Browsing by Author "Porch, N"
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- ItemHigh-resolution record of vegetation and climate through the last glacial cycle from Caledonia Fen, southeastern highlands of Australia.(Wiley-Blackwell, 2007-07) Kershaw, AP; McKenzie, GM; Porch, N; Roberts, RG; Brown, J; Heijnis, H; Orr, ML; Jacobsen, GE; Newallt, PRA blocked tributary has provided a rare site of long-term sediment accumulation in montane southeastern Australia. This site has yielded a continuous, detailed pollen record through the last ca. 140000 years and revealed marked vegetation and environmental changes at orbital to sub-millennial scales. Radiocarbon and optically stimulated luminescence (OSL, or optical) ages provide some chronological control for the last ca. 70 000 years. Most of the sediment is inorganic but with well preserved pollen that accumulated under unproductive and probably largely ice-covered lake conditions. The lake was surrounded by low-growing plants with an alpine character. Exceptions include three discrete periods of high organic sedimentation in the basin and forest development in the surrounding catchment. The two major periods of forest expansion are related to the last interglacial and the Holocene, with the third, shorter period considered to represent an interstadial in the early part of Marine Isotope Stage (MIS) 3. The latter part of the last glacial period is characterised by abrupt sub-millennial, amelioration events that may relate to documented global oscillations emanating from the North Atlantic. There are systematic changes through the record that can be partly attributed to basin infilling but the progressive reduction and regional extinction of some plant taxa is attributed to along-term trend towards climatic drying. © 2007, Wiley-Blackwell.
- ItemA multi-proxy record of environmental change at a glacial Nothofagus refugium, Wyelangta, Victoria(Australasian Quaternary Association, 2022-12-06) Matley, KA; Drinnan, AN; Sniderman, JMK; Hua, Q; Porch, NDespite its widespread use in palaeoecology, pollen-based reconstructions are limited by coarse taxonomic resolution. Pollen of narrow-range species that might be used as ecological indicators, for example, can be difficult or impossible to distinguish from the pollen of geographically widespread, and therefore less informative, taxa. Plant macrofossils, by contrast, are routinely identified to species level, and a majority of the species present in Southeast Australia during the late Quaternary still exist today. These improvements to the taxonomic precision of palaeobotanical records allow for the use of bioclimatic niche models to quantitatively reconstruct palaeoclimate, based on fossil species’ modern day climatic niches. Combining these two proxies, we are able to produce a more nuanced interpretation of late-Quaternary vegetation and climate. We sampled for pollen and plant macrofossils at a known late Quaternary palynological site in the Otways, Victoria (McKenzie & Kershaw, 2000). Here, we present a detailed pollen record and use plant macrofossil remains to confirm species identifications and conduct bioclimatic niche modelling. Our study reveals that, although the site has remained a rare mainland refugium for Nothofagus cunninghamii throughout the entire period of the record, the regional vegetation has undergone significant environmental change. By employing a multi-proxy approach that encompasses both pollen and macrofossil analysis, this study provides precise new estimates of the composition of Southeast Australian biotic communities and climates. These results contribute to the globally significant debate around the influence of the late Quaternary climate over the generation and maintenance of terrestrial biodiversity, and to the increasingly urgent discussion of the degree of sensitivity of Australian plant taxa to changing climate in general.
- ItemSoutheast Australian palaeofloras of the late Pleistocene and their implications for glacial palaeoclimate reconstructions(International Union for Quaternary Research (INQUA), 2019-07-29) Matley, KA; Sniderman, K; Drinnan, A; Porch, N; Hua, QThe climatic extremes of the last glacial period (approximately 100,000 to 12,000 years ago) and particularly the last glacial maximum (approximately 20,000 years ago) are thought to have exerted a significant influence over the current distribution of mesic forest taxa in southeast Australia. However, limited taxonomic resolution afforded by fossil pollen has meant that the nature of glacial biotic communities remains poorly understood. Pollen-based palaeoclimate reconstructions of southeast Australia have invoked a mostly treeless, ‘glacial steppe’ environment characterised by cold, dry, windy conditions. But, in contrast with the Northern Hemisphere evidence of continental-scale migration to and from southern refugia during successive Pleistocene glaciations, contemporary patterns of species diversity and endemism suggest that forest taxa persisted widely in southeast Australia, in multiple, localised refugia. Resolving this conflict is the focus of this study. Based on species-level identifications of plant macrofossils, we will provide precise new insights into the southeast Australian glacial climate and biotic communities. Improvements to the taxonomic resolution of palaeobotanical records will allow for the use of bioclimatic niche models to quantitatively reconstruct palaeoclimate. Porch (2010) demonstrated this concept elegantly, but at Spring Creek, too few beetle taxa available for analysis resulted in an inconclusive finding. By applying this method to the plant macrofossil assemblage from this site, we hope to reconstruct the environmental parameters likely to have predominated at the time. Preliminary results suggest that the climatic tolerances of the late-Pleistocene flora of Spring Creek did not differ substantially from those of the modern-day assemblage. The results of this study will contribute to a globally significant debate about the role of the Pleistocene glacial-interglacial cycles in the generation and maintenance of terrestrial biodiversity, and also to the increasingly urgent discussion of the degree of sensitivity of iconic Australian plant taxa to changing climate in general. © The Authors.