Under the direction of Drs. Richard Lesure and Charles Frederick, Aleksander Borejsza will collect data for his doctoral dissertation in the state of Tlaxcala, in the highlands of Central Mexico. He will conduct archaeological excavations of prehispanic agricultural terraces, and examine alluvial sedimentary sequences influenced by past land use. The data will be used to evaluate changing relationships between land use, land tenure and social structure, from the time of the first sedentary communities (ca. 850BC) to the early Colonial period (ca. AD1650).
Most slopes in Tlaxcala are or have been terraced for cultivation. Cultivated and abandoned fields are interspersed with vast areas where the soil has been stripped away by erosion. Intermittent streams flow in deeply entrenched gullies, making irrigation impossible. This degraded landscape is a human creation, but its origin is unclear. In other parts of Mexico land degradation has been blamed on the population collapse that followed Spanish conquest, and the introduction of the plough and grazing animals. In Tlaxcala this picture is complicated by the effects of two millennia of intensive aboriginal agriculture. Changes in prehistoric settlement patterns suggest that different agro-ecosystems had repeatedly been created, abandoned and reclaimed in that time span.
Anthropologists have observed that the investments required by intensive agriculture bind farmers to the land. The increased costs of leaving a community where land has been improved create opportunities for social exploitation by emerging elites. At the same time checks are imposed on the severity of exploitation, by creating agro-ecosystems that require intensive management by motivated and skilled smallholders, whose direct supervision or replacement is too costly for the elite. Conditions are set for the appearance of individual and hereditary claims to land. The terracing of slopes exemplifies this process, as the means of both intensifying agriculture and demarcating property. Episodes of land degradation can have equally far-reaching social consequences, by decreasing the value and amount of available farmland.
Whether such relationships obtained in the past, however, cannot be known until firmly dated regional sequences of agricultural change are established. Borejsza will make a step in that direction by dating the construction and abandonment of terrace systems and relating them to the phenomena of soil erosion and stream entrenchment. The techniques employed in terracing and their influence on yields will be assessed through excavation and laboratory analysis. The age of terraces will be established by dating the organic matter, charcoal and artifacts in soils buried by terrace construction or included in the retaining walls and fill. River valleys downstream from terraces will be surveyed for cutbanks where alluvial deposits are exposed. There, cycles of sedimentation and soil development will reveal alternating episodes of slope erosion and stability.
The research will contribute to the debate about how 'pristine' the landscape of the Americas was at contact, and to what extent its modern degraded condition is the effect of the introduction of technologies developed in different environments and therefore ill-adapted to local conditions. It will also explore the social context necessary for the successful introduction of particular innovations in agriculture and the continued maintenance of artificial agro-ecosystems.
