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

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.