School of Agriculture, Food and Ecosystem Sciences - Theses

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    Exploring the indirect effects of climate change on fire activity in Australian wet Eucalypt forests
    Brown, Tegan Paige ( 2022)
    Understanding the impacts of climate change on future fire activity is critical for assessing the risks posed to biodiversity and communities. However, the mechanisms through which climate change may influence fire activity are varied. In temperate forests, climate change is expected to directly increase fire activity through elevated temperatures and more variable rainfall, resulting in weather conditions conducive to large fire events. However, climate change may indirectly influence fire activity through effects on forest structure and composition. While the direct effects of climate change are well studied, indirect mechanisms are poorly understood. These mechanisms are important because changes to vegetation structure and composition have the potential to amplify or dampen the direct effects of climate change on fire activity through their effects on fuels, particularly dead fuel moisture content (FMC). Forest structure and composition moderate microclimate conditions compared to the open, which is an important factor affecting the moisture content of understorey fuels. FMC is a key determinant of fire activity, particularly in wet Eucalypt forests with high biomass loads. However, our understanding of the magnitude of forest structure and composition effects on microclimate and subsequently FMC dynamics, is a critical knowledge gap in our understanding of climate change effects on future fire activity more broadly. In this thesis, I aimed to quantify the potential for indirect effects of climate change to influence fire activity, through their influence on dead FMC in the wet Eucalypt forests of south-eastern (SE) Australia. In these forests, recurrent high-intensity fire has altered vegetation structure and composition, resulting in a range of alternative forest states to the dominant wet Eucalypt system. To quantify the magnitude of these on potential fire activity, seven alternative forest states and two adjacent open weather stations were instrumented with automated fuel moisture sticks and micrometeorological sensors. FMC and microclimate were measured over a 2-year observation period, and lidar data were used to evaluate the role of forest structure in FMC dynamics. I used a process-based fuel moisture stick model to quantify the relative importance of forest structure effects on microclimate to FMC variability. This model was then used in conjunction with new methods to estimate microclimate from open conditions, and a 48-year climate dataset to model FMC at alternative forest states across the range of climate conditions characteristic to the region. I also evaluated the potential contribution of live species to changes in fuel moisture in a conifer forest and related this to the potential impacts of forest conversion to alternative states. Overall, I found significant differences in dead FMC across alternative forest states, with potentially meaningful implications for fire activity. The sensitivity of FMC to forest structure was examined, with longwave radiation and vapor pressure deficit emerging as key drivers of FMC variability related to structural change. These findings informed the modelling process, where results indicated that differences in FMC related to alternative forest state were greater than the direct effects of climate change (modelled at an open reference site), indicating strong positive and negative feedback processes in this system. Overall, my results suggest that the indirect effects of climate change on potential fire activity are meaningful for fire management, exceeding the role of direct effects in the context of FMC. Consequently, the potential for forests to convert to alternative states is a key issue for land and fire managers.
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    Dynamics of a flammable species in a forest landscape: A case study on forest wiregrass Tetrarrhena juncea R.Br.
    Cadiz, Geofe ( 2022)
    Species abundance often determines the extent of influence of a species to ecosystem function and processes. Typically, the abundance of a species is constrained by environmental factors within its habitat. However, there are instances where native species becomes prolific and the shift in abundance greatly impacts the ecosystem. Such is the case when a flammable species becomes prolific within its range and alters the flammability of the ecosystem. This is a concern with climate change, as conditions might be tipped in favour of such species. Hence, it is crucial to understand the drivers of abundance to understand how native species can be released from environmental constraints of abundance to become prolific within their own range, and to predict the potential effect of changing environmental conditions on their abundance. Thus, the overarching aim of this thesis was to understand how a flammable native species can become prolific within its own range. This is achieved using a case study species – forest wiregrass Tetrarrhena juncea R.Br. (hereafter wiregrass) – an understorey native species that is of high importance to flammability in the eucalypts forests of south-eastern Australia and grows prolifically under certain conditions. The overarching aim of the thesis was addressed using a mix of research methods to identify the key drivers of wiregrass distribution and abundance. Firstly, a database of the current distribution for wiregrass were analysed using species distribution modelling to identify highly suitable habitat for wiregrass (Chapter 2). Temperature seasonality, precipitation of the driest month, rainfall seasonality, annual mean temperature, the minimum temperature of the coldest month and soil pH were strongly associated with the suitable habitat of wiregrass. The high importance of climatic factors indicates the distribution of wiregrass may be sensitive to climate change. Highly suitable habitats do not necessarily harbor abundant wiregrass because site-specific factors can also control abundance. Hence, Chapter 3 sought to identify the factors most important to wiregrass abundance in the highly suitable habitat of Mountain Ash-dominated forest. Wiregrass cover was assessed in a field survey across a chrono-sequence of 126 sites with contrasting disturbance histories. Canopy cover and net solar radiation were the most important predictors of wiregrass abundance, with wiregrass cover highest in recently disturbed areas with sparse canopy cover, high light levels, and low precipitation. The final component of the thesis used a glasshouse experiment to quantify causal links between resource availability and wiregrass abundance. Wiregrass growth was more sensitive to water availability than light, whereas biomass allocation and leaf morphology were more sensitive to light availability. Collectively, the results showed that, where wiregrass is present (distribution), three key conditions will greatly favour its prolific growth (abundance): (i) non-limiting water resource; (ii) reduced canopy cover and increased light; and (iii) recent disturbance. These key results strongly suggest wiregrass can become prolific when resources are increased, and the vegetation community is substantially disturbed. Under such conditions, increased wiregrass abundance could create a window of increased flammability for the forest ecosystem. Since climate change can alter resource availability and disturbance regime, shifts in wiregrass abundance are likely to occur under future climate scenarios.
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    Predicting future fire regimes and the implications for biodiversity in temperate forest ecosystems
    McColl-Gausden, Sarah Catherine ( 2022)
    Fire regimes are changing around the world. Fire seasons are lengthening, high severity fires are occurring more often and in unexpected places. Relationships among fire, climate, and vegetation are varied, dynamic, and under-examined in many ecosystems. While some studies have explored links between fire, climate, and vegetation such as species distributions or future fire weather under changing climate, relatively few have considered the dynamic interactions among all three simultaneously. In this thesis, I develop and apply modelling approaches to predict future fire regimes in south-eastern Australia and explore the implications for fire-responsive functional plant types. In the first quantitative chapter of my thesis (Chapter 2), I develop a new fuel model for south-eastern Australia. I use edaphic, climatic, and fire variables to build a predictive fuel model that is independent of vegetation classes and their future distributions. In Chapter 3, I use my fuel model in a landscape fire regime simulator, alongside multiple predictions of future climate, to examine the immaturity risk to an obligate seeder tree species (Eucalyptus delegatensis). My simulations indicate that this species will be under increased immaturity risk under future fire regimes, particularly for those stands located on the periphery of the current distribution, closer to roads or surrounded by a drier landscape at lower elevations. In Chapter 4, I expand the application of the above simulation approach to examine the relative importance of future fuel and future climate to changing fire regimes in six case study areas across temperate south-eastern Australia. My results indicate that the direct influence of climate on fire weather will be the principal driver of changes in future fire regimes (most commonly involving increased extent, decreased intervals, and an earlier start to the fire season). The indirect influence of climate on vegetation and therefore fuel was also important, acting synergistically or antagonistically with weather depending on the area and the fire regime attribute. Finally, in my fifth chapter, I consider future climate and fire impacts on plant persistence by combining the landscape fire regime simulator with spatially explicit population viability analyses. Obligate seeder species were at risk of population extinction or reduction in more simulation scenarios than facultative resprouters. However, my approach highlighted that the resilience of facultative resprouters might also be tested by climate related changes in demographic processes and fire regimes. Overall, my research has provided new methods and scientific insights into the changing nature of fire regimes in temperate south-eastern Australia. Some negative impacts on biodiversity from a changing fire regime, particularly on more vulnerable plant functional types like obligate seeders, appear inevitable. Further understanding of the complex interactions among fire, climate, and vegetation will enable improved integration of risks to people, property, and biodiversity into land and fire management planning.
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    Finding the hidden smoke: Exploring the use of digital technologies for assessing grapevine smoke contamination and taint in grapes and wine
    Summerson, Vasiliki ( 2021)
    Grapevine smoke contamination and the subsequent development of smoke taint in wine has resulted in significant financial losses for winemakers throughout the world. Unfortunately, the incidence of grapevine smoke exposure is expected to rise as the number and intensity of wildfires increase due to the effects of climate change. Wines produced from smoke affected grapes are characterised by unpleasant smoky aromas, rendering them unpalatable and therefore unprofitable. Traditionally, chromatographic techniques such as gas chromatography-mass spectrometry (GC-MS) and high-performance liquid chromatography (HPLC) have been used for assessing the levels of smoke-derived volatile phenols and their glycoconjugates in grapes and wine. However, these methods are time consuming, expensive and require destructive sample preparation as well as the use of trained personnel. Furthermore, sensory evaluation of wine samples using human panels may be subject to bias due to individual variability of the participants, as well as being expensive and time consuming as large groups of participants must be recruited and trained. In addition to this, a number of methods have been identified for ameliorating smoke taint in wine such as the use of activated carbon and reverse osmosis. While effective at reducing levels of volatile phenols for smoke taint amelioration, they are unable to act on glycoconjugates, and therefore a gradual resurgence of smoky aromas may arise as these glycoconjugates are hydrolysed back into their free active forms over time. This research therefore investigated alternative methods for assessing the degree of grapevine smoke exposure and the level of smoke taint in wine using digital technologies coupled with machine learning (ML) modelling based on artificial neural networks (ANN), and whether the use of a cleaving enzyme prior to the addition of activated carbon could be effective at ameliorating smoke taint in wine. Near-infrared (NIR) spectroscopy was used to obtain a chemical fingerprint of grape berries, leaves, must and wine. These readings were then used as inputs to develop ANN models that showed high accuracy in the classification of berries and leaves according to the level of smoke exposure and degree of taint (97% – 98%), as well as predicting the levels of smoke-derived volatile phenols and their glycoconjugates in grapes, must and wine (R = 0.98 – 0.99). Additionally, models predicting consumer responses towards smoke tainted wines using NIR berry and wine spectral readings were created which displayed high accuracy in their predictive abilities (R = 0.97 – 0.98). The results demonstrated that NIR spectroscopy coupled with ML modelling can provide accurate, rapid and non-destructive tools for assessing grapevine smoke contamination and smoke taint in wine, in addition to predicting the sensory responses of consumers towards smoke tainted wines. Furthermore, the models developed can be used together to form an integrated smoke taint detection system that growers and winemakers can use in-field or in the winery to assess grapes and wine. A low-cost electronic nose (E-nose) was used to assess the aroma potential of smoke-tainted wines. Readings from the e-nose were used as inputs to develop ML models that showed high accuracy in predicting the levels of eight volatile aromatic compounds in wine (R = 0.99), the degree of smoke aroma intensity (R = 0.97). These two models may be used together with previously developed models that predict the levels of smoke-derived volatile phenols and their glycoconjugates and 12 wine descriptors to provide winemakers with a greater picture of the degree of smoke taint and the aroma profiles of smoke-tainted wines. In addition to this, the use of a cleaving enzyme (ZIMAROM, Enologica Vason) prior to treatment with activated carbon was found to be effective in ameliorating smoke taint and may help delay the resurgence of smoky aromas by hydrolysing glycoconjugates into their free volatile phenol forms which can then be removed by the addition of activated carbon. An ANN model displaying high accuracy (98%) was also developed using the readings from the e-nose to classify wine samples according to the type of smoke-taint amelioration treatment applied to assess their effectiveness. The model may offer winemakers a cost-effective, non-destructive, rapid, and accurate tool to assess the effectiveness of smoke taint amelioration treatment by activated carbon with/without the addition of a cleaving enzyme.
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    Regime resistance and accommodation in sustainable energy transitions
    Ford, Adrian Stuart ( 2020)
    To help accelerate the decarbonisation of electricity generation and meaningfully mitigate climate change, a more nuanced understanding of the power and influence of incumbent electricity firms in government policymaking is required. Building on sustainability transitions literature, concepts from neo-Gramscian political economy and insights from strategic management, this study investigated the ways in which incumbent electricity generators, network operators, retailers, and their industry organisations sought to influence residential solar power policy. The single case study is focused on Victoria, Australia, using data obtained from multiple sources, including: legislation; policy submissions, reports and documents; organisational documents and materials; media releases and articles; and transcripts of in-depth, semi-structured interviews with key informants from electricity utilities and their industry peak bodies. The study examined federal and state government policy instruments that supported the installation of residential solar power before it explored attempts by incumbent electricity firms and their industry organisations to influence the development of Victorian feed-in tariffs, the State Government’s primary policy instrument. The research found that incumbent actors contributed to the (re)production of a socio-technical regime by drawing on material, institutional and discursive forms of power to execute strategies of resistance and accommodation. Incumbent actors resisted feed-in tariffs by discussing them in negative terms, building alliances with opposed civil society organisations, lobbying policymakers and reminding them of their mutually dependent relationship. However, incumbent actors accommodated feed-in tariffs by working with government to implement its policy initiatives. Incumbent firms accommodated renewables more generally by operating renewable energy business units and joining renewable energy industry organisations, although the later served to moderate support for feed-in tariffs. The study also found that a number of external and internal factors shaped the strategic approach of incumbent electricity firms and limited the extent of their resistance. High public support for residential solar power and strong government determination to implement feed-in tariffs were key external factors that discouraged greater resistance from incumbent firms. Key internal factors included the assessment of feed-in tariffs as low risk to the ongoing profitability of incumbent firms, and higher policy priorities, the achievement of which necessitated good relations with government and the sacrifice of lower policy priorities. These findings suggest that a neo-Gramscian approach to understanding politics and power in sustainable energy transitions offers useful insights for policymakers, incumbent and renewable energy firms, and civil society organisations who seek to accelerate the decarbonisation of electricity generation.