Late Pleistocene fossil flora of Henty Bridge, Tasmania, and their implications for glacial climate reconstructions
Ms Kia Matley1, Dr Quan Hua2, Dr Kale Sniderman3, Associate Professor Andrew Drinnan1
1University Of Melbourne School of BioSciences , Parkville , Australia, 2Australian Nuclear Science and Technology Organisation , Lucas Heights , Australia , 3University of Melbourne School of Earth Sciences , Parkville , Australia
The climatic extremes of the last glacial period (approx.100,000 years ago to 12,000 years ago) and in particular the last glacial maximum (LGM, 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.
In southeast Australia, pollen-based palaeoclimate reconstructions of the LGM suggest a mostly treeless, ‘glacial steppe’ environment characterised by cold, dry, windy conditions. But phylogeographic evidence suggests that forest taxa persisted widely in southeast Australia, in multiple, disjunct, local refugia. Resolving this apparent conflict is the focus of our study.
Pollen is ubiquitous and virtually indestructible, which makes it remarkably useful for palaeoenvironmental reconstruction, particularly in lacustrine or cave environments where sediments accumulate over timescales of millennia. But despite 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 that were present at the LGM still exist today. These improvements to the taxonomic precision of palaeobotanical records allow for the use of bioclimatic niche models to quantitatively reconstruct palaeoclimate. Using our understanding of fossil species’ modern-day climatic niche, we hope to gain a more nuanced reconstruction of the climate at the time of their deposition.
We sampled for plant macrofossils at a known LGM palynological site in Henty Bridge, Tasmania (Colhoun, 1985). Using the AMS radiocarbon dating facility at ANSTO, we produced a series of dates which indicate that these fossils were deposited at least 10,000 years prior to the LGM, a significant change to what was previously known of the site. Bioclimatic niche modelling of these fossil species suggests that, in the period preceding the LGM, the climate of western Tasmania was cooler than present by at least 2°C. Moreover, our data show clear evidence of species migration in response to changes in climate; some of the species in the Henty Bridge assemblage are today confined to higher elevations.
These results contribute to the globally significant debate around the influence of the Pleistocene climate over the generation and maintenance of terrestrial biodiversity, and also to the increasingly urgent discussion of the degree of sensitivity of Australian plant taxa to changing climate in general.
Colhoun EA. (1985) Pre‐last glaciation maximum vegetation history at Henty Bridge, western Tasmania. New Phytologist 100: 681-690.
Kia Matley is a PhD student at the University of Melbourne. Her research examines the potential of plant macrofossils as a proxy for palaeoclimate reconstruction. Kia completed a Postgraduate Diploma thesis in arid-zone palaeoecology in 2017, examining fossil pollen recovered from speleothems.