Human Ecology of the Rio Verde Drainage Basin, Oaxaca, Mexico

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With National Science Foundation support Dr. Arthur Joyce and his collaborators will conduct one field season of archaeological and paleoecological research in the Rio Verde drainage in the state of Oaxaca, Mexico. The upper watershed of the river is situated in the Oaxaca highlands and derive from valleys which witnessed the rise of Monte Alban, one of the largest and most complex prehistoric Mesoamerican states. In its lower reaches the Rio Verde crosses the coastal plain and empties into the Pacific Ocean. In prior research in the lowland region, Dr. Joyce has noted that before 500 B.C. habitation is extremely scarce in contrast to many other areas along the Pacific coast of Mexico. After 500 B.C. population density and degree of land utilization increase dramatically. Dr. Joyce has suggested an environmental explanation for this phenomenon. He has noted an apparent period of heavy upland erosion just prior to the lowland expansion and believes it was caused by deforestation as burgeoning highland groups cleared extensive areas for agricultural production. Upstream sediments were deposited, he believes, downstream thereby increasing the fertility of the coastal plain. This in turn fostered an increase in lowland population density. Although archaeologists and paleoecologists have recognized for many years that prehistoric Mesoamerican agriculture had major negative environmental impacts, this Rio Verde case is particularly interesting because of its broad regional scale and the possibility that upland degradation had just the opposite effect at lower altitudes. The region provides an excellent case study into the complexity of human environment interaction. Dr. Joyce and his colleagues will conduct coordinated environmental and archaeological studies. In the Rio Verde headwaters the archaeological sequence is well known and the team will focus on the collection of geological and ecological data. They will examine river cuts to construct a geological sequence. They will also collect pollen to monitor vegetation change. With these data it should be possible to reconstruct erosional timing and sequence and determine the relative inputs of climatically and humanly induced factors. In the coastal area the research includes both archaeological and environmental components. Through a series of cores, soil formation will be studied and paloecoastline reconstructed. Archaeological surface survey combined with settlement excavation will provide insight into the changes in population size and social complexity over time. This research is important because it with provide an excellent case study in prehistoric human-environmental interaction. The timing of population growth and increase (and decrease) in complexity varies from region to region in Middle America and Dr. Joyce's research should provide insight into potential causes.