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Easter Island: The mystery of population collapse
Today, Easter Island (also known as Rapa Nui) is a primarily pastoral (grassland) island in the south-eastern Pacific Ocean, some 3,600 kilometres west of Chile. However, less than a thousand years ago, the island supported a tropical forest that included the world’s largest palm tree and dandelions of tree height, and there were at least six species of land birds and 37 species of sea birds.
The story of Easter Island reads like a pre-industrial version of The Lorax. Around 800 AD, Polynesians travelling across the Pacific Ocean arrived on Easter Island. The islanders thrived for several hundred years, with a population estimated at around 10,000 to 15,000 at its peak. The people of the island carved many huge statues (called moai), which remain as sentinels on the island today.
At some point in their history, probably around 1600, the population began to collapse, their numbers quickly dropping to around 2,000. Popular theory is that the islanders cut down all the trees to use as fuel and building materials, and to move the huge statues from the quarry to their positions around the island. As well as using all the precious wood resource, the deforestation resulted in accelerated soil erosion. As the collapse continued, they were plagued by civil war over resources, cannibalism and, towards the final decades of their dwindling civilisation in the 19th century, smallpox brought by explorers, raids by slave ships, and tuberculosis brought by a missionary. However, the exact nature of the initial cause of the sudden collapse and how the community overshot the capacity of the island to sustain life has remained a mystery.
Now, a group of scientists, led by environmental scientist Dr Troy Baisden of GNS Science and plant ecologist Dr Mark Horrocks of Microfossil Research Ltd, plans to test a hypothesis that the Easter Island population overshot the carrying capacity of their aged and weathered volcanic soils. The project is entitled, ‘Was collapse inevitable on Easter Island (Rapa Nui)? Reconstructing a civilisation’s failure’.
Dr Baisden says that often the most valuable possession of ancient civilisations was their soil.
“Easter Island developed a remarkable agricultural civilisation that was capable of erecting stone statues weighing up to 80 tonnes each. However, while the clans on Easter Island were competing to build the most impressive statues, we suspect their populations overshot the carrying capacity of their fragile soils.”
Dr Baisden and his colleagues believe it is possible that soil nutrient depletion coincided with the island’s population reaching a maximum.
If the same situation occurred today, Dr Baisden says the population would either migrate from the island or top-dress with industrial fertilisers.
The scientists from New Zealand, Australia and the US will use a range of scientific techniques to reconstruct the biogeochemistry of collapse to see if it occurred at the same time as soil nutrient depletion. In craters where settlement occurred, they will collect about a dozen sediment cores for analysis in New Zealand. The aim is to precisely determine the timing of changes in plant, animal and human populations, as well as soil fertility.
They will examine plant microfossils such as pollen and starch grains, nitrogen isotopes, the DNA of native forest species and steroid biomarkers from humans, animals and plants.
Dr Baisden says they want to know if Easter Island’s collapse holds lessons for modern society. “If the Easter Islanders overshot the carrying capacity of their soils, there’s a strong parallel to the current financial crisis, in which Wall Street overestimated the returns from the housing market.”
