University Of Tasmania
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Macrofossil evidence for Quaternary plant extinction and vegetation change in western Tasmania

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posted on 2023-05-26, 05:51 authored by Jordan, GJ
Macrofossils from Pleistocene sediments in western Tasmania are investigated in order to reconstruct vegetation from this critical period. in the history of Australia's vegetation. The microfossil record shows that many taxa. notably the common Tertiary taxa Nothofagus subgenus Brassospora. Araucariaceae. Dacrycarpus and Dacrydium. were present in western Tasmania during the Latest Pliocene or Earliest Pleistocene but are now extinct from Tasmania. Most of these taxa are likely to have been rainforest species, but some may have been from sclerophyll vegetation (e.g. Beauprea). A few of these persisted into the Early-Middle Pleistocene and only Quintinia to the Late Pleistocene. Macrofossils of now globally and regionally extinct taxa occur in the Early Middle Pleistocene Regatta Point sediments. Most of these extinct taxa are not distinct in the relatively good microfossil record of that area. Some clearly sclerophyllous taxa have become extinct e.g. Banksia strahanensis and Oxylobium sp. nov. Rainforest taxa no longer occurring in Tasmania have affinities with species from temperate New Zealand (e.g. Quintinia sp. nov.), montane north-eastern New South Wales and Queensland (e.g. Rubus cf. moorei forma glabra, aff. Austromyrtus and Laurophyllum sp.). Macrofossils of only one extinct species occur in sediments younger than Regatta Point: Banksia kingii from the Late Pleistocene Melaleuca Inlet sediments. Local climatic and vegetation reconstructions for the times of deposition are made -for the Regatta Point, the middle Pleistocene Regency and the late Pleistocene Melaleuca Inlet sediments based on floristics. Vegetation reconsttuctions include analysis of diversity using both floristics and a modified rarefaction method. Both climatic and vegetation reconstructions are interpreted in terms of taphonomic studies both in this work and elsewhere. Regression modelling of the leaf size of N. cunninghamii from modern forest floor litter against BIOCLIM synthetic climatic parameters indicates that leaf length is well correlated to temperature of the growing season and palaeo-temperatures are estimated for the fossil floras. The extinctions are interpreted in terms of the climatic and vegetation reconstructions of the sites and broader scale knowledge of late Cenozoic climate, vegetation and glacial history. Many Tertiary taxa survived the climatic disruptions of the Early Pleistocene, but probably become extinct directly or indirectly due to the glaciations of the Middle Pleistocene. Rainforest diversity is lower now than during the Early Pleistocene, but the results are ambiguous for overall diversity. There is no reason to suspect that Tasmania could not support more diverse rainforest under modern conditions.


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