Dendroclimatic interpretation of tree-rings in Agathis australis (kauri): 2. Evidence of a significant relationship with ENSO

Abstract

Part I of this investigation (Buckley et al. 2000) found consistent significant correlations between tree growth and climate for nine New Zealand kauri tree-ring chronology sites. The nature of these correlations suggests that Agathis australis (kauri) may carry a useful signal of the El Nino-Southern Oscillation (ENSO) phenomenon. We have explored the potential of kauri for ENSO reconstruction through statistical analysis of the relationship between the Southern Oscillation Index (SOI) and the tree-ring indices previously derived. Results showed a consistent SOI-kauri growth relationship for eight of the nine sites. A significant negative correlation was found between kauri growth and concurrent seasonal mean SOI, and a positive correlation with the seasonal mean SOI recorded over the preceding two years. The former is consistent with a hypothesised ENSO-kauri growth model, but the two-year lag suggests an additional relationship, perhaps associated with kauri phenology. Decadal-scale variability was evident in the strength of the SOI-kauri growth relationships, particularly in autumn (March-May) and winter (June-August). Comparison of SOI and extreme kauri growth years indicated general consistency in the growth response to ENSO, but also identified some anomalies, suggesting that kauri ring-width is an imperfect ENSO proxy. However, combined with the spatial scale at which ENSO operates, and the known variability of links with regional climates, we conclude that kauri growth-rings could provide a useful ENSO proxy, particularly within the context of multi-proxy spatially distributed studies.