The response of aboriginal burning practices to population levels and El Nino-Southern oscillation events during the mid- to late-Holocene: a case study from the Sydney basin using charcoal and pollen analysis

Pollen and macroscopic charcoal have been analysed from a sedimentary sequence representing approximately 6100 years from a site within Wollemi National Park. This is located to the north- west of Sydney and forms a part of the Greater Blue Mountains World Heritage Area. The overall aim of the work was to examine the prehistoric interrelationships between vegetation, fire and human activity. There were relatively minor changes in the vegetation over the last similar to 6000 years, perhaps reflecting the climate- and fire- resilient nature of the sclerophyllous vegetation found on Hawkesbury Sandstone throughout the Sydney Basin. Casuarinaceae declined in the late Holocene, a trend that has been detected in numerous palaeoecological studies throughout south- eastern Australia. This decline was unrelated to fire, which has been a persistent feature at the site over the entire analysed sequence. The fire regime at the site changed from 5.7 ka, which is interpreted as reflecting the onset of increased climatic variability associated with El Nino Southern Oscillation ( ENSO) events. Another dramatic change in the fire regime occurred at 3 ka, which was coeval with archaeological changes in the region. It is possible that the change in fire activity from 3 ka represented an alteration to Aboriginal management strategies associated with an increasing population and/ or the increased risk of conflagrations in an ENSO- dominated climate.