Anomalous tree-ring identification facilitated by AMS 14C analysis in subtropical and tropical Australian Araucariaceae samples enables development of a long-term, high-resolution climate reconstruction
Dr Heather Haines1,2,3, Dr Jonathan Palmer1,2,3, Dr Quan Hua4, Dr Nathan English5, Dr William Hiscock3,6, Prof Chris Turney1,2,3, Dr Christopher Marjo3,6, Mrs Patricia Gadd4, Dr Justine Kemp7, Prof Jon Olley7
1School of Biological, Earth and Environmental Sciences. The University of New South Wales (UNSW), Sydney, Australia, 2ARC Centre of Excellence for Australian Biodiversity and Heritage, UNSW Node, Sydney, Australia, 3Earth and Sustainability Science Research Centre (ESSRC), The University of New South Wales, Sydney, Australia, 4Australian Nuclear Sciences and Technology Organisation, Sydney, Australia, 5School of Health, Medical and Applied Sciences & Flora, Fauna and Freshwater Research Group, Central Queensland University, Townsville, Australia, 6Chronos 14Carbon-Cycle Facility, Mark Wainwright Analytical Centre, University of New South Wales, Sydney, Australia, 7Australian Rivers Institute, Griffith University, Brisbane, Australia
In Australia the majority of tropical and subtropical regions lack long-term instrumental climate records. Paleoclimate reconstructions from tree rings provide one alternative but very few dendrochronological investigations have so far been undertaken. Early assessments of mainland Australian tree species were discouraging due to the high prevalence of anomalous ring boundaries. Some species, however, were seen as more favourable than others including those in the Araucariaceae family which is common along the subtropical-tropical Australian east coast. These trees are longer lived than many other species in the region and contain growth rings known to be annual in nature and responsive to climatic conditions. There is however, a heavy prevalence of anomalous ring boundaries in species from this family which must be accounted for when dating these species.
Here we describe the tree-ring characteristics and growth response from two stands of Hoop pine (Araucaria cunninghamii) trees located in subtropical and tropical Queensland, Australia (regions known for experiencing extreme hydroclimatic events). Confirmation of annual growth driven by moisture sensitivity was determined using radius dendrometers on four trees in Lamington National Park (c. 28º S). Tree cores were collected from both the Lamington stand as well as a stand at Hidden Valley near Paluma, Queensland (c. 19º S). Ring-width assessment showed the presence of false, faint, locally absent, and wedging rings in both sites. Results of bomb-pulse radiocarbon dating of selected single tree rings demonstrated that trees from this species can fall into one of three categories: A – those with locally-absent rings around the circumference of the trees, B – those where false rings were observed, and C – those with many wedging and locally-absent rings. Only trees in the first two categories were able to be included in the master chronologies.
Traditional dendrochronological analysis with age validation by bomb-pulse radiocarbon dating allowed for a robust ring-width chronology from 1805-2014 CE to be developed for the Lamington National Park site. Growth-climate analysis of the master tree-ring chronology determined that the strongest environmental correlation was to wet season drought conditions. The strength of this response was compared to local and regional drought indices as well as to a long-term drought reconstruction. The combined analysis led to the development of a 200-year drought reconstruction for the region which shows influences from both the El Niño Southern Oscillation and the Interdecadal Pacific Oscillation.
Dr Heather Haines is a dendrochronologist with a specialization in tropical regions, non-traditional species and methods, and a focus on radiocarbon dating. Her interests lie in developing high-resolution paleoclimate reconstructions, understanding hydroclimate variability, protecting native vulnerable species, and helping to extend the Australian tree-ring network. She has a preference for working with tree species that present a challenge for dendrochronological analysis due to anomalous ring boundaries, of which there are many within Australia.