The vegetation history of the last glacial–interglacial cycle in eastern New South Wales, Australia

Abstract

We present a reconstruction of the vegetation history of the last glacial-interglacial cycle (ca. 75 k cal. yr BP-present) at Redhead Lagoon, an enclosed lake basin in coastal, eastern New South Wales, Australia. The sequence of vegetation change at the site is broadly comparable with the pattern of climatically induced changes observed in many other pollen records in southeast Australia. Open woodland-herbland and woodland-forest communities correspond with glacial and interglacial periods respectively, with an additional change towards a more open understorey vegetation assemblage over the last 40 000 yr. The driest conditions appear to have occurred during the height of the last glacial (some time between 30 and 20 k cal. yr BP). This is consistent with other records from southeast Australia, and provides support for a poleward shift in the subtropical anticyclone belt and, less certainly, for the thesis that the Southern Hemisphere westerlies intensified during this period. In marked contrast to most sites in southeast Australia, Casuarinaceae dominates the pollen record through the height of the last glacial period and into the Holocene. The postglacial climatic amelioration is accompanied by the general reappearance of tree pollen in the record, by the disappearance of several open and disturbed environment indicator taxa, by increases in organic sediment deposition and pollen taxon diversity, and by higher water balances. While climate appears to have been the major control on patterns of vegetation change at this site throughout most of the last glacial-interglacial cycle, changes in depositional environment and hydrology have also played a role. Significantly, substantial increases in the rate and magnitude of many indicators of environmental disturbance since European settlement suggest that humans are now the most important mechanism for environmental change.

Intraspecific Divergence Associated with a Biogeographic Barrier and Climatic Models Show Future Threats and Long-Term Decline of a Rainforest Conifer

“…The southern climatic envelope model shows a contraction in response to post-glacial warming (21 -0 ka) and this is in agreement with the observed fossil record [37,[39][40][41]. Interestingly in the fossil record a longer-term decline since the last interglacial (130 -0 ka) has been observed among other podocarps [20,61,62], including P. elatus [39][40][41].…”

“…The palynological record suggests that in the Australian Wet Tropics, gymnosperms expanded during glacial maxima [20], and it is likely that the cool, dry conditions of the last glacial maximum (LGM; 21 ka) also favoured P. elatus. However, while southern fossil records support a decline in abundance for P. elatus since the LGM [37,40,41], in the north the co-occurrence of a number of Podocarpus species and the classification of pollen to generic-level reduce the interpretative power of the limited deposits available.…”

Climatic records over the past 30 ka from temperate Australia – a synthesis from the Oz-INTIMATE workgroup

“…Redhead Lagoon, Blue Mountains composite records), a peak in regional precipitation is recorded at ~10-8 ka . Edney et al, 1990;D'Costa et al, 1993;D'Costa and Kershaw 1995;Williams et al, 2006). At higher altitude, Eucalyptus pollen at Caledonia Fen (Fig.…”

“…The analysis of microscopic charcoal fragments (typically <100 µm) is frequently used in Australia, as tallying microscopic charcoal fragments can be done in tandem with pollen counting (e.g. Newsome and Pickett, 1993;Dodson and Lu, 2000;Williams et al, 2006;Kershaw et al, 2007).…”

“…Casuarinaceae, Eucalyptus) at the expense of herbs and shrubs (e.g. Asteraceae, Chenopodiaceae) in temperate Australia, indicating the onset of warmer and/or wetter conditions (MacPhail, 1979;Markgraf et al, 1986;Harle, 1997;Hopf et al, 2000;Williams et al, 2006;Darrénougué et al, 2009). Rainforest taxa became more prolific in western Tasmania from ~14 ka (MacPhail, 1979;Colhoun et al, 1999;Fletcher and Moreno, 2011).…”