Cross-dating of tree ring δ18O and δ13C time series

The science of dendrochronology relies on cross-dating techniques to ensure that a particular tree ring is associated with a specific year. Some tree species and environments produce ring-width time series that are difficult to cross-date. The objective of this preliminary study was to determine if stable isotope time series of oxygen (δ18O) or carbon (δ13C) could provide useful data for cross-dating purposes. Ring-width and stable isotope time series for three to four trees from multiple sites were statistically analyzed with a computer program commonly used in dendrochronology (COFECHA). For pine (Pinus ponderosa), both δ18O and δ13C time series produced as good and occasionally better between-tree correlations than ring-width series. Coast redwood (Sequoia sempervirens) is a species that can be difficult to cross-date using ring-width data due to complacent growth and ring anomalies. For the Prairie Creek redwood site, between-tree δ18O time series were more strongly correlated than ring-width series. In some instances within-tree, ring-width series (multiple cores from each tree) were not significantly correlated, again indicating that using ring-width data for cross-dating redwood can be problematic. Although, using isotope chronologies for routine cross-dating is not practical, this study demonstrates that for short sections that are difficult to date or when trying to link limited numbers of cores into an extended chronology, patterns of δ18O and δ13C variation could be used to clarify tree ring dating.