School of Ecosystem and Forest Sciences - Theses
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ItemLeaves to landscapes: what drives litter bed flammability?( 2022)Fire is an important disturbance globally, shaping the structure and composition of many forested ecosystems. While fire is a natural process, large, extreme fire events can have devastating consequences on people and the environment. Predicting when and where fires occur is key to being able to manage these impacts. Most forest fires start as small fires, igniting and initially spreading in the litter bed – the layer of dead leaves, twigs and bark on the forest floor. Despite the importance of litter beds to wildfire occurrence and intensity, our understanding of the drivers of litter bed flammability remains incomplete. Thus, the over-arching aim of this thesis was to examine the drivers of litter bed properties and flammability, in order to better understand the mechanisms underpinning litter bed flammability. Starting at the leaf-scale, I reviewed the literature on leaf traits, litter structure and flammability to summarise current knowledge and identify knowledge gaps (Chapter 2). I performed a meta-analysis using existing data collated from key laboratory flammability studies in different fire-prone biomes. Leaf traits predominately influenced flammability indirectly, via litter structure. The packing ratio and bulk density of the litter bed were influenced by different combinations of leaf traits and, in turn, they aligned with different flammability metrics. Importantly, the effects of the leaf and litter traits were consistent across a wide range of taxa and biomes. However, uncertainty remained regarding whether the relationships identified in simple litter beds continue to be important at field-scales in litter beds which are more complex in relation to their structure, composition, and moisture content. Hence, I developed and tested the effectiveness of a laboratory method to measure ignitability of litter beds collected from the field (Chapter 3). I examined how the results of this laboratory method matched a similar but more logistically complex field method, to better understand the scalability of laboratory experiments. I found that laboratory experiments can be adequate surrogates for field experiments, particularly under low wind conditions and where there is little near-surface fuel and litter beds are the dominant receiving fuel for firebrands. I used this laboratory method to examine how flammability varies as a function of moisture, in combination with other factors, at two spatial scales: the litter bed and the vegetation community, sampling forested sites along an aridity gradient (Chapter 4). At the litter bed-scale, moisture content was a key predictor of ignition and flame spread rate. Moisture thresholds varied with leaf cover for ignition and leaf size for flame spread rate. Conversely, bulk density was a key predictor of flame duration, not moisture. At the community-scale, Vapour Pressure Deficit (VPD) was the best predictor of site-level ignitability. Aridity shaped the relationship between VPD and ignitability, reflecting differences in canopy cover and its influence on forest microclimate and fuel moisture dynamics. Less arid parts of the landscape had a higher VPD-threshold for ignition than more arid parts, meaning they are available to burn less often. Finally, I considered how management actions influence litter beds and understorey fuel (Chapter 5). Using data from a long-term ecological burning experiment, I examined how frequent prescribed burning and timber harvesting influenced the amount and composition of fine fuel, and the implications for flammability. Frequent fire had consistent effects irrespective of harvesting, increasing the amount of leaves in the litter bed and decreasing the amount of live understorey fuel. Overall, this research provides insight into the mechanisms underpinning litter bed flammability, from leaves to vegetation communities. This information can be used to improve fire prediction and fuel management.
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ItemBuddhist beliefs, value orientations, and human well-being: an investigation of the interactions between human and wildlife in the Himalayan Kingdom of Bhutan( 2022)Human-wildlife conflict (HWC) is a growing concern globally, it is however more prevalent in developing countries where subsistence farmers pursue livelihoods in the context of high and endangered biodiversity. In common with many Asian and African countries, subsistence farmers in Bhutan are increasingly experiencing HWC which threatens the food security of the rural population and the success of biodiversity conservation. Most existing research lacks the conceptual charity of the underlying drivers of HWC and integration required to inform practical policy formulation for conflict mitigation in subsistence contexts. This research aimed to build on existing studies and fill this knowledge gap. Framed within a social-ecological system, guided by a post-positivist research tradition, this research used mixed methods across four districts in Bhutan to explore the social, the economic and the ecological dimensions of HWC in relation to livelihood types, land tenure and HWC mitigation practices. Both quantitative and qualitative data was collected from diverse and complex socio-economic circumstances and was analyzed and interpreted by using qualitative and quantitative analytical tools and techniques. The findings showed that religious aspects played a significant role in this setting. The Buddhists beliefs of rural people in Bhutan are important in shaping peoples’ value orientations, attitudes and behaviours toward wildlife protection and conflict management. In situations of high economic loss and a lack of alternative livelihood options, this foundation of Buddhist beliefs however is at risk with a general lack of compassion towards wildlife leading to cognitive dissonance between the need to adhere to societal norms and values and the need to provide for livelihoods. Another important finding was that subsistence farmers are impacted directly and indirectly by wildlife and not only economically and physically but also psychologically. These impacts are unevenly distributed across the studied landscapes. Adaptative capacity and vulnerability to wildlife impacts are to a large extent influenced by socio-economic and socio-demographic factors. This thesis adds at least four new insights to the broader HWC literature and strengthens and expands our understanding of HWC in relation to gender and wealth. Firstly, the thesis adds new insights into how Buddhists beliefs shape value orientations, attitudes and behaviours towards wildlife and HWC management and how the negative wildlife impacts lead to personal and community dissonance between societal religious beliefs and value orientations. Secondly, another contribution from this thesis is that the research has demonstrated how psychological capital can be considered alongside traditional livelihood capitals. The poor psychological health of farmers resulting from: the on-going loss of sleep, loss of peace of mind, persistent fear and worry, and frustration; and, feeling of stress and insecurity, drive farmers into situations of anxiety and depression, highlighting that psychological capital must be considered along with other livelihood capitals as a significant facet of long-term HWC management in communities impacted by HWC. Third, this is the first research demonstrating how HWC impacts affect several sustainable development goals (SDG) and domains of gross national happiness (GNH), highlighting achievement of these broader development goals in subsistence livelihood contexts in communities impacted by HWC can be challenging. Fourth, compared to the usual attention given to the flagship species such as large predators, this research found meso-scale predators (e.g., Asiatic wild dog, Tibetan wolf, wild pigs) have caused the greatest total economic losses. The research also demonstrates how elephants represent a “pulse” impact on some farmers’ livelihoods, while smaller wildlife species (e.g., wild pig, Asiatic wild, dog) represent a “press” impact on livelihoods. Finally, the thesis adds insights into how gender and wealth influence severity of wildlife impacts, further compounding their vulnerability to HWC and food insecurity. Overall, this thesis contributes an integrative framework that clarifies the underlying drivers of the conflict, and empirical advancement of our understanding of HWC in subsistence livelihood contexts. Findings from this thesis have implications beyond Bhutan to landscapes in other regions where subsistence farmers share landscapes with wildlife.
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ItemInvestigating the seed ecology, functional traits and ecological strategies of Australian annual plants to create diverse, flowering green roofs( 2022)A diverse vegetation layer on green roofs is important to achieving and maximising green roof ecosystem services. Previous green roof research has mostly examined succulents and perennial plants with less attention to annuals and few green roofs incorporate annuals in the planting designs. This is despite annual species having an important role in some natural habitats with conditions that are analogous to green roofs. Their ability to escape seasonally harsh conditions as seeds, fast and cheap establishment via sowing, rapid growth, and the biodiversity and aesthetic value of their colourful flowers are also potential advantages of using annual plants on green roofs. Australia is a continent with a diverse annual flora with colourful and attractive flowering species and high potential to be used in horticultural applications such as green roofs. Therefore, the objective of this project is to develop an attractive flowering, resilient plant palette of Australian annual species suitable for green roofs in Mediterranean-like climates. However, to achieve this, we need more knowledge regarding annual species seed germination, functional traits and ecological strategies. Seed germination capacity is one of main constraints in seed-based projects. A high proportion of wild plant species in Australia produce seeds that are dormant upon maturity and will not germinate without a suitable pre-treatment. Increasing knowledge about factors such as seed mass and climate variables that may influence or predict germination percentage is helpful if species are to be used in horticultural applications, like green roofs. To do so, we commercially sourced seeds of 58 Australian annual species from a wide range of habitats and performed germination tests using different germination stimulants and temperatures in growth chambers. Only 20 out of 58 species germinated regardless of the applied treatments and no optimal treatment was found for all species. No relationship was found between seed mass, and germination percentage and speed. Lower germination was observed in species from hotter and drier environments as well as environments with more variable rainfall. Moreover, germination speed was greater in species from drier environments and environments with lower climate variability. Finding significant relationships between climate variables and germination attributes, and no relationship between seed mass and germination, shows that climate is a better indicator of germination and could be a more useful way to select annual species for horticultural applications than seed mass. The plant functional traits of plant species growing on green roofs are major factors determining the ecosystem services green roofs provide. Moreover, flowering plants which can quickly achieve high cover, growth and biomass are desirable for aesthetic reasons and to meet green roof construction guidelines. Annual species are generally drought escapers with acquisitive strategy and ‘fast’ traits, rapid growth and flowering. However, since annuals grow successfully in different habitats and climates, it is expected that they have different strategies to live and complete their life-cycle. To quantify plant strategies of annuals and evaluate the ecosystem services they may offer on green roofs and to develop a trait-based plant palette of annuals for green roofs, I undertook a common garden experiment with 18 annual plant species (successfully germinated in the previous experiment). It explored the relationships among traits related to drought resistance and resource acquisition, competitive and reproductive ability and also aimed to determine whether differences in plant strategies would influence their growth rate, shoot biomass and flowering time. Species with higher acquisitive strategy were more competitive, fast growing and produced higher final biomass. Two opposing strategies were observed in the studied annual species in regard to their flowering time and relative growth rate. Plant species also showed a trade-off between their flowering time and specific leaf area (SLA). Fast flowering species with higher SLA were considered less drought resistance (drought escapers), as earlier flowering and higher SLA are both evolutionary responses of annual species to escape stress. Fast growing species with resource acquisitive strategy could be more desirable on green roofs as they have higher water use and therefore, stormwater mitigation ability. It is also more preferable to select species with a range of time to flowering onset and SLA to achieve a long-term flowering community with different levels of drought resistance. Finally, I created a seed mixture using 16 species which we found had higher than 50% germination in the earlier study. I then sowed them in extensive green roof modules, to assess the effects of water availability on annual plant growth and diversity. Species abundance and richness were not significantly different between irrigation levels but showed a significant reduction through the experiment. Plant cover was significantly higher when the mixes were irrigated at a higher frequency; however, > 80% plant cover was achieved in all irrigation treatments. At the community level, functional diversity was unaffected by irrigation frequency. This study showed that annual species seed mixes can have good germination and establishment on green roof substrate and attain high species and functional diversity and cover with little irrigation.
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ItemExploring individual engagement in urban nature experiences( 2022)The benefits of spending time in nature are well-documented, however, so too are the diminishing opportunities that urban populations have to experience nature. In an effort to increase such opportunities, a growing literature examines nature-based interventions that aim to enhance individual engagement with nature, for example, through mindfulness. These studies typically use short exercises that direct one to attend to some feature of their nature experience, with aims to strengthen outcomes such as psychological restoration or connection with nature. This emerging literature, however, lacks the integration that is needed to develop a useful evidence base to inform practical application of engagement interventions in nature. To address this gap, I first developed a conceptual framework based on the concept of mindfulness to identify and understand existing engagement forms in the literature. I then empirically investigated how individuals engage within urban nature, the efficacy of different nature-based engagement interventions, and the influence of personal and environmental aspects of the nature experience that shape engagement and nature outcomes. This research used mixed methods to explore the role of individual engagement in nature experiences. An exploratory study first used a qualitative, semi-structured interview method, to explore how individuals engage in urban nature experiences. Participants (n = 20) were interviewed about their brief experience in an urban green space, and I used thematic analysis to identify engagement forms that connected to individual and environmental contexts of each experience. A second study used an experimental design to evaluate the effect of different engagement interventions in nature. Participants (n = 215) were randomly allocated into four different intervention groups, which were directed to engage in different ways during a 20min outdoor experience. The intervention groups were a mindful engagement group, a directed engagement group, a mind wandering group, and a control group who received no engagement directions. I analysed the effects of the interventions on post-experience restoration and nature connection and tested environmental and personal influences on engagement during the experience. Further, I analysed the subfactors of mindfulness and mind wandering to test their influence on outcomes of nature experiences. A key empirical outcome was identifying diverse forms of engagement in nature, which expands understanding of the various ways individuals might experience and relate to nature. The findings across the two studies additionally revealed patterns in the forms of engagement best suited to improve restoration and nature connection. Enhanced sensory engagement, positive mind wandering, and decentering (an aspect of mindfulness that involves detachment from thoughts and emotions) were associated with improved mood and nature connection. Mindfulness in nature was beneficial for those who were familiar with the practice in the qualitative study; in the experimental study, there was little evidence that instruction to engage mindfully led to better outcomes. Forms of engagement that required judgment and elaborative thought were associated with worse outcomes for restoration and nature connection. The analysis of contextual aspects of the nature experiences highlighted personal capacities (i.e., trait-level of mindfulness, current mood) that influenced how participants engaged during the experience; for instance, those with a lower mood were more likely to feel distracted and mindless in nature, while they benefitted from sensory engagement. The influence of environmental contexts showed that the perceived restorativeness of environments was strongly related to an individual’s engagement with the experience. Overall, this thesis contributes 1) an integrative framework that clarifies the characteristics of engagement forms in nature and their relation to psychological restoration and nature connection, and 2) empirical advancement of nature-based engagement interventions by evaluating their effectiveness. The results demonstrate meaningful differences in how engagement forms relate to psychological outcomes, and the practical feasibility of applying engagement interventions. The findings in this thesis encourage future examination of engagement forms that suit a diverse range of individual capacities and needs, specifically by targeting engagement that requires little effort and complements restorative qualities in nature (such as mind wandering and sensory engagement). I conclude with practical recommendations for designing and implementing nature-based engagement interventions. Refinement of such interventions offers future pathways to enhanced functioning and nature connection among urban populations.
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ItemSatellite Remote Sensing of forest productivity and water status in an asynchronous climate and its application to the seasonal forecast of soil moisture( 2022)Soil moisture controls the vegetation water status, which is a prominent contributor to defining overall forest ecosystem health. Moreover, it has a crucial connection with forest growth, catchment water yield, bushfire risk, forest fuel moisture, forest carbon sink and streamflow, making real-time mapping and forecasting soil moisture status crucial. In Southeastern (SE) Australia, the plot scale short term feedback of vegetation to soil moisture deficit had been studied in detail; however, long term interaction at a large spatio-temporal scale remains largely unexplored. SE Australia represents an asynchronous climate where the vegetation growth drivers, i.e., rainfall and temperature, are seasonally out-of-phase. This asynchronicity suggests forests survive on deep soil moisture stores during the extensive dry season. However, these soil moisture stores are unknown, complicating the connection between past rainfall events, available moisture, and forest growth response in such climate settings. Consequently, there are limitations in our capability to map vegetation water status and forecast soil moisture. This study aimed to explore the potential of satellite observations in mapping real-time vegetation water stress and soil moisture forecast at a large spatio-temporal scale in SE Australia's forested landscape. Three different methods were developed to address the presented aim. The first method focused on the real-time retrieval of vegetation water stress. It was hypothesized that an improved water stress index could be constructed by the representation of canopy water content information to the Land Surface Temperature (LST) – Normalized Difference Vegetation Index (NDVI) trapezoid model. A new parameterizing method was developed to construct a temporally transferrable vegetation water stress index from the newly augmented spectral space. The performance of the new index was assessed by its capability to predict soil moisture from 60 study sampling windows and soil water fraction from four contrasting FLUXNET sites over the forested landscape in Victoria. Finally, the superiority of the index was presented by comparing its performance against the existing remotely sensed vegetation water stress indices. The second method focused on understanding the long-term relationship between rainfall and Eucalyptus growth. Being an asynchronous climate and forests have access to deep soil moisture stores, the study hypothesized that in SE Australia, there exists a sequential link between some distant (in time) rainfall event, soil moisture stores, and Eucalyptus growth response. It was assumed that NDVI represents yearly accumulated biomass in the Eucalyptus Forest, and it has a link with deep soil moisture dynamics. To address this hypothesis, lagged relationship between antecedent accumulated rainfall and observed NDVI from 2160 study sampling windows was analyzed. The result showed that Eucalyptus forests have a long memory of the previous rainfall, and this memory has a pattern across aridity. This pattern revealed that the middle aridity range forests have a relatively short-term memory of the past rainfall compared to the forests at two extreme ends of aridity, and that this memory pattern correlates with soil depth across the landscape. The third methodology has used this sequential connection between antecedent rainfall, soil moisture stores and forest growth response to forecast soil moisture. The focus centered on using the past rainfall condition, site-specific landscape attributes, and remotely sensed vegetation response in forecasting soil moisture three months in advance. An integrated system was constructed using these as input to the machine learning model trained and tested over 2160 study sampling windows. It was hypothesized that incorporating Moderate Resolution Imaging Spectroradiometer (MODIS) into the machine learning (ML) method will improve the skill for seasonal soil moisture forecast compared to the base model (ML model with all inputs excluding MODIS) and can probably reduce some of the base model's input parameters. A novel methodology was applied where the amount of rainfall driving Eucalyptus growth was back calculated using vegetations response in summer to wintertime rainfall. The result showed that in Mediterranean regions like SE Australia, antecedent rainfall and remotely sensed vegetation response has great potential in forecasting soil moisture three months in advance. Overall, results show that satellite observations have great potential in mapping real-time vegetation water stress and soil moisture forecast over southeastern Australia’s forested landscape.
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ItemDecision-Support Tools for Wetland Management and Biodiversity Conservation( 2022)Wetlands play crucial roles for biodiversity and in ecosystem services, yet, they are one of the most threatened ecosystems in the world. While they require increased conservation attention, it is important that conservation decisions are well-thought out. There are well-developed decision-support tools for terrestrial and riverine systems, however, development and application to wetlands has received limited attention. This is important because wetlands and their biodiversity have unique characteristics and requirements that may require modified approaches. More broadly, there are several challenges in conservation decision-making that this thesis aims to address. Decision-support tools exist for prioritising areas for one-off and binary actions (e.g., protect versus not-protect), however, methods for prioritising incremental or ongoing actions, while accounting for uncertainty, remain uncommon. Cost-effectiveness is recognised as a fundamental objective in systematic conservation planning and natural resource management, yet, there is limited access to and use of cost data. Difficulties also remain in predicting management effects under different settings, at a region-wide scale, when key habitat variables are not spatially explicit. This hinders identification of real cost-efficiencies. This thesis presents five studies that extend current decision-support tools and explores how inputs to those tools can be improved to support wetland spatial planning. The studies are applied to a waterway management region in Victoria, Australia. Firstly, an approach is presented that combines metapopulation viability and cost-effectiveness analyses to select among alternative conservation actions, while explicitly accounting for uncertainty. The second study applies a spatial conservation prioritisation to the region of ~65,000 wetlands while identifying and incorporating species-specific connectivity requirements. Thirdly, an approach is developed that integrates species distribution models with structured expert elicitation to capture expert understanding of likely outcomes of management actions for species, and uses this to spatially predict the management effects on multiple species. The fourth study explores the process and challenges of deriving and computing costs of management actions, while applying them to a large-scale resource allocation problem. Finally, a spatial conservation prioritisation approach is developed to balance management cost-effectiveness with species representation, while accounting for species-specific connectivity, multiple candidate management actions and spatially variable costs. These studies resulted in various useful insights and outputs that will support resource allocation problems. It was found that estimated costs and benefits can vary dramatically depending on how site-specific details are accounted for. This emphasises the need to apply methods that adequately account for site-specific details in large scale prioritisations. Defensible methods are presented that allow a decision-maker to: identify the suite of wetland-specific actions to undertake, and the top fraction of the landscape to target, in order to achieve the best possible conservation outcomes for a given budget; explicitly justify investments; and, understand trade-offs when there are multiple objectives. This thesis contributes to filling the gap in accounting for the species-specific habitat and connectivity requirements of wetland biodiversity in a spatial prioritisation. Applying and building on these methodological improvements should help facilitate the identification and adoption of resource allocation solutions that more closely align with the objectives and preferences of decision-makers.
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ItemStreamflow variability across the Australian temperate zone under wildfires, droughts, and non-stationary and dynamic climate conditions( 2022)Water is a vital natural resource required for domestic, industrial, agricultural, and ecological uses. The amount of streamflow and consequently water availability around the world, particularly in temperate zones, are changing. Across the Australian temperate zone, streamflow is highly variable temporally and spatially, and is under increasing stress because of non-stationary and dynamic climate and increasing extreme events such as wildfires and droughts. Non-stationary climate (climate change) influences the long-term trend of streamflow, and dynamic climate (climate variability modes) leads to seasonal, annual, and decadal oscillations in streamflow. Non-stationary and dynamic climate also alter the frequency and magnitude of the eco-hydrological processes such as wildfires and droughts, and subsequently, these eco-hydrological processes alter the amount of streamflow and water availability. While the effects of non-stationary and dynamic climate, wildfires, and droughts on streamflow variability are well established individually, understanding about their relative influence and the implications of their interactions on streamflow variability at broad spatial scales are not well defined. In this research, regional datasets and innovative analyses were used to explore the relative influence of these drivers (climate change, climate variability modes, wildfires, and droughts) on annual streamflow variability and to define interactions and evaluate implications for water availability. The analysis was performed using climate mode indices, wildfire, topographic, land cover, rainfall, and streamflow data from 1975 to 2018 for 92 predominately forested catchments located across three hydroclimate regions of the Australian temperate zone. Results showed that the relative influence of climate variability modes on annual streamflow variability, directly through variability in precipitation (51% - 84% depends on the region), was higher than the relative influence of indirect ecohydrological effects associated with wildfire (8.8%) and droughts. Climate variability modes had different influences on streamflow (36% - 70%) in comparison with rainfall (51% - 84%), and their influences vary between and within hydroclimate regions of the Australian temperate zone. The analysis highlighted that at broad temporal and spatial scales, streamflow variability is mainly governed by the effects of non-stationary and dynamic climate, while at the catchment scale it is increasingly influenced by the effects of changing eco-hydrological processes mediated through drought and wildfire. The influence of droughts and wildfires varies depending on the hydroclimate settings, with higher effects in drier regions. This suggests that under projected climate change and an increasingly dynamic climate, it is essential to consider both exogenous drivers of streamflow (non-stationary and dynamic climate) and endogenous drivers of streamflow (ecohydrological processes such as wildfires and droughts) for modelling and predicting streamflow variability and future water resource availability. For predicting and modeling streamflow at regional scales, where both the amount of water and interannual variability is essential, the role of climate variability modes and how they change with global warming require particular consideration. Of particular importance is increasing the understanding of the occurrence of extreme wet and dry years, even if the mean annual streamflow remains unchanged. The results in this thesis provide new insights into hydrological regimes and water availability across the hydroclimate regions of the Australian temperate zone and highlight the implication of non-stationary and dynamic climate and increased frequency and magnitude of wildfires and droughts on streamflow variability and water resource availability.
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ItemExploring the indirect effects of climate change on fire activity in Australian wet Eucalypt forests( 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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ItemDynamics of a flammable species in a forest landscape: A case study on forest wiregrass Tetrarrhena juncea R.Br.( 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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ItemManaging Interacting Invasive Predators for Biodiversity Conservation( 2022)Predators can have devastating impacts on biodiversity when introduced beyond their native range, and so are often lethally controlled. However, control of a dominant invasive predator can backfire if it frees subordinate invasive predators from top-down suppressive and competitive effects, a process referred to as ‘mesopredator release’. Identifying whether mesopredator release is occurring is important for biodiversity conservation, particularly as integrated management of co-occurring invasive predators is often costly or infeasible. Lethal control of the introduced red fox *Vulpes vulpes* (hereafter ‘fox’) is a common conservation strategy in Australia. Concerningly, there are reports of dramatic declines in native prey species following targeted fox control, frequently attributed to mesopredator release of the feral cat *Felis catus* (hereafter ‘cat’). However, evidence for the mesopredator release hypothesis is limited--both in regards to cats and more generally. The primary aim of my thesis was to test whether lethal fox control (1080 poison-baiting) causes mesopredator release of cats, in terms of their population density, occurrence, and behaviour. In the process, I derived the first estimates of cat density for Australia wet forest environments as well as investigated the relative importance of fox control, fire and other environmental drivers on the occurrence of these invasive predators and two threatened native prey species. My study was conducted across two regions in temperate south-eastern Australia, where foxes and cats are the only medium-large sized terrestrial predators (dingoes *Canis familiaris* being absent). In one region, I spatially replicated a landscape-scale control-impact experimental design three times within a long-term fox control program. In the other region, I used a before-after control-impact-paired-series design around a new fox control program. I led the deployment of 949 camera-traps (63,560 trap nights) to survey mammal communities and identify individual cats based on unique pelage markings, as well as collated data from an additional 2,831 camera-traps deployed by government research partners. I found that fox suppression varied with spatial and temporal variation in lethal control effort. Fox occurrence declined across gradients of poison-bait density: from ubiquitous to a near-zero occurrence probability in the region with long-term and consistent fox control, but relatively weakly in the region where fox control was less frequent and had only recently commenced. In contrast to expectations, my estimates of cat density in wet forests are among the highest recorded in 'natural' Australian environments. Cat density was higher with fox control across both regions. The strength of this effect appeared dependent on the degree of fox suppression: from negligible to a 3.7-fold higher density of cats. In addition, when localised fox activity was reduced, in some areas cat (i) detectability increased, (ii) movement rates decreased, and (iii) diel activity patterns reversed, potentially facilitating spatial coexistence. There was some indication that cats effectively employed avoidance behaviours when foxes were rare, but only declined in population density when fox activity was moderate - high. Long-term and spatially intensive fox control appeared strongly beneficial to the long-nosed potoroo *Potorous tridactylus*, but not the southern brown bandicoot *Isoodon obesulus*. This may reflect species-specific variability in susceptibility to foxes relative to cats. Further work is needed to understand the implications of mesopredator release on a wider range of shared prey species, particularly those more vulnerable to cat predation. My thesis provides robust experimental evidence that dominant predator suppression can cause mesopredator release in terms of both population density and behaviour. The singular control of an invasive predator may therefore take the pressure off some native prey, but alone is unlikely to improve the persistence of all species in systems where multiple invasive predators co-occur.