Humans, climate or introduced rats – which is to blame for the woodland destruction on prehistoric Rapa Nui (Easter Island)?

Abstract

When the first Polynesian settlers arrived on Rapa Nui, about 70% of the island was covered with dense woodland in which Jubaea palms dominated. Our investigations of extended soil profiles provide evidence that more than 16 million palm trees grew on the island. Nearly all palms were removed by the 16th century. Teeth marks on nutshells of the Jubaea palms from the 13th or 14th centuries attest to the activity of Pacific rats ( Rattus exulans) on Rapa Nui, which were probably imported there by the first Polynesians settlers. Did the rats perhaps prevent the germination of palm seeds and thus the regeneration of the dense palm woodland of Rapa Nui? The results of our investigations refute this hypothesis and support the assumption that people cut the trees. Burned relicts of palm stumps and widespread burned soil layers containing charred endocarps of the palms testify to intensive slash and burn activities between 1250 AD and 1500 AD. However, in one area on Rapa Nui, evidence for regeneration of palm woodland following the first clearing was found. This finding provides evidence against a major rat impact. Furthermore, the Jubaea chilensis woodland in central Chile illustrates that small rodents and Jubaea palms can coexist. We conclude that people, not rats, were the dominant destroyers of the palm woodland on Rapa Nui.