Thresholds Database > Social and ecological collapse, Easter Island

Background

Easter Island was settled around 800AD. It was covered by a tropical forest, with six species of land birds and 37 species of breeding sea birds. The trees were felled for firewood, making gardens, building canoes and for rolling and levering the giant statues carved on the island. By 1600 A.D. all of the trees, land birds and all but one of the sea birds were extinct.

Alternate Regimes

1. Tropical forest, land and sea birds

2. Eroded landscape, grassland (no trees), extinction of land and sea birds

Mechanism

This example shows a shift in both the ecological system (native flora and fauna) and the social system (human population, social norms). The population grew to an estimated high of around 10,000 people. The level of forest felling exceeded the rate of regeneration. Without trees, soil erosion occurred, the statues could no longer be constructed and canoes, used for catching large fish and mammals for food, could no longer be built. The society resorted to cannibalism and the population collapsed to an estimated 2,000 people.

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Addendum:
A 2006 paper by Terry Hunt and Sergio Rapu-Haoa suggests an alternate mechanism.
This competing mechanism illustrates the difficulty of using indirect information and reconstructed 'models' of system dynamics.

The paper was by Hunt and Rapu-Haoa, "What (really) happened on Rapa Nui? Ecological Catastrophe and Cultural Collapse." suggests that ecological collapse (and the decline of the palm trees) started long before serious human settlement (1200 CE) and was caused by rats (who exploded on Rapa Nui ca. 900 CE). Most shells excavated show signs of rats gnawing. Hunt and Rapu-Haoa also pointed out that the first Dutch explorers in the 17th century had recorded seeing many trees and a healthy population. The population had stabilized by 1600 and had adapted to the rat-caused ecological decline. The real population decline came after sustained European contact which gave diseases to the islanders and took those who did not succumb as slaves between the 18th and 19th centuries. So Easter Island is not a good example for a proven ecological threshold as evidence shows that humans adapted to the ecological changes that were taking place between first contact (900 CE) and colonization (1200 CE) and successfully managed a stable population and sustainable agriculture.

Hunt and Rapu-Haoaart's paper was of the 2006 AAA Session: Exploring Scholarly and
Best-Selling Accounts of Social Collapse and Colonial Encounters, Chair: Patricia
McAnany and organized by Norman Yoffee and Patricia McAnany.

Management Decisions in Each Regime