Drivers of Demographic Dynamics

Project Information

DEMODRIVERS

Grant agreement ID: 101043738

DOI

10.3030/101043738

EC signature date 4 May 2022

Start date 1 January 2023

End date 31 December 2027

Funded under

• European Research Council (ERC)

Total cost

€ 2 765 537,00

EU contribution

€ 2 765 537,00

Coordinated by

UNIVERSITAT AUTONOMA DE BARCELONA
Spain

Periodic Reporting for period 1 - DEMODRIVERS (Drivers of Demographic Dynamics)

Reporting period: 2023-01-01 to 2025-06-30

Summary of the context and overall objectives of the project

DEMODRIVERS aims to reconstruct human demography in SW Amazonia during the Holocene, shedding light on the impact of environmental and cultural changes. Despite decades of research, determining the relative importance of environmental versus cultural factors in prehistoric population growth remains a significant challenge in archaeology. This challenge persists due to the fragmentary, incomplete, and biased nature of archaeological records. DEMODRIVERS is designed to overcome this issue.
This interdisciplinary project spans five years and focuses on a regional case study: the Llanos de Moxos in the Bolivian Amazon. This area possesses a uniquely extensive archaeological record, comprising 4700 sites spanning 8300 years across 100,000 km2. These sites, known as forest islands (FIs) or islas de monte in Bolivia, are elevated earthen structures in seasonally flooded savannahs. Remaining above water year-round, they support tree growth, creating forest islands within a sea of savannah.
This record is unparalleled globally, offering a rare opportunity to quantify how demographic trends responded to exogenous (climate, landscape) and endogenous (culture, technology) variables. The project takes an unconventional approach, measuring occupation density, spatial distribution, and temporal boundaries by studying 150 stratigraphic cores from 100 evenly distributed archaeological sites. The interdisciplinary methodology integrates conventional archaeology with state-of-the-art geoarchaeology, biomarkers, paleoclimatology, palaeoecology, and artificial intelligence.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

DEMODRIVERS relies heavily on the success of its bold field-work component and intensive laboratory analyses. These are the two most critical aspects of the research program.
Fieldwork (relating to WP1, WP2, WP5 and tasks 2,4,6,7 and 8) The first two fieldwork seasons have been successfully completed.
*WP1-Survey and mapping of forest islands.
We have produced 120 Digital Elevation Models from 120 forest islands across the two seasons(Task 6). These will be essential to calculate the volume of forest islands, which, together with the elemental analysis and the radiocarbon program, will allow us to quantify the total amount of phosphorus accumulated in the totality of the archaeological sites per unit of time. Phosphorus can then be used as a proxy for the number of people, providing a quantitative reconstruction of the demographic curve, which is one of the main goals of DEMODRIVERS.
*WP2-Coring of forest islands.
We have modified the sampling strategy from what was planned in the original proposal. The original idea was to core and sample clusters of 5 forest islands and survey 10 more islands in the surrounding locality. However, when we started working in the field, obtaining the permits from the surrounding properties proved to be very time consuming, slowing down the entire campaign. On the other hand, once we had the permit to core in a property, we were able to take cores from more than 5 forest islands relatively easily and rapidly. So, the final strategy we decided to use, was to work with small clusters, but coring all the forest islands within each cluster (task 7), not only 5. Eventually, this will provide us with a larger number of samples and a more robust database. A total of 279 plastic liners with sediments have been retrieved from 117 forest islands belonging to 14 clusters and shipped to Barcelona. These correspond to 146 cored locations, as for some forest island we performed a transect rather that a single core in the centre.
*WP5-Archaeological excavations
Archaeological excavations (task 8) are needed to unveil the changes in cultural practices and technological innovations that can then be linked to changes in palaeo-demographics. We performed excavations in three sites along a east-west transect. Two forest islands were excavated in 2023 and one in 2024. Isla Encanto, in the proxtorimity of Trinidad and Isla Chuchíos in the eastern
extreme of the Llanos de Moxos, were excavated in 2023, while Isla Curupaú, on the western side of the Llanos de Moxos was excavated in 2024. All the artefacts will be analysed in situ during the 2025 field campaign, mostly by local experts.
*Unplanned activity–Building a phytolith reference collection.
A phytolith reference collection is a key element in AI training (WP6). In the original proposal we planned to use already existing reference collections stored by project collaborators J.Iriarte andF.Mayle.In collaboration with Bolivian botanist M.Moraes we have collected 170 plant specimens from forest islands and plants with local economic value in order to improve our reference collection.
* Laboratory analyses and AI
We have implemented a complete workflow to process all the samples from Bolivia.We are currently in the process of digitizing the reference collection gathered last field season to train the AI and perform the initial large-scale classifications.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Our recent paper in Nature (Lombardo et al. 2025) shows that a pre-Columbian society in theAmazon developed a sophisticated agricultural engineering system that allowed them to produce maize throughout the year. This work, which was possible thanks to our international network of collaborators including researchers from Universities of Exeter, Nottingham, Oxford, Reading andSouthampton (UK); the University of São Paulo (Brazil) and Bolivian collaborators, contradicts previous theories that dismissed the possibility of intensive monoculture agriculture in the region.
The pre-Hispanic Casarabe society designed and implemented an innovative landscape engineering system, including the construction of extensive drainage canals and farm ponds. This advancement allowed the transformation of flooded tropical savannahs into highly productive fields, thereby driving the development of the “neolithic revolution” in the Amazon. This system enabled them to drain excess water from flooded fields during the rainy season, facilitating agricultural productivity. In addition to the drainage canals, the Casarabe people constructed clusters of farm ponds that served as water reservoirs. These ponds enabled pot-irrigation, allowing maize
cultivation to continue throughout the dry season. This dual water management system enabled at least two harvests of maize per year, ensuring a stable food supply year-round, which was essential for sustaining a relatively large population. We documented the first grain-based agrarian economy in the Amazon, where until now it was believed that agriculture was based on agroforestry polyculture and not on large-scale monocultures.
Our research not only sheds light on thetechnological capabilities of pre-Columbian civilizations but also offers valuable lessons for modernagricultural sustainability. This discovery is a testament to the ingenuity and adaptability of the Casarabe people, who thrived due to their ability to design long-term sustainable agricultural solutions in an adverse environment.