COS 300-4 - Pre-Columbian forest recovery in Amazonia

Abstract: The pre-European history of Amazonia is a dynamic field with implications for forest succession, biodiversity, and carbon storage. An emerging view presents a picture of heavily modified landscapes with a human population growing exponentially to 4 - 8 million people prior to European arrival. European contact is said to have caused a c. 90% decline in the human population within a century. That loss is suggested to have caused widespread abandonment of the land, which prompted forest regrowth and carbon sequestration that, in turn, cause the Orbis Spike, a c. 10 ppm decline in global atmospheric CO₂ concentrations at c. 1620.





Paleoecology shows that pre-Columbian inhabitants of Amazonia had heterogeneous impacts on the forest. Lakes are natural attractants and so they commonly have a history of human occupation marked by reduced forest pollen, increased abundances of pollen of weedy species, maize cultivation, and burning. Two neighboring lakes in Amazonian Ecuador provide complimentary but contrasting high-resolution paleoecological histories. While both have histories of human occupation, Lake Ayauchⁱ shows a long relatively continuous history of use for over 3000 years, whereas Kumpak^a shows only occasional occupation over the last two millennia. Both sites show some deforestation and maize agriculture followed by a strong forest recovery between c. AD 1100 and 1300. These data suggest that site abandonment occurred long before European arrival. This finding is contra the expectation that Amazonian populations were growing exponentially until their collapse following European Contact. In a broader study of 39 Amazonian pollen records, the peak of forest clearance, as at Ayauchⁱ and Kumpak^a, appears to have been between AD 250 and 550, with a marked period of forest recovery between AD 950 and 1150. These data align with estimates of recent archaeological analyses suggesting that human population density peaked c. AD 1000. Archaeological data, such as the building of defensive structures and increased rates of cranial trauma, suggest a period of intensified social unrest. Our data indicate that the period between c. AD 950-1150 to be critically important in Amazonian pre-history with greater ecological impact than the period of initial European contact (1550-1750). Our data do not reveal any forest signature connected to a major population collapse or forest recovery that could account for the Orbis Spike.