Fire history inferred from charcoal accumulation at Dunphy Lake, Warrumbungle Mountains

The long-term history of fire and environmental conditions in the Warrumbungle Mountains in eastern Australia are relatively unknown. Here we synthesise recent research that reconstructed fire history and catchment conditions using a macro-charcoal record from sediment cores in Dunphy Lake, Warrumbungle National Park (WNP). Dunphy Lake is a small, ephemeral wetland and the only lake basin in the highlands of WNP (~700 m.a.s.l.). We used sedimentology, geochemistry and macro-charcoal to characterise phases of sediment deposition and charcoal accumulation, as well as radiometric dating to constrain the age of depositional units. Presently, Dunphy Lake has infrequent wet phases related to local rainfall and runoff in its catchment. Pollen found in the upper 80 cm of the sediment profile indicated the presence of a Myrtaceae-dominated vegetation community (including Eucalypts) adapted to periodic wet and dry conditions for at least the last 450 years. The macro-charcoal record spanning the last ~2,200 years shows that the main periods of charcoal accumulation – interpreted as enhanced fire activity in the catchment – occurred between 450 and 200 years ago. High macro-charcoal concentrations tend to coincide with coarse sediment (sand) layers, suggesting that fires that generated large quantities of charcoal occurred at similar times to episodes of significant runoff and sediment flux from the catchment. This was certainly the case in 2013, when a rainstorm following the Wambelong fire caused significant flash flooding and severe erosion of waterways and hillslopes, with subsequent deposition of sediment and charcoal in the landscape. Our results suggest that over the long-term, periods of enhanced fire activity in WNP may coincide with an intensification of El Niño Southern Oscillation (ENSO). Further research is required to ascertain the nature of the relationships between past fire events, post-fire sediment aggradation and other environmental conditions, which are part of a complex biophysical response to environmental change, and possibly anthropogenic impacts, in the region.