The dendrochronology of Callitris intratropica in northern Australia: annual ring structure, chronology development and climate correlations

Abstract

In this study we demonstrate the significant dendrochronological potential of Callitris intratropica, a native conifer distributed across much of the seasonal tropics of northern Australia. We developed two rigorously cross-dated chronologies from sites in the Northern Territory, Australia. The first chronology (1965–2004) was developed from plantation C. intratropica of known-age at Howard Springs and was heavily replicated both within and among trees to evaluate the quality of cross-dating for the species. The second chronology (1847–2006) was developed from trees growing naturally near Pine Creek and compared with long-term instrumental climate records to assess the potential for dendroclimatic reconstructions. Both chronologies had mean interseries correlations >0.65, the highest reported for a tropical tree species. The Howard Springs chronology demonstrated that C. intratropica produces anatomically distinct annual growth rings with the consistent ring-width variation within and among trees necessary for rigorous dendrochronological studies. The Pine Creek chronology exhibited statistically significant correlations with rainfall and the Palmer Drought Severity Index (PDSI; integrated measures of plant water stress), and to a lesser extent temperature. The strongest correlations between the climate data and tree-ring width indices were for early monsoon rainfall (October–December; Pearson’s r = 0.53) and late monsoon PDSI (May; Pearson’s r = 0.41). Our study demonstrates the significant potential of high-quality dendrochronological research on mainland Australia in general, and of C. intratropica, specifically, to reconstruct historical variation of the Australian monsoon system. In addition, C. intratropica may be able to provide novel insights into the dynamics of forests in the seasonal tropics of northern Australia and the role of disturbances, such as fire and cyclones, on these ecosystems.