Current Research
I am particularly interested in uncovering past environmental histories and species responses under the pressing influences of climate change. My current research aims to reconstruct landscapes and wildfire activity across temperate and subtropical Australia in response to human activities and climatic change. I specifically work on integrating multiple proxies bridging natural and social sciences within Indigenous-curated landscapes and disentangling post-colonial management implications.
Past Research
Latest relevant publications:
Mariani, M., Wills, A., Herbert, A., Adeleye, M., Florin, S.A., Cadd, H., Connor, S.E., Kershaw, P., Theuerkauf, M., Stevenson, J., Fletcher, M., Mooney, S., Bowman, D.M.J.S., Haberle, S. (2024) Shrub cover declined as Indigenous populations expanded across southeast Australia. Science. DOI: 10.1126/science.adn8668. Featured in the media (selection): The Conversation (Australia); ABC Radio (various locations); Radio Sveriges, UNDDR Prevention Web; The Guardian (Australia). Top 5% of outputs ever tracked by Altmetric.
Wildfires in forests globally have become more frequent and intense because of changes in climate and human management. Shrub layer fuels allow fire to spread vertically to forest canopy, creating high-intensity fires. Our research provides a deep-time perspective on shrub fuel loads in fire-prone southeastern Australia. Comparing 2833 records for vegetation cover, past climate, biomass burning, and human population size across different phases of human occupation, we demonstrated that Indigenous population expansion and cultural fire use resulted in a 50% reduction in shrub cover, from approximately 30% from the early to mid-Holocene (12 to 6 thousand years ago) to 15% during the late to mid-Holocene (6 to 1 thousand years ago). Since the start of British colonization to the present, shrub cover has increased to the highest ever recorded (mean of 35% land cover), increasing the risk of high-intensity fires.
Mariani, M., Connor, S., Theuerkauf, M., Herbert, A., Kuneš, P., Bowman, D., Fletcher, M.-S., Head, L., Kershaw, P., Haberle, S., Stevenson, J., Adeleye, M., Cadd., H., Hopf, F. & Briles, C. (In press). Disruption of cultural burning promotes shrub encroachment and unprecedented wildfires. Frontiers in Ecology and the Environment. Featured in the media (selection): The Conversation (Australia); Nature Research Highlights (https://doi.org/10.1038/d41586-022-00509-5); ABC Radio (various locations); The Independent, The Daily Mail, The Telegraph (online news). Top 5% of outputs ever tracked by Altmetric.
Recent catastrophic fires in Australia and North America have raised broad-scale questions about how the cessation of Indigenous burning practices impacted fuel accumulation and structure. For sustainable coexistence with fire, we need to better understand the ancient nexus between humans and flammable landscapes. We use novel palaeoecological modelling and charcoal compilations to reassess evidence for changes in land-cover and fire activity, focusing on southeast Australia before and after British settlement. We provide the first quantitative evidence that the region's forests and woodlands contained fewer shrubs and more grass before colonization. Changes in vegetation, fuel structures and connectivity followed different trajectories in different vegetation types. The pattern is best explained by the disruption of Indigenous vegetation management caused by British colonization. Combined with climate change impacts on fire weather and drought the widespread absence of Indigenous fire management practices likely preconditioned fire-prone regions for wildfires of unprecedented extent.
Mariani, M., Fletcher, M.-S., Haberle, S., Chin, H., Jacobsen, G., Zawadzki, A. - Climate change reduces resilience to fire in subalpine rainforests. Global Change Biology, 25: 2030- 2042.
Climate change is affecting the distribution of species and the functioning of ecosystems. For species that are slow growing and poorly dispersed, climate change can force a lag between the distributions of species and the geographic distributions of their climatic envelopes, exposing species to the risk of extinction. Climate also governs the resilience of species and ecosystems to disturbance, such as wildfire. Here we use species distribution modelling and palaeoecology to assess and test the impact of vegetation-climate disequilibrium on the resilience of an endangered fire-sensitive rainforest community to fires. First, we modelled the probability of occurrence of Athrotaxis spp. and Nothofagus gunnii rainforest in Tasmania (hereon "montane rainforest") as a function of climate. We then analysed three pollen and charcoal records spanning the last 7,500 cal year BP from within both high (n = 1) and low (n = 2) probability of occurrence areas. Our study indicates that climatic change between 3,000 and 4,000 cal year bp induced a disequilibrium between montane rainforests and climate that drove a loss of resilience of these communities. Current and future climate change are likely to shift the geographic distribution of the climatic envelopes of this plant community further, suggesting that current high‐resilience locations will face a reduction in resilience. Coupled with the forecast of increasing fire activity in southern temperate regions, this heralds a significant threat to this and other slow growing, poorly dispersed and fire sensitive forest systems that are common in the southern mid to high latitudes.
Mariani, M., Holz, A., Veblen, T., Williamson, G., Fletcher, M.-S., Bowman, D. - Climate change amplifications of climate-fire teleconnections in the Southern Hemisphere. Geophysical Research Letters, 45, 5071-5081.
Recent changes in trend and variability of the main Southern Hemisphere climate modes are driven by a variety of factors, including increasing atmospheric greenhouse gases, changes in tropical sea surface temperature, and stratospheric ozone depletion and recovery. One of the most important implications for climatic change is its effect via climate teleconnections on natural ecosystems, water security, and fire variability in proximity to populated areas, thus threatening human lives and properties. Only sparse and fragmentary knowledge of relationships between teleconnections, lightning strikes, and fire is available during the observed record within the Southern Hemisphere. This constitutes a major knowledge gap for undertaking suitable management and conservation plans. Our analysis of documentary fire records from Mediterranean and temperate regions across the Southern Hemisphere reveals a critical increased strength of climate-fire teleconnections during the onset of the 21st century including a tight coupling between lightning-ignited fire occurrences, the upward trend in the Southern Annular Mode, and rising temperatures across the Southern Hemisphere.
Future Research
The following funded projects are ongoing:
- Uncovering the spatial extent of native food plants in pre-colonial Australia (Leverhulme Trust Research Project Grant):
[PI: Michela Mariani, CO-Is: Barry Lomax, Andrew Clarke and Janelle Stevenson]
The project aims to reveal the nature and extent of food production by Indigenous peoples within a changing climate. We will explore Australia's ancient agricultural systems, providing new perspectives on food production over the last 12,000 years. Successful completion of the research will allow us to disentangle one of the most ancient, least-studied and cryptic agricultural systems. The project integrates multi-disciplinary approaches to offer the first long-term quantification of native food plant cover in pre-colonial southeast Australia, by using molecular and biochemical markers found in lake sediments in conjunction with well-tested pollen-based landscape modelling techniques.
- Fuels for fire: quantifying vegetation through changing climates in Australia (Leverhulme Trust)
[Leverhulme Trust Newsletter - May 2023 by Leverhulme Trust - Flipsnack, PI: Michela Mariani ]
Project summary: In Australia, the unprecedented wildfires of 2019-2020 sparked debates around managing forest fuel loads in a context of climatic warming and increased fire risk. Reinstating Indigenous cultural burning is gaining momentum as an option for mitigating such disastrous events, but empirical evidence for its efficacy is limited. This fellowship aims to quantify vegetation cover across southeast Australia through a phase of rapid warming analogous to the present, but during which management was only carried out by Indigenous peoples (i.e. Late Pleistocene). This reconstruction will be compared to present-day fuel dynamics derived from decades of post-colonial fire suppression and rising temperatures.