Detecting the initial impact of humans and introduced species on island environments in Remote Oceania using palaeoecology

Abstract

The isolated archipelagos of Remote Oceania provide useful microcosms for understanding the impacts of initial human colonization. Palaeoecological data from most islands reveal catastrophic transformations, with losses of many species through over-hunting, deforestation and the introduction of novel mammalian predators, the most ubiquitous and devastating being commensal rats. Two case studies from the Austral Islands and New Zealand demonstrate the potential of direct human proxies from palaeoecological archives to detect initial human impacts on islands. We show how pollen from introduced crop plants, and buried seeds with gnaw marks from the introduced Pacific rat (Rattus exulans) provide a reliable means of detecting initial human colonization and highlight the downstream ecological consequences of agriculture and rat introduction on previously uninhabited pristine island ecosystems. Previous studies have relied on indirect signals of human arrival based on charcoal and associated vegetation changes, the causes of which are often more difficult to interpret with certainty.

The deep human prehistory of global tropical forests and its relevance for modern conservation

“…Early Polynesians similarly carried a range of domesticated crops, animals and commensals that have contributed to the alteration of tropical forests across the region [76][77] . On Tonga, for example, tropical forest tree species declined in abundance following Polynesian colonisation 78 .…”

Holocene environmental history of a small Mediterranean island in response to sea-level changes, climate and human impact

“…pre-anthropic) occurred rapidly and quite simultaneously between ca. 1200 and 1500 yr A.D. (Prebble and Wilmshurst, 2009;Mieth and Bork, 2010;Wilmshurst et al, 2013). These studies provide a rare opportunity to compare the pre-human environment to the post-impact phase at an historical scale.…”

Epilogue: Changing Archaeological Perspectives upon Historical Ecology in the Pacific Islands

“…These two features of transported food production plus accomplished voyaging underwrote migration success and created interacting colonies of metapopulations (in the ecological terms of Lindenmayer and Fisher [2006:57] Research on the prehistoric introduction of domesticated plants has been slow to develop because of the difficulty of recovering and identifying material remains. Pollen from taro, for example, although identified from a number of sites in Hawai'i, has never been found at prehistoric levels in sedimentary cores from New Zealand, although taro occurred in both archipelagos at European arrival (Prebble and Wilmshurst 2008). Macroremains, such as dessicated tissue or charcoal from taro, sweet potato, and other crops, have seldom been identified, and the sample of sweet potato tissue thought oldest in Polynesia (Hather and Kirch 1991) has still not been radiocarbon dated directly.…”

“…and may reflect various factors unconsidered by Rolett and Diamond: the prevalence of very steep slopes in young volcanic islands east of the Andesite line, the effects of climatic instability with strongly increased El Niñ o-Southern Oscillation frequency <1,600 B.P., and biogeographic differences from west to east in faunal-floral coevolutionary histories. A potentially important factor, as Hunt and Lipo argue, was the impact of introduced Rattus exulans seed predation on native vegetation, including the Easter Island Jubaea and Hawaiian Pritchardia palm forests ( but see Prebble and Wilmshurst 2008).…”

“…As Hunt and Lipo observe, the formerly prevailing long chronology of Easter Island reflects an older belief that people reached many Pacific islands substantially earlier than can be shown evidentially (Anderson 1995, 2003a, Prebble and Wilmshurst 2008: the archaeological myth of cryptic colonization. The date at which manufacture and transport of giant stone figures ceased is unknown, and the great size of many that were uncompleted suggests that technical limitations were being reached, while changes in monumental construction and rising levels of warfare are manifested in archaeological evidence throughout late prehistoric Polynesia, whether islands were substantially deforested or not (e.g., Samoa, northern New Zealand versus Mangareva, Rapa).…”