This project National Science Foundation brings together a highly qualified group of international investigators led by Dr. Christopher M. Stevenson to conduct archaeological research on Rapa Nui (Easter Island), Chile. Team members from Rapa Nui New Zealand and the United States will focus on climate change, environmental degradation, and dramatic subsistence changes to develop an empirical assessment of how these may, or may not have, influenced pre-European contact societal collapse on Easter Island. The island is an ideal study area for documenting the dynamic nature of these processes. It is a relatively small isolated island where environmental variables (e.g., rainfall, elevation, temperature, levels of physical erosion, age of volcanic substrates, and soil nutrients) vary significantly over space and time. The archaeological landscape is very well preserved due to low modern population densities. The short period of pre-European contact occupation (ca. AD 1100-1722), and relatively low levels of inter-island contact, facilitate an understanding of why society might have changed with time.
This program of paleo-ecological, landscape and archaeological investigations will develop a highly resolved cultural time-line. The team will use geomorphology and geochemistry to assess the history of Rapa Nui soils and determine the impacts of erosion and sustained agriculture. The morphological and functional variation of various classes of gardens will be addressed through an analysis of environmental setting, remotely sensed satellite data, and precise geographical locations. We will Obsidian hydration dating in conjunction with radiocarbon dating will be used to determine the age of agricultural activities. Using a series of GIS and ecodynamic models these data will be analyzed to achieve a robust and comprehensive understanding of how, when and why Rapa Nui terrestrial resources changed through time and the impact that this might have had on prehistoric societal change.
The research focuses on Rapa Nui, yet the issues addressed are global. Rapa Nui is often depicted as a model for global environmental degradation. Relatively simplistic linkages have been made between agricultural activities and processes of deforestation, physical erosion, and societal collapse. Utilizing an interdisciplinary team with innovative theoretical and methodological approaches allows scientists to advance understanding of change on Rapa Nui and the suitability of this isolated small island as a model of the world. The research involves empirically measuring a limited number of variables to facilitate complex modeling of the island ecology. This effort will establish whether changes in terrestrial resources were a critical factor in a pre-European contact societal collapse. The Rapa Nui context provides an excellent comparison to continental, large archipelago, and small Pacific island settings and fills a critical gap in understanding the linkages and relationships between social and natural processes. The research will contribute to the development of the dynamic modeling of past human activity. These findings will enable social scientists to understand the impact of people both on the local island level and the wider global scale.
The major goal of this project was to examine how a prehistoric population responded strategically to the process of long-term environmental degradation brought on by human-induced changes to the landscape and surface ecology. To shed light upon behavioral responses, we selected the case example of Rapa Nui (Easter Island, Chile) to evaluate a long-term debate about resiliency of that population and its response to island wide deforestation and higher agricultural risk that made successful farming increasingly difficult. The core aspect of the debate is whether or not the ancient Rapa Nui population grew to such a size where the demands of feeding a large population exceeded the productive capacity of the farming economy and reached a point where there was a human demographic collapse that occurred prior to European contact in the 18th century (AD 1722). It has been well-established that a drastic loss of population occurred in the mid-19th century as a result of the lack of biological immunity from European pathogens such as syphilis, smallpox and tuberculosis. However, the demographic trends in the centuries preceding this final catastrophic event are less clear and some scholars have argued that Rapa Nui society was resilient and unaffected until Western contact. To evaluate these two scenarios our research team sought to reconstruct the prehistoric population profile from the period shortly after human settlement of the island in AD1100 until AD 1860 by applying regional absolute dating to a large number of archaeological artifacts and features. In addition, we supported our time sensitive paleodemographic reconstruction by modeling the Rapa Nui agricultural system, focusing on the inputs and limitations dictated by rainfall, soil nutrients, and fertility of the geological substrate, to estimate the number of persons that could have been supported on a volcanic island that is 65 square miles in size. We developed a population growth curve for Rapa Nui based upon the completion of 467 obsidian hydration dates from six 1km2 survey areas. The summed statistical probabilities for the obsidian dates indicated that a small number of persons had settled on Rapa Nui by AD 1200. In the centuries to follow, the growth of the population was rapid and population levels peaked in the early AD1500s, declined and rebounded, only then to plummet in the middle AD1600s. Population trends within each survey area showed slight deviations from the island wide pattern. This reflected population dynamics associated with specific regions. It was clear from this variability in population densities during the following post-collapse AD 1700-1860 period that the latter part of Rapa Nui prehistory was undergoing a significant and lasting demographic rearrangement. What had caused this process was initially unclear but we hypothesized there had been a withdrawal from intensive, surplus-driven, agricultural production. The fact that population peaked a century earlier in the AD 1500-1600s, may have been the turning point. At this time period a limit to the intensification of dry-land farming economy was reached and high population levels could not be sustained. To examine the environmental constraints on agricultural intensification we conducted island-wide soil sampling of soil horizons on distinct geological substrates at different elevations, and within and outside of prehistoric rock gardens. A nutrient analysis of these different locations demonstrated that Rapa Nui agriculture was constrained by leached soils at higher elevations (>300m) and by numerous old and leached substrates where volcanic ash derived soils restricted the amount of available phosphorus that plants could use for growth. A rain shadow effect on the western side of the island that reduced precipitation was also identified by our weather stations installed around the island. The simulation of these parameters on sweet potato productivity showed that high yields could be achieved only with large plot farming and full population involvement (including women). Our conclusion was that a large, surplus driven economy could not have been sustained once populations were high and land became nutrient degraded and of limited availability. Our research effort involved a Rapa Nui co-investigator and team collaborators included under-represented groups such as women and Pacific Islanders. The field teams included many Rapa Nui indigenous residents and at times representatives from the National Park Service of Chile. Rapa Nui student training was part of the investigation and involved laboratory work in the United States in archaeological methods, artifact chemical analysis, and the hydration dating of obsidian. A present, three publications in peer-reviewed archaeological journals have been completed and three more are in preparation.
