Short-Lived Plant Materials, Long-Lived Trees, and Polynesian 14C Dating: Considerations for 14C Sample Selection and Documentation

Abstract

For over 2 decades, there have been calls for Polynesian archaeologists to identify radiocarbon samples to taxon and material type, and preferentially date short-lived materials. This stems from recognition that even modest amounts of inbuilt age are problematic in this oceanic region where human settlement dates to the last 3 millennia or less. Despite programmatic statements to this effect, and empirical demonstrations of value, uptake of these practices has been slow. This article suggests that short-lived materials be defined as those with lifespans of 10 yr or less, recognizing that reducing the distance between target event and the dated material is an ongoing aim for archaeology. We identify both short-lived materials that are suitable for dating and long-lived species (>75 yr) that should be avoided given their potential for inbuilt age. Additionally, we suggest that given the destructive nature of 14C dating there is value to (1) obtain high-resolution photographs of samples prior to analysis, (2) split samples and archive residuals when possible, and (3) routinely report the tools and expertise used in identification. Past and recent dating analyses at a Polynesian site in the southern Cook Islands are used to illustrate how the suggested protocols might enhance current and future studies. We also establish that mature Calophyllum inophyllum, a common coastal tree and valued timber species, has been in the southern Cook Islands for at least the last 700 yr and is likely to be indigenous and long-lived.