Her study of Red River Valley flooding, as told by old oak trees, may show what happened centuries ago.
Erika Wertz might measure her college career in tree rings.
Wertz, a University of Minnesota senior, has been studying what the rings in bur oak trees in the Red River Valley can reveal about floods in the distant past, which someday may also indicate what the future might hold for the flood-prone Red and its broad, populated, level valley.
She will graduate in May with a double major in geography and environmental science policy and management (and double minors in forestry and Spanish). But she's already earned a rare academic honor, having been invited to speak about her research at the recent annual meeting of the Association of American Geographers in New York City. She was the only student to speak at the conference, said Scott St. George, an assistant professor of geography at the U and Wertz's faculty adviser.
Wertz's research is similar to other studies in "paleoclimatology," in which researchers look for clues about past weather and climate events by studying ice cores as well as layers of pollen, volcanic ash and the like laid down long before the advent of modern record-keeping. Along the U.S. portion of the Red, records only go back to 1882 at Grand Forks.
"It's hard to say how high to build a flood wall with only 100 years of flood history," she said.
As a freshman from Milwaukee, Wertz took a course called "Biogeography of the Global Garden," which led to summer work in Montana taking core samples from trees in the mountains, as part of a study of an outbreak of mountain pine beetles. Last summer, she sampled bur oaks on two trips from the headwaters of the Red at Breckenridge north to the Canadian border. One trip was with St. George, a Winnipeg native who has studied the history of flooding in Canada along the Red, and the other with her stepfather, combining the research with camping and family time.
Using a hand-powered, hollow drill called an "increment borer," they extracted 16-inch-long samples about one-fifth of an inch in diameter from 20 trees at 10 sites. That's 200 samples, some of which, because of hangups in the wood, required up to an hour of heavy twisting of the drill while kneeling on sometimes still-flooded ground.
The work itself -- often in parkland where passersby referred to them as "woodpeckers" -- was rewarding without being quite as physically challenging as in the Rockies, Wertz said.
"It was flat," she noted.
The core samples have shown some distinct reactions to floods. Rings in non-flood years have water-transport vessels clustered on the edge along the inner side of the tree; in flood years, the vessels are smaller but are distributed from edge to edge. Wertz isn't sure why that is, but the patterns can help researchers learn more abut the timing and duration of floods, and where they were most severe, Wertz said. For now, the variations have corroborated the known flood record, supporting the idea that tree rings might provide an accurate flood record going back centuries.
After graduating, Wertz will take a job studying forest health with the Colorado State Forest Service.
"She's such an important member of our research lab," St. George said. "You just put a goal in front of her and she gets there. We're really going to miss her."
Bill McAuliffe • 612-673-7646
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