The Fall of Easter Island: Ecological Destruction or Rats? by Amber Colosimo, Jade Woolsey, and Doan Truong Those of us who know anything about Easter Island tend to only know anything in regards to the many monumental stone statues, called moai, built by the ancient Rapanui people that attract thousands of tourist from around the world each year. But what many don t know, is that during the time that the Rapanui people inhabited the island, they experienced a gradual decline of their natural resources, and in turn, a weakening of their civilization. What exactly happened to this culture is still a subject of much debate. Some argue that ecological destruction created by the Rapanui people themselves squandered all of their natural resources, others are now suspecting that an infestation of rats was is really to blame for the fall of Easter Island. Which is really the culprit for the fall of Eastern Island Civilization?
Characteristics and Background Information of Easter Island The flora and fauna of Rapa Nui are limited. Other than chickens and rats, there are few land vertebrates. Many of the species of birds that once inhabited the island are now locally extinct. Large palm trees from the genus Jubaea long covered much of the island, but they, too, eventually disappeared. A recent survey of the island found only 48 different kinds of native plants, including 14 introduced by the Rapanui. Ecological Destruction Scholars have argued that the Rapanui culture and society rose and fell because of deforestation. In 2003, geologist Dan Mann and his colleagues studied the radiocarbon dates from bits of charcoal found in soils across the island then concluded that the deforestation took place between 1200 and 1650 AD.
Figure 1. Two segments of soil profile in South West Poike. Summarized stratigraphy: (1) Weathered volcanic bedrock. (2) Cone of palm root molds. (3) Pre- clearing garden soil. (4) Accumulation of charcoal from a burned palm stump containing in situaggregates of burned soil. Result of intentional burning by humans. (5) Charcoal layer. Charcoal layers are best preserved in concave down-slope sections. (6) Post-clearing garden soil with planting pits. (7) Fine layered sediments, resulting from post-clearing sheet erosion of unprotected soil. The graph shows the evidence for slash and burn. Soil profiles in many areas of Rapa Nui provide evidence of fires in the former palm woodland. Over large areas, a single layer of charcoal and ashes several millimeters in thickness can be found deep below the recent
surface and on top of the prehistoric garden soils that belong to the period of woodland gardening. The extensive distribution of charcoal layers can only have one explanation: widespread fires in the woodland of Rapa Nui. Numerous remains of burned palm stumps in the soils at several locations on the island suggest that the burning was caused by humans, not by natural events. Many trees had been cut down to make room for agriculture; others had been burned for fire and used to transport statues across the island. John Flenley, who with Paul Bahn co-authored The Enigmas of Easter Island, took sample from several lake beds formed in the island s volcanic craters and found evidence of charcoal. He concluded that the Rapanui had certainly burned the vegetation which was even more destructive. By identifying 78,000 bits of burned wood from radiocarbon-dated ovens and middens, Orliac and Orliac recognized more than 20 other tree and woody plant species exterminated during human settlement. After which the islanders had to burn grasses and sedges instead of wood for fuel. Around A.D. 1280, the islanders began cutting the palms, removing the trunks (presumably for timber), and burning the debris, as shown by a radiocarbon-dated charcoal layer, burned roots and palm nuts, and burned palm stumps chopped off near the ground, but no large pieces of trunk wood at these sites. The loss of the palm canopy exposed soil to heating, drying, wind, and rain. The end of the forest brought other huge losses for islanders. resources for food and building were now gone. When Captain James Cook visited Easter Island in 1774, he saw no trees taller than about 10 feet.
It was this Easter Island society that built the famous statues and hauled them around the island using wooden platforms and rope constructed from the forest. The construction of these statues peaked from 1200 to 1500 AD, probably when the civilization was at its greatest level. However, pollen analysis shows that at this time the tree population of the island was rapidly declining as deforestation took its toll. Rats, not men, were to blame for the fall of Easter Island When archaeologist Terry Hunt first began doing research on Easter Island, he expected to confirm the story outlined by Jerry Diamond as an self-induced environmental morality tale. Instead, he found evidence that countered the underlying timeline and overall data. Radiocarbon dating related to paleoenvironmental data point to a different explanation for what happened on the island, and the story is a more complex than previously thought. The Island was a paradise for Rats Archaeologist Terry Hunt of the University of Hawai'i may indicate a different version of events. In 2000, Hunt, archaeologist Carl Lipo of California State University, Long
Beach, and their students began excavations at Anakena, a white sandy beach on the island's northern shore. The researchers believed Anakena would have been an attractive area for the Rapanui to land, and therefore may be one of the earliest settlement sites. In the top several layers of their excavation pit, the researchers found clear evidence of human presence: charcoal, tools even bones, some of which had come from rats. Underneath they found soil that seemed absent of human contact. This point of first human interaction, they figured, would tell them when the first Rapanui had arrived on the island. Hunt sent the samples from the dig to a lab for radiocarbon dating, expecting to receive a date around 800 A.D., in keeping with what other archaeologists had found. Instead, the samples dated to 1200 A.D. This would mean the Rapanui arrived four centuries later than expected. The deforestation would have happened much faster than originally assumed, and the human impact on the environment was fast and immediate. Hunt suspected that humans alone could not destroy the forests this quickly. In the sand layers, he found a potential culprit a plethora of rat bones. Scientists have long known that when humans colonized the island, so too did the Polynesian rat, having hitched a ride either as stowaways or sources of food. However they got to Easter Island, the rodents found an unlimited food supply in the lush palm trees, believes Hunt, who bases this assertion on an abundance of rat-gnawed palm seeds. It is not a new observation that virtually all of the shells housing palm seeds found in caves or archaeological excavations of Rapa Nui show evidence of having been gnawed on by rats, but the impact of rats on the island's fate may have been underestimated.
Evidence from elsewhere in the Pacific shows that rats have often contributed to deforestation, and they may have played a major role in Rapa Nui's environmental degradation as well. Archaeologist J. Stephen Athens of the International Archaeological Research Institute conducted excavations on the Hawaiian Island of Oahu and found that deforestation of the Ewa Plain took place largely between 900 and 1100 A.D. but that the first evidence of human presence on this part of the island was not until about 1250 A.D. There were no climatic explanations for the disappearance of palm trees, but there was evidence that the Polynesian rat, introduced by the first human colonists, was present in the area by about 900 A.D. Athens showed that it was likely rats that deforested large areas of Oahu. Paleobotanists have demonstrated the destructive effect of rats on native vegetation on a number of other islands as well, even those as ecologically diverse as New Zealand. In areas where rats are removed, vegetation often recovers quickly. And on Nihoa Island, in the northwest Hawaiian Islands, where there is no evidence that rats ever became established, the island's native vegetation still survives despite prehistoric human settlement. Whether rats were stowaways or a source of protein for the Polynesian voyagers, they would have found a welcoming environment on Rapa Nui an almost unlimited supply of high-quality food and, other than people, no predators. In such an ideal setting, rats can reproduce so quickly that their population doubles about every six or seven weeks. A single mating pair could thus reach a population of almost 17 million in just over three years. On Kure Atoll in the Hawaiian Islands, at a latitude similar to Rapa Nui but with a
smaller supply of food, the population density 418 American Scientist, Volume 94 of the Polynesian rat was reported in the 1970s to have reached 45 per acre. On Rapa Nui, that would equate to a rat population of more than 1.9 million. At a density of 75 per acre, which would not be unreasonable given the past abundance of food, the rat population could have exceeded 3.1 million. Under ideal conditions, rats reproduce so rapidly that their numbers double every 47 days; unchecked, a single mating pair can produce a population of nearly 17 million in just over three years. Research in the Northwest Hawaiian Islands shows that when available food is taken into account, populations can reach 75 to the acre.