Impact of pre-Columbian “geoglyph” builders on Amazonian forests

Abstract

Over 450 pre-Columbian (pre-AD 1492) geometric ditched enclosures ("geoglyphs") occupy ∼13,000 km 2 of Acre state, Brazil, representing a key discovery of Amazonian archaeology. These huge earthworks were concealed for centuries under terra firme (upland interfluvial) rainforest, directly challenging the "pristine" status of this ecosystem and its perceived vulnerability to human impacts. We reconstruct the environmental context of geoglyph construction and the nature, extent, and legacy of associated human impacts. We show that bamboo forest dominated the region for ≥6,000 y and that only small, temporary clearings were made to build the geoglyphs; however, construction occurred within anthropogenic forest that had been actively managed for millennia. In the absence of widespread deforestation, exploitation of forest products shaped a largely forested landscape that survived intact until the late 20th century.

New Insights From Pre-Columbian Land Use and Fire Management in Amazonian Dark Earth Forests

“…Despite recent declines in edible plants, the enriched levels have not returned to pre-human occupation levels at LC or in modern vegetation surveys of ADE and non-ADE forest plots in the surrounding area (Maezumi et al, 2018;Almeida et al, in review). Additionally, enriched levels of palms and other useful plants have been documented in modern forests growing on pre-Columbian mounds, anthropogenic soils, and geoglyphs abandoned more than 400 years ago in other parts of the Amazon, suggesting the persistent legacy of pre-Columbian enrichment, irrespective of modern land use histories (Erickson and Balée, 2006;Walker, 2011;Quintero-Vallejo et al, 2015;Watling et al, 2017). These data indicate pre-Columbian vs. later periods of human land use was the primary driver of ADE forest enrichment.…”

How People Domesticated Amazonian Forests

“…Future multidisciplinary studies that combine alternative methods may help to reconstruct forest composition dynamics (Stahl, 2015), as Watling et al (2017b) did in the geoglyph region of Acre, revealing more details of the influence of past peoples in Amazonian forests. The integration of paleoecology, archaeology, archaeobotany and forest ecology is a promising combination (Mayle and Iriarte, 2014;Iriarte, 2016;Watling et al, 2017a,b).…”

“…Domesticated species adapted to stable soil conditions created by management practices, such as TPI, may persist for a long time after abandonment (Quintero-Vallejo et al, 2015). This may explain why domesticated palms dominate modern forests growing on pre-Columbian mounds, anthropogenic soils and geoglyphs abandoned more than 400 years ago (Erickson and Balée, 2006;Quintero-Vallejo et al, 2015;Watling et al, 2017b). Another possible explanation for this persistence is the continuous recruitment of useful and domesticated plants present in the forest seed bank .…”

“…Although some scholars argue for a localized impact involving these three practices in preColumbian Amazonia, associating them with the margins of the main rivers (McMichael et al, 2012(McMichael et al, , 2014Bush et al, 2015;Piperno et al, 2015), the impact of long-term management practices has been detected in the forests of interfluvial areas (Levis et al, 2012;Franco-Moraes, 2016;Watling et al, 2017b) and across the Amazon basin (Levis et al, 2017b). These findings suggest that even in remote areas, far from known archaeological sites, contemporary people also manage the forest, protecting useful species and removing the non-useful, which are the most frequent practices reported by contemporary societies.…”

“…In southwestern Amazonia, archaeobotanical remains have revealed that past peoples consumed a rich diet, including many palm fruits (Dickau et al, 2012). The increase in palm abundance is also visible in soil profiles of archaeological sites across the region Watling et al, 2017b), suggesting that past societies enriched the forest with useful palms to improve food production. Today, useful and domesticated palms are dominant in southwestern Amazonian forests (Levis et al, 2017b), growing on abandoned pre-Columbian mounds, anthropogenic soils and geoglyphs created by past management practices (Erickson and Balée, 2006;Quintero-Vallejo et al, 2015;Levis et al, 2017b;Watling et al, 2017b).…”