Lake Xere Wapo

a long terrestrial record for comparison with the key site of Lynch's Crater, northeastern Australia

Janelle Stevenson & Geoffrey Hope

Department of Archaeology and Natural History, Research School of Pacific and Asian Studies, Australian National University, Canberra ACT 0200 Australia

Introduction

Lynch's Crater is one of Australia's key palaeoenvironmental sites[see refs] [Figure 1], recording 220 k years of vegetation change in the tropical northeast. Of great interest is the decline in Araucaria forest, the rise of sclerophyll vegetation and a sharp increase in charcoal 40,000 yrs ago.

There has been much debate about the relative contributions of climate and human impact to this change. Nearby ocean cores have contributed to refining the climatic story in the record, but until now no terrestrial sites comparable to Lynch's Crater have been found. We present a long terrestrial record from New Caledonia that suggests climate and not people was the significant factor leading to the Araucaria decline 40,000 yrs ago.

New Caledonia

New Caledonia is an ideal place to independently assess vegetation changes seen in the late Quaternary pollen record of Lynch's Crater as: the island is a remnant of the Gondwanan landmass and thus floristically related (in particular they have in common the genus Araucaria);

• (i) it is at a similar latitude with a similar climate;
• (ii) it was not inhabited by people until around 3 ka removing the complicating factor of possible human impact in the late Pleistocene

Summary of Major Findings

• The Araucaria record's from Lynch's Crater and Lake Xere Wapo are remarkably similar [Figure 3]
• Araucaria decline at Lake Xere Wapo is not associated with an increase in charcoal, suggesting that climate change alone drove this decline
• Unlike Lynch's Crater, fire is more prevalent in New Caledonian landscape prior to 50 ka [Figure 3 and Figure 4]
• Dacrydium disappears from Lynch's Crater after 25 ka and is now extinct in Australia. However at Xere Wapo, Dacrydium and Podocarpus flourish after the Araucaria decline
• This upper part of Xere Wapo record has no precedent in the earlier record [Fig. 4]

Conclusions

• A major shift in climate occurred at around 40ka in the region that led to the loss of lowland Araucaria forest in both New Caledonia and northeastern Australia
• This is supported by both the absence of people from the New Caledonia at this time and any significant change in charcoal accumulation in the Xere Wapo record
• The question of whether early human activity led to increased charcoal influx at Lynch's Crater remains open

References

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