School of Ecosystem and Forest Sciences - Theses

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    Streamflow variability across the Australian temperate zone under wildfires, droughts, and non-stationary and dynamic climate conditions
    Khaledi, Jabbar ( 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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    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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    Managing Interacting Invasive Predators for Biodiversity Conservation
    Rees, Matthew Wayne ( 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.
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    Promoting growth and regeneration of riparian trees in a degraded swamp
    Fischer, Sarah ( 2022)
    Humans and wildlife rely on resources and functions provided by healthy riparian forests. The ecological integrity of riparian forests largely depends on their key elements: trees. Riparian trees adjust resource allocations to survival, growth and reproduction in response to the flooding regime. Throughout much of the world, anthropogenic flow alteration has disrupted the natural flooding regimes upon which riparian forests depend. Consequently, many riparian forests fail to regenerate and are declining in their extent. Effective restoration approaches informed by knowledge of regeneration ecology of riparian trees is needed. Focusing on the role of flooding, I investigated how temperate evergreen riparian tree species regenerate and maintain themselves and how these processes can be promoted by restoration practice. I integrated ecological research and restoration practice to design three complementary field studies (Chapters 2–4). In Chapter 2, I coupled tree surveys and hydrological modelling to investigate how extant trees have developed and regenerate in response to past flood regimes. In Chapters 3 and 4, I conducted two manipulative field experiments to trial how sexual reproduction (via seedlings) and asexual reproduction (via resprouting) can be promoted via restoration. One experiment investigated whether restored river-floodplain connectivity benefits the establishment of planted tree seedlings and the role of flooding for seedling survival and growth. The other experiment tested whether, in the absence of flooding, coppicing may be a suitable means to initiate vegetative reproduction and if resprouting depends on disturbance timing and severity. Chapter 2 provides evidence that flood disturbance affects morphology and reproduction of woody riparian plants. Increased flooding was generally associated with greater stem numbers and stem leaning—morphologies associated with asexual reproduction—whereas sexual reproduction was more common in taller plants with single, more upright stems. This correlational study suggested that different aspects of the flooding regime (e.g. inundation duration vs frequency) prompt growth and regeneration responses in different tree species. Chapter 3 demonstrates that restored river-floodplain connectivity promotes woody plant establishment. Planted seedlings had higher growth rates when they were exposed to flooding after planting. However, survival rates and temporal growth patterns differed between species according to variation in flood duration and soil moisture, illustrating the different hydrological requirements of the coexisting species. Variable flooding and drying patterns, arising from river-floodplain connectivity, create recruitment niches for different riparian tree species. Chapter 4 reveals that riparian trees resprout regardless of timing and severity of disturbance by coppicing. The resprout shoot volume did not differ between trees coppiced in either autumn or spring at ground level or at 90 cm height. Coppice timing and height affected use of stored starch reserves but resprouting was not limited by starch availability. Thus, coppicing may be an efficient means to promote rejuvenation and persistence of tree species where site and tree condition are degraded and no longer support recruitment. Combined, my empirical studies provide evidence that temperate evergreen riparian forests rely on flooding to sustain their self-maintenance processes, structural integrity and function. Thus, reintroduction of appropriate disturbance (i.e. reinstated flooding and physical tree damage) should facilitate riparian tree regeneration and counteract riparian forest loss.
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    Modelling the biogeography of Australian Fungi
    Hao, Tianxiao ( 2021)
    Biogeography – the study of biological patterns in space – has often overlooked the Kingdom Fungi in the past, because the geographic distributions of fungi are difficult to document and study. However, increasing availability of fungi data collected across large spatial scales, and development of modelling-based methods allowing the interpolation of patterns between sampled locations, have enabled for the first time the study of continental scale mycogeography (biogeography of fungi) using quantitative methods. Focusing on Australia, this thesis explores this new research direction in detail, by accessing fungi distribution data at continental scales, interrogating the issues and characteristics of such data and developing appropriate ways to deal with them, and studying the prominent biogeographic trends and patterns emerging from the data using the species archetype modelling approach. This thesis has several major findings. First, for studying continental-scale mycogeography, data based on observations and specimen collections are the most readily available, but contain errors in geocoordinates and taxonomy and require thorough quality filtering and taxonomic curation. The sampling effort of these data is incomplete in space and biased towards easier-to-access areas, and such biases need to be addressed in analyses. Methods for checking data quality and dealing with biases are proposed. Second, environmental DNA (eDNA) collections of fungi in the soil provide an important alternative source of data, but exploring these data in detail reveals that their spatial patterns are different from observational data on the same species, and archetypal patterns based on eDNA data can be biologically unrealistic, signalling issues in identifying sequences to species and in detection success. The need to better understand the caveats of eDNA data motivates future systematic side-by-side observational and eDNA surveys. Third, by using species archetype models to group species into archetypes according to their shared environmental responses, this thesis reveals several main archetypal distribution patterns across Australia. Specifically, spatial patterns of Australian fungi can be partitioned into those strongly aligning with the southeast and the southwest coastal regions, those occurring in the arid centre, and those occurring in either the dry or the wet tropical regions. These analyses produce the first continental scale quantitative maps linking fungi to regions, and provide important support for further research on these fungi. Finally, by applying the relatively new species archetype modelling approach on challenging datasets at a continental scale, this work produces a valuable methodological knowledge base on the use of the method, and identifies worthwhile directions for future development, such as developing new approaches for selecting the number of archetypes in the model. Overall, this thesis thoroughly explores and applies appropriate methods for processing data and recently developed analytical methods, and significantly advances knowledge on continental scale patterns of mycogeography. The knowledge produced by this thesis provides a foundation for further research in Australia, and demonstrates a novel approach for mycogeography suitable for applications across the globe.
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    Environmental filtering shapes plant turnover and species occurrence in post‐logging regrowth forest in southeastern Australia
    Singh, Anu ( 2021)
    Environmental factors play a more influential role in shaping plant community composition, while disturbance shapes plant community composition in southeastern Australian temperate forests. Plant communities in forests subjected to timber harvesting have been found to differ from wildfire sites in the montane forests of the Central Highlands in Victoria; however, a quantitative understanding of the factors that shape post harvesting plant communities is lacking. Quantifying the factors that shape plant community composition in post logging regrowth forest is important for understanding how timber harvesting influences plant biodiversity. Here, I aimed to explore the role environmental filtering species turnover and composition of the species in post logging regrowth forests. I focused my studies on the forested landscapes of southeastern Australia, where bushfires and timber harvesting are the primary catalysts for regeneration in Eucalyptus regnans, E. delegatensis, and high elevation mixed species forests. I investigated the post disturbance regeneration dynamics in these forests and sought to determine the direct impact of climate variability on regeneration and the interactive effects of climate, topography, and edaphic factors on the regeneration success of Eucalyptus. Untangling the roles of climate, topography and edaphic conditions on plant regeneration is important for understanding current and future risks of climate change to plant species richness. To test the influence of climatic, topographic, and edaphic variables on the occurrence and abundance of Eucalyptus regeneration, I used machine learning models. Declines in number of seedling regeneration of eucalypt during the period of drought were greater in E. regnans and E. delegatensis than HEMS forests, suggesting that regeneration in the HEMS forests is more resistant to drought. I furthermore found that seasonal precipitation and temperature had the greatest influence on regeneration success of Eucalyptus. My findings highlight the importance of seasonal and annual climate variability on Eucalyptus regeneration and portend potential declines in regeneration success in a warmer and drier future, particularly for E. regnans and E. delegatensis. A fundamental requirement of sustainable forest management is that stands are adequately regenerated after harvesting. To date most research has focused on the regeneration of the dominant timber species and to a lesser degree on plant communities. Relatively few studies have explored the impact of regeneration success of the dominant tree species on plant community composition and diversity. Therefore, I quantified the influence of environmental filtering on plant species diversity in montane regrowth forests dominated by Eucalyptus regnans in mainland southeastern Australia. I found that Acacia density shaped plant biodiversity more than Eucalyptus density. I also found that edaphic factors, in particular soil nutrition and moisture availability, played a significant role in shaping species turnover and occurrence. My findings suggest that the density of Acacia is a key biotic filter that influences the occurrence of many understorey plant species and shapes plant community turnover. This should be considered when assessing the impacts of both natural and anthropogenic disturbances on plant biodiversity. In this thesis, I also explore the role of soil seedbank as a source of plant propagules in these forests. Our ecological understanding of plant community response to disturbance and environmental variation is largely restricted to the above ground species pool. Plant community composition often changes dramatically after disturbance due to mortality of above ground vegetation and recruitment of species that respond to a change in resource availability. To quantify the relative importance of environmental gradients on individual species occurrence and community composition, I used a joint analysis approach. In total there were 113 plant species in the combined species pool. A total of 39 species were shared between above ground and soil seedbank pools. There were 41 species exclusive to the above ground vegetation. Aridity was the main environmental covariate explaining plant community across all pools of plant diversity and across non woody and woody life forms. Environmental covariates explained more than 59 percent of the variance for 43 species in the combined species pool. The composition of the soil seedbank and above ground diversity was distinct, with low similarity 14 percent, which highlights the importance of the soil seedbank as a reservoir for plant diversity not captured in above ground vegetation. Finally, I aimed to quantify the influence of Acacia and Eucalyptus composition and configuration on species turnover to provide an important tool for mapping patterns of plant diversity in post disturbance forests. To achieve this, I combined remotely sensed UAS imagery with ground survey data of plant composition from post logging regrowth forests. I found that spatial predictions of forest configurations providing Eucalyptus and Acacia cover metrics such as spatial aggregation were useful in estimating understorey plant beta diversity. Significant relationships between the aggregation metrics derived from UAS imagery as well as site aridity and beta diversity were observed. Increasing aggregation of Acacia, aridity and number of Acacia patches had a significant negative effect on plant beta diversity, whereas number of patches of Eucalyptus had a positive influence. This research highlights how remote sensing can provide and improve measures of forest plant biodiversity in regrowth forests which can support forest managers and conservation efforts to quantify and map patterns of plant diversity at the stand scale and beyond. Overall, my findings highlight that post logging regrowth forests are systematically shaped by soil and climatic factors while also being filtered by stand structure and composition. I demonstrate the role of climate, topography, soil, and light availability in shaping plant communities in post logging regrowth forests. The success of eucalypt regeneration in the stand reinitiation phase influences overstorey composition and structure. I found that that soil nutrition and moisture availability played a significant role in shaping plant community composition at fine scales and aridity at broad scales. I further found that Acacia density shaped plant biodiversity more than Eucalyptus density. My study highlights the role of environmental filtering on plant community composition in post logging regrowth and how it must be considered when assessing the impacts of anthropogenic disturbances on plant biodiversity in the temperate forest of southeastern mainland Australia.
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    Investigation of bark properties and cambium cell viability of Eucalyptus in relation to heat exposure
    Subasinghe Achchige, Yasika Medhavi ( 2021)
    Fire is integral to many temperate forest ecosystems. Given increasing occurrence of wildfires around the world, forest management applications such as low and moderate intensity burnings are required to reduce fuel loads to decrease the severity of wildfires. However, little is known about the effect of low to moderate intensity fires on vascular cambium necrosis in trees. During a fire, heat is transferred through the tree bark towards the vascular cambium (i.e., a vital tissue layer inside a tree stem which ensures the perennial growth of a tree) potentially increasing cambium temperature to lethal levels. As tree bark shields the vascular cambium from thermal damage, a better understanding of the bark traits that protect the vascular cambium during fires is required. Genus Eucalyptus is broadly distributed in fire-prone ecosystems thus, exhibits different fire adaptive traits such as post-fire regeneration strategies (i.e., resprouting via epicormic strands) and has a wide range of different bark types. As a native plant genus and the dominant species in open forests of southern Australia, Eucalyptus species present a great opportunity to investigate bark properties in relation to cambium cell viability. In this study, firstly, cambium sections were exposed to heat treatments in vitro to determine the best method to estimate a cell viability index (CVI) to allow a detailed investigation of heat degradation of cellular function in relation to fires. A tetrazolium reduction method (TTC method) was compared to a Neutral Red method applied to different tissue sizes to quantitatively determine CVI and to derive a critical temperature threshold for cambial cell viability in vitro (Chapter 2). The interactive effect of temperature and exposure time on cambium cell viability in vitro was investigated in the third Chapter. Based on findings of Chapters 2 and 3, properties of the bark i.e., bark thickness, moisture content, bark density, thermal diffusivity, and thermal conductivity of the three Eucalyptus species of contrasting bark types (E. obliqua - stringy bark, E. radiata - Fibrous bark and E. ovata - Smooth bark) were investigated in Chapter 4. In Chapter 4, stem sections of freshly felled trees were exposed to a fixed heat flux which simulated conditions of low to moderate intensity fires; thermocouples were inserted into sapwood, cambium and bark to measure the temperature and time to reach critical temperature of 60oC was recorded. Cell viability was measured against the untreated control samples. Bark properties of three species were measured and analyzed against cell damage. The key results of this study were: (i) Tetrazolium reduction method (TTC method) is the preferred method to assess cell viability of Eucalyptus species, while Neutral Red method can be used to cross check the results of the TTC method; (ii) Critical temperature for cambium cell viability is 60oC; (iii) A prolonged exposure to sublethal temperatures (40-50oC) causes similar effect as a short exposure to lethal temperatures (>50oC); (iv) Critical exposure time in-vitro for cambium cell viability of Eucalyptus species is 1-5 minutes; (v) Bark moisture and thickness play the major roles in regulating heat transfer through bark; (vi) A thicker, dryer, lower density and lower thermal conductivity stringy bark of E. obliqua shows greater insulation ability than the other two bark types tested; (vii) Critical exposure time for cambium cell viability in-vivo may vary between 20 to 40 minutes depending on bark type and bark thickness; (viii) Among the trees tested the radiant energy required for the cambium-phloem cells to reach critical temperature ranged between 3.5 and 13.6 MJ m-2; (ix) Prolonged exposure to low heat flux like 10 kW m-2 can also cause significant cambium damage. Findings of this study have provided significant insights in relation to properties of tree bark, to better understand the heat tolerance levels of Eucalyptus species during low to moderate intensity fires. The study developed a novel method to assess the cambium cell viability of Eucalyptus species following heat exposure. Overall, this study provides a better understanding for land managers to perform low intensity fuel reduction burns to avoid tree damage. Findings of this work will guide and expand future research on stem heat transfer models and fire behavior models to improve tree survival following fires.
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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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    Enhancing Environmental Benefits of Rainwater Harvesting Systems Using ‘Smart’ Real-Time Control Technology
    Xu, Wei ( 2021)
    Urban centres face numerous challenges related to the urban water cycle, including flooding, degradation of receiving waters, and scarcity of water resources. Among the stormwater control measures (SCMs) being increasingly adopted worldwide to improve the way stormwater is managed, rainwater harvesting (RWH) systems can potentially simultaneously address all of these issues. However, their performance has, until now, been limited by their passive and static nature, lacking the ability to adapt to changing conditions, such as rainfall variability, and climate and urban expansion. Recent advances in real-time control (RTC), so called “smart” technology, offer great promise to transform the conventional RWH systems into highly adaptive systems. To date however, little is known about the benefits of such technology in improving the performance of RWH systems. Understanding, testing and exploring this potential is the primary focus of my research. My thesis aims to develop and test RTC strategies that improve the simultaneous objectives of RWH systems related to water supply, flood mitigation and restoration of more natural flow regimes. This analysis is undertaken at a range of scales, given the potential for such technology to be applied to rainfall captured from individual buildings, or to networks of rainwater storages distributed throughout a catchment. This thesis comprised four major components. It first comprehensively reviewed the literature and examined the state-of-art of the application of RTC technology in a range of SCMs. Many studies have shown that the use of RTC can improve the performance of various type of SCMs at the site scale, in terms of both runoff quality and quantity (hydrology). On the other hand, there is a relatively untested potential to apply such technology at a mix of scales. The second component developed and modeled a range of RTC RWH systems that utilised a 7-day rainfall forecast to examine the impact of increasing rainfall forecast window on the performance of these systems in water supply, flood mitigation and restoration of more natural flow regimes. Using a relative long lead-time rainfall forecast was shown to enhance the ability of RTC in mitigating flood risks, while delivering an outflow regime that is close to reference streamflow. Such a design has also demonstrated to minimise the effect of forecast errors, given that the longer prediction window provides greater opportunity to adapt, before the forecast rainfall event occurs. Based on such RTC strategies, the network-scale impacts of RTC RWH systems on the behaviour of a stormwater network were also assessed through a modelling study. RTC was found to substantially reduce the risks of urban flooding in both current and future climates, while simultaneously providing a decentralised water supply. Applying RTC on a greater proportion of the RWH systems showed larger relative benefits than simply increasing the storage capacity, providing an important insight to guide investment in flood mitigation by storage. To advance the control strategy at the network scale, the final component developed and evaluated the performance of a centralised optimisation-based RTC model that enabled collaboration between multiple RWH systems. Modelling results have shown that such a strategy was able to deliver a synergy benefit in achieving better baseflow restoration, without any real detriment to the supply and flood mitigation performance of the integrated system. This is achieved by allowing larger storages to compensate for smaller, underperforming storages, thus achieving higher overall performance. More importantly, analysis across the three modelling components has shown that RTC-based rainwater harvesting systems can fundamentally modify the flow regime of stormwater runoff, leading to a promising potential to restore the natural flow regime in urban streams. While future work is required to address both technical and social-economic challenges, this research demonstrates the technical feasibility of using smart technology to better manage urban stormwater in a range of contexts and for a suite of environmental objectives. Its application has the potential to fundamentally transform the way rainwater harvesting—and stormwater management more broadly—are applied. Doing so will maximise the benefits to urban communities and to receiving environments.