HERCA focuses on SW Amazonia (the Upper Madeira river basin). The region has unique potential to address our research questions. Firstly, it has the longest sequences of human occupation in Amazonia, spanning most of the Holocene. Secondly, it has remarkably diverse environments that supported some of the most diverse pre-Columbian societies in Amazonia. Thirdly, it is a major centre of domestication of numerous globally important crops, especially manioc (cassava), which today feeds over half a billion people. Finally, it has 1500-year, annually-resolved speleothem palaeoclimate records, which are currently being extended to the entire Holocene by Co-Investigator Francisco da Cruz. This sector of Amazonia is therefore ideally suited for examining relationships between cultural change, land use and environmental conditions across space and time. We focus on three study areas within SW Amazonia which encompass a spectrum of environmental conditions, in terms of forest cover, flooding regime, and soil fertility.
- Study Area 1 — Beni Province of Bolivia
This study area is located within a vast, seasonally-flooded, savanna-dominated landscape (the Llanos de Moxos, LM) of the Beni province of Bolivia. It contains over 100 earthen monumental habitation mounds (MM), up to 20 m high and 20 ha in area, comprising pyramidal structures atop platforms built on forested palaeo-river levees. Detailed mapping studies show that MM features form a complex spatial network, connected to each other and adjacent rivers and lakes by a sophisticated transportation and communication network of canals and causeways. Detailed excavations of two of these mounds (‘lomas’ Salvatierra and Mendoza), reveal continuous occupation from ca. 400 to 1400 CE, based upon a rich ceramic record comprising five distinct cultural horizons, each lasting ca. 150 – 200 years. Robust chronologies are derived from 39 (Salvatierra) and 41 (Mendoza) AMS 14C dates (on plant macrofossils, charcoal, bones) on the stratigraphic contexts of ceramic phases. The evidence for monumentality, complex communication and transport networks, and high-status burials, signify a highly stratified society. Archaeobotanical data also reveal the cultivation of a wide range of crops (maize, manioc, squash, peanut, cotton, yams, and palms) throughout this occupation history. Stable carbon isotopic evidence from abundant human skeletal remains indicates a maize-based agricultural economy from 400 to 1100 CE, succeeded by a mixed subsistence economy. Within the open savanna are hundreds of small, isolated forest islands of diverse origin, a few metres in elevation and 10-20 m diameter, three of which have been excavated and shown to be anthropogenic shell mounds built by hunter-gatherers, dating from ca. 8000 – 2000 BCE, among the oldest evidence of human occupation in Amazonia. Crucially, however, a 2,400 year gap in the archaeological record between 2000 BCE and 400 CE currently precludes understanding of the processes by which the stratified MM societies succeeded the shell-mound societies. Furthermore, despite the robust chronologies for the Salvatierra and Mendoza mounds, it is uncertain whether there was a synchronous or progressive abandonment of habitation mounds across the region and whether the most recent AMS 14C dates of 1400 CE reflect the timing of site abandonment or whether younger occupation layers have eroded.