Climate change, deforestation patterns, freshwater availability and cultural shifts on prehistoric Easter Island (SE Pacific)

Abstract

The remote and isolated Easter Island (Rapa Nui) has been the arena for classic debates on the potential consequences of human overexploitation of natural resources as a microcosmic model for the whole planet. Human-deterministic hypotheses have traditionally been preferred to proposals involving climate changes as drivers of socioecological shifts, especially in relation to the collapse of the ancient Rapanui civilization inhabiting the island before European contact (1722 CE). However, recent paleoecological studies have provided evidence for past climatic shifts, especially droughts, which have stimulated a paradigm shift from deterministic and exclusive views to a more holistic framework that considers both natural and anthropogenic factors as well as their feedbacks and synergies. This paper reviews the latest climatic, ecological and cultural reconstructions of precontact times and evaluates the potential impact of the different drivers on socioecological shifts. Especially noteworthy is the occurrence of some droughts in the last millennium that, coupled with human deforestation, severely affected the access of the prehistoric Rapanui civilization to freshwater but did not compromise the continuity of this ancient culture. Two main hypotheses have been proposed for how the Rapanui bypassed freshwater scarcity. According to the intraisland migration hypothesis, the latest drought recorded (1570-1720 CE) would have led to the abandonment of the former cultural center of the ancient Rapanui civilization (Lake Raraku) to move to Lake Kao, which became the new cultural core. This would have been linked to a profound cultural shift from the moai cult to the Birdman cult. In contrast, the coastal groundwater hypothesis proposes that coastal seeps were the main freshwater source during climatic droughts. These hypotheses are evaluated using the available archaeological and paleoecological evidence, and it is concluded that neither can be rejected; therefore, they could be complementary, rather than exclusive. The continuity of the Rapanui civilization in spite of landscape degradation is a good example of cultural resilience that challenges earlier deterministic explanations and emphasizes human adaptability to changing environments.

The ethnohistory of freshwater use on Rapa Nui (Easter Island, Chile)

“…Water from coastal sources was likely stored using gourds and supplemented with water from the crater lakes, inland springs, lava tubes, taheta and sugarcane. Historical and archaeological evidence suggest it is unlikel that Rapanui relied heavil on water from the island s crater lakes, which challenges recent claims that the crater lakes were the only or most important sources of drinking water (e.g., Rull 2016, 2019Rull et al 2018. The diversity of freshwater procurement strategies and reliance on coastal seeps highlights the successful adaptations and resilience of Rapanui communities to the challenges posed b the island s marginal environment.…”

“…Regarding possible climatically induced droughts, some evidence for sedimentation and vegetation changes from cores taken from the island s crater lakes suggests that a drought possibly occurred from the 1500s to 1700s (e.g., Cañellas-Boltà et al 2013Rull 2016. Rull (2016Rull ( , 2018Rull ( , 2019 argues that this drought would have necessitated population migration to Rano Kau to access its fresh water as other sources, such as coastal seeps, became depleted. While droughts are well documented historically and certainly would have reduced fresh water available from taheta and the crater lakes (e.g., a drought in 2018 left the crater lake at Rano Raraku nearly completely dry), the impact on coastal seeps is uestionable.…”

“…hile Rapa Nui does have a few crater lakes and numerous coastal freshwater seeps (Brosnan et al 2018 errera andCustodio 2008), places to access freshwater resources are relatively scarce, patchy and likely predictable, which makes them good candidates for highly contested and "economically defendable" resources (D son-udson andmith 1978 DiNapoli andMorrison 2017). Indeed, man argue that the distribution of this scarce et vital resource had a major in uence on the structure of Rapanui settlement locations and patterns of competitive interaction (e.g., DiNapoli et al 2019McCo 1976Rull 2016, 2019 ogt and hlem 2018 ogt and Moser 2010). ncertainties and debates persist, however, about the range of freshwater sources used and which sources were likely the most important in the past.…”