Palaeoecology of southeast Australian ecosystems, with a focus on the Bass Strait area: Implications for ecosystem management

Abstract

Global change poses a major threat to ecosystems and biodiversity. This is particularly evident in southeast Australia, where never-before-seen wildfires are associated with ecosystem destruction, as well as loss of wildlife, human lives and infrastructures. In order to tackle these challenges, there is a need for better understanding of long-term ecosystem changes in the region. This understanding will help in building robust knowledge baselines for management and restoration goals. The Bass Strait islands (BSI) provide a rare opportunity to investigate the long-term roles of climate and human land use in driving ecosystem and fire regime changes, due to their unique history of human occupation, which contrasts with surrounding southeast Australian regions. The BSI saw declining populations at the same time as population intensification occurred in southeast (SE) Australia in the mid-late Holocene. The BSI can thus be regarded as rare natural laboratories where climatic and anthropogenic drivers of long-term ecological dynamics can be disentangled. The knowledge of the different roles of climate and anthropogenic land use on ecosystems and fire regimes gained from these natural laboratories can be applied to areas of SE Australia to inform management strategies in an era of significant ecological changes. Therefore, this thesis provides a deeper understanding of past links between ecosystem change, changes in climate, fire regimes, and human land use in SE Australia, using the Bass Strait area as a case study. Specific questions addressed include, (1) What drove vegetation and wetland changes in SE Australia during the last glacial and Holocene? (2) What was the role of humans in vegetation and fire-regime changes in SE Australia during the Holocene? (3) How can this deep-time knowledge contribute to better managing the ecosystems and fire regimes of the BSI and SE Australia at large? In order to answer these questions, multiple wetland sediment cores were analysed to reconstruct vegetation, fire, and wetland histories of one of the least researched BSI (i.e. truwana/Cape Barren Island) and compared to existing palaeoecological records from neighbouring regions of SE Australian mainland and Tasmania. The thesis places these findings into a broader regional context, by analysing changes in vegetation and fire regimes and associated drivers of change across SE Australia, applying a quantitative approach for the first time. The results suggest that climate primarily drove ecosystem change across SE Australian region in the last ~35,000 years. Specifically, temperature change and shifts in Southern Westerly Winds (SWW) were key drivers of vegetation and wetland changes during the last glacial period, while sea-level change, and precipitation changes related to El Nino Southern Oscillation and SWW were more important during the Holocene. Indigenous people used fire to maintain open and diverse woodlands during the Holocene, and a combination of climate and anthropogenic land use controlled Holocene fire regimes across SE Australia. On a finer spatial scale, insights from the BSI suggest Indigenous frequent burning reduced the area burnt by climate-driven fires during the Holocene. Indigenous fire management minimized contiguous woody fuel accumulation over the landscape, which in turn reduced fire spread. The suppression of Indigenous cultural fire management by European colonisation, combined with climate change, created novel fire regimes in SE Australia in the last 200 years. The reinstatement of an Indigenous cultural burning approach is recommended to help reduce the occurrence of destructive fires in SE Australian forests and to preserve rare ecosystems, such as heathlands. This will help in restoring ecosystem health and biocultural heritage in SE Australia. Monitoring of wetland hydrology and salinity is also recommended to preserve wetlands of significant ecological values in Bass Strait and the wider region.