Wet and dry events influenced colonization of a mid-elevation Andean forest

Few paleoecological records are available to document the history of mid-elevation montane forests in the tropical Andes between 1500 and 2500 m above sea level. Archaeological studies have identified late-Holocene human modification of these landscapes, but it is not clear when and to what degree such alteration began. Here, we report fossil pollen, X-ray fluorescence, and charcoal data from Lake Progreso, which lies at 2013 m elevation in the eastern Peruvian Andes. The reconstruction of the effects of climate and human activity on an Andean lower montane forest is the first such high-resolution paleoecological record to span the Holocene. The record begins in the early Holocene, with lake formation in a forested setting that lacked fire. Marked erosive events were recorded in the early and late Holocene, but not the mid-Holocene. The first evidence of human disturbance in the record was the appearance of charcoal c. 6300 cal BP. This onset of burning was followed by maize cultivation c. 4520 cal BP. The basin surrounding Lake Progreso was disturbed and burned by humans intermittently thereafter but retained a predominance of forest throughout its history. The pollen, charcoal, and XRF data suggested that the site was generally used by small groups of people or settled by a small community. The Progreso record bore overall similarities in the timing of human occupation to records from nearby Lake Pomacochas, and the lower elevation site of Lake Sauce, though both those sites showed far greater deforestation. Collectively, these data suggested that Lake Progreso supported much smaller human populations and retained more of its forest than lakes Sauce or Pomacochas. While all sites shared a history of forest burning and maize cultivation, sufficient dissimilarities existed to indicate contrasting histories of site usage.