CR2025_51 Human-environment relationships in the Bolivian Amazon since the middle Holocene

Lead Supervisor: Frank Mayle, Department of Geography and Environmental Sciences, University of Reading

Email: f.mayle@reading.ac.uk

Co-supervisors: Stuart Black, Department of Geography and Environmental Sciences, University of Reading; Chris Vane, British Geological Survey; Suzanne Maclachlan, National Oceanography Centre; Siwan Davies, Department of Geography, Swansea University

This project seeks to improve understanding of past human-environment relationships in Amazonia, over centennial-millennial timescales. Amazonia’s long-term history is of interest to ecologists, archaeologists and climate scientists alike.  Once thought to be a virgin wilderness, home to sparse semi-nomadic tribes, recent archaeological and palaeoecological discoveries are revealing complex sedentary societies which domesticated their surroundings (Peripato et al. 2023) and helped shape patterns of rainforest biodiversity we see today (Levis et al. 2018).  Furthermore, an expanding network of speleothem records is starting to unravel the complexities of South America’s climate history (Della Libera et al. 2022).

Nevertheless, despite these advances, major uncertainties remain over the nature of these past human-environment relationships due to a scarcity of palaeoclimate and palaeoecological records in Amazonia, which can be hundreds of kilometres away from each other and from the nearest archaeological sites, hampering efforts to establish robust linkages between these different types of data (de Souza et al. 2019).

This project focuses on sediment cores collected from two ox-bow lakes (lagunas San Jose and Tumichucua) near the town of Riberalta in Bolivia, SW Amazonia, dating to 9,000 and 6,000 years BP (before present), respectively.  They are ideal for examining past human-environment relationships because: a) they are located among the hundreds of geometric earth-works (fig. 1) built by the pre-Columbian (pre-1492) ‘geoglyph’ culture (ca. 450 BC and 950 AD) (de Souza et al. 2018; Peripato et al. 2023; Saunaluoma and Schaan 2012) enabling robust correlation between archaeological and sediment core data, b) the surrounding forests were at the epicentre of the late 19^th century rubber boom (Van Valen 2013), which may have had significant rainforest impacts (Nascimento et al. 2024), and c) they have unusually high sedimentation rates (10-15 cm/yr) – ideal for capturing rapid climate and land-use changes, and ecological impacts and responses.   These sediment cores therefore provide a rare opportunity to robustly cross-correlate palaeo-environmental, archaeological, and historical archive data to investigate past human-environment relationships.

The overall aim is to determine the nature of past human-environment relationships in northern Amazonian Bolivia since the early-mid Holocene.

Specific research questions:

1. What was the impact of mid-Holocene drought (ca. 8,000 – 4,000 yr BP) upon Amazon rainforests of northern Bolivia? – e.g. a) forest-savanna biome turnover? b) increase in fire frequency? c) forest stability, but floristic turnover?
2. What impact did the pre-Columbian geoglyph culture have upon their rainforest environment? – e.g. a) evidence of deforestation for earthwork construction or agriculture? b) evidence of altering the biodiversity – selecting useful plant species (e.g. edible palms) over less useful species? c) evidence of plant domestication/crop cultivation (e.g. cacao, maize, manioc)? d) use of fire?
3. What was the impact (if any) of the Medieval Climate Anomaly (MCA, 900-1250 AD) and Little Ice Age (LIA, 1450-1850 AD) upon: a) rainforest structure and floristic composition, b) fire regime, c) the pre-Columbian geoglyph culture?
4. What was the impact of the rubber boom at the turn of the 20^th century (1875 – 1910 AD)? – e.g. scale of forest clearance and burning associated with the massive influx of settlers and urban growth (e.g. Riberalta)?
5. What legacy (if any) of these past disturbances (whether climate or human driven) remains in today’s rainforests of the region?

Note: The student may not necessarily wish to address all these questions, but instead a sub-set of them, depending on their interests.

The following analyses will be undertaken on the sediment cores:

1. Pollen and charcoal analyses to reconstruct vegetation and fire histories (supervised by Mayle at Reading). 2. Plant lipid extraction (supervised by Vane at the BGS) for C- and H-isotope analysis (supervised by Black at Reading) as a palaeo-precipitation proxy. 3. High-resolution elemental analysis using the ITRAX facility at NOC-BOSCORF (supervised by MacLachlan) to reconstruct limnological changes and catchment erosion.  4. Lead-210 dating to pinpoint the rubber boom (NOC, supervised by MacLachlan) and C-14 dating (NERC facility) for older sediments.  5. Explore presence of crypto-tephra (volcanic ash) as a potential chronological marker (supervised by Davies at Swansea).

These palaeoenvironmental data will be cross-correlated with previously published archaeological data from nearby geoglyph excavations, as well as historical written archives of the rubber boom.

Training opportunities: 

The student will receive training in a diverse range of complementary palaeo-environmental proxies, as outlined above.

Furthermore, although the cores have already been collected, there will be an opportunity for a fieldtrip to Bolivia to collect additional samples and gain important field skills (e.g. plant identification), in collaboration with Bolivian project partner – the Noel Kempff Mercado Natural History Museum, Santa Cruz. 

Student profile: 

This project would be suitable for students with at least an upper second class Bachelors degree in an environmental or physical science subject, such as: physical geography, biological science, or environmental/scientific archaeology.  Good numerical/quantitative skills are required, and some experience with labwork and fieldwork would be beneficial.

References:

• Della Libera, M.E., et al. (2022). Paleoclimatic and paleoenvironmental changes in Amazonian lowlands over the last three millennia.  Quaternary Science Reviews, 279, 107383.
• De Souza, J., et al. (2018). Pre-Columbian earth-builders settled along the entire southern rim of the Amazon.  Nature Communications, 9(1), 1125.
• De Souza, J., et al. (2019). Climate change and cultural resilience in late pre-Columbian Amazonia.  Nature Ecology and Evolution, 3(7), 1007-1017.
• Levis, C., et al. (2018). How people domesticated Amazonian forests.  Frontiers in Ecology and Evolution, 5, 171.
• Nascimento, M., et al. (2024). Indigenous and colonial influences on Amazonian forests.  Plants People Planet, 6, 803-823.
• Peripato, V., et al. (2023). More than 10,000 pre-Columbian earthworks are still hidden throughout Amazonia.  Science, 382(6666), 103-109.
• Saunaluoma, S., and Schaan, D. (2012). Monumentality in Western Amazonian formative societies: geometric ditched enclosures in the Brazilian state of Acre.  Antiqua, 2:e1.
• Van Valen, G. (2013). Indigenous agency in the Amazon : the Mojos in liberal and rubber-boom Bolivia, 1842–1932.  The University of Arizona Press.