The New York Times has a story about Cahokia, which was a Native American city in pre-Columbian times.  Cahokia was located near Collinsville, IL across the Mississippi River from what is now St. Louis, MO.  It rose around 1050 CE and reached its zenith around 1100 CE.  At its apex with a population of 20,000, it was larger than both contemporaneous London and Paris.  Dr. Caitlin Rankin, an archaeologist at the University of Illinois at Urbana-Champaign, did some recent excavations to uncover why it had disappeared by 1350 CE.  Her research was published in the May/June issue of Geoarchaeology.  It turns out one of the proposed reasons for its demise – ecological degradation by the population – was not the cause of its abandonment.

In the 1990s, interpretations of archaeological research led to the proposal that the Cahokians at the height of their city’s population had cut down many trees in the area. This practice, they said, led to widespread deforestation, erosion and increasingly severe and unpredictable local flooding.

Dr. Rankin and her colleagues set out to discover more about how Cahokia’s environment changed over the course of its development, which they hoped would test whether that hypothesis was true. Excavating in Cahokia’s North Plaza — a neighborhood in the city’s central precinct — they dug at the edge of two separate mounds and along the local creek, using preserved soil layers to reconstruct the landscape of a thousand years ago. This area had the lowest elevation, and they presumed it would have endured the worst of any flooding that had occurred.

Those soil layers showed that while flooding had occurred early in the city’s development, after the construction of the mounds, the surrounding floodplain was largely spared from major flooding until the industrial era.

“We do see some negative consequences of land clearance early on,” Dr. Rankin said, “but people deal with it somehow and keep investing their time and energy into the space.”