Cahokia's soils

Presenting person: Prof. William Woods, PhD, Department of Geography, Southern Illinois University
Th. 2002-05-02 (16:15), H6

One thousand years ago a city existed on the Mississippi River floodplain directly to the east of the present St. Louis. Called Cahokia after the historic aboriginal group who inhabited the site in the 18th century, this was the most extensive expression of urbanism to have been produced prehistorically in America to the north of Mexico. The structure of the city was planned with clearly defined administrative/ceremonial zones, elite compounds, discrete residential neighborhoods, and even suburbs. High organizational skills and great expenditures of labor are evidenced by an enormous central plaza and numerous immense earthworks. With a population peak of perhaps 15,000 individuals, Cahokia existed for approximately four centuries (ca. AD 900-1300) as the primary center of the Middle Mississippian culture. Although specialists were present within the society, most of its members were engaged in primary production activities with maize agriculture the central focus. Mississippian food procurement and production strategies at Cahokia and elsewhere were focalized around the place of habitation. Indeed, the city was favorably located from an environmental standpoint. Cahokia\'s five kilometer radius catchment contained a diversity of microhabitats including expanses of open water and marshes from which the essential, renewable fish protein could be procured. In the eastern half of its catchment was found the largest zone in the local region of soils characterized as optimal for prehistoric hoe cultivation; i.e., readily tilled, fertile nonacid soils whose fertility was periodically renewed by additions of alluvium, but whose flood regimes did not extend into the growing season. Here, on the floodplain and along its bordering alluvial fans, the large maize outfields were situated, while the multi-crop infields and house gardens were placed on-site within the habitation zone on soils which had often been culturally enriched by prior occupation. As successful as this strategy might have been for dispersed populations in such a plentiful environment, nucleation of large numbers of people at Cahokia provided a different adaptive context which ultimately led to ruinous consequences. Hypotheses for the decline and abandonment of this settlement and its hinterland have included disease, climatic change, and external warfare as primary causative agents. However, it is becoming clear that the seeds for the city\'s destruction were inherent and centered on anthropogenically produced environmental degradation. Demands on wood resources for fuel and construction were substantial and agricultural field clearance was in forested rather than prairie settings. The resultant upstream watershed deforestation produced greatly increased rates of erosion, runoff, and unseasonable downstream flooding during the summer growing season; and, perhaps, even the diversion of the major local river through, rather than around, the city and its associated fields. The economic and social consequences of the resultant declining production and localized crop failures would have been disastrous. Unfortunately, the relatively slow rates of detrimental change insured that adequate countermeasures were not implemented.

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