How natural are the forests of Amazonia? A growing case is being made among anthropologists and archaeologists that prior to European contact in 1492, native people manipulated much, perhaps most, of Amazonia. If fire was used across the Amazon basin to clear land for agriculture then forest ecosystems that ecologists have assumed were mature may in fact be only one to several generations removed from intensive management. Given that Amazonia is the largest rainforest and home to unparalleled biodiversity, understanding the extent to which wildlife and people have interacted in the past is vital for effective planning and management. A further aspect of this debate is that if much of Amazonia is truly the product of disturbance, the forest must be considered to be relatively young and is probably not at equilibrium with respect to carbon cycling.
To test the hypothesis of widespread disturbance, this project will conduct the first systematic survey of Amazonian soils for charcoal. Fires in Amazonia are almost always human-induced, and each burn leaves ash and charcoal that become incorporated into soil. Over 300 soil pits will be sampled on transects across Amazonia, to determine the distribution and age of buried charcoal. Prior soil descriptions also will be used to determine where other scientists have located charcoal and compare data gathered in this project with a new model for pre-Columbian settlement of Amazonia. Through these analyses, the collaborating team from Florida Tech, Wake Forest, University of Florida, The National History Museum, and Guarulhos University, Brazil, will hope to inject real data into the policy arena of Amazonian development and conservation.
PI: Mark Bush What did the Amazon rainforest look like when the first Europeans arrived in 1541A.D.? For decades, it was thought that Amazonia was so resource-poor that the native inhabitants were unable to develop complex societies as they did in other parts of the Andes or Central America. But recent archaeological discoveries suggest otherwise. Earthworks and enriched soils, termed terra pretas, have been discovered in a few areas, leading many researchers to suggest that most of Amazonia was a transformed landscape. The overall population density and distribution of native inhabitants of Amazonia is now fiercely debated. The research project "Pre-Columbian Human Impacts on Amazonian ecosystems" addressed this debate. This project was the first landscape-scale analysis of pre-Columbian impacts in Amazonia, with ~ 400 soil cores collected over stratified-randomized survey design in a 3 x106 km2 section of central and western Amazonia. Phytoliths, which are silica bodies deposited in soils when many plant species decay, were analyzed to provide vegetation histories from the sampled sites. Charcoal was used to reconstruct fire histories at those locations, many fragments were dated to confirm that the fires were from the pre-Columbian era. As fire is not natural in Amazonia, the fire histories were indicative of anthropogenic forest burning. None of the sampled sites contained artifacts or terra preta soils, indicating that the sampled regions did not contain landscape-scale forest clearing and large societies. However, low-impact human activity was found in most regions, and these activities were spatially patterned according to environmental features. Fire and disturbance-indicating plant taxa were most frequently found near major rivers and areas far-removed from rivers contained a much lighter disturbance signature. The ever-wet western forests also had a much lighter disturbance signature than the central forests, which are drier and easier to burn. Even in areas with known maize agriculture, human impacts were localized and heterogeneous. We did not find evidence that the ~180,000 km2 of bamboo-dominated forests in western Amazonia resulted from pre-Columbian societies, as had been previously suggested. Our projects results indicated that before European arrival, Amazonia was not a completely transformed landscape, and in western Amazonia pre-Columbian impacts ranged in degree but may be predictable in space. But why should anyone care? Assuming that intensive and extensive pre-Columbian disturbances occurred throughout Amazonia was becoming the norm, and generated an array of hypotheses. If Amazonian forests were mostly deforested only 500 years ago, does that mean the forests are resilient to disturbance? Was the ultra-diverse Amazonian plant and animal diversity structured by ancient people? Did the pre-Columbian population collapse in Amazonia result in a massive forest re-growth that decreased global CO2 levels? Our results suggested that conclusions based on assumptions of a pre-Columbian parkland need reassessing.
