Sustainability and sensitivity to climatic change of (Pre-Inca) Wari irrigated terrace agricultural systems in the southern Peruvian Andes
by
Rob Kemp
Department of Geography, Royal Holloway, University of London, UK
Coauthors: Nick Branch, Barbara Silva, Frank Meddens, Alan Williams (Royal Holloway, University of London, UK), Anne Kendall (Cusichaca Trust, London, UK), Cirilio Vivanco (University of Ayacucho, Peru)

A combined palaeopedological, palaeoecological and archaeological approach was used to assess the sustainability of (Pre-Inca) Wari irrigated terrace agricultural systems during a period of climatic change in Pampachiri (near Andahuaylas) in the southern Peruvian Andes. Our focus was on i) a mire core and ii) vertical sections through three nearby terraces that contained buried palaeosols, suggesting abandonment or failure of the systems and subsequent reconstruction and reuse.

Radiocarbon dates and archaeological records (pottery and nature of terrace construction) indicate that the buried palaeosols can be correlated to each other and are probably Middle Horizon (550-1000 AD) in age. The rebuilding of the terraces likely took place during the Late Intermediate (1000-1400 AD). The Middle Horizon period is represented in the mire basin stratigraphy by reduced levels of peat humification and high mineral sediment content, probably indicating increased mire wetness and erosion of the surrounding slopes. Firm correlation of the mire’s pollen stratigraphy to the ice core records from Quelccaya requires a higher resolution radiocarbon chronology than currently possessed, though it is noticeable that the i) Middle Horizon and ii) Late Intermediate lithostratigraphic units correspond approximately to respective phases of i) increased and ii) reduced precipitation levels identified from the ice cores.

Phytoliths extracted from A horizons of the palaeosols indicate that the Middle Horizon terraces were cultivated, with maize (and probably other) crops having been grown. The palaeosols’ neutral pHs and relatively high levels of phosphorus suggest that soil chemical fertility was probably adequate prior to burial. The main limitation to agriculture may have been water: the coarse soil textures would have been conducive to rapid drainage.

Although it cannot be unequivocally proven at this stage, it is tempting to relate the abandonment of cultivation at the end of the Middle Horizon to climate change. Archaeological and ice core records suggest that the Wari civilisation fell as a response to drier climatic conditions at 1100 AD, or possibly slightly earlier (900-1000 AD). The timing of changes in mire stratigraphy at Pampachiri and the physical fertility limitations of the soils may support this interpretation.

Date received: November 23, 2004