PRE- AND POST-HISPANIC LANDSCAPE CHANGE IN MICHOACÀN, MEXICO: A MULTIDISCIPLINARY INVESTIGATION

Lake basins in the central Mexican highlands have experienced environmental degradation due to anthropogenic disturbance. Debate focuses on the timing of the onset of degradation: was it initiated by European settlers after the Spanish Conquest in 1521 or was the landscape already substantially modified by Pre-Hispanic populations? This study focuses on three lake basins in the highlands of Michoacan: Zacapu, Patzcuaro and Zirahuen, which all lie within the territory of the Post-Classic Tarascan, or Purepecha Empire (13th century AD – 1521). We have integrated evidence from lake sediments with archaeological and historical data to investigate the relative magnitude of environmental impact of Pre and Post-Hispanic human activity against a background of varying climatic conditions.

Multiple cores spanning the last c. 3,500 years were obtained from each basin and analysed for diatoms, pollen magnetic susceptibility, stable isotopes C:N and available P. A chronological framework is provided by ¹⁴C dating, ²¹⁰Pb dating and tephrochronology where possible. Colonial documents in the Archivo General de la Nacion and in regional archives provide information on changes in population, land use and climate. Documents relating to land grants and land disputes were the most useful. Combined with existing archaeological data, recent census data and instrumental records, it has been possible to build up a more detailed picture of changing human activity through time.

All three basins show evidence of human occupation over the last 3,500 years. Patzcuaro appears to be the most severely affected. It had been thought that the Zirahuen Basin had suffered only minimal impacts, but our results indicate evidence of erosion and the occurrence of Zea mayspollen dating back 2,300 years. It is likely, therefore, that the Tarascans settled in a modified landscape. The arrival of Spanish settlers does not appear to have resulted in immediate change, probably related to the catastrophic decline in the indigenous population during the early Colonial period. The most significant environmental changes associated with Colonial activity occurred in the 17th and 18th centuries. Recent change in all three basins has been dramatic, indicating rapid eutrophication associated with the intensification of anthropogenic activity.