Vegetation changes and human settlement of Easter Island during the last millennia: a multiproxy study of the Lake Raraku sediments
Vegetation changes and human settlement of Easter Island during the last millennia: a multiproxy study of the Lake Raraku sediments
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DOI：
10.1016/j.quascirev.2013.04.004
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发表时间：
2013-07-15
影响因子：
4
通讯作者：
Giralt, Santiago
中科院分区：
文献类型：
--
作者：
Canellas-Bolta, Nuria;Rull, Valenti;Giralt, Santiago
早期对复活节岛湖泊沉积物的孢粉学研究表明，该岛最近经历了一次突然的草原取代以棕榈树为主的森林，这被解释为土著人民的森林砍伐。然而，现有的证据是不确定的，因为在大多数研究的沉积层序中存在延长的间歇期和模糊的年代学框架。这引发了关于假定的生态退化和文化崩溃的时机和原因的持续辩论。我们对从Raraku湖中发现的岩芯进行的多代理研究突出了该流域及其周围地区在全新世晚期的植被动态和环境变化。与以前恢复的岩心相比，该序列包含的间歇期更短，并提供了更连续的环境变化历史。结果显示，从棕榈林到草原，景观经历了一个漫长、渐进和阶梯式的转变。这一变化始于公元前450年左右，持续了大约两千年。在花粉记录中，与人类活动有关的常见杂草马鞭草的存在，木炭流入转变之间的显著相关性，以及主要的花粉类型表明人类对植被的干扰。因此，人类在岛上的定居大约发生在公元前450年，比人们假设的早了大约1500年。气候变化也对环境变化产生了重大影响。记录中的两个沉积空隙被解释为干旱时期，在中世纪气候异常和小冰期分别可能阻止泥炭的生长和有利于泥炭的侵蚀。大约在公元1200年，地下水位上升，以前的Raraku沼泽变成了一个浅水湖，这表明更高的降水/蒸发速率与更凉爽和更潮湿的泛太平洋1300年事件是一致的。花粉和硅藻记录显示，大约在公元1200年，由于人类活动，植被发生了巨大的变化。最近由于人类活动引起的其他植被变化也需要引入分类群(例如番石榴、桉树)。在过去的两个世纪里，本土植物如苦豆子的消失。尽管证据不是确凿的，但是关于美洲印第安人在复活节岛的人类殖民中可能扮演的角色的争论，再次引发了关于美洲原住民起源的争论。(C)2013爱思唯尔有限公司。保留所有权利。
Earlier palynological studies of lake sediments from Easter Island suggest that the island underwent a recent and abrupt replacement of palm-dominated forests by grasslands, interpreted as a deforestation by indigenous people. However, the available evidence is inconclusive due to the existence of extended hiatuses and ambiguous chronological frameworks in most of the sedimentary sequences studied. This has given rise to an ongoing debate about the timing and causes of the assumed ecological degradation and cultural breakdown. Our multiproxy study of a core recovered from Lake Raraku highlights the vegetation dynamics and environmental shifts in the catchment and its surroundings during the late Holocene. The sequence contains shorter hiatuses than in previously recovered cores and provides a more continuous history of environmental changes. The results show a long, gradual and stepped landscape shift from palm-dominated forests to grasslands. This change started c. 450 BC and lasted about two thousand years. The presence of Verbena litoralis, a common weed, which is associated with human activities in the pollen record, the significant correlation between shifts in charcoal influx, and the dominant pollen types suggest human disturbance of the vegetation. Therefore, human settlement on the island occurred c. 450 BC, some 1500 years earlier than is assumed. Climate variability also exerted a major influence on environmental changes. Two sedimentary gaps in the record are interpreted as periods of droughts that could have prevented peat growth and favoured its erosion during the Medieval Climate Anomaly and the Little Ice Age, respectively. At c. AD 1200, the water table rose and the former Raraku mire turned into a shallow lake, suggesting higher precipitation/evaporation rates coeval with a cooler and wetter Pan-Pacific AD 1300 event. Pollen and diatom records show large vegetation changes due to human activities c. AD 1200. Other recent vegetation changes also due to human activities entail the introduction of taxa (e.g. Psidium guajava, Eucalyptus sp.) and the disappearance of indigenous plants such as Sophora toromiro during the two last centuries. Although the evidence is not conclusive, the American origin of V. litoralis re-opens the debate about the possible role of Amerindians in the human colonisation of Easter Island. (C) 2013 Elsevier Ltd. All rights reserved.