Yellow-cedar blue intensity tree ring chronologies as records of climate, Juneau, Alaska, USA

Abstract

This is the first study to generate and analyze the climate signal in Blue Intensity (BI) tree-ring chronologies from Alaskan yellow-cedar (Callitropsis nootkatensis D. Don; Oerst. ex D.P. Little). The latewood BI chronology shows a much stronger temperature sensitivity than ring-widths (RW), and thus can provide information on past climate. The well-replicated BI chronology exhibits a positive January-August average maximum temperature signal for 1900-1975, after which it loses temperature sensitivity following the 1976/77 shift in northeast Pacific climate. The positive temperature response appears to recover and remains strong for the most recent decades although the coming years will continue to test this observation. This temporary loss of temperature sensitivity from about 1976 to 1999 is not evident in RW or in a change in forest health, but is consistent with prior work linking cedar decline to warming. A confounding factor is the uncertain influence of a shift in color variation from the heartwood/sapwood boundary. Future expansion of the yellow-cedar BI network and further investigation of the influence of the heartwood/sapwood transitions in the BI signal will lead to a better understanding of the utility of this species as a climate proxy.