Expressing tree-ring chronology as age-standardized growth measurements

Abstract

Tree-ring data of individual trees show lifelong biological trends as a function of cambial age. The compilation of a tree-ring chronology entails standardization (detrending) of the series. Tree-ring standardization commonly derives detrended series of dimensionless tree-ring data that are devoid of the original growth measurements (millimeter, density). A new method is proposed in this study. This method derives modeled tree-ring growth variations to calculate age-standardized tree-ring chronology that allow comparisons between the absolute growth measurements of different sites, regions, or species and between the absolute growth measurements and environmental factors such as climate variables. The modeled tree-ring growth is simply obtained through ranked transformation of the tree-ring values within the user-defined reference age class (RAC) and all remaining cambial age classes. The chronology is thus presented on the scale of growth measurements of the specific tree’s age, instead of dimensionless tree-ring indices. This presentation allows the accurate estimation of both the short- and long-term growth variations. The RAC method used at the timberline sites in northern Finland revealed a nonlinear age-dependent association between mid-summer (July) temperature and Scots pine growth of 0.072 mm/° C and 0.014 mm/° C for cambial age ranges of 1 to 5 to 226 to 330 years.