Due to its high biodiversity and ongoing threats from human development and climate change, the eastern Andean flank is of particular interest. Paleoecological records in the foothills of the Andes are rare, and yet, necessary to understand long-term natural variability of vegetation assemblages and their response to climate change. A new paleoecological record has been analyzed from a previously undescribed lake, Lake Palotoa, located in southern Peru at 1370 m in elevation. Pollen and charcoal analyses were performed on a sediment core collected from Lake Palotoa, which spanned the last c. 3700 cal. yr BP. Fifty-five samples with a volume of 0.5cm3 were taken at 5 cm intervals and processed for analysis. To investigate the climate-vegetation linkages, the fossil pollen record was compared with well-established Andean climate reconstructions produced from speleothems from Huagapo cave, Peru. The Palotoa record was used to evaluate: (1) if the vegetation of Lake Palotoa was strongly influenced by humans in the pre-Columbian period, (2) if the record was representative of Late Holocene climatic conditions, (3) if, within the context of Andean climate change over the last 4000 years, the Medieval Climate Anomaly (MCA) or the Little Ice Age (LIA) were extreme events.
Results/Conclusions
Pollen analysis indicated that Palotoa had been continuously forested for the last 3700 years. The record was absent of pollen from crop taxa often associated with human presence. The adjacent forest is naturally mesic and the occurrence of charcoal would strongly suggest the presence of human alteration to the landscape. Charcoal was, however, absent throughout. Patterns in climate change were reflected in the Palotoa record by variations in the balance between pre- and lower-montane forest taxa. As precipitation increased, pre-montane taxa decreased while lower-montane taxa increased. Lake Palotoa appeared to be a blend of local and regional signals, but overall the major responses seemed to follow those of regional climate change. Vegetation assemblages appeared to be influenced predominantly by low-altitudinal cloud variability. A novel approach to determine cloud condition was developed using a dominant but elevationally range-limited palm species, Dictyocaryum lamarckianum, as a proxy. A thickening and thinning of the cloud base was inferred from declines and rises in Dictyocaryum abundance, respectively. Vegetation changes associated with the MCA were detectable within the Palotoa record, as the increase in precipitation appears to have caused a shift in the dominant driving force behind vegetation assemblages. Contrastingly, the LIA signal was not clear.