Early to mid-Holocene human activity exerted gradual influences on Amazonian forest vegetation

Abstract

Humans have been present in Amazonia throughout the Holocene, with the earliest archaeological sites dating to 12 000 years ago. The earliest inhabitants began managing landscapes through fire and plant domestication, but the total extent of vegetation modification remains relatively unknown. Here, we compile palaeoecological records from lake sediments containing charcoal and from pollen analyses to understand how human land-use affected vegetation during the early to mid-Holocene, and place our results in the context of previous archaeological work. We identified gradual, rather than abrupt changes in forest openness, disturbance and enrichment, with useful species at almost all sites. Early human occupations occurred in peripheral sites of Amazonia, where natural fires are part of the vegetation dynamics, so human-made fires did not exert a novel form of disturbance. Synchronicity between evidence of the onset of human occupation in lake records and archaeological sites was found for eastern Amazonia. For southwestern and western Amazonia and the Guiana Shield, the timing of the onset of human occupation differed by thousands of years between lake records and archaeological sites. Plant cultivation showed a different spatio-temporal pattern, appearing ca 2000 years earlier in western Amazonia than in other regions. Our findings highlight the spatial–temporal heterogeneity of Amazonia and indicate that the region cannot be treated as one entity when assessing ecological or cultural history. This article is part of the theme issue ‘Tropical forests in the deep human past’.

Long‐term fire and vegetation change in northwestern Amazonia

“…The frequency and abundances of charcoal fragments and phytoliths indicating disturbance across our three study sites were lower than has been reported at other sites in central and eastern Amazonia where similar analyses have been performed on terrestrial soils (McMichael et al, 2012 , 2015 ). Data from lake sediments have also indicated that the frequency of forest opening and burning by people in the pre‐Columbian era was lower in northwestern Amazonia compared with the southwestern and central regions of the basin (Gosling et al, 2021 ; Nascimento et al, 2022 ).…”

Tropical forests in the deep human past

“…This appears to have initially taken place along river banks and drier fringes of the lowland and montane forest zone. However, within a few millennia, human occupation pushed deeper into the Amazon forest, primarily along river networks, although archaeological evidence may be biased to such accessible sites [ 19 , 20 ]. Human occupation modes ranged from hunting and gathering to agricultural systems which were based either on locally originated domestications such as manioc and squashes, or imported from Mesoamerica, such as maize.…”

“…Cultivation dating to 9 ka also appears in the forest zone north of the savannahs [ 91 ], and there are signs of cultivation near campsites in northwest Amazonia [ 80 ]. In regions away from plant cultivation, early- to mid-Holocene foragers consumed palms, tree fruits and nuts [ 20 ]; many of these species are now hyperdominant in Amazonia and it has been suggested that the elevated abundance of these species across Amazonia may reflect selection and stewardship by indigenous populations over millennia [ 84 ].…”

Past human‐induced ecological legacies as a driver of modern Amazonian resilience

“…Charcoal fragments are evidence of human activity in the closed canopy forests of Amazonia, as fire rarely spreads from natural ignitions because of the everwet conditions (Bush et al, 2008; Malhi et al, 2009; Uhl & Kauffman, 1990). Although interdisciplinary archaeological and palaeoecological datasets unanimously indicate that fire, cultivation and cultural complexity increase over the last several millennia, these patterns were not uniformly intense across the vastness of Amazonia (Heckenberger & Neves, 2009; McMichael et al, 2012; Nascimento et al, 2022; Oliver, 2008; Piperno, 2011; Riris & Arroyo‐Kalin, 2019).…”