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Soil Savers Volume 56 Number 4, July/August 2003
by Colleen P. Popson

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Many terraced landscapes in Mexico may have eroded as a result of declining populations. (Courtesy Christopher Fisher)

Archaeologists have long associated environmental degradation with overpopulation, but new research in central Mexico demonstrates that, to the contrary, severe erosion can occur when populations disappear.

Christopher Fisher of Kent State University and Helen Pollard of Michigan State University led a team that investigated the ecological history of the Lake Patzcuaro basin, the heart of the Postclassic period (A.D. 900-1520) Tarascan Empire, rival of the Aztecs to the east. Tying evidence for soil erosion to population estimates, the researchers found the period of greatest landscape stability was between A.D. 775 and 1520, a time of high population, packed urban centers, and widespread agricultural intensification. "When you have a large population," explains Fisher, "people invest their labor in the landscape--in this case in the form of terraces--which tends to stabilize it." When the Spanish arrived around 1520 with diseases that decimated the local populations, there were not enough people to maintain the terraces. The result was large-scale erosion.

The research could challenge prevailing theories in other parts of Mesoamerica, like the Maya area, where scholars have long thought environmental degradation caused by population stress was a culprit in the collapse of cities around A.D. 800. Better dating might reveal that erosion was a result of site abandonment following collapse.

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© 2003 by the Archaeological Institute of America
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