Beyond tree-ring widths: stable isotopes sharpen the focus on climate responses of temperate forest trees.

Abstract

[Extract] Tree rings provide an indispensable tool for assessing a tree's response to variability in its environment, oftentimes also pro¬viding a means of reconstructing that variability beyond instru¬mental records. The wood that trees produce is laid down sequentially, creating an archive of temporally ordered material that is rich in physiological and environmental information. This is made all the more useful because trees are globally distrib-uted, can live for thousands of years and in some cases remain intact long after they die. Tree-ring archives are used in a wide variety of studies, including, but not limited to, climate recon¬structions (Cook et al. 2010), archaeological dating of ruins (Cufar 2007), reconstructions of fire history and recurrence intervals (Swetnam et al. 1999), and assessments of tree physiological responses to drought (McDowell et al. 2010). The number of applications for tree rings has grown steadily in recent decades, and the variety of measurements that can be made on tree rings has grown as well (Speer 2010). The simplest measurement that can be made is in-series whole-ring widths. From this starting point, additional information can be gained from measuring early-wood and late-wood widths, wood density, elemental abundances, microfibril angles, radial diameters of xylem conduits and stable-isotope ratios of the organic material in tree rings. A tree-ring record based on a single sample from a tree is referred to as a series, whereas a composite of many series is referred to as a chronology.