School of Ecosystem and Forest Sciences - Theses

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    Using field experiments to test associations between plant traits and fire regimes
    Kreger, Isaac Daniel ( 2021)
    Conservation of biodiversity in fire-prone landscapes requires a thorough understanding of how plants are impacted by fire regimes. Altered fire regimes, due to changes in climate and land use, will likely impact many plant species in arid and semi-arid ecosystems. The study of functional traits – including fire-related traits that help plants to persist in areas subject to recurrent fire - provides a way to understand how plants respond to contemporary and future fire regimes. In my first chapter I studied the influence of a large-scale fire and climate gradient on variation of functional traits of a serotinous tree species, Callitris verrucosa. I measure intraspecific variation in fire-related traits including level of serotiny, bark thickness and tree size on C. verrucosa populations along a 340 km north-south gradient in semi-arid southeastern Australia. Level of serotiny was strongly associated with fire frequency: tree-level of serotiny increased at stands estimated to experience higher fire frequency, while the variation in level of serotiny at standsincreased with lower fire frequency. After accounting for tree size, relative bark thickness was also strongly associated with fire frequency and average annual rainfall. Thicker bark is allocated to smaller stems in areas that experience more frequent fire. In my second chapter, I used a field experiment to explore topkill of resprouting eucalypts after a planned burn in a semi-arid mallee woodland. I measured fire-related traits of eucalypt trees and stems including bark thickness, basal diameter, and canopy height, as well as elements of fuels including litter depth, ground cover, and vertical strata. The probability of topkill declined with taller stems (>3 m): taller mallee eucalypts appear to ‘escape’ low intensity fire. Fuels were also important, with topkill higher in areas with increased cover of hummock grass. Overall, my research demonstrates clear relationships between plant functional traits -including serotiny, 3 height and bark thickness - and fire regimes. This knowledge can be used to inform manipulations of fuels, habitat structure and plants through planned burning, to achieve a wide range of social and environmental objectives. Moreover, the demonstrated variation in C. verrucosa fire-related traits could be used to guide restoration efforts. For example, seeds sourced from southern locations, where populations have higher levels of serotiny, may promote resilience under a scenario of more frequent fire. While the extent to which fire regimes will change is uncertain, field experiments help us learn about contemporary processes and forecast future changes.
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    The role of tubulins in secondary cell wall deposition in woody tree species
    Machado Tobias, Larissa ( 2020)
    Woody trees are an essential source of timber, pulp, paper and biofuel, and advances in biotechnology provide opportunities for the improvement of traits of interest for specific end uses. Cellulose microfibrils, the basic structural component of plant cell walls, are responsible to a large degree for wood mechanical and physiological properties. The angle between the direction of the helical windings of cellulose microfibrils in plant secondary cell walls, or microfibril angle (MFA), plays critical roles in a tree’s development and has become a subject of major interest in forest biotechnology, particularly in detailed studies of the secondary cell wall of xylary (wood) cells. While our knowledge of how exactly the cellulose synthase complex (CSC) acts in response to environmental and genetic cues remains sketchy, guidance of cellulose deposition has been repeatedly accredited to microtubules, a cytoskeleton component formed of protein dimers of alfa- and beta-tubulin. Nevertheless, few studies explore the cytoskeleton roles in secondary cell wall deposition in woody tree species. Reaction wood (RW) develops in response to gravitational stimulus through a series of changes at the cellular and molecular levels. Tubulin genes have been previously reported to be upregulated during RW formation and differences in their expression might lead to differences in microtubule assembly. This differential microtubule organisation might be related to changes on cell wall morphology, including MFA. In this study, cortical microtubule array organisation was therefore assessed in samples from trees forming RW and stems growing upright (normal wood). To further investigate if perturbation of microtubule organisation would impact wood formation, microtubule-interacting drugs were applied to wood tissue depositing SCW in vivo and in vitro. Together, results indicate that tubulins play an essential role in cellulose deposition in the secondary cell wall of woody tree species to ensure appropriate microfibril orientation.
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    Tree pit stormwater control measures as a tool to improve street tree growth and mitigate the urban stream syndrome
    Grey, Vaughn ( 2018)
    Cities globally are embracing stormwater control measures (SCMs) to mitigate the environmental damage to urban waterways caused by impervious runoff. Concurrently, efforts are underway to increase urban forest canopy to reduce urban heat and green neighbourhoods. Tree pits are a promising SCM with potential to address both of these issues in dense urban areas. As tree pits may have a small footprint, they allow for implementation without competing for highly-valued space, and may promote tree growth, thus enhancing the benefits provided by the tree. This thesis investigates how effective tree pits may be at reducing runoff and promoting tree growth and which design characteristics drive their performance. A streetscape experiment was conducted, comparing four tree pit designs to a standard street tree planting. Tree growth and runoff retention were measured over an 18-month period and the relationship between the tree pit water regime and tree growth investigated. Tree pits substantially increased tree growth, with median growth in tree pits with an underdrain approximately double that of the standard street tree planting. For tree pits where the tree received stormwater directly at the tree root ball but did not have an underdrain, tree growth was strongly correlated with the soil exfiltration rate. Low exfiltration rates (<20 mm hr-1) resulted in poor growth or death of the tree, whereas pits with higher exfiltration rates showed equal or increased growth compared with the standard street tree planting. A tree pit water balance model was developed and calibrated using the streetscape experiment data to identify tree pit characteristics influencing runoff retention. Sensitivity analysis of the water balance model identified pit exfiltration rate and impervious catchment area as the key drivers of runoff retention. The model was then applied to possible implementation scenarios to explore circumstances where tree pits may achieve meaningful reductions in runoff. For the streetscape experiment scenario, large catchment areas and overall low exfiltration rates resulted in poor runoff retention performance (runoff volume reductions of only 5%). However, if the tree pit area to catchment area ratio was significantly increased (from 0.1% to 4.4%) through increasing tree pit density and tree pit area, and decreasing the catchment areas for each pit, the model suggests that it may be possible to achieve runoff volume reductions of 90% and reduce the frequency of runoff to 15 days per year, returning runoff flows to near pre-development conditions. In practice, achieving significant runoff reductions with tree pits will be most practicable when tree pits are implemented alongside a suite of complimentary SCMs such as rainwater tanks and permeable paving. Such an approach allows tree pits to treat the runoff fromthe public road and footpath surfaces only, requiring smaller tree pits that may integrate into the streetscape without competing for space. This study is the first fully replicated field experiment testing alternative designs for street tree pits. The findings of this thesis highlight that tree pits may increase tree growth and achieve meaningful reductions in runoff and improves understanding of the factors that should be considered in their design.
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    The influence of urbanization on stream temperature regimes
    Lekammudiyanse, Manuja Udeshi ( 2017)
    Streams draining urban catchments are relatively warmer than non-urban streams. Catchment urbanization and subsequent stormwater drainage systems are likely a primary cause of this warming of urban streams, however, the extent of these causes and their relative contribution to the degradation of thermal regimes still remain unclear. Addressing this knowledge gap is important to provide guidelines for thermal regime restoration measures. Stream temperature data were collected continuously at a 15 minute time step from temperature loggers deployed across 82 sites around the city of Melbourne (population ~5 million people), in south-eastern Australia, over a 3 year period. After screening for periods with zero flow and removing logger errors, 53 sites with >80% of good quality data over a >30 month period were selected to calculate a set of temperature metrics that indicate the spatial patterns of thermal regimes (mean, mean daily maximum, mean daily minimum, mean diel change, maximum weekly average temperature, mean summer, mean winter, summer maxima and number of days exceeding threshold levels of 24, and 29C per year). To indicate temporal dynamics, the maximum amplitude of temperature surges during storm events was calculated (a surge was defined as >1 C temperature change recorded over 30 minute intervals). All temperature metrics were then linearly regressed with catchment and climatic variables to identify the main drivers of surges in temperature. The thermal regime of the study streams was also examined with reference to the thermal tolerances of native fish occurring in the region. The majority of streams in the study were unlikely to exceed tolerable temperature limits for most Australian native fish species. Spatial variation in temperature (~88%) were most plausibly predicted by models that included attenuated impervious cover (a measure of urban drainage systems), attenuated forest cover (a measure of riparian deforestation), mean annual discharge volume and mean annual air temperature. Stream temperature surges were observed most commonly after rain events and depending on the antecedent weather, the amplitude of surges was either positive or negative. Positive surges (i.e. increases in temperature) were most commonly observed in autumn, with fewer positive surges in summer than in winter. Negative surges (i.e. decreases in temperature) were most common in spring and summer, and least common in winter and autumn. The variations in the amplitude of negative surges (~74%) were explained by the attenuated imperious cover; however, the drivers of spatial variations in positive surges remained unclear. Surges are small and less common and thus, the potential degradation of stream ecosystem cannot be expected from temperature surges. Therefore, temperature surges were appeared not to be an important aspect of urban stormwater impacts on stream ecosystems in Melbourne water region. The temperature models suggest that increasing the extent of drainage systems and riparian deforestation in future climate change would have a potential to limit thermal habitats suitable for temperature-sensitive fish species. Moreover, riparian reforestation was shown not to be able to overcome the influence of drainage systems.
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    Social evaluations and ecological outcomes of management actions in urban grassland conservation reserves: a case study of endangered temperate grasslands in south-eastern Australia
    Farrar, Alison ( 2016)
    Temperate grasslands have been transformed by changes to historic biotic and abiotic habitat conditions caused by urbanisation. Urbanisation has led to reduced fire frequency (an important ecological process in highly productive grasslands) and in some instances, to woody plant encroachment (considered synonymous with reduced ecosystem function, although this view is contested). The lowland temperate grasslands of south-east Australia are considered critically endangered with many important remnants confined to isolated patches in urban areas. It is useful to critically evaluate assumptions about the ecological outcomes of prescribed burning and removing or allowing woody vegetation to grow in grasslands in highly modified urban landscapes. Furthermore, relatively little is known about the urban public’s attitudes towards grasslands and these management practices. Drawing on the fields of ecology and social psychology, this interdisciplinary thesis critically evaluates assumptions about plant community responses to ecologically important management practices: prescribed burning and removing or allowing woody vegetation to grow in highly modified urban grasslands, and provides empirical evidence about the ways the urban public think about grasslands and these management actions. Using the remnant temperate grassland of the Victorian Volcanic Plain in Melbourne, Australia, as a case study, this thesis specifically addresses the questions: 1) what shapes public attitudes towards grasslands and the ecologically important management actions; prescribed burning and, removing, or allowing regrowth of woody vegetation (trees and large shrubs) in grasslands in cities? And, 2) what is the ecological outcome of these practices on grassland vegetation composition? To address the first question, a survey of 477 residents living adjacent to grassland conservation reserves in Melbourne, explored how people’s values and beliefs influence attitudes towards grasslands and their acceptance of the management actions: prescribed burning and removing or allowing woody vegetation to grow in grasslands. The survey also explored the way landscape design features (i.e. style of fence, presence of paths, interpretative signage and facilities) influence people attitudes towards their local grassland reserve. To address the second question, the study investigated grassland vegetation community response to the common management treatments: recent burning (burnt < 1 year ago), unburnt (burnt > 3 years ago), and allowing woody vegetation to grow. The findings presented in this thesis identify the social expectations and ecological requirements of prescribed burning and removing or allowing woody vegetation to grow, appear to have some complementary implications for the management of Melbourne’s grasslands: prescribed burning is socially acceptable and ecologically important and allowing woody vegetation to grow is socially acceptable and adds to species heterogeneity. This study makes a novel contribution to the research and management of grasslands in urban landscapes by offering empirical evidence about the ways the urban public think about grasslands and their management, and by critically evaluating the ecological outcome of important ecological management actions in novel urban habitat conditions.
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    Innovative use of CNC technology for the manufacture of furniture in batch size of one
    Ashley, Philip Neil ( 2016)
    While the adoption of CNC technologies in Australia has been rapid by World standards, the successful integration of machines and systems into the Australian solid timber furniture factory has been harder to achieve. This dissertation aims to assess elements of the furniture manufacturing process using CNC equipment to identify best practice and lean manufacturing solutions. Small batch sizes suitable for flexible manufacturing are the goal of every manufacturer; however variations in part design, order quantities, delivery deadlines and setup times make actual batch size calculations difficult to define. This study will assess methods that could be used to reduce batch sizes; in particular the viability of combining all of the components for one piece of furniture into a single CNC program. A number of examples will be presented and the advantages and disadvantages to small batch sizes evaluated and discussed. CNC machinery, cutting tools, tool holding devices and emerging technology will be assessed for performance and suitability for lean manufacturing and small batch sizes. Practical methods to improve production efficiency by organizing workflow and re-thinking how components are processed will be demonstrated. This work concludes that there is no commercial gain in combining all of the parts of a piece of furniture in the one CNC program. It (rather) finds that utilizing appropriate cutting tools and smart processes will bring about gains in productivity that is currently unrealized. It finds that the capability exists within the current performance of CAD and CNC processing to reduce setup and machining times further than are presently achieved in the Australian furniture industry. It finds that training does not adequately provide industry with the skilled workers required and it finds that industry does not always purchase machinery suitable for small batch sizes or for processing the variety of materials used in Australian furniture manufacture. The major findings were that for the processing of kitchen cabinets; a nested manufacturing solution delivered the most benefits for small batch-size production. Rail machines are recommended for small batch sizes of furniture using predominantly solid wood. The smallest batch size is not always the best batch size. It was determined that in the case of a small batch processing multiple parts in the same cycle with a jig in solid wood; there is no saving in time. The use of high-performance tools is highly recommended in order to take advantage of lessened runout, quick-change tool systems and stacked tooling. Applying the tool in a “power feed” direction may not always be the most ideal in terms of breakout; tool life and power consumption. More efficient ways of processing parts are available to the manufacturer and this was demonstrated by combining common parts into one processing cycle. The layout of the furniture factory has a direct effect on the material flow and productivity. The range of issues identified in Mo et al. (2001) can be improved with training. Skilled workers are required to investigate the production sequence and put in place best practice for CNC production.
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    Improved modelling of post fire hydro-geomorphic risks
    Mason, Craig Ian ( 2016)
    Hundreds of millions of people rely on forested water catchments for potable drinking water. However, rainfall subsequent to widespread wildfire can result in high concentrations of suspended sediment entering waterways, and eventually, water supply reservoirs. Calculation of the risk wildfire poses to water quality of supply reservoirs involves consideration of both probabilistic and deterministic processes which intersect at a wide range of scales and resolutions, in time and space. Two of the key requirements necessary to develop a suitable risk model are i) the generation of spatially distributed burn intensity data of future fires to inform subsequent erosion models, and ii) an improved understanding of the relationship between spatial scale and post fire hydro-geomorphic processes. This thesis addresses these two areas, to support the future development of a post fire hydro-geomorphic risk model. A probabilistic wildfire burn area simulation model is developed and presented which delivers the required spatially distributed burn intensity data, while also replicating the fire frequency and magnitude of the local fire regime. The model relies on historical fire records and the adaption of an existing fire behaviour simulator to produce the desired output data. These data can then parameterise deterministic hydrological and erosion process sub-models to determine local post fire water quality risk. Further development of the wildfire model will allow more accurate simulation of the local fire regime. The relationship between spatial scale and post fire hydro-geomorphic processes is poorly understood, which prevents further development of a post fire hydro-geomorphic risk model. This thesis includes an analysis conducted to improve understanding of wildfire effects on peak discharge at the large catchment scale. Pre and post wildfire rainfall and runoff data from six large catchments in Australia’s southeast upland forests were analysed to determine whether wildfire causes significant increases in peak discharge. No significant change in peak discharge following wildfire at the large catchment scale was detected, however, substantial data quality issues clouded clear conclusions. This analysis concurs with the few local studies available, implying that at large catchment scales, post fire suspended sediment loads measured in stream networks after large volume rainfall events may come from near-channel, channel bank, or in-channel sources. This may also suggest that large volume rainfall events may not need to be considered when modelling hillslope erosion processes, possibly reducing the necessary complexity of an overall risk model. This thesis provides additional tools and knowledge to support future modelling of post fire hydro-geomorphic risks. A variety of other processes still require investigation and sub-model representation before the range of post fire suspended sediment loads delivered to water supply reservoirs by the hydro-geomorphic system can be reliably calculated.
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    Looking for expansins : a molecular approach to the investigation of tylose development and heartwood formation in Eucalyptus nitens
    Tonkin, Miriam Ruth ( 2006)
    Advanced stages of stem development in many tree species, including eucalypts, are marked by the transition of conductive sapwood to non-conductive heartwood. Heartwood formation follows a characteristic sequence of events involving the accumulation of phenolic compounds in ray parenchyma cells, the occlusion of vessels by tylose and/or gum formation, cell death and the subsequent release of phenolic compounds into the surrounding tissue. These events are dependent upon the activity of ray parenchyma cells, but the molecular processes involved, particularly with regard to tylose formation, remain largely unknown. The identification of molecular pathways leading to tylose formation might yield insights into heartwood formation. A molecular approach to the investigation of tylose formation is hampered by the paucity and inaccessibility of ray parenchyma cells and the asynchronous nature of tylose formation. Based on the assumption that wound-induced tyloses and those formed during the transition of sapwood to heartwood develop via a common mechanism, these difficulties were overcome by using the wounding response of the tree (a 12-year-old Eucalyptus nitens sapling) to induce extensive and simultaneous development of tyloses. Tylose formation involves the marked extension of a primary cell wall structure. Elsewhere, such wall extension has been closely associated with the activity of expansins. These constitute a large, multi-gene family of proteins which are widely distributed throughout higher plants and which have been shown to induce relaxation and extension of primary cell walls, often in a cell- and tissue-specific manner. It is proposed that expansins are likely to be involved in tylose formation. Ray and axial parenchyma cells are the only living cells found in sapwood, and primary cell wall extension is only possible through tylose formation. Thus, gene expression associated with wall extension occurring in sapwood is likely to be associated with tylose formation. Cellular material from outer sapwood showing extensive wound-induced tylose development was successfully harvested and partial cDNA sequences displaying significant homology with a-expansins were identified. This provides circumstantial evidence that expansin gene expression is associated with tylose formation and should encourage further investigation of the molecular pathways involved in this process.
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    Perceptions of ecoforestry in selected project sites in Papua New Guinea
    Alkam, Frank Sengesil ( 2005)
    Land and forest resources in Papua New Guinea are held under customary ownership by clans. But clans have participated little in decision-making processes in any major forest resource development projects, although these have often had major effects on their areas and lives. The decisions about industrial logging have been made mainly by the government and multinational logging companies - though royalties have been paid to clans for extraction of the timber. Past logging operations have provided some infra-structural benefits but have also led to many environmental and socio-economic problems that affect the livelihoods of rural people. In an attempt to halt the further spread of large-scale logging, and under pressure from the World Bank, the European Union Commission to PNG and the Government of Papua New Guinea entered into a bilateral agreement to initiate the Papua New Guinea Ecoforestry Program in 1995. This was to be implemented through the involvement of clans as the forest resource owners. This study explores the experiences and views of clan members in two ecoforestry projects in West New Britain Province. The aims of the study were to describe the ecoforestry program in general and the two project study sites, and then to explore clan members' perceptions of the ecoforestry approach being promoted, based on their experience. The study was conducted with a view to identifying ways of improving the effectiveness of ecoforestry development projects in Papua New Guinea. Two ecoforestry project sites were chosen as case studies. The main data collection techniques were in-depth interviews with clan members participating in the ecoforestry projects, and observations of activities. The qualitative data collected were analysed using elements of a 'grounded theory' approach, which involved transcription of interviews from PNG Pidgin/English to word processed files in English, then examining and coding the transcripts for main themes. From these themes theory was developed about the way clan people viewed ecoforestry, and the prospects for the future of the approach. Data from secondary sources were used in description of the sites, and in the analysis and interpretation of data from interviews. The findings revealed strong views among some respondents about their gains in mechanical and management skills through the ecoforestry projects, and also on problems of transparency in financial management of projects, the hard work involved in ecoforestry, and difficulties faced by their female members left at home alone. Other difficulties mentioned were those of maintaining equipment and of sourcing spares for machines and securing reliable markets. Despite the many negative views expressed on ecoforestry, there was quite wide acceptance that the approach had major potential advantages in terms of self-determination for clans, learning skills, employment and income, village infrastructure and environmental care of the forest - when compared to industrial logging. In the final chapter a Force Field Analysis is used as a framework to discuss the implications of the main finding - for future efforts in ecoforestry in PNG. In general, the clan members were reluctant to give definite views on the future prospects of ecoforestry after withdrawal of the supporting aid agency. In answer to questions on this topic they tended to express views on the need for certain types of support in the future, and other ways for overcoming the difficulties of the past. There was a general desire to be given the opportunity to continue with the ecoforestry approach, in the hope that there would be improvement in community participation, skills and hence in benefits to their clans and communities.