The pyrogeography of Amazonia: a Holocene perspective

Amazonian forest fires rarely, if ever, ignite and spread in the absence of humans. The first colonization of people into South America happened in the late Pleistocene, and by 10,000 years ago, humans had introduced fire into a naive landscape. Here we build on previous databases of burned 14 C dated archaeological material and 14 C dated charcoal fragments retrieved from soils and reconstruct spatiotemporal patterns of fire in Amazonia for the last 10,000 years. We ask whether fire histories are regionally synchronous, and whether major demographic events such as the ‘Great Dying’ or ‘Early abandonment’ appear in the fire histories within or between regions. We found that most of the earliest fires occurred in the peripheral areas and spread into central Amazonian forests mostly around 2000–3000 years ago. The frequency and recurrence of burned 14 C dated material also showed a two-phase decline over the last 700 years. Most regions show a decrease in fire occurrence ca. 700–500 years ago and then again during the last 400 years when European influence spread across Amazonia. The restructuring of Amazonian pyrogeography over the last 2000 years has likely played a large role in shaping modern forests. Fire in Amazonian forests rarely if ever occurs in the absence of human ignition, and we used compilations of 14 C dated charcoal from paleoecological soil surveys and from archaeological material to reconstruct regional spatio-temporal patterns of fire occurrence (pyrogeography). Human-ignited fires began in the peripheral regions and around the main Amazon River channel, began geographically spreading around 6000 years ago, and by 2000 years ago were found across all regions and the interior of the forests. Fire frequency across all regions declined around 600–700 years ago, several centuries before European arrival, supporting the ‘early abandonment’ hypothesis. A second wave of site frequency decline occurred across all regions after Europeans arrived in the landscape, supporting the ‘great dying’ hypothesis. The significant changes in Amazonian pyrogeography over the last 2000 years likely play a large role in structuring modern forests.