HOLOCENE FIRE HISTORY IN THE SYDNEY BASIN, NSW, AUSTRALIA: THE CLIMATE, HUMANS & FIRE NEXUS

There are several contentious issues regarding the history of fire in the humid environments of south-eastern Australia. This includes claims that the manipulation of fire by Aboriginal people resulted in significant vegetation change. Bowman (1998 in New Phytol.), for example, noted that palaeoecological studies do not objectively shed light on these issues, largely because of uncertainties associated with previous charcoal analyses.

This study presents the results from several studies located in the Sydney Basin where the ‘Oregon sieving method’ and image analysis of charcoal has been undertaken with the aim of untangling any inter-relationships between climate, humans and fire.

Results from the last ~25 ka at Gooches Crater (~33º28’S, 150º16’E), are particularly highlighted. This site has revealed an initial increase in charcoal at 12.6 cal. ka BP, which agrees with archaeological evidence of people in the region. Charcoal is then elevated, but with major oscillations (notably, one is coeval with the European Younger Dryas), until a period of low charcoal between 8.9 and 5.5 cal. ka BP. This is followed by a relatively abrupt increase in charcoal at 5.5 cal. ka BP, after which charcoal accumulation remains high.

This mid-Holocene increase in charcoal may reflect the increased anthropogenic use of fire, as it is coincident with an intensification of Aboriginal populations described in archaeological sequences. Alternatively, the increase in fire activity may reflect climatic forcing directly, and/or human responses to any climate change. The increase in fire, for example, may reflect the crossing of a critical threshold as ENSO strengthened through the Holocene (eg. Moy et al., 2002 in Nature). The change at 5.5 cal. ka BP is also coeval with the end of the African Humid Period (eg. deMenocal et al., 200 in Quat. Sci. Rev.). Ongoing palynological work is aimed at separating these hypotheses, however the nexus between climate, humans and fire potentially represents a complex interaction.