A RECORD OF RECURRENT PREHISTORIC AND HISTORIC LAND USE FROM THE CAHOKIA REGION, ILLINOIS USA

In 1050 CE, Cahokia emerged as an agricultural and political center in the central Mississippi River valley with a population of roughly 10,000 individuals and thousands more in neighboring settlements. By 1350 CE, however, the entire Cahokia region was almost completely abandoned. Resource shortages resulting from land-use change and/or hydroclimatic variability have previously been invoked to explain Cahokia’s abandonment, but no appropriate records of environmental change previously existed from the Cahokia region to test these hypotheses. Here, we present a multi-proxy paleoenvironmental record (pollen, macroscopic charcoal, loss-on-ignition, δ¹³C_org) from Horseshoe Lake (Madison Co., Illinois), an oxbow lake adjacent to Cahokia.

The Horseshoe Lake record spans roughly the last 2,000 years, covering four distinct episodes of human occupation. During the Middle and Late Woodland periods (100-800 CE), the region was largely forested and occupied by seasonally-mobile people. Population growth and agricultural intensification accompany the emergence of Cahokia during the Mississippian period (800-1350 CE), during which widespread deforestation, expansion of agricultural fields, and increased biomass burning occurs. Afforestation follows abandonment of the region at the end of the Mississippian period, until settlement by the French (1700-1800 CE) who grew cereals in the floodplain. American settlement after 1800 CE is marked by its characteristic Ambrosia rise, widespread deforestation, and increased burning.

While this record provides no evidence to support the hypothesis that pronounced drought contributed to Cahokia’s abandonment, we find evidence of a large flood during the Mississippian period. Widespread deforestation and land-use change are clearly associated with Cahokia’s emergence, shaping resource availability and the decisions of Cahokia’s inhabitants.

Our paleoenvironmental record demonstrates that the Cahokia region has been heavily impacted by human activities for the last two millennia, with each episode of occupation characterized by its own biological and geochemical signature. The length of nearly continuous human impact we observe in this record, together with the diversity of human-environment systems represented, make it unique in eastern North America.