The great majority of Amazonian lakes show signatures of human disturbance within the last 2000 years. Lakes were preferred occupation sites, and deforestation and burning masked the natural responses of plant assemblages to climatic shifts such as the medieval climate anomaly (950-1250 AD) or the Little Ice Age (1450-1800 AD). The Hill of Six Lakes, NW Brazil, is a classic site for paleoecological studies of vegetation change in the late Pleistocene, but relatively little attention has been paid to its late Holocene record. The Hill is edaphically dry, with very thin soils and is an inhospitable landscape. Lake Pata, which lies on the Hill of Six Lakes, was suggested to have been free from human activity. We wanted to test this hypothesis and take the opportunity to investigate late-Holocene climate-vegetation relationships in Amazonia. In 2009 a 1-m long piston core was raised from the center of Lake Pata. 7 14C dates provide a chronology that indicates a steady rate of sedimentation. Pollen samples were taken at $ cm intervals throughout the core, providing a sub-centennial scale (c. 40 yr interval) record of vegetation change over the last 2000 years. Samples were analyzed for macroscopic (>180 μm) charcoal at similar intervals.
Results/Conclusions
We found 225 morphotypes of pollen, reflecting the high biodiversity of the region. Poaceae pollen was present at trace amounts until the uppermost sample where 6% of pollen was from grasses. Charcoal was absent from all samples, and weedy taxa such as Trema and Cecropia were minor components of he pollen spectra. From these data we affirm that no evidence exists for human occupation on the Hill of Six Lakes in the last 2000 years. The slight increase in weedy taxa from c. 3% of the pollen sum to 12% in the last 400 years may reflect regional disturbance, ie. on the plains surrounding the Hill of Six Lakes rather than from the hill itself. These changes could reflect European arrival, altered land use and the population growth associated with the rubber boom. The Medieval Climate Anomaly and the Little Ice Age induced no apparent signal in the vegetation and this system appears to have been highly resilient to changes that are reflected in regional speleothem records.