Hydroclimatic variation in Far North Queensland since 1860 inferred from tree rings

Abstract

In tropical Australia, palaeoclimatic proxies derived from tree rings are sought after sources for reconstructing climate variations. However, dendroclimatology has not been widely applied in tropical forests and even less so in the Australian tropics due to the extreme rarity of species producing anatomically distinct annual growth rings. Furthermore, most Australian tree species exhibit rather strong opportunistic growth with non-annual growth zones that are less suitable for dendrochronology. Recent studies on the Australian Red Cedar (Toona ciliata) in the Upper Kangaroo Valley near Sydney revealed that tree-ring based climate reconstructions are feasible with this species. This study moved 2500 km further north and concentrated on the tropical stands of T. ciliata because it is one of the few deciduous tree species in tropical Australia likely characterised by a dormant period of the cambium and thus annual tree rings. Although dendroclimatological studies indicate that some Australian tree species are suitable for reconstructing climate patterns, a well replicated tree-ring record from Far North Queensland has not been developed until now. Tree cores of T. ciliata were developed into a 140-year tree-ring widths index chronology. The analyses showed that the ring-widths indices correlate with March-June precipitation as recorded at Kairi research station. March-June precipitation was reconstructed using the tree-ring data with 35% of the variance explained. The reconstructed series contains both high- and low-frequency climate signals. This suggests that growth of T. ciliata is influenced by climate phenomena of different wave lengths which can be associated with El Niño Southern Oscillation (ENSO) and Interdecadal Pacific Oscillation (IPO).