Tree-ring dating of commercially available alerce boards in Japan

Abstract

Alerce (Fitzroya cupressoides) is a rare and long-lived cypress that grows in southern Chile and Argentina. Considerable efforts have been devoted to developing millennium-long tree-ring chronologies of alerce, and this has led to a published 5682-year-long tree-ring width chronology that was used to reconstruct the temperature record from the mid-Holocene to the present. Such long-lived trees can also be analyzed to develop radiocarbon calibration curves. In this study, tree-ring dating was conducted on commercially available alerce boards, which are thought to have been felled before the harvest of alerce was banned by the Convention on International Trade of Endangered Species. Although the samples have groups of micro-rings that could not be cross-dated, selected samples with relatively wide rings were successfully cross-dated against the tree-ring width master chronology. Some of these dated samples covered the period 693–1058 Common Era (CE, which is standard notation for the Gregorian calendar). An abrupt radiocarbon spike observed globally at 774–775 CE was identified in annually resolved radiocarbon data for one of our dated samples, which provides independent verification of the tree-ring dating. Although the sample size is limited, dating based on tree-ring widths yields robust age constraints on alerce boards. The results confirm the viability of dendrochronology for dating commercially imported alerce and highlight the potential use of such material in paleoclimatic studies.