School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemFlow and geomorphic drivers of instream plants and their biogeomorphic role in riverine ecosystems( 2023-12)Streams are important ecosystems providing multiple benefits to both biodiversity and humans. Despite their importance, many streams are severely degraded globally, driven by anthropogenic impacts such as flow regulation, urbanisation and channelisation. Instream vegetation is a critical component of the stream ecosystem providing many benefits to biota such as provision of habitat and refuge, primary production and nutrient cycling. Instream plants also act as ecosystem engineers, impacting sediment, propagule and organic matter transport and deposition. Despite their importance, many gaps exist in our understanding of the flow and geomorphic drivers of instream plants, and their biogeomorphic role. Field surveys, glasshouse trials and an experiment were combined to investigate questions related to identifying the flow and geomorphic drivers of instream vegetation, and how instream vegetation interacts with propagule and sediment transport. First, a range of streams were surveyed for instream vegetation and geomorphic components, with further geomorphic complexity and flow metrics calculated. Relationships were then investigated between the metrics and amphibious and aquatic vegetation. I then ran an experiment to assess propagule bank and sown seed emergence under a range of flooding durations and frequencies to assess relationships between flow regime and early plant recruitment. Finally, two glasshouse studies were undertaken to assess different preferential deposition locations for propagules, fine sediment and organic matter and the potential for emergent and aquatic plants to act as ecosystem engineers. More frequent flood events with a steeper rate of rise (flashier flows) were negatively associated with amphibious vegetation outcomes but less so for aquatic species. Greater geomorphic complexity, including less bank incision and more stream width and depth variation, were positively associated with instream vegetation outcomes, however, increasingly flashy flows reduced these benefits. More frequent, short flood events also reduced plant recruitment from propagules, however, effect sizes were small, suggesting a range of species may recruit under flashy flows provided other factors are suitable (e.g. refuge from high flow velocity). Greater geomorphic complexity and instream vegetation patches were also associated with more propagule, fine sediment and organic matter deposition, although bare bank samples were also highly retentive. Building on the previous study, emergent vegetation and aquatic vegetation both trapped more propagules, fine sediment and organic matter compared with non-vegetated stream locations. Importantly, however, this trapping function diminished from rural to urban streams. The findings from this thesis suggest that geomorphic complexity promotes instream vegetation outcomes, at least partially through greater deposition of propagules in a range of channel locations. Further deposition of fine sediment and organic matter likely improves recruitment of instream plants. Flashy flow regimes need to be addressed, however, if increasing instream vegetation is a priority in stream restoration, likely through various stormwater control measures. My findings also provide evidence for the importance of instream vegetation on propagule, fine sediment and organic matter deposition. Combined, these results highlight the biogeomorphic importance of instream plants, with their potential to trap propagules, fine sediment and organic matter leading to biogeomorphic succession and driving stream morphodynamics. Both passive and active revegetation approaches may be used to promote the benefits of instream plants, but further research is required. Ultimately, my research highlights the importance of instream vegetation and how to effectively restore instream plants to promote biogeomorphic processes that aid in process-based stream restoration.
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ItemSpatially analysing tree crown growth in cities: modelling progress towards canopy cover targets and sensitivity to rainfall gradients( 2023-10)Urban forests can play a significant role in mitigating some of the negative impacts of urbanization. Thus, canopy cover targets are becoming increasingly important for cities, to maximize the benefits of trees in urban environments. To meet these targets, selecting tree species that can thrive in the city is important, especially in the face of climate change. Climate- and trait-based approaches for selecting urban tree species are increasingly common as global datasets become freely available, but the logic of their selections are rarely validated. Validating these approaches could involve measuring tree crown growth in cities to assess species' suitability for future planting. Species-specific growth models can facilitate comparisons among species and cities located across environment gradients. Furthermore, these models can be used to predict urban forest canopy cover development and the time needed to reach set targets. This thesis spatially analysed remote sensed urban forest crown polygon data with georeferenced tree inventory data to identify individual tree crown growth in new residential areas of Melbourne. Specifically, I aimed to i) develop species-specific growth models and assess growth rate differences among species and between rainfall zones; ii) test climate- and trait-based approaches for species selection; and iii) predict canopy cover in a residential precinct over a 30-year period. Species-specific models were developed for the 20 common street tree species in two distinct rainfall zones. Species showed four different growth responses at 10 years after planting based on average crown area and sensitivity to rainfall: Fast and consistent growth; Fast but sensitive growth; Slow and consistent growth; Slow and sensitive growth. Urban forest managers can use this information to identify tree species to plant in drier or irrigated (passive or active) areas to better achieve canopy cover targets. The measured crown growth sensitivity to rainfall was used to examine i) the relationship with climate metrics based on occurrence data extracted from a global database and an urban tree database; and ii) with trait-based metrics as indications of stress tolerance strategies. Metrics derived from climate- and trait-based metrics were found to be weak predictors of tree crown growth sensitivity in these two areas of Melbourne. Finally, tree crown growth models were applied to three planting scenarios, based on the number of trees planted in the streetscapes and parks of a typical new residential precinct over a 30-year period. Results show that although canopy cover can be improved by prioritising the planting of more large trees, canopy cover target cannot be achieved in new residential areas. This thesis highlights the significance of developing not only species-specific growth models but also zone-specific growth models to improve urban tree canopy cover prediction accuracy. Further, results indicate limitations of climate- and trait-based approaches, emphasizing the need for a more comprehensive assessment of species vulnerability in urban areas. These methods can be replicated for a wide range of species, climates, and site conditions. By increasing our knowledge of species-specific growth patterns, we can develop more effective approaches to urban tree selection and canopy expansion in changing climates.
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ItemEarly life-stage nutrition and its effects on growth, immune competence, and metabolic characteristics of the developing dairy cow( 2023-08)The primary objective of dairy heifer rearing is to produce resilient replacement cows with a high milk production potential. Early life nutrition is widely understood to affect development of physiological systems in all species; it is therefore essential that effective calf rearing strategies are in place to ensure a productive and profitable dairy industry. The research detailed in this thesis evaluated the effects of different pre- and postweaning nutritional strategies that lead to parameters linked to superior resilience of Holstein-Friesian dairy cows. Growth, Immune competence, and metabolic characteristics were compared with the use of repeat immune challenges in dairy replacement heifers reared under various pre- and postweaning nutritional strategies from birth until 20 months of age. Results indicate a positive influence of accelerated preweaning nutrition on growth and the immune development of dairy cows, and therefore do not support the current industry feeding practices.
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ItemThe mechanisms through which fire shapes plant life cycles in heathlands( 2023-11)Fire is a key driver of plant diversity, and many plants have adaptations that help them thrive in fire–prone ecosystems. However, changes to fire activity threaten thousands of plants worldwide. To understand the future of plant populations under fire regime changes, empirical research on fire’s influence on demographic processes is required. This thesis explored how patterns of fire influence plant species across their life cycle, from seeds to mature life stages, and how this relates to plant functional traits. I examined a Mediterranean-type heathland ecosystem as a case study, to examine the mechanisms through which fires impact plants at different life-stages, including those that take place above and below ground. I established 57 study sites in Gariwerd, southeastern Australia, which has experienced substantial variation in fire history. First, I investigated whether knowledge of plant traits can be used to make robust predictions for how fire influences plant relative abundance. I deductively assigned species to plant functional types, based on their persistence traits, establishment capacity, and the timing of key life stages, and made a priori predictions on how relative abundance changes as a product of time since fire. Using empirical data I collected on species relative abundance, I then built nonlinear models to test species’ model conformity to a priori predictions for plant functional types. Predictions of the direction of changes in relative abundance (increase or decrease from 0-81 years since fire) were correct for 18 of 24 species modelled. Predictions of the shape of changes in relative abundance were not as accurate, but still useful: 13 out of 24 species showed ‘excellent’ conformity with shape predictions, 7 ‘good’ conformity, and 4 ‘poor’. This suggests plant functional types can be used to generalise fire responses across species that share similar traits, and thus inform fire management and biodiversity conservation. Second, I examined how fire severity and time since fire interact to influence plant maturity. I collected data on the proportion of plants that had reached reproductive maturity at a site. I used this field data, alongside satellite-based fire severity mapping, to build non-linear models of plant-fire relationships. The results indicated that the proportion of mature plants was influenced by time since fire, regardless of fire severity. For example, for Banksia marginata, the proportion of mature plants increased from 13% (1-year post-fire) to 58% (15 years post-fire), and maturity of this species showed minimal variation between low and high severity fire. Interestingly, no relationships were observed between time since fire and the relative abundance of plants. That is, only when plant life stages were considered, did I detect an effect of fire on plants. Ecological studies that distinguish between plant life stages will help to predict the impacts of fire on populations and enhance decision-making. Third, I investigated how time since fire and mean fire interval influence canopy seedbank production, based on a suite of plant traits. I surveyed all individual plants with canopy cones present at each of the 57 study sites. On each mature individual, I measured plant height and width, and counted the number of cones. I sampled a subset of these cones across individual plants, and then germinated them in a laboratory trial. I used regression models to explore the relationship between fire frequency and variables relating to different aspects of canopy seedbank production. The interval between fires influenced canopy seedbank production and viability. For example, no canopy cones were observed on plants at short mean fire intervals: such as fire intervals more frequently than every 18 years for the obligate seeder tree Callitris rhomboideia. Quantifying the fire intervals which supports canopy seedbanks provides a new understanding of an important above ground process and helps to determine how frequently to burn ecosystems containing serotinous species. Last, I examined how time since fire and fire frequency influence the occurrence of different species in the soil seedbank and, again, examined ecological relationships through the lens of plant traits. I sampled the soil seedbank at 57 sites, treated soil samples with heat and smoke product to promote germination, and grew seedlings in a germination trial lasting 14 months. I used non-linear modelling to explore relationships between fire and species occurrence. Fire frequency influences the occurrence of species in the soil seedbank, and the nature of these relationships depends on plant traits such as plant and seed longevity. For example, frequent fires (every <15 years) will reduce the occurrence of herbaceous species with long-lived seed. However, for other types of plants, such as perennials with short-lived seed, I observed no relationship between fire and soil seedbank occurrence, demonstrating many species have soil seedbanks resilient to frequent fires. Overall, my research advances understanding of how fire impacts different species and groups of plants across their life cycle. Notably, a mix of field research, laboratory studies and empirical models provide evidence that the traits of plants can be used to identify how fire affects species in the soil and canopy seedbanks, and as juvenile and mature plants. By examining plant life stages above and below ground, this work also helps to define the fire regimes that support plants in the heathy woodlands of Gariwerd. Because it is based on mechanisms, I anticipate that the trait-based approaches I have developed and tested could be used to understand and predict fire-related changes in plant populations in a wide range of ecosystems.
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ItemPredicting redistribution of species and communities under environmental change: Improving the reliability of predictions across time( 2023-04)Ecological models used to forecast range change (range change models; RCM) have recently diversified to account for a greater number of ecological and observational processes in pursuit of more accurate and realistic predictions. Theory suggests that process-explicit RCMs should generate more robust forecasts, particularly under novel environmental conditions. RCMs accounting for processes are generally more complex and data-hungry, and so, require extra effort to build. Thus, it is necessary to understand when the effort of building a more realistic model is likely to generate more reliable forecasts. During my thesis, I investigated how explicitly accounting for processes improves the temporal predictive performance and transferability of RCMs. I first identified key knowledge gaps, and the challenges of evaluating temporal predictive performance and transferability. One of the main challenges is the lack of robust metrics to assess predictive performance and transferability. To address this I implemented and tested the use of new emerging tools to enable fair comparisons of predictive performance across samples with varying degrees of imbalance (e.g. species with low and high observed prevalence). I then tested a couple of hypotheses related to whether modelling observational processes explicitly results in better forecasts. In particular, I evaluated under what circumstances the benefits of explicitly accounting for imperfect detection and allowing information sharing across multiple species are retained when the models are extrapolated to generate predictions beyond the training temporal window. The findings should shed light on how to address remaining knowledge gaps, and how to generate more reliable forecasts on species’ responses to global change scenarios.
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ItemTrees Need Closure Too: Unveiling The Molecular Control Of Wound-Induced Secondary Vascular Tissue Regeneration In Trees( 2023-09)Trees play a pivotal role in terrestrial ecosystems and are an important natural resource. These attributes are primarily associated with the capacity of trees to continuously produce woody tissue from the vascular cambium, a ring of meristem cells located just beneath the bark between phloem and xylem tissue layers. Long-lived trees are exposed to a myriad of biological and environmental stresses that may result in wounding, leading to a loss of bark and the underlying vascular cambium. This affects both wood formation and the quality of timber arising from the tree. In addition, the exposed wound site is a potential entry point for pathogens that cause disease and may even lead to the death of the whole plant. In response to wounding, trees have the capacity to regenerate lost or damaged tissues at a wound site. Investigating gene expression changes associated with different stages of wound healing reveals complex and dynamic changes in the activity of transcription factors, signalling pathways and hormone responses. This thesis investigated molecular regulators of wound-induced secondary vascular tissue (SVT) regeneration. It summarises current literature on primary and secondary vascular tissues and bark wounds and related revascularisation processes, specifically on genes and hormones. Using this information, eight genes from Eucalyptus, including WUSCHEL RELATED HOMEOBOX 4 (EgrWOX4), Arabidopsis thaliana HOMEOBOX GENE 8 (EgrATHB8), CORONA (EgrCNA), PHABULOSA/PHAVOLUTA (EgrPHX), REVOLUTA (EgrREV), AUXIN RESPONSE FACTOR 5 (EgrARF5), PIN-FORMED 1 and 3 (EgrPIN1 and EgrPIN3) were chosen for subsequent experiments on wound-induced SVT regeneration. During these in-planta experiments, Induced Somatic Sector Analysis (ISSA) was used as a molecular tool to assess promoter activity and gene function of these candidate genes in wild-type stems and those where auxin transport was chemically inhibited. Endogenous auxin (IAA) concentrations were quantified using LC-MS to understand how varying auxin concentrations might be required for proper vascular tissue patterning during various stages of regeneration. Results show that the remaining xylem tissues on the wound surface regenerate all lost tissues in a four-step process. EgrPIN1/3 are expressed in all tissue types, EgrWOX4, EgrARF5 and EgrREV predominantly in cambium tissues and EgrATHB8, EgrCNA and EgrPHX in cambium and xylem tissues. Overexpressing micro-RNA-resistant REV leads to faster regeneration rates, while over-expressing miR166 and chemical inhibition of polar auxin transport leads to slower regeneration rates. Samples from overexpression experiments and auxin inhibition also lead to defects in cell anatomies, arrangement, and organisation. Quantification of IAA levels suggests alternating high and low auxin signalling during different stages of regeneration. Together, this thesis provides novel insights into spatial-temporal expression patterns of the selected molecular regulators and discusses how they relate to our current understanding of vascular cambium formation and xylem differentiation during secondary growth. Based on the findings, I propose a model for wound healing that provides the conceptual foundations for future studies aiming at understanding this intriguing process.
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ItemThe ecology and functionality of spontaneous vegetation on green roofs( 2023-11)Green roofs can provide social and ecological benefits in urban areas that lack open space, but their success relies on good vegetation cover. Ensuring sufficient plant coverage on green roofs is often difficult, especially in arid climates, where drought conditions reduce plant survival. Additionally, the high costs associated with constructing and maintaining green roofs often limit their application to wealthier areas, and in less affluent communities their implementation can exacerbate inequalities by driving up property and housing costs. A cost-effective solution is needed to encourage plant cover and make green roof benefits more accessible. Over time and without routine maintenance, the vegetation on green roofs changes as spontaneous plants, commonly viewed as ‘weeds’, colonise and become established. Although this shift might be perceived as a departure from the green roof’s original design intent, these spontaneous species, when forming good cover, could offer benefits such as rainfall retention, habitat provision, and building cooling. Green roofs intercept and retain rainfall in substrates before it is evapotranspired or enters the urban stormwater drainage system. This reduces stormwater volumes and delays and reduces peak flow rates. Rainfall retention is significantly influenced by the type and cover of vegetation. Yet, the specific influence of spontaneous species on green roof rainfall retention are not well understood. Ideally, plants selected for rainfall retention should have high transpiration rates as this will help replenish the substrate's capacity to store water after rainfall. This is often linked to 'fast' traits like rapid growth or large leaf areas. However, 'slow' traits, such as slower growth or lower biomass, are beneficial for plant survival in dry conditions. Since spontaneous plant species can establish and survive on green roofs, they might play a role in rainfall retention. In addition to understanding the contribution of spontaneous plants to rainfall retention, understanding how their traits relate to their drought and water use strategies could also inform better plant selection for non-weedy species on green roofs. Sedum species are commonly used on shallow 'extensive' green roofs and in drier climates may require irrigation during summer to sustain their cover. Yet, the interaction between spontaneous vegetation, Sedum cover, and water availability remains poorly understood. Clarifying this relationship could help reduce maintenance efforts, preserve Sedum cover, or maximise the diversity of spontaneously colonising species. Finally, gaining a deeper understanding of the factors that shape spontaneous plant communities on green roofs globally is crucial due to the significant role vegetation cover and composition play in green roof functionality. These insights can inform better decisions in designing and maintaining green roofs to meet specific ecological or aesthetic goals. This thesis consists of a general introduction (Chapter 1), a literature review (Chapter 2), four experimental data chapters (Chapters 3-6) and a concluding synthesis chapter (Chapter 7) that address the following questions: 1. Can spontaneous vegetation cover help expand green roofs into areas that are funding or space limited, or does the inherent ‘weediness’ of this vegetation type make it an unwelcome addition to urban landscapes? 2. What are the water use and drought resistance strategies of spontaneous green roof plants? Are their traits, such as relative growth rate and leaf size, correlated with their drought tolerance and water consumption, and is there a trade-off between water use efficiency and drought survival? 3. What impact does the presence of existing vegetation cover (Sedum mexicanum) and water availability (irrigation) on a green roof have on the growth, abundance, traits, and diversity of spontaneous plant species on extensive green roofs? 4. Can spontaneous vegetation cover contribute to rainfall retention on green roofs, and how do substrate depth and rainfall patterns affect rainfall retention and spontaneous plant community diversity and composition? 5. How do factors such as roof design, accessibility, maintenance, irrigation, vegetation cover in the surrounding landscape, season, and local climate shape the species richness and functional traits of spontaneous vegetation on green roofs worldwide? In Chapter 2, I reviewed existing research to understand how spontaneous vegetation impacts the social and ecological aspects of green roofs. While some people may view spontaneous plants as undesirable 'weeds’, studies indicate that these plants become more accepted as their coverage on green roofs increases. Spontaneous species, which can grow without needing irrigation or fertilisers, could also lower the costs of green roofs. This would be particularly beneficial in areas with lower socio-economic demographics or without an established green roof industry. Additionally, in hot and dry climates where deeper substrate layers or irrigation are needed for plant survival, spontaneous species can be advantageous as they can grow in thinner soils and regenerate from their seeds. Using spontaneous vegetation based on social and ecological needs could make green roofs more affordable and prevent them from contributing to increased property values and housing costs, thereby helping urban communities become more resilient. In Chapter 3, I conducted an eight-week glasshouse experiment to determine the water use and drought response of nine spontaneous green roof species under well-watered (WW) and water-deficit (WD) conditions. Under WW conditions, higher transpiration was associated with 'fast' traits such as increased biomass, leaf area, and growth rate. A clear trade-off emerged between water use under WW conditions and drought resistance under WD. 'Fast' species, while reducing transpiration by 57-72% and biomass by up to 50% under WD, failed to maintain adequate leaf water content (leaf RWC <90%) to avoid drought stress. Conversely, 'slow' species, with their smaller biomass, used less water in both WW and WD conditions, successfully maintaining their leaf water status and showing greater drought resistance. This diversity in water-use and drought responses among the spontaneous species mirrors the variable conditions on green roofs, suggesting different strategies may be advantageous at different times. Spontaneous species are likely to offer rainfall retention comparable to planted species, particularly where good plant coverage is achieved. In Chapter 4, I conducted a 10-month study to investigate the interaction between planted vegetation cover (Sedum mexicanum) with increasing coverage (0%, 25%, 50%, 75% and 100% cover) subjected to two irrigation treatments (well-watered; WW, or water-deficit; WD). The microcosms were seeded with a mix of 14 species typically found as spontaneous vegetation on green roofs. I measured the abundance, community biomass, and functional traits like specific leaf area (SLA), leaf dry matter content, and relative growth rate, and assessed species and functional richness of the spontaneous vegetation communities. Increasing S. mexicanum cover inversely affected the abundance and richness of spontaneous species but did not significantly impact community biomass or functional richness. The interaction between S. mexicanum cover and irrigation treatment played a key role in determining species richness, with the highest richness observed in WW microcosms devoid of S. mexicanum cover. The biomass of spontaneous plants was greater in WW than WD modules. The SLA of spontaneous communities was significantly higher in WW conditions where S. mexicanum cover was less than 100%. These results suggest that maximising Sedum cover while restricting water availability would likely reduce the abundance, biomass, and diversity of spontaneous vegetation on green roofs. In contrast, green roofs that embrace spontaneous species could benefit from increased water availability via occasional irrigation, leading to a richer and more diverse community. In Chapter 5, I conducted a 100-day rainfall simulation study with green roof modules planted with 14 spontaneous plant species typically found on green roofs in Mediterranean-type climates to determine their rainfall retention. For this study, green roof modules were prepared with either 7 cm (shallow) or 14 cm (deep) substrate layers. These were either left bare or planted with a community of spontaneous species, which achieved approximately 100% coverage before commencement of the experiment. The rainfall simulation consisted of two phases – a 'dry' phase replicating the driest period on record, and a 'wet' phase with rainfall depths based on the highest recorded rainfall percentiles (90th, 95th, and 99th) in Melbourne, Australia. Across 17 rainfall events, I measured rainfall retention, evapotranspiration, runoff initiation time, and soil water content. Additionally, I assessed the spontaneous vegetation cover, and species and functional diversity at the end of each rainfall phase, and biomass at the conclusion of the wet phase. Results showed that during the dry phase, modules with spontaneous vegetation retained 88% of the applied rainfall, irrespective of substrate depth, outperforming bare substrates by 6%. In the wet phase, modules with deep substrates and spontaneous vegetation achieved 30% greater rainfall retention compared to other combinations. By the end of the wet phase, spontaneous vegetation in deeper substrates had 42% higher biomass, 19% greater coverage, and over twice the functional richness than in the shallower substrates. These findings indicate that spontaneous vegetation significantly enhances rainfall retention on green roofs compared to bare substrates and performs similarly to designed plant communities. However, rainfall retention by spontaneous vegetation is contingent upon factors critical for rainfall retention, such as substrate depth and rainfall patterns, and will likely differ in other climates. Finally, in Chapter 6, I gathered data from presence/absence surveys of spontaneous vegetation for 192 green roofs around the world to investigate how green roof design characteristics (including age, surface area, substrate depth, and elevation), pre-existing vegetation, accessibility, maintenance, irrigation, landscape vegetation cover and local climate, shape spontaneous plant communities. Using regression analyses, I evaluated the impact of these variables on species richness. Additionally, I applied a Hierarchical Modelling of Species Communities (HMSC) approach to determine how these factors influence the dispersal and establishment of spontaneous species, focusing on their specific traits. The results indicate that seasonal variation affects the composition of spontaneous communities due to its effects on both dispersal and establishment of spontaneous plant species. Dispersal traits of spontaneous vegetation on green roofs were predominantly influenced by the vegetation cover in the surrounding landscape. Conversely, the establishment of spontaneous plant species was primarily determined by climatic conditions, though green roof design features (such as roof height, accessibility, and maintenance intensity) also shaped spontaneous plant communities. Spontaneous species richness was higher during spring and winter, and in both deeper green roof substrates and older roofs. These findings can help inform the design and maintenance of green roofs to achieve specific ecological goals or aesthetic preferences. This study also highlights the interplay between green roof design choices, maintenance practices, landscape and climate context, and the development of spontaneous vegetation communities. By examining the ecology and functionality of spontaneous vegetation on green roofs this thesis revealed several key findings: 1. Spontaneous species display diverse water use and drought response strategies, with fast growing species using more water but exhibiting greater drought stress under water deficit. 2. The composition and richness of spontaneous green roof vegetation are significantly influenced by vegetation cover (Sedum mexicanum) and water availability (irrigation). 3. Spontaneous species can enhance rainfall retention, performing comparably to traditional green roof plantings. 4. Globally, spontaneous plant communities on green roofs are shaped by a multitude of factors, including roof design, local climate conditions, and the surrounding landscape. Overall, this research suggests that spontaneous vegetation could contribute substantial benefits to green roofs due to their ability to establish on shallow substrates and provide functionality in terms of rainfall retention, habitat provisioning, and building cooling. The insights drawn from this research can be used to guide green roof design to support spontaneous plant communities or apply more appropriate maintenance and irrigation regimes to designed plant communities on green roofs. Embracing spontaneous vegetation cover on green roofs could offer a cost-effective solution, potentially making the benefits of green roofs more accessible and equitable across different urban settings.
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ItemThe role of green roofs as native bee habitat and their potential to provide three-dimensional habitat connectivity in urban landscapes( 2023-09)With ongoing urbanisation, cities around the world experience a continuing loss of biodiversity habitat. Green roofs have the potential to add crucial habitat on vertical built structures in neighbourhoods where ground-level habitat is lacking. Green roofs are also known to provide additional ecosystem services related to urban heat island mitigation, stormwater capture, and human health and wellbeing benefits. For these reasons, green roof uptake is encouraged in many urban areas and this thesis sets out to understand to what extent green roofs currently function to support biodiversity in the context of Australian cities, such as Melbourne. Despite more than a decade of incentives for installing green roofs in Australian cities, their current extent is largely unknown. However, if cities aim to include green roofs into their biodiversity targets, their abundance, distribution, and typology needs to be understood. Since native bees are essential ecosystem service providers and bees in general are known to be experiencing a global decline, it is of high importance to understand how native bees perceive green roofs as habitat, and to what extent green roofs can help improve functional connectivity for bees in urban landscapes. The three research questions addressed in this thesis are: 1) what is the current distribution, abundance and typology of green roofs in Melbourne and how has this changed over last 20 years; 2) which bee species utilise green roofs in Melbourne, and what are the characteristics of the green roof and surrounding landscape that influence their abundance and richness; and 3) how can we model functional connectivity in a way that captures the 3-D arrangement of green roofs, and what do these models reveal about the role that green roofs play in supporting native bees in dense urban landscapes in Australia? To address the first question, I applied a remote sensing approach to identify and map the location and characteristics of green roofs across 17 of the 30 municipalities in the Melbourne metropolitan area. By 2020, there were 224 green roofs in Melbourne, 56% of which were constructed after 2014, and 65% were located within 5 km of the Central Business District. While these green roofs were recorded across most of the municipalities and included large public green roofs on commercial buildings, or smaller, non-accessible biodiversity green roofs at family houses, 65% formed a distinct green roof typology that is typical of many green roofs in temperate Australian cities. These typical green roofs in Melbourne are located on mid- to high-rise apartment buildings, offer passive recreation for the building residents, and contain approximately 30% vegetation cover mostly comprising of lawn. This is a distinctly different typology of green roof to those that have historically been constructed in cities across Europe and North America and reinforces previous studies which have highlighted that the climatic conditions in south-eastern Australia have an important influence on the types of green roof plantings that can be successfully maintained. Given that the typical green roof in Melbourne is quite distinctive and differs from the types of green roofs that have been studied internationally, my second question sought to understand whether green roofs in Melbourne were utilised by native bees, and how the design and spatial location influenced their composition and abundance. I used the database developed in the previous question to identify 20 green roofs which were surveyed for native bees using a combination of passive and active sampling techniques. During the survey, I recorded a total of 114 individuals belonging to 18 native bee species and 186 individuals belonging to 2 exotic bee species. Using Generalised Linear Models (GLM) and Hierarchical Modelling of Species Communities (HMSC) revealed that the abundance and species richness of bees were positively affected by increasing species richness of flowering plants, the proportion of native flowering plants and the overall floral availability on the green roof. The proportion of impervious groundcover in the surrounding 500 m and the increasing height of a green roof, on the other hand, had a negative effect on bee abundance and richness. Bee surveyed on green roofs were all polylectic, mostly ground-nesting but varied in their body size. Although, native bees were all generalist foragers, most were observed foraging from native plants only. These findings highlight that green roofs do offer valuable habitat, indeed may even play an important role in supporting ground-nesting bees in urban areas as the green roof substrates may remain more open and less compacted than exposed soil at ground level. Having determined that native bees do utilise green roofs as habitat, the final component of my thesis investigated the role that green roofs play in the functional connectivity of 3-D urban landscapes. To address this question, the first step was to develop a 3-D functional connectivity model that represents the reality that green roofs may be isolated from other greenspaces vertically as well as horizontally. This was achieved by combining a habitat suitability model with a combination of least-cost path and graph theory modelling. Partial dependence plots from the habitat suitability model revealed a stepped negative relationship between height of green roof and the probability of occurrence for native bees. This is the first time a non-linear relationship has been recorded and it offers a useful framework to inform the placement of green roofs where biodiversity gain is an intended goal. The 3-D functional connectivity analysis revealed that ground-level greenspaces are highly isolated within the inner city of Melbourne (Scenario 1) but the presence of existing green roofs (Scenario 2) increases the number of patches functionally connected for native bees with short (101 m), medium (205 m) and long (586 m) dispersal ranges. Hypothetically maximising the green roof area across the landscape (Scenario 3) led to an increase in overall connectivity, however, it mostly improved the inter-connectedness between green roofs rather than improving the connectivity of ground-level greenspaces. However, for all the scenarios and native bee dispersal distances modelled, the most important role that green roofs played in connectivity was as additional patches of habitat (dPCintra values of 56 – 92%), followed by local connected networks (dPCflux values of 8 – 44%), but their role as critical stepping stones (dPCconnector) were consistently less than 0.1%. This suggests that while green roofs should continue to be added to support biodiversity of native bees, we need to reframe their role in urban landscapes as they are most likely to be used as a habitat patch, rather than as stepping stones. The findings of this thesis highlight the existence of a distinct typology of green roofs in Melbourne, Australia, provide evidence that green roofs can be important habitat for Australian native bees if offering sufficient floral resources and being located at an adequate height, and that green roofs have higher value in providing habitat than improving connectivity. This new knowledge and the novel 3-D functional connectivity approach can help inform local policies and stakeholders on how to design and where to prioritise new green roof installations if the goal is to create a more biodiversity-friendly urban landscapes.
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ItemSome critical determinants of goat meat quality( 2023-11)Goat meat serves as a major source of meat in developing countries while it is less popular in western countries. Nevertheless, the perceptions about goat meat are changing due to the health benefits of consuming lean meat with reduced fat and cholesterol content. Australia is the largest exporter of goat meat globally. Although there is increasing demand for goats domestically the supply chain is highly inconsistent. There is a significant knowledge gap in understanding the factors influencing goat meat quality and these factors that need to be explored to ensure consistent and better quality goat meat. Therefore, this PhD project was designed to investigate some of the critical factors affecting goat meat quality such as slaughter age, post-mortem ageing, retail storage, muscle type, cooking temperature and electrical stimulation. This PhD thesis consists of three animal experiments and one meta-analysis study. The first experiment compared two age groups (Adult goats, n=12, 2 years of age; Young goats, n=12, 6-9 months of age) of farmed Boer goats. This was a preliminary study to understand the meat quality of goats slaughtered in a commercial plant in Australia. This chapter demonstrated that post-mortem ageing for 14 days could reduce the toughness of goat meat in two age groups of goats. The retail color stability was also assessed from 0 to 10 days on the retail shelf, which was validated using Thiobarbituric acid reactive substances (TBARS) analysis. The second study was a meta-analysis research on the effect of electrical stimulation (ES) on small ruminant meat quality, including sheep, lamb, and goat. The meta-analysis provided statistical evidence of the positive impact of electrical stimulation (ES) on the meat quality of small ruminants. This was evident in terms of ultimate pH, tenderness, increased proteolysis, and elevated colorimetric values. It was observed that pH24 and WBSF showed a decrease in electrically stimulated goat carcasses, compared to non-stimulated carcasses through the forest plots. Overall, the research indicates that ensuring the optimum quality meat in Boer goats involves managing factors from the farm to the abattoir and incorporating considerations such as the ideal age of the animal, post-mortem ageing, and specific cooking methods or temperatures specific to the muscle, should be developed and implemented. The third experiment compared meat quality of three muscles namely, longissimus thoracis et. lumborum, semimembranosus and psoas major, representing different muscle fiber types, to understand the association between fiber type and goat meat quality. The variations observed in the muscle fiber composition and cross-sectional areas (CSA) of type I, IIA, and IIB muscle fibers are reflected in the meat quality of Boer goats. A higher percentage of type I fibers and a lower CSA of all three fibers contribute to reduced toughness in goat meat. This experiment also elucidated the effect of cooking end -point temperature on goat meat quality. Furthermore, the underlying mechanism associating fiber type and cooking temperature has been explained by the protein denaturation at different temperatures in the three muscles using differential scanning calorimetry (DSC). The cooking end-point temperature is a critical factor influencing the quality of cooked goat meat. As the cooking temperature rises, parameters such as WBSF, cooking loss, and volume shrinkage increase, leading to tougher meat. The fourth experiment explored how certain crucial factors, such as intramuscular fat, collagen content, and muscle fiber characteristics, influence the meat quality attributes in two distinct age categories of Boer goats (Adult, n=10, 24 months of age; Young, n=10, 6 months of age). For this study, four muscles, namely longissimus thoracis et lumborum (LTL), semimembranosus (SM), cutaneous trunci (CT) and biceps femoris (BF) were harvested from 20 Boer wether goats. The muscle data obtained will enable well-informed decision-making to improve muscle-specific marketing approaches, aiming to enhance the consumer acceptability of goat meat. Overall, adult goats had a higher type I fiber percentage, but a lower type IIB percentage compared to young goats, and animal age increased the CSA of the fibers in different muscles. Higher type IIB fiber number % and higher CSA were correlated with increased toughness.
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ItemThe Logic of Innovation: How Institutional Logics Shape Innovation in Australian Agriculture( 2023-12)This research aimed to improve how institutional dimensions of innovation in agriculture are described and enhance the understanding of their impact on innovation. By exploring systems perspectives on innovation within industrial and agricultural contexts, I explain how institutions are predominantly defined as functional and structural elements of innovation systems (IS). This demonstrates how innovation has been rendered technical in agriculture, and I argue for an institutional turn to rebalance IS towards the social and political. By applying a new institutionalist lens, I expand on the current view of institutions to define them as socially constructed, recursive, material, symbolic and political. I use this expanded definition to highlight the lack of approaches for institutional analysis in agricultural innovation systems (AIS) and introduce the institutional logics (IL) perspective as a basis for my research design. This research is a case study of the influence IL have on managing nutrient pollution in agriculture. It draws data from two contexts that have grappled with this issue for decades, namely the Australian sugarcane industry and agriculture in the Netherlands. My analysis centred on the discourse surrounding each context, drawing on data from unstructured interviews with 22 innovation actors, 119 submissions to an Australian senate inquiry, and 59 documents. Interviews covered actors in the policy, program management, intermediary and farming practices, while documents included those addressing the cases technical, policy and strategy dimensions. My analytical framework draws on the foundational elements of IL and seeks to describe the interrelationship between problem framing, chosen theories of action and justifications used to legitimise action. This was used to develop an initial position on IL observed in the case. I then used qualitative content analysis of data from two discursive hotspots to explore how IL impact innovation activity and performance. Through this process, I describe a dominant discourse within the Australian context anchored in what I label a scientific logic. While this logic dominates the discourse, another competing logic drives an alternate discourse. This I label the experiential logic, which is characterised by a contrasting relativism that questions every aspect of the scientific logic. This resulted in a polarised problem domain leading to diminished action to address the problem and limited progress towards nutrient pollution targets. In the Netherlands, the discourse revealed a dominant societal logic that frames the problem legally and justifies action on the grounds of human and ecosystem health. This precipitates an instrumental theory of action that continually layers expectations for actors in agriculture around compliance with various standards and limits. Sitting behind this instrumental facade was a social process built over centuries and focused on a pragmatic approach to building consensus. This resulted in a fusion of the instrumental approach to defining what must change with a social process of settling on how to achieve this. The polarisation observed in the Australian case was absent in the Netherlands; however, questions exist as to whether the consensus based approach to decision making can withstand the various social, political and functional pressures facing Dutch society. Synthesis of my findings showed how limited awareness of institutional processes, epistemological divergence and weak legal frameworks contribute to poor innovation performance in the Australian context. These insights demonstrate a divergence from the dominant technical and economic interpretations of innovation performance in agriculture and challenge the functional and structural black box approach to representing institutions within AIS. This has implications for the relative emphasis placed upon institutional analysis within AIS. Subsequently, this highlights the need for innovation actors to engage with the institutional dimensions of innovation if progress is to be made in complex problem domains. I propose an enhanced role for innovation brokers to facilitate this process and a representation of AIS that better captures this institutional turn.