Anthropologist Terry Hunt is digging up intriguing evidence about causes of deforestation on Easter Island and raising questions about the role of rats in the Pacific

Throughout their voyages across the Pacific, ancient Polynesians were accompanied by rats. Anthropologists believe these rodents either stowed away on sailing vessels or, more likely, were brought along as a source of protein for the human colonists. Until recently, however, the ecological and societal impact of these well-traveled rodents had come under scant consideration. In March 2006, Terry Hunt, a professor of anthropology and an archaeology specialist at UH Mānoa, published a paper in the journal Science asserting that colonization of Rapa Nui likely occurred around 1200 AD. This date was far later than that posited by the prevailing scholarly view. Most scholars believed that colonists had arrived 400 to 800 years earlier.

A key finding of Hunt’s paper was that rats may have played a more significant role in the well documented rapid deforestation of Rapa Nui, or Easter Island, than was previously thought. In September 2006, Hunt published a more detailed examination of the state of the current evidence on Rapa Nui deforestation in The American Scientist, including further discussion of the role of rats and how the activity of the rodents fits with current evidence. Hunt also has an article going to press in the Journal of Archaeological Science addressing the rat issue.

According to Hunt, upon arrival in Rapa Nui the rats feasted on the seeds of endemic trees, in particular on the seeds of Jubaea palms that were the primary forest cover of the island. The mushrooming rodent population quickly consumed greater and greater numbers of seeds. This would have effectively halted the palms’ reproduction, leading to the disappearance of the forest. Hunt’s assertion directly questioned the prevailing wisdom that the human inhabitants of Rapa Nui, who call themselves Rapanui, had deforested the island themselves. Hunt believes that researchers to date may have greatly underestimated the environmental impact of rats in island ecosystems across the Pacific. “Rats could be introduced to other islands without really devastating [them], but as you get into the remote parts of the Pacific, the impacts would likely have been much greater,” says Hunt.

Hunt’s Rapa Nui articles have caused a firestorm in the world of archaeology. The case of Rapa Nui had long been held up as an example of the sad inability of humans to rein in damaging behaviors leading to societal demise. In his book, Collapse: How Societies Choose to Fail or Succeed, the noted geographer and physiologist Jared Diamond cited Rapa Nui as one of the most prominent examples of what happens when societies choose to fail. He built his cautionary tale on the assumption, generally accepted among archaeologists and anthropologists, that a small group of Polynesian settlers colonized Rapa Nui around 800 to 900 A.D. From these early arrivals the island’s population slowly increased.

Then, around 1200 A.D., population density hit a critical mass, causing significant stress to natural resources on Rapa Nui. At the same time, the Rapanui were building hundreds of moai, megalithic statues that dot the island today. Most rest on massive platforms of stone, called ahu. Scientists still have limited understanding of the social purpose of the moai. Diamond asserted that the Rapanui cut down large numbers of trees to build wooden sleds to transport the moai from the quarry, deforesting Rapa Nui over several centuries. The deforestation accelerated soil erosion and turned fertile lands into windswept wastelands. This tragedy plunged the Rapanui’s complex society into chaos, war, and, ultimately, extended decline. Diamond and others have posited that, over four or five centuries, the population of Rapa Nui quickly plummeted from a peak of 15,000 to approximately 3,000 as a result of this chain of events.

Hunt initially accepted this view. He began to have doubts after an extensive dig at Anakena Beach on Rapa Nui, the easiest landing point on the island and likely the site of early settlement. He found clear signs of human colonization – charcoal, rat bones, and flaked obsidian – embedded in an ancient clay soil at the base of Anakena’s stratified sand dunes. Below that, Hunt found no signs of human presence. He did find molds in the clay created by the roots of the native Jubaea palms, implying that the palms existed in greater numbers immediately before man’s arrival. When Hunt received word from the radiocarbondating laboratory that his samples from the bottom layers dated back only to 1200 AD, he began to consider whether colonization had actually occurred centuries later than Rapa Nui scholars had previously supposed. Earlier radiocarbon samples had implied similar dates but none were as technically sound as those Hunt retrieved and analyzed.

This did not change the date of deforestation; other researchers had determined fairly conclusively that the number of trees on the island went into a steep decline soon after 1200 AD. The new radiocarbon evidence, combined with clear evidence of rat consumption of Jubaea seeds, caused Hunt to ponder whether the rodents’ impact could have been a more important factor in the disappearance of Rapa Nui’s forests than generally believed, and whether the peak Rapanui population had perhaps never risen above roughly 3,000. Signs of deforestation should not have become apparent as quickly as they did if a small number of settlers were the only source of the island’s deforestation.

Hunt’s hypothesis represents a sea change in thought but one that does build on other evidence. On the island of Oahu in the Hawaiian Islands, researchers from the International Archaeological Research Institute (IARI) in Honolulu uncovered in recent years what they believed was evidence that rats had contributed to a significant decline in palm trees on the Ewa Plain, an area that was largely deforested soon after the arrival of Polynesians on the islands. Likewise, digs by paleo-ecologists from IARI produced pollen evidence implying rapid decline among certain types of palm trees in marshes on the Windward Coast of Oahu. “The idea of my article is that we need to take a closer look at what rats can do. Rats might be able to do many of the things that we’ve said humans had done, and maybe we’ve overlooked this,” says Hunt. With Donald Drake, a UH professor of botany, Hunt has arranged a conference in the spring of 2007 that will bring together experts in island ecology, geography, and anthropology to more closely examine the impacts rodents may have on islands.

At the same time, other long held beliefs about Rapa Nui have come into question. Recent studies on Rapa Nui have concluded that the soil was always of poor quality. And, according to Hunt, the early Rapanui used rock mulching techniques (packing fields of crops with rocks) to reduce soil erosion and protect plantings, implying that soil erosion due to high winds was always a problem on the island. Ultimately, Hunt believes, it will become clear that there never was a self-induced population crash on Rapa Nui and that, in part due to the prolific rats, the island was never able to support more than about 3,000 inhabitants. Further, he believes that diseases brought by European explorers were the primary cause of population collapse on Rapa Nui, rather than rats or deforestation.

Not all scholars have accepted Hunt’s hypotheses. Diamond, for his part, declared in a newspaper interview that Hunt was wrong and that rats had arrived on every other Polynesian island and nowhere else did the forest go into rapid decline. Hunt points to evidence for rats and deforestation in Hawai‘i, and counters that Pacific islands are not all the same, and some, like Rapa Nui, may be far more vulnerable to rats than others. Many skeptical Rapa Nui experts believe Hunt may be onto something but does not yet have sufficient physical evidence to convincingly make his claim. Regardless, Hunt’s work has forced scientists to refocus their efforts on Easter Island. “I believe Terry’s real accomplishment, at a minimum, has been to shift on whose shoulders the burden of proof lies. In my view, the burden of proof now rests with the early settlement believers. They now will have to go out and, by dint of unequivocal new data, demonstrate that their position is valid,” says J. Stephen Athens, senior archaeologist at IARI.

Hunt and his colleagues are pressing forward with more research to corroborate his initial findings. In early January he and colleagues from New Zealand plan to take new cores from the wet sediment on the banks of three Rapa Nui lakes. Hunt hopes they will find chewed nuts that can be dated to the same time period as the previous Anakena beach findings, corroborating Hunt’s rodent thesis and, possibly, further supporting the thesis of the later colonial arrival. He hopes that his work will induce archaeologists to take a second and third look at long-held beliefs. “Archaeology needs to be more scientific. We have the obligation to try harder to prove ourselves wrong and learn something from that,” says Hunt. “A lot of archaeologists are tied to the ideas, not the evidence.”

Terry Hunt is a faculty member in the Department of Anthropology at UH Mānoa. His specialty is Pacific Island archaeology. He has conducted archaeological field work and related research in Hawai‘i, Samoa, Fiji, Rapa Nui (Easter Island), New Zealand, and Papua New Guinea.

   Rapa Nui Photos: Terry Hunt, UH Department of Anthropology