ACCELERATED SOIL-EROSION AROUND A MEXICAN HIGHLAND LAKE CAUSED BY PRE-HISPANIC AGRICULTURE

THE severely degraded landscape of the volcanic highlands of central Mexico has been the focus of considerable debate1-5. Although it is widely believed that the Spanish encountered an almost pristine landscape in AD 1521 (refs 1-3), some archival and palaeolimnological studies have suggested that extensive land clearance began before European contact, during the Preclassic to Postclassic periods (approximately 3,500-350 C-14 yr before present, BP)5-11. Here we analyse sediment cores from Lake Patzcuaro, Michoacan (Fig. 1), to derive a quantitative estimate of variations in soil erosion in central Mexico since 4,000 yr BP. We identify three periods of accelerated erosion and conclude that erosion rates during both the late Preclassic/early Classic periods (2,500-1,200 yr BP) and the later Postclassic period (850-350 yr BP) were at least as high as those after the Spanish conquest. One implication of these results is that soil erosion caused by the Spanish introduction of plough agriculture was apparently no more severe than that associated with traditional agricultural methods; it is therefore questionable whether a return to traditional methods would have significant environmental benefits.