School of Geography - Theses
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ItemPalaeofire activity in western Tasmania: climate drivers and land-cover changes( 2017)Under the current changing climatic regime, in which wildfires are predicted to increase in frequency and magnitude, it is important we gain a better understanding on past climatic trends and fire activity to properly manage fires and landscapes, preserve valuable natural ecosystems and protect human lives and properties. Fire activity is especially projected to increase in temperate regions, such as Australia’s southeast. In this context, western Tasmania represents a key region where the environmental impacts of wildfires can be disastrous for the remnant pockets of fire-sensitive vegetation. Climate influence on fire activity and vegetation dynamics operates at multiple timescales, from inter-annual to multi-millennial. Given the time limitation of historical records, we need to look at long-term records to gain a better understanding on what modulates fire activity and how changes in fire regimes influence ecosystem dynamics. This PhD project aimed to a) identify the climate drivers of short- and long-term fire variability in western Tasmania and b) quantify climate- and firedriven vegetation changes in this region throughout the Holocene. To understand the short-term drivers of fire activity in western Tasmania, I explored the relationship between the main climate modes of the Southern Hemisphere and a documentary record of fire occurrence from this region. This analysis suggested that the Southern Annual Mode (SAM) -an index for the position and strength of SWWis strongly correlated with inter-annual fire activity across western Tasmania during the last 25 years. Moreover, the persistent positive trend in SAM recorded during the last 500 years was found to be tightly coupled to increased biomass burning within the same region. To understand the long-term landscape changes in western Tasmania, I combined high resolution pollen and charcoal analyses, coupled with recently developed mathematical modelling of pollen dispersal and productivity. Within this Thesis, I applied pollen dispersal models to calibrate the pollen-vegetation relationship for the first time in Australia. This method involves two steps: (1) a modern pollen analysis coupled with distance-weighted vegetation data to calibrate the present-day pollen-vegetation relationships and (2) an application of these relationships to a fossil pollen record to produce past vegetation cover estimates. The application of pollen dispersal models proved the biases inherent in previous interpretations of pollen spectra from western Tasmania. Specifically, the results from these analyses showed that this region was mostly dominated by treeless moorland vegetation, supporting the identification of western Tasmania as a cultural landscape. Moreover, my results showed that land-cover changes throughout the Holocene occurred in response to climatic change and a shift in fire regimes due to ENSO/SWW interactions.