research but you also want to help students succeed. Mentoring students, particularly in the sciences, takes more than one semester. Long-term relationships are really beneficial to that end.”

In August, Druckenbrod will lead another research trip, this time to West Virginia. With support from a recent National Science Foundation grant, junior geosciences major Imani Guest will travel with Druckenbrod as part of his research team to study the impact of mercury pollution and acid rain on eastern deciduous forests. The project, which is part of a collaboration with Dr. Todd Scanlon of UVA, aims to shed light on how changing soil compositions affect the ability of trees to use water and nutrients efficiently.

Like Munyan, Guest has been working with Druckenbrod since her freshman year. A geosciences major, she is attracted to the kind of fieldwork she’ll be conducting in West Virginia because it allows her to step outside of the lab and participate in scientific work that touches multiple disciplines. This year, she received the Sylvia Husch Endowed Scholarship, which provides financial support for outstanding GEMS students, and became a part of the Ronald E. McNair Post-Baccalaureate Achievement Program, which aims increase the number of doctoral applicants and terminal degrees attained by first-generation students and underrepresented groups in graduate school.

Originally from Union, N.J., Guest has been attracted to science for most of her life. “With science, there’s always something new to discover,” she says. “People are discovering new things every day. I want to be one of those people and be a be part of that.”

Druckenbrod’s discoveries have implications that could affect thinking around important environmental issues. For example, the research in West Virgina may help illuminate the effect the 1990 Clean Air Act had on reducing acid rain. In general, the research into historical weather patterns and their effect on Eastern forests could help scientists make more accurate models that predict climate change.

“The kind of work Dr. Druckenbrod is conducting demonstrates new ways that weather can be recorded,” Munyan says. “It's important to know how the climate has changed and what kind of things can happen as a result — because they can happen again.”