Roles of Holocene Climate and Pastoralism in Shaping Andean Landscapes
Shadik, Courtney Renee
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The Holocene (c. 11,700years ago –present) was a time rich in Andean climatic, environmental, and cultural changes. Assemblages were reforming after the last ice age, millennial scale wet and dry events caused the largest changes in lake level of the last 100,000 years, and humans came to dominate the landscape. Against the backdrop of ecological change, this study asks the following questions-Was the onset of camelid domestication associated with mid-Holocene aridity? Are modern, high-elevation vegetation assemblages a product of manufactured landscapes? What are the long-term effects of intense agropastoralism on paleoecological reconstructions of Andean landscapes? Did Holocene agropastoral domesticates coevolve? The study sites are located on the eastern flank of the Andes in climatically distinct regions: central Ecuador, and southern Peru. Lake sedimentary records from these sites span c. 8000 years ago –present, encompassing the peak of the Mid-Holocene Dry Event (c. 9000 –4000 years ago). Using a multiproxy approach combining the coprophilous fungus Sporormiella, fossil pollen, charcoal, X-Rayfluorescence (XRF), and sediment color, this study examined trends in pastoralism and climate, and subsequent landscape modification from agropastoralism. A c. 7000-year XRF and sediment color history is presented for Acopia in the highlands of southern Peru. Drought was found to be an integral part of this system with landscape structure heavily influenced by erosion. Erosion increased with intensifying agropastoralism, but decreased c. 2200 BP. At this time, erosional inputs were mostly clay indicating erosion of subsoil rather than topsoil, suggesting the onset of terracing at c. 2200 BP. The data offer valuable insight into previously observed chronological problems in high Andean records. Extensive 14C age reversals in the last 2000 years are explained by past terracing erosion. One proxy, sediment color, has been used to provide indices for rainfall anomalies associated with El Niño Southern Oscillation. Analyses of Acopia lake sediment comparing sediment color with XRF suggest that red intensity in sediment studies may not align with assumed trends in precipitation, and sediment color must be tested geochemically before use in paleoclimate reconstructions. The Acopia record also provided a c. 7000-year history of herding, cultivation, and vegetation. Here, the vegetation composition was impacted early-on by fire, but was later controlled by intense herding and maize cultivation. The onset of camelid domestication here was not associated with mid-Holocene aridity. The c. 4300-year record of herding and maize cultivation, combined with terracing activities beginning c. 2200 years ago created a landscape altered physically and ecologically by human activity. This manufactured landscape may represent an ecological tipping point at Acopia. Also presented is a c. 8000-year record of vegetation change from Rodeococha in central Ecuador. Here, fire is present in small amounts throughout the history. Only two maize grains were found in the sequence, and there was no signal of pastoralism until c. 1600 years ago. At Rodeococha, human occupation was limited by volcanic activity, and this high, wet landscape, was not modified as intensely as Acopia. Despite human presence, vegetation responded to taphonomic changes as the lake fluctuated between a peatland and a lake. This suggests that in combination, long-term human modification and less resilient systems may be necessary to create manufactured landscapes. Lastly, the study presents an analysis of synchronicity between quinoa and camelid domestication in Andean paleoecological records. Eight sites with 5 records of both quinoa and Sporormiella were analyzed to test hypotheses of coevolution between mid-Holocene domesticates. I determined that temporally overlapping adoption of new technologies does not necessarily indicate coevolution. The results support independent inventions of pastoralism in the northern and southern tropical Andes. In hypotheses of agropastoral links, it is important to consider local-scale variation as the Andes represent a climatically and culturally diverse system.