Inequality in paleorecords.

Paleorecords provide information on past environmental variability, and help define ecological reference conditions by means of changes in their characteristics (accumulation rate, geochemical composition, density, etc.). A measure of temporal dissimilarity, which has traditionally been used in dendrochronology and is called "mean sensitivity," only focuses on first-order time-series lags. In this paper mean sensitivity was extended to all possible lags to derive a mean sensitivity function (MSF). The MSF is equivalent to a one-dimensional form of the paired relative madogram, a tool used in geostatistics to quantify spatial dependence. We then showed that the sum of madograms for all possible time-series lags is encapsulated by a single parameter, the Gini coefficient. This parameter has long been used by econometricians, social scientists, and ecologists as a synthetic, quantitative measure of inequality and diversity. Considering the connection between the MSF and the madogram, and the convenience of summarizing data heterogeneity with a single number, the Gini coefficient is therefore particularly appropriate for succinctly evaluating the diversity of paleorecords. An example of this application is provided by focusing on public domain dendrochronological data for the western conterminous United States.