The adoption of agropastoralism and increased ENSO frequency in the Andes

Abstract

Humans have been present in the Andes since about 12,000 calibrated years before present (cal yr BP), transitioning from hunter-gatherers to agropastoralist societies in the mid-Holocene. Yet, the timing and effects of this change in behavior on the ecosystem are largely unknown. Using titanium from XRF analysis, loss-on-ignition (LOI), fossil pollen, Sporormiella, and charcoal, we present a high-resolution 12,000-yr paleoecological history of Lake Llaviucu, a mid-elevation lake in the Ecuadorian Andes. For the entire period of study, humans were active in this landscape, with signs of agropastoralism being present since c. 6100 cal yr BP. Apparent ENSO activity, inferred from titanium inputs to the sediment is also heightened at c. 6100 cal yr BP. A trajectory of increasing landuse seems to have peaked in terms of maize production between c. 2900 and 800 cal yr BP. Thereafter, larger abundances of Sporormiella spores suggest that pastoralism was of increasing importance; a pattern disrupted by European arrival. Apparent peaks in El Niño Southern Oscillation (ENSO) appears to be linked to fire and maize frequency. We investigated the relationship between the Lake Llaviucu record and that of nearby Lake Pallcacocha, which is often cited as providing a regional ENSO history.