Wetland soil moisture complicates the use of Sporormiella to trace past herbivore populations

Recent measurements on dendrochronologically-dated wood from the Southern Hemisphere have shown that there are differences between the structural form of the radiocarbon calibration curves from each hemisphere. Thus, it is desirable, when possible, to use calibration data obtained from secure dendrochronologically-dated wood from the corresponding hemisphere. In this paper, we outline the recent work and point the reader to the internationally recommended data set that should be used for future calibration of Southern Hemisphere 14 C dates.

The pristine island ecosystems of East Polynesia were among the last places on Earth settled by prehistoric people, and their colonization triggered a devastating transformation. Overhunting contributed to widespread faunal extinctions and the decline of marine megafauna, fires destroyed lowland forests, and the introduction of the omnivorous Pacific rat (Rattus exulans) led to a new wave of predation on the biota. East Polynesian islands preserve exceptionally detailed records of the initial prehistoric impacts on highly vulnerable ecosystems, but nearly all such studies are clouded by persistent controversies over the timing of initial human colonization, which has resulted in proposed settlement chronologies varying from approximately 200 B.C. to 1000 A.D. or younger. Such differences underpin radically divergent interpretations of human dispersal from West Polynesia and of ecological and social transformation in East Polynesia and ultimately obfuscate the timing and patterns of this process. Using New Zealand as an example, we provide a reliable approach for accurately dating initial human colonization on Pacific islands by radiocarbon dating the arrival of the Pacific rat. Radiocarbon dates on distinctive rat-gnawed seeds and rat bones show that the Pacific rat was introduced to both main islands of New Zealand approximately 1280 A.D., a millennium later than previously assumed. This matches with the earliest-dated archaeological sites, human-induced faunal extinctions, and deforestation, implying there was no long period of invisibility in either the archaeological or palaeoecological records.

Debate continues to rage between enthusiasts for climate change versus humans as a cause of the catastrophic faunal extinctions that have occurred in the wake of human arrival in previously uninhabited regions of the world. A global pattern of human arrival to such landmasses, followed by faunal collapse and other ecological changes, appears without known exception. This strongly suggests to some investigators that a more interesting extinction debate lies within the realm of potential human-caused explanations and how climate might exacerbate human impacts. New observations emerging from refined dating techniques, paleoecology and modeling suggest that the megafaunal collapses of the Americas and Australia, as well as most prehistoric island biotic losses, trace to a variety of human impacts, including rapid overharvesting, biological invasions, habitat transformation and disease.