Easter Island - Ecology

Ecology

Easter Island, together with its closest neighbor, the tiny island of Isla Sala y Gómez 415 kilometers (258 mi) further east, is recognized by ecologists as a distinct ecoregion, the Rapa Nui subtropical broadleaf forests. The original subtropical moist broadleaf forests are now gone, but paleobotanical studies of fossil pollen and tree moulds left by lava flows indicate that the island was formerly forested, with a range of trees, shrubs, ferns, and grasses. A large extinct palm, Paschalococos disperta, related to the Chilean wine palm (Jubaea chilensis), was one of the dominant trees as attested by fossil evidence. Like its Chilean counterpart it probably took close to 100 years to reach adult height. The Polynesian rat, which the original settlers brought with them, played a very important role in the disappearance of the Rapanui palm. Rat teeth marks can be observed in 99% of the nuts found preserved in caves or excavated in different sites, indicating that the Polynesian rat impeded the palm's reproduction. That, and the clearance of the palms to make the settlements, led to their extinction almost 350 years ago. The toromiro tree (Sophora toromiro) was prehistorically present on Easter Island, but is now extinct in the wild. However the Royal Botanic Gardens, Kew and the Göteborg Botanical Garden are jointly leading a scientific program to reintroduce the toromiro to Easter Island. With the palm and the toromiro virtually gone, there was considerably less rainfall as a result of less condensation. After the island was used to feed thousands of sheep for almost a century, by the mid 1900s the island was mostly covered in grassland with nga'atu or bulrush (Schoenoplectus californicus tatora) in the crater lakes of Rano Raraku and Rano Kau. The presence of these reeds, which are called totora in the Andes, was used to support the argument of a South American origin of the statue builders, but pollen analysis of lake sediments shows these reeds have grown on the island for over 30,000 years. Before the arrival of humans, Easter Island had vast seabird colonies containing probably over 30 resident species, perhaps the world's richest. Such colonies are no longer found on the main island. Fossil evidence indicates five species of landbirds (two rails, two parrots and a heron), all of which have become extinct.

The immunosuppressant drug sirolimus was first discovered in the bacterium Streptomyces hygroscopicus in a soil sample from Easter Island. The drug is also known as rapamycin, after Rapa Nui. It is now being studied for extending longevity in mice.

Trees are sparse, rarely forming natural groves, and it has been argued whether native Easter Islanders deforested the island in the process of erecting their statues, and in providing sustenance for an overpopulated island. Experimental archaeology demonstrated that some statues certainly could have been placed on "Y" shaped wooden frames called miro manga erua and then pulled to their final destinations on ceremonial sites. Other theories involve the use of "ladders" (parallel wooden rails) over which the statues could have been dragged. Rapanui traditions metaphorically refer to spiritual power (mana) as the means by which the moai were "walked" from the quarry. Recent experimental recreations have proven that it is fully possible that the moai were literally walked from their quarries to their final positions by use of ropes, casting doubt on the role that their existence plays in the environmental collapse of the island.

Given the island's southern latitude, the climatic effects of the Little Ice Age (about 1650 to 1850) may have exacerbated deforestation, although this remains speculative. Many researchers point to the climatic downtrend caused by the Little Ice Age as a contributing factor to resource stress and to the palm tree's disappearance. Experts, however, do not agree on when exactly the island's palms became extinct.

Jared Diamond dismisses past climate change as a dominant cause of the island's deforestation in his book Collapse which assesses the collapse of the ancient Easter Islanders. Influenced by Heyerdahl's romantic interpretation of Easter's history (as he acknowledges in chapter 2 of Collapse), Diamond insists that the disappearance of the island's trees seems to coincide with a decline of its civilization around the 17th and 18th centuries. He notes that they stopped making statues at that time and started destroying the ahu. But the link is weakened because the Bird Man cult continued to thrive and survived the great impact caused by the arrival of explorers, whalers, sandalwood traders, and slave raiders.

Midden contents show that the main source of protein was Tuna and Dolphin. With the loss of the trees, there was a sudden drop in the quantities of fish bones found in middens as the islanders lost the means to construct fishing vessels, coinciding with a large increase in bird bones. This was followed by a decrease in the number of bird bones as birds lost their nesting sites or became extinct. A new style of art from this period shows people with exposed ribs and distended bellies, indicative of malnutrition, and it is around this time that many islanders moved to living in fortified caves and the first signs of warfare and cannibalism appear. Soil erosion because of lack of trees is apparent in some places. Sediment samples document that up to half of the native plants had become extinct and that the vegetation of the island drastically altered. Polynesians were primarily farmers, not fishermen, and their diet consisted mainly of cultivated staples such as taro root, sweet potato, yams, cassava, and bananas. With no trees to protect them, sea spray led to crop failures exacerbated by a sudden reduction in fresh water flows. There is evidence that the islanders took to planting crops in caves beneath collapsed ceilings and covered the soil with rocks to reduce evaporation. Cannibalism occurred on many Polynesian islands, sometimes in times of plenty as well as famine. Its presence on Easter Island (based on human remains associated with cooking sites, especially in caves) is supported by oral histories.

Benny Peiser noted evidence of self-sufficiency when Europeans first arrived. The island still had smaller trees, mainly toromiro, which became extinct in the 20th century probably because of slow growth and changes in the island's ecosystem. Cornelis Bouman, Jakob Roggeveen's captain, stated in his logbook, "... of yams, bananas and small coconut palms we saw little and no other trees or crops." According to Carl Friedrich Behrens, Roggeveen's officer, "The natives presented palm branches as peace offerings." According to ethnographer Alfred Mètraux, the most common type of house was called "hare paenga" (and is known today as "boat house") because the roof resembled an overturned boat. The foundations of the houses were made of buried basalt slabs with holes for wooden beams to connect with each other throughout the width of the house. These were then covered with a layer of totora reed, followed by a layer of woven sugarcane leaves, and lastly a layer of woven grass. There were reports by European visitors who said they had seen "boles of large palm trees". Peiser claims that these reports indicate that large trees existed at that time, which is perhaps contradicted by the Bouman quote above. Plantations were often located further inland, next to foothills, inside open-ceiling lava tubes, and in other places protected from the strong salt winds and salt spray affecting areas closer to the coast. It is possible many of the Europeans did not venture inland. The statue quarry, only one kilometre from the coast with an impressive cliff 100 m (330 ft) high, was not explored by Europeans until well into the 19th century.

Easter Island has suffered from heavy soil erosion in recent centuries, perhaps aggravated by agriculture and massive deforestation. This process seems to have been gradual and may have been aggravated by sheep farming throughout most of the 20th century. Jakob Roggeveen reported that Easter Island was exceptionally fertile. "Fowls are the only animals they keep. They cultivate bananas, sugar cane, and above all sweet potatoes." In 1786 Jean-François de La Pérouse visited Easter Island and his gardener declared that "three days' work a year" would be enough to support the population.

Rollin, a major in the Pérouse expedition, wrote, "Instead of meeting with men exhausted by famine... I found, on the contrary, a considerable population, with more beauty and grace than I afterwards met in any other island; and a soil, which, with very little labor, furnished excellent provisions, and in an abundance more than sufficient for the consumption of the inhabitants."

According to Diamond, the oral traditions (the veracity of which has been questioned by Routledge, Lavachery, Mètraux, Peiser and others) of the current islanders seem obsessed with cannibalism, which he offers as evidence supporting a rapid collapse. For example, he states, to severely insult an enemy one would say, "The flesh of your mother sticks between my teeth." This, Diamond asserts, means the food supply of the people ultimately ran out. Cannibalism, however, was widespread across Polynesian cultures. Human bones have not been found in earth ovens other than those behind the religious platforms, indicating that cannibalism in Easter Island was a ritualistic practice. Contemporary ethnographic research has proven there is scarcely any tangible evidence for widespread cannibalism anywhere and at any time on the Island. The first scientific exploration of Easter Island (1914) recorded that the indigenous population strongly rejected allegations that they or their ancestors had been cannibals.