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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - EPP-Am (The Early Peopling of Amazonia and the Beginning of Plant Domestication)

Teaser

Summary

Epp-Am investigates two topics in the prehistory of the Neotropics: the social-ecological dynamics of earliest people of SW Amazonia and the role these early Holocene populations played in the domestication of Neotropical plants. This area has a great potential for reconstructing early human-environment interactions in South America and offers a unique opportunity for exploring the domestication of several Amazonian plants and the origin of agriculture in the Neotropical lowlands. About half of the domesticated crops of America seem to have originated in the Amazon Basin. In particular, based on genetic studies that look at the similarities between domesticated plants and their closest wild relatives, SW Amazonia has been proposed as the potential area for the domestication of cassava, peanuts, jack bean, two species of chilli pepper and peach palm. So far, the genetic evidence is not supported by archaeological data, which is difficult to produce as organic remains are poorly preserved in the dry/humid environments of SW Amazonia. A specific innovative aspect of this proposal is the use of plant micro-remains (mostly phytoliths) from recently discovered early and mid-Holocene archaeological sites (shell middens) to study plant exploitation strategies in these difficult preservation environments.
Phytoliths are also used to reconstruct vegetation changes throughout the Holocene in the Llanos de Moxos (LM), where the shell middens are. The Holocene environmental history of most of the LM is largely unknown; there is no paleoecological archive going back to the mid-Holocene. The main reason for this lack of data is that the lacustrine sediments from the lakes that dot the central and southern LM are extremely difficult to core due to their stiff clay sediments and, if cored, provide very shallow sedimentary archives, spanning only a few thousand years. For this reason, this project is based on stratigraphic archives built by past river inundations. These archives contain many phytolith-rich paleosols, which we use for paleoenvironmental and paleoclimatic reconstructions.
Epp-Am contributes to thedebate of the origin of domesticated plants in the Amazon and the peopling of Amazonia. The nature of the early occupation in SW Amazonia, including the antiquity, settlements patterns, subsistence strategies, processes of social change and environmental impacts is largely unknown. Understanding the nature of the first human settlements is much-needed to understand the regionâ€™s cultural diversity. Moreover, this work will help assess the environmental impact of early Amazonians. This data is key in order to correctly interpret paleoecological archives, in particular lacustrine sediments where pollen and charcoal signals could be the results of human disturbance. This research integrates archaeological evidence from hunter-gatherers/early cultivators with multiproxy environmental and archaeobotanical data. The new data contributes to the understanding of the early Holocene environment, population dynamics and the economy of ancient South Americans, which will be valuable to policy makers at a continental and global level: understanding environmental change and the way it affected different societies in the past is key to inform future planning; traditional ecological knowledge on early uses of domesticated plants can support the work of NGOs and local government to achieve the sustainable exploitation of Amazoniaâ€™s natural resources; collected data will improve current environmental modelling.

Work performed

The project followed 2 lines of investigation: reconstructing human-environmental interactions and unveiling the time and the processes of plant domestication.
1. Holocene landscape evolution in the LM
Rivers are the main actor shaping the landscape. Field and remote sensing observations of small rivers along the Bolivian Andean piedmont allowed to discover a new process where, frequent (sometimes on yearly basis) blockages of the river course due to the accumulation of woods (logjams) cause large scale forest die-off events, with important consequences in terms of forest biodiversity and flood risk in a large area of the LM. In studies published before the starting of this project, the presence of several paleosols below the alluvial plains of the LM was already documented. During the 2016 field work, the sampling of these paleosols along a 300 km long transect from the Andes to the central LM was completed. The analysis of 36 stratigraphic profiles plus 50 radiocarbon ages from paleosols intercalated with fluvial sediments permitted to reconstruct the most important changes in floodplain dynamics on a millennial scale and the links between pre-Columbian cultural processes and environmental change. These paleosol are currently the only paleoecological archive available for the reconstruction of past vegetation. The analyses of stable carbon isotopes, from 36 paleosols, and biogenic silica, from 29 paleosols, show that the patchwork of forests and savannahs that we see today was established after the 4 kyr BP climate change. During the dry period between 8 and 4 kyr BP, most of the central LM, nowadays covered with seasonally flooded savannah, were covered by Cerrado-like savannah in the west and by forest in the east. However, results also suggest that, at both regional and local scales, vegetation cover has been influenced by changes in topography resulting from the regionâ€™s river dynamics. The paper presenting these results is currently under second round of revisions in the journal Global and Planetary Change and should be published between the end of 2018 and the beginning of 2019.
2. Early Holocene peopling of SW Amazonia and the domestication of Neotropical plants
2017 field work focused on surveying and sampling of forest islands, small patches of forest surrounded by savannah under which most of the Moxosâ€™ early and mid-Holocene archaeological sites are found. Some 300 samples from 70 sites have been taken; 43 have been processed for phytolith extraction and 38 have been radiocarbon dated. The counting and identification of the phytoliths from these 43 samples has been recently completed. In parallel to the phytolith analysis, FI have been mapped and spatial patters analysed.

Final results

This research has advanced our knowledge on the fluvial processes that have shaped the LM during the Holocene and on how these processes have influenced pre-Columbian settlement patterns. Understanding fluvial dynamics in the LM is a key aspect of flood risk management strategies in a region that has recently been heavily affected by catastrophic floods and that will be likely subject to increasing worse floods because of climate change. Our results allow to address the role of the LM in the process of domesticating many important crops, such as cassava and squash among others. Also, we are going to unveil to what extent early and mid-Holocene inhabitants of the LM shaped the landscape by building earthworks that, not only are still visible today, but provide important ecological services. Our work had an important impact on the population and political institutions in the LM. By showing the breath and importance of the pre-Columbian past of the LM we provided the local population with a reason to be proud of their past. In recognition for the impact our work had on local populations, Dr. Umberto Lombardo was awarded the title of â€œFriend of the Beniâ€ by the Beniâ€™s Civic Comity.