The legacy of 4,500 years of polyculture agroforestry in the eastern Amazon

Abstract

The legacy of pre-Columbian land use in the Amazonian rainforest is one of the most controversial topics in the social and natural sciences. Until now, the debate has been limited to discipline-specific studies, based purely on archaeological data, modern vegetation, modern ethnographic data or a limited integration of archaeological and palaeoecological data. The lack of integrated studies to connect past land use with modern vegetation has left questions about the legacy of pre-Columbian land use on the modern vegetation composition in the Amazon, unanswered. Here, we show that persistent anthropogenic landscapes for the past 4,500 years have had an enduring legacy on the hyperdominance of edible plants in modern forests in the eastern Amazon. We found an abrupt enrichment of edible plant species in fossil lake and terrestrial records associated with pre-Columbian occupation. Our results demonstrate that, through closed-canopy forest enrichment, limited clearing for crop cultivation and low-severity fire management, long-term food security was attained despite climate and social changes. Our results suggest that, in the eastern Amazon, the subsistence basis for the development of complex societies began ~4,500 years ago with the adoption of polyculture agroforestry, combining the cultivation of multiple annual crops with the progressive enrichment of edible forest species and the exploitation of aquatic resources. This subsistence strategy intensified with the later development of Amazonian dark earths, enabling the expansion of maize cultivation to the Belterra Plateau, providing a food production system that sustained growing human populations in the eastern Amazon. Furthermore, these millennial-scale polyculture agroforestry systems have an enduring legacy on the hyperdominance of edible plants in modern forests in the eastern Amazon. Together, our data provide a long-term example of past anthropogenic land use that can inform management and conservation efforts in modern Amazonian ecosystems.

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

“…There is mounting evidence that pre-Columbian people had a more substantial impact on vegetation composition in modern Amazon ecosystems than previously thought (Clement et al, 2015;Levis et al, 2017;Maezumi et al, 2018). New findings show a disproportionate number of plants (accounting for half of all trees in the Amazon) are hyperdominant, and domesticated species are five times more likely to be hyperdominant than non-domesticated species (ter Steege et al, 2013;Levis et al, 2017).…”

“…Defining the Anthropocene however, is complicated by the fact that the history of human land use and fire management is poorly characterized in large parts of the world that are known to have long histories of indigenous occupation, such as the Amazon Basin (Waters et al, 2016). Past human land use and fire management has the potential to alter the composition and structure of forest ecosystems, impacting fire susceptibility and creating an enduring anthropogenic legacy in modern ecosystems (Roberts et al, 2017;Levis et al, 2018;Maezumi et al, 2018;Turney et al, 2018). To date however very little is known about the history of human land use and fire management in the Amazon.…”

“…ADE formation progressively expands in the region indicated by the formation of ADEs until European conquest (∼450 cal yr B.P.) (Heckenberger and Neves, 2009;Gomes, 2011;Arroyo-Kalin, 2012;Alves, 2016;Iriarte, 2016Iriarte, , 2017Maezumi et al, 2018). Nutrient rich ADEs are abundant in charcoal and ash, along with other organic additives, including human waste, domestic refuse, crop residues, compost, and mulch, which release nutrients and carbon into the soil (Sombroek, 1966;Denevan, 1995;Kato, 1998;Lehmann et al, 2003b;Oguntunde et al, 2004;Steiner et al, 2007;Fraser et al, 2011;Eriksson et al, 2016).…”

“…Therefore, we interpret it as evidence for sweet potato, manioc, and squash cultivation. Pollen taxa were grouped into edible trees, palms, and herbs, crops, other trees and herbs in the pollen diagram based on modern botanical classifications (Clement, 1999;Hanelt et al, 2001;Levis et al, 2017;Maezumi et al, 2018;Supplementary Methods M5). Pollen zones were calculated using CONISS (Grimm, 1987;Bennett, 1996) combined with a broken-stick model in R to determine the number of statistically significant zones (Bennett, 1996).…”

“…Three peak magnitude episodes are associated with the apex of pre-Columbian activity, the largest of which is synchronous with the presence of maize and squash cultivation and the formation of ADEs on the Belterra Plateau ∼520 cal yr B.P. (Maezumi et al, 2018;Supplementary Figure 3, Supplementary 100 cal yr B.P., influx values progressively increase during the last century with record high influx and peak magnitude values occurring in the past decade (Figure 8). RCC values from the 11 egional records (Table 2) follow a similar pattern of biomass burning to LC.…”