Ratios of C3 Plants: Implications for Palaeodiet Studies

The äC value of a C3 plant is influenced by the species’ response to its environment, which is subject to natural changes with space and time. This paper reviews the magnitude of the resulting variations in plant äC values—the differences between species, and the variations at different spatial and temporal scales—with particular emphasis on studies of tree wood. Because of these variations, any attempt to estimate the absolute äC values of a plant food resource at a particular place and time in the past, even when based on analysis of archaeological plant remains, will be subject to uncertainties. Uncertainties due to a single factor are commonly 1‰, and in many cases a combination of factors will lead to uncertainties of at least 2‰. Many of these factors are also relevant to archaeological studies based on differences between the äC values of different individuals or populations of animal/humans. Where such differences are only a few per mil it may be difficult to unambiguously ascribe them to palaeodietary, rather than to palaeoenvironmental, causes. ? 1999 Academic Press