Dendroecological potential of Callitris preissii for dating historical fires in semi-arid shrublands of southern Western Australia

Historical fire regimes in the semi-arid shrublands of southern Western Australia are poorly understood, largely owing to a lack of quantitative historical data. We sought to determine the dendroecological potential of fire-sensitive Callitris preissii Miq. trees to date historical fires and extend the length of fire-history data available from remotely sensed imagery. We sampled C. preissii trees from known fire areas in the Lake Johnston region in southern Western Australia. Our objective was to assess the capacity to date historical fires using stand establishment date as a proxy measure of time since fire. We measured stem basal diameter and height and collected stem sections of C. preissii trees and saplings from five areas that were burnt on known dates between 1974 and 2001. We also sampled older trees (>35 years), which were used to create a master chronology to assist with dating of seedlings and saplings. Tree age could not be reliably estimated from stem basal diameter and tree height, with 95% prediction intervals of more than 17 years. However, we were able to successfully determine tree age and develop a ring-width chronology using standard dendrochronological techniques. The cross-dated chronology showed a relatively high inter-series correlation in ring width (r=0.63) indicating consistency in growth rate among samples and sites, while mean sensitivity (0.39) signified high inter-annual variability in ring width. The age structure of C. preissii stands revealed consistent recruitment within 1 year of fire occurrence and maximum intra-stand variation in tree age of 4 years. Our results confirm that C. preissii has significant dendroecological potential to accurately date past fire events and that this approach will assist in extending fire-history records beyond recent decades for much of southern semi-arid Australia.