Can riparian eucalypts be used for hydroclimatic reconstruction? The case for Eucalyptus coolabah to define palaeo-flood events

In the Australian semi-arid–arid zone, hydrological records are typically only 40–60 years long, prohibiting an understanding of long-term hydrological variability. Kati-Thanda – Lake Eyre Basin (KT-LEB), is the fifth largest terminal lake in the world, experiences highly variable flows and supports myriad flora and fauna. The opportunistic and highly irregular growth of trees in KT-LEB means that tree-ring records have not been developed in the region. E. coolabah is a keystone species in the KT-LEB and can live for more than 300 years. In this study, we find that trees in the riparian zone exhibit larger and more diffuse vessels compared to trees on the flood plain. ¹⁴C dating indicates that clear temporal variations in vessel size and density are synchronous across trees at the same site and consistent with changes in hydrological conditions recorded in instrumental records. More diffuse and larger vessels in the floodplain trees are congruous with wetter events, while bands of wood with smaller and denser vessels co-occur with drier conditions. These results suggest the species has potential as a high-resolution, albeit not annual, palaeohydrological indicator in the semi arid–arid zone - potentially a major step forward in deriving palaeohydrological tree-ring records for this region.