The origins of Amazonian landscapes: Plant cultivation, domestication and the spread of food production in tropical South America

Abstract

During the last two decades, new archaeological projects which systematically integrate a variety of plant recovery techniques, along with palaeoecology, palaeoclimate, soil science and floristic inventories, have started to transform our understanding of plant exploitation, cultivation and domestication in tropical South America. Archaeobotanical studies are providing a far greater appreciation of the role of plants in the diets of early colonists. Since~13ka, these diets relied mainly on palm, tree fruits, and underground tubers, along with terrestrial and riverine faunal resources. Recent evidence indicates two areas of precocious plant cultivation and domestication: the sub-Andean montane forest of NW South America and the shrub savannahs and seasonal forests of SW Amazonia. In the latter area, thousands of anthropic keystone structures represented by forest islands show a significant human footprint in Amazonia from the start of the Holocene. While radiocarbon date databases show a decline in population during the middle Holocene, important developments happened during this epoch, including the domestication of cacao, the adoption of maize and the spread of manioc across the basin. The late Holocene witnessed the domestication of rice and the development of agricultural landscapes characterised by raised fields and Amazonian Dark Earths (ADEs). Our multi-proxy analysis of 23 late Holocene ADEs and two lakes from southern Amazonia provides the first direct evidence of field polyculture agriculture including the cultivation of maize, manioc, sweet potato, squash, arrowroot and leren within closed-canopy forest, as well as enrichment with palms, limited clearing for crop cultivation, and low-severity fire management. Collectively, the evidence shows that during the late Holocene Amazonian farmers engaged in intensive agriculture marked by the cultivation of both annual and perennial crops relying on organic amendments requiring soil preparation and maintenance. Our study has broader implications for sustainable Amazonian futures.

Anthropogenic soil and settlement organisation in the Bolivian Amazon

“…Macrocharcoal was counted as particles/cm 3 samples. The full archaeobotanical analysis is presented elsewhere (Iriarte et al, 2020), with key results being discussed here.…”

“…The three soil profiles (ADE, ABE and control) at Triunfo (Figure 7) are dominated by arboreal phytoliths, representing a closed-canopy forest (Iriarte et al, 2020). Arboreal phytoliths constitute >50% phytoliths in both the ADE and ABE.…”

“…Like ADE, when reported, ABEs have been documented from the western to eastern Amazon (Kern et al, 2017). They have been reported in various locations in the Lower Amazon (Alves, 2017; Costa et al, 2013; Sombroek et al, 2002; Stenborg, 2016; Troufflard & Alves, 2019; Woods & McCann, 1999), Central Amazon (Arroyo‐Kalin, 2010; Gonda, 2018), upper Tapajos (De Souza et al, 2018; Iriarte et al, 2020), southwest Amazonia (this paper; Quintero‐Vallejo et al, 2015) and the Colombian Amazon (Mora et al, 1991). As a pan‐Amazonian phenomenon, they are heterogeneous and not always present, even when ADE is present (e.g., Alho et al, 2019).…”

“…Recent integrated archaeobotanical and paleoecological research has revealed ADE and ABE to be distinct components of a sustainable polyculture agroforestry system that combines anthropogenic soil fertilisation, closed‐canopy forest enrichment, limited forest clearance for crop cultivation and low‐severity fire management (De Souza et al, 2019; Iriarte et al, 2020; Maezumi et al, 2018). ADE and ABE soils are utilised differently as part of a holistic settlement and subsistence system.…”

Archaeology and ethnography demonstrate a human origin for Amazonian Dark Earths

“…Their view rejects anthropic factors as main drivers for soil enrichment, both excluding inputs from domestic waste and arguing that indigenous land use regimes cannot produce comparable enrichment. However, ethnographic evidence shows that the highest elemental enrichment in ADEs reflects inputs associated with settlement refuse rather than agricultural management (9), which in ancient Amazonia was based on polyculture agroforestry of domesticated and nondomesticated plants in both extensive and intensive systems (13)(14). Both high elemental enrichment and soil modification associated with settlement practices, as well as microfossils of maize, palms and tubers, revealing use of agroforestry systems, are found at the nearby site of Hatahara (6, 15), less than 4 km away and contemporaneous with the Caldeirão archaeological occupation.…”