School of Ecosystem and Forest Sciences - Theses
Now showing items 1-12 of 317
Quantifying wildfire impacts on the structure of fire-tolerant eucalypt forests using airborne lidar data
Most of the native forests in temperate south-eastern Australia are dominated by resprouter fire-tolerant eucalypts, which are often assumed to quickly recover from even the most severe fires. However, very few studies have quantitatively assessed the effects of fires of different severity on eucalypt forest structure, which limits quantitative analyses of broad-scale fire impacts over time. My Thesis examines wildfire impacts on the structure of fire-tolerant eucalypt forests from tree- to landscape-scales. Using field-based assessments and metrics derived from multi-temporal airborne lidar (Light Detection And Ranging) data, I quantify fire severity effects on the structure of tree crowns, canopy, and understory fuel in a single forest type nearly a decade after an extensive wildfire in south-eastern Australia that started on ‘Black Saturday’, 7 February 2009. I then use the lidar metrics as a basis for evaluating the potential of Landsat satellite imagery to accurately represent variation of forest cover across landscapes. My research provides quantitative evidence that wildfire impacts on the structure of fire-tolerant eucalypt forests are influenced by wildfire severity and can persist for several years after fire. At the scale of individual trees, I quantify impacts of four wildfire severities (unburnt, low, moderate, high) on crown structure using estimates of cover, density and vertical distribution derived from 2016 lidar data validated with field measurements of 51 field plots (0.05 ha). This analysis indicated legacy effects of wildfire at moderate- and high-severity sites where tree crowns were comparatively narrow and more evenly distributed down the tree stem. I then extend my analyses to the forest canopy using a comprehensive set of lidar-derived metrics representing the horizontal and vertical structure of three strata in 1084 pre- and post-fire lidar plots across an area of ~30,000 ha. My results confirm persistent effects of high-severity fire at stand- to landscape-scales, including significant decreases in canopy cover and mean canopy height, and changes in the canopy relief ratio and rumple index consistent with a more heterogeneous and fragmented dominant stratum. Persistent effects of high-severity fire were also evident in my subsequent analysis of lidar-derived understory metrics, namely, increases in the cover and horizontal connectivity of the elevated and midstory strata and increased potential for crown fires through increased vertical connectivity. Using Random Forest (RF) models, I demonstrate that both post-fire canopy and understory fuel structures were more clearly associated with fire severity and pre-fire structural metrics than climatic and topographic variables. Variations in lidar-derived estimates of forest cover (understory, canopy, full profile) were only weakly represented by Landsat spectral indices either alone or combined in RF models with environmental variables. My Thesis demonstrates the utility of airborne lidar data in quantitative assessments of fire impacts on native eucalypt forests of complex structure. My analyses indicate legacy effects of severe fires towards more open and fragmented forest structures, which could influence multiple processes, including ecosystem productivity. These effects combined with increased fuel connectivity could lead to feedbacks in these fire-tolerant forests that narrow future windows for full structural recovery between wildfires.
Quantifying fire-severity patterns using optical remote sensing data in temperate eucalypt forests of south-eastern Australia
Wildfires have significant biophysical and ecological impacts on ecosystems worldwide from local to regional and national scales. The magnitude of such impacts is related to wildfire severity. Recent increases in wildfire occurrence have been associated with climate change, however whether there has also been a change in fire severity remains underexamined in many biomes. Better understanding of fire-severity patterns is required for effective wildfire management, particularly in the fire-prone landscapes of temperate south-eastern Australia, which support a diversity of forests varying in species composition, structure, and post-fire regeneration strategies. Thus, the overarching aims of my Thesis were to accurately quantify wildfire severity at landscape scales and to examine spatial and temporal variation in wildfire severity across a range of forest types in Victoria, south-eastern Australia. To meet the overarching aims, my Thesis involves: (1) identification of optimal optical spectral indices for mapping fire severity across the dominant and most fire-prone forest types in Victoria; (2) a comparison of the accuracy of two different fire-severity mapping approaches, namely single spectral indexing thresholding and machine learning; (3) using the acquired knowledge, the development of fire-severity maps for large (>1000 ha) wildfires occurring in Victoria between 1987 and 2017, and a retrospective analysis of changes in spatial patterns of high-severity fires over that period; and (4) an analysis of the relative importance of four groups of environmental variables (namely fire weather, fuel, topography and climate) as predictors of high-severity fire extent and landscape configuration. My evaluation of remote sensing based spectral indices indicated that the best-performing indices of fire severity varied with forest type and forest functional group, but that there is scope to group forests by structure and fire-regeneration strategy to simplify fire-severity classification in heterogeneous forest landscapes. Results from my comparative analysis confirmed that machine learning outperformed the spectral index thresholding approach for mapping fire severity in most cases, increasing overall accuracy by 11% on a forest-group basis, and 16% on an individual wildfire basis. My results also confirmed that the accuracy achieved with a reduced set of predictor variables that included the previously identified optimal indices of fire severity was not improved by adding more variables. Greater overall accuracies (by 12% on average) were achieved when in-situ data (rather than data from other fires) were used to train the machine-learning algorithm. As such, my study demonstrates the utility of machine-learning algorithms for streamlining a robust fire-severity mapping approach across heterogeneous forested landscapes. Analysis of spatial patterns highlighted that high-severity wildfires in temperate Australian forests have increased in extent and aggregation in recent decades. The total and proportional high-severity burned area increased through time from 1987 to 2017. While the number of high-severity patches per year remained unchanged in that period, the variability in high-severity patch size increased, and high-severity patches became more aggregated and more irregular in shape. Finally, key findings from my models on the relative importance of environmental drivers (climate, fire weather, fuel, and topography) were that fuel type and fire weather were the most important predictors of the extent and configuration of high-severity fires in Australian temperate forests. My Thesis presents one of the most comprehensive analyses of fire-severity patterns from remote sensing data in Australia. My research results support the reliable estimation of wildfire severity from optical images using machine-learning algorithms once optimal spectral indices are identified and when in-situ training data are available for individual fires. Importantly, the quantified shifts in fire regimes across Victoria’s forested landscapes may have critical consequences for ecosystem dynamics, as fire-adapted temperate forests are more likely to be burned at high severities relative to historical ranges, a trend that seems set to continue under projections of a hotter, drier climate in south-eastern Australia. It is therefore critical that forest scientists and land managers continue to acknowledge and quantify changing wildfire-severity patterns so that they are better informed to address the ecological consequences.
The effects of rooting volume, greywater irrigation and reduced sunlight on climbing plants for indirect green façades in urban environments
Dense urban areas with limited ground space are often deprived of vegetation. By growing climbing plants on buildings as indirect green facades, vegetation can be implemented in a way that uses limited space and seamlessly integrates man-made structures with nature. Benefits of indirect green facades include air purification, noise reduction, micro-climate regulation, provision of natural habitats and improvement of the physical and psychological well-being of urban residents. However, in order to provide effective ecosystem services, indirect green facades need to develop great vegetation coverage to cover buildings, which can be challenging due to small rooting volumes, lack of potable water availability for irrigation and variable light conditions, imposed by site constraints and weight loading of containers on elevated structures. Therefore, it is important to research how indirect green facades can be successfully developed for cities in the presence of unfavorable growing conditions to ensure their sustainability. In this thesis, I have investigated how woody climbing plants respond to different growing conditions by evaluating their morphological and physiological traits. The three objectives of this thesis are: 1. To evaluate the effect of rooting volume on climbing plant growth, coverage and thermal tolerance in the first growing season (Ch 2); 2. To investigate whether greywater is a viable irrigation resource for indirect green facades in cities by assessing changes in substrate chemical properties and the growth response of six climbing plant species (Ch 3); 3. To explore how shade affects leaf traits and thermal tolerance of climbing plant species assisting green facade design and plant selection (Ch 4). In chapter two, to examine the impacts of rooting volume on climbing plant species during the first growing season for their establishments, three rooting volumes (21, 42 and 63 L) were utilised to grow two climbing plant species; the slower-growing Akebia quinata and the faster-growing Pandorea pandorana, on east- and west-facing aspects. It was hypothesised that the reduced rooting volume will adversely affect growth, wall coverage and thermal tolerance of climbing plant species. The smallest rooting volume (21 L) significantly reduced plant biomass growth, specific leaf area and percentage wall coverage for both species over the measured six-month period. Surprisingly, neither climbing plant species significantly increased in growth and vegetation coverage when provided with the largest rooting volume (63 L) as compared with medium rooting volume (42 L). The shoot:root ratio and thermal tolerance of climbing plant species however remained unchanged across three different rooting volumes. A significant decline in the ratio of variable to maximum fluorescence (Fv/Fm) was observed for all climbing plants on the west-facing aspect due to heat stress, irrespective of rooting volume treatment. The outcomes of chapter two suggests that, for a wall area of 2.8 m2 with stainless-steel mesh (1.45 m (W) by 1.95 m (H)), 42 L rooting volume is adequate to support plant growth and coverage of indirect green facades for the first growing season. Practically, for every cubic metre of rooting volume, A. quinata and P. pandorana could approximately achieve 10.2 m2 and 21.3 m2 of wall coverage at the end of the first growing season. In chapter three, an 18-week glasshouse experiment was conducted to evaluate the effects of greywater irrigation on substrate chemical properties (pH and electrical conductivity) and the growth of six climbing plant species. I hypothesised that domestic greywater would change substrate properties by increasing pH and electrical conductivity, and thereby adversely affect the growth and health of climbing plant species. Synthetic greywater formulated to conform with domestic greywater was used in this study. Three irrigation treatments were applied to container-grown climbing plants: (1) potable water irrigation, (2) greywater irrigation, and (3) greywater irrigation with a potable water ‘flushing’ once every three weeks. After 18 weeks, the results showed that substrate pH did not differ among treatments; however, increased substrate electrical conductivity was evident in containers receiving the greywater with potable water flushing treatment. Both greywater treatments had no significantly detrimental effects on plant biomass, leaf area, gas exchange rates, or water use when compared with potable water irrigation. The outcomes indicated that domestic greywater can be safely used to irrigate climbing plants for indirect green facades, reducing the need for the use of potable water and supporting more sustainable design of indirect green facades in urban environments. In chapter four, a 15-week field experiment was designed to assess how seven climbing plant species respond to changing light conditions from full-sun to shade, with respect to the adjustment in leaf morphology, physiology, and photochemistry for mature plants. The hypotheses were (1) a change from sun to shade will increase specific leaf area (SLA), leaf expansion rate, and chlorophyll content of climbing plants; whilst decreasing leaf photosynthetic rate (A1500), stomatal conductance (gs), light compensation point (LCP) and thermal tolerance (T50), and (2) deciduous climbing plant species will be more plastic (greater changes in morphology and physiology) in response to shade than evergreen species. Significant increases in SLA, and unchanged gs, LCPs and T50 were observed in all seven climbing species after being provided shady conditions. In contrast, the variation in species response to reduced light intensity levels was evident in leaf expansion rates, A1500 and Chl a+b. Leaf expansion rate and A1500 remained unchanged for most of the climbing plant species by the shade treatment. However, significant increases in leaf expansion rate were observed in evergreen Gelsemium sempervirens and Jasminum azoricum. In addition, significant decreases in A1500 were recorded in deciduous Ampelopsis brevipedunculata and Vitis ‘Ganzin Glory’ as well as evergreen Pandorea pandorana under the shade treatment. On the other hand, leaf Chl a+b was significantly increased in most of the climbing plant species by the shade treatment, except for deciduous V. ‘Ganzin Glory’ and evergreen G. sempervirens. Irrespective of light intensity levels, deciduous climbing plant species displayed significantly greater SLA, leaf expansion rates, A1500, gs, and Chl a+b, whilst lower LCP than evergreen species in this study. On the contrary, deciduous climbing plant species were not more plastic than evergreen species in the overall response to the reduced light intensity levels. However, a greater reduction in A1500 in response to shade was observed in deciduous climbing species as compared with evergreen species. The findings of chapter four demonstrated that these seven climbing plant species can maintain growth and health by adjusting leaf morphology and physiology when experienced changing light conditions from full-sun to shade. The findings suggested that the seven climbing plant species can maintain or increase vegetation wall coverage and provide ecosystem service benefits in cities with variable light conditions. Overall, this thesis has indicated that climbing plants can grow successfully with relatively small substrate volume (42 L). It was also shown that a lower limit exists for the rooting volume required to support the early growth and vegetation wall coverage of indirect green facade climbing plants. This thesis also raises the possibility that domestic greywater can replace potable water irrigation of building indirect green facades in urban environments, as there was no deleterious effect on either substrate properties or climbing plant growth. Furthermore, the seven climbing species evaluated in this thesis all could adapt to the changing light conditions from full-sun to shade by adjusting leaf traits to maintain growth (leaf expansion). Despite the limitation noted in rooting volume, woody climbing plant species were quite resilient and adaptable to the different growing conditions evaluated in this thesis. This would likely enable them to maintain their function and performance and thereby continue to deliver ecosystem services under fast-changing urban environments. The findings of this thesis have significant implications for the understanding of how woody climbing plants respond to potentially unfavorable growing conditions, providing insights into plant selection for indirect green facades in urban environments. This thesis further supports the possibility to implement indirect green facades as an integrated approach of sustainable urban greening and water management on high-rise buildings. Further research should be undertaken however with a longer experimental period (beyond six months), the inclusion of more climbing plant species and field studies (i.e., existing indirect green facades on buildings). The research should also be conducted with the inclusion of different types of substrates with the application of on-site greywater and various light intensity levels (e.g., lower or higher).
Divergence in forest structure and evapotranspiration over a chronosequence between Eucalyptus regnans and Acacia dealbata
Abstract Climate-induced changes in fire regimes in south east Australia have the potential to alter ecosystem and ecohydrological resilience in native Eucalyptus forests. A drier, hotter climate is triggering short-return, high-intensity, mega-fire events across Australia. In Victoria, over 189,000 ha of fire-sensitive, Eucalyptus regnans and Eucalyptus delegatensis forests have been burned two or more times within the past 18-years. Under these multiple burn conditions, fire-sensitive forests are highly vulnerable to ecological tipping points. Naturally occurring E. regnans is a dominant species in the higher rainfall regions of south east Australia. However, short interval fires (15-20 years) hinder the regeneration potential of this serotinous, obligate-seeder species, which then allows fast-growing, co-occurring understorey species such as Acacia dealbata to replace E. regnans as the dominant forest type. Replacing long-lived E. regnans forests (250-300 years) with short-lived A. dealbata (80-90 years) may have significant ecohydrological implications in water supply catchments. A bottom-up, plot-based approach was used to measure Et in typical E. regnans and A. dealbata forests of various ages to develop empirical models of the hydrological response of forested water catchments to vegetation change. Field-based measurements of the various components of Et were taken from 10, 35 and 75/80-years old stands of each forest type. A forest inventory survey was carried out to quantify structural trajectories, including stand mean dbh, stand basal area and stand sapwood area in the two forest types. Transpiration was measured at the field using the heat ratio method together with micrometeorological conditions in the two forests. Throughfall, stem flow and evaporation from the forest floor were measured across the age sequence of each forest type. Throughout this research, eco-hydrologic processes along the chronosequence are modelled and then compared between the life cycles of E. regnans and A. dealbata forests. Regeneration response to fire and ecohydrological properties of both forest types were similar during the initial stage of stand development up to age 10. However, stand structure, including mean stem diameter, basal area, stocking density and sapwood area, begins to diverge significantly between the two forest types after age 20. In both forest types, sapwood area reduces with stand age after age 20, but at a faster rate in A.dealbata. Once the forest structure starts to diverge, overstorey transpiration, overstorey Et and total Et of the two forest types also begin to diverge, driven primarily by divergence in sapwood area. In addition, mean sap velocity averaged for the 20, 35- and 75-80-years age classes was about 34% higher in E. regnans, although the difference was only statistically significant at age 20. This suggests that differences in sap velocity between the two forests also partly explained the divergence in overstorey Et between the two forest types. VPD is the strongest predictor of sap velocity in both forest types under non-water limited conditions. Daily sap velocity model for E. regnans could be further modified by accounting for forest age. The results provide a strong indication that after age 20, overstorey transpiration in Acacia-dominated forests is substantially lower than in the E. regnans forests they replace. Therefore, overstorey transpiration was the primary driver of differences in total Et between the two forest types, followed by differences in canopy interception. Soil evaporation contributed only 3% to the differences in Et between the two forest types. Differences in Et partitioning between the two forest types imply a link between forest structure and the forest water budget. In senescing A. dealbata, understorey transpiration contribution of 29.8% to system Et was similar to that of overstorey transpiration (31.2%), indicating the understorey and overstorey contribute equally to total Et at the final stage of Acacia forests. This suggests that, after the Acacia life cycle finishes, the Et regime will transit into a new state that will be dominated by shrubby understorey species. The findings of this research suggest that climate-driven high-frequency wildfires alter the composition and structure of E. regnans forest as a result of a change in the dominant overstorey species from E. regnans to A. dealbata. This species shift alters forest hydrological parameters, especially mean sap velocity and sapwood area, leading to changes in eco-hydrologic processes in the forest. These results highlight that species shift due to climate change can have important ecohydrological implications, resulting in evapotranspiration regime shift. Further, the present research suggests that climate-related species change from E. regnans to A. dealbata will alter the hydrologic response of water supply catchments. This type of eco-hydrologic response may be played out in many ecosystems in the future. By considering all studied changes in forest structure, evapotranspiration and water yield, this climate-induced species replacement is an ecologically significant vegetation change in the native E. regnans forests, reflecting extensive hydrological implications for the water supply catchments.
The Role of Brassinosteroids in the Regulation of Senescence in Lilium Orientalis
Fresh flowers of cut lily plants often have a long postharvest life, but this changes after cold storage, which is often an essential process in the horticultural industry. In many cut lilies, a relatively short period of cold storage of 1 week often leads to early leaf and flower senescence. Early leaf and flower senescence are likely ethylene-dependent, either due to a higher level of ethylene production or a change in ethylene sensitivity. Such changes could be due to alteration in the expression of ethylene biosynthesis, perception, and signalling genes. Brassinosteroids (BRs) can delay the onset of senescence and chilling injury in crops but their effects on chilling tolerance in cut flowers have not been investigated. In this thesis, I investigated the role of BR and cold storage on cut lilies (Lilium orientalis) and the role of ethylene in cold-related injuries. More specifically, I investigated: i) the effects of cold storage and BR on postharvest function and ethylene production in a range of cut lily cultivars (Chapter II); ii) the effects of cold storage and BRs + cold storage on the expression pattern of ethylene related genes and a BRs-related transcription factor gene in cut lilies ‘Premium Blonde’ and ‘Marlon’ (Chapter III); and iii) the effects of ethylene on senescence processes and the expression pattern of its biosynthesis, receptor, and signal transduction pathway genes during senescence with and without cold storage in cut lily ‘Marlon’ (Chapter IV). The results of chapters 2 and 3 indicated that: 1) the cut lily cultivars had different levels of sensitivity to cold storage; 2) BR decreased ethylene production and the detrimental effects of cold storage; 3) BR treatment resulted in a greater expression LoBZR1 and a lower expression of most ethylene-related genes compared to cold storage treatment in ‘Premium Blonde’ and ‘Marlon’ lilies. Together, these findings suggest that the chilling injuries in cut lilies are ethylene mediated which could be due to either higher ethylene biosynthesis or higher ethylene sensitivity or a combination of both as a result of alteration in the expression of the related genes. Thus, delayed chilling injuries by application of BR is likely caused by the suppression of the over-expression of ethylene-related genes which results in less ethylene biosynthesis and possibly sensitivity. To understand whether chilling injuries are ethylene-dependent cut lily ‘Marlon’ plants in chapter IV were subjected to ethylene and 1-Methylcyclopropene (1-MCP; an ethylene action inhibitor) before and after cold storage. In non-cold-stored plants, ethylene and 1-MCP treatments did not affect postharvest quality, ethylene production, and the expression pattern of the investigated genes. Cold storage led to much earlier leaf yellowing and while bud opening was not affected, flowers senesced and abscised three days earlier. In cold-stored plants, ethylene and 1-MCP had no effects on bud opening and leaf yellowing but flower senescence and abscission were hastened by ethylene and delayed by 1-MCP. Similarly, the expression of all the genes examined and ethylene production were significantly increased by ethylene but significantly decreased by 1-MCP in cold-stored plants, although not at all time points. These results indicate that there is no sensitivity to ethylene in fresh-cut lily ‘Marlon’. But the response significantly differs following cold storage, in a tissue-dependant manner as flower senescence and abscission were delayed by 1-MCP but leaf senescence was not. Hence, ethylene does influence flower senescence following cold storage but leaf senescence is under the control of other currently unknown factors. Together this research indicates that focus on ethylene blockers to prolong postharvest life in lilies will be effective for flowers but not leaves. However, BR application was not seen to be beneficial at a practical level in all cultivars particularly in cultivars with a low level of sensitivity as the delays of senescence were very short.
Reconstruction of paleo-environments in Southern Germany during the Last Glacial Maximum with mammoth teeth
The paleo-environments of South-West Germany during Marine Isotope Stage 3 (MIS 3) and Marine Isotope Stage 2 (MIS 2), from approximately 50 – 23 thousand years ago, were reconstructed at both millennial and sub-annual scale using temporally successive oxygen (δ18O ) and carbon (δ13C) isotopes in the tooth enamel of woolly mammoth (Mammuthus primigenius). The mammoth teeth were discovered in the sediments of the Upper Rhine Graben, and their ages were determined to roughly fit into three time windows: 50ka (Early MIS 3), 40ka (Middle MIS 3) and 23ka (Last Glacial Maximum, LGM) respectively. The δ18O values were used to infer the isotopic compositions of mammoth water source, which in turn tracks local precipitation and air temperature conditions. The δ13C values were analyzed to deduce the mammoth dietary behaviour as well as reconstruction of paleo-vegetation. The approach we used for high-resolution reconstruction was developed during this research, with few prior studies at this scale. This new approach successfully reconstructed the paleo-environments of SW Germany and the paleo-ecology of mammoths, and we obtained the following results: The oxygen isotopic analysis at millennial scale indicated the trend of 18O depletion in the mammoth water source from MIS 3 to the LGM, with the mean δ18O values ranging from -9.33‰ to -7.12‰. We estimated the mean annual temperature during the LGM from the δ18O values, and it was around 4-10℃ lower than present. Our results were compared to other studies which involved paleo-environmental reconstructions with mammoth remains. We found that, during the 40ka time window, mammoth in SW Germany had 1.1-4.7‰ higher δ18O values compared to those in Sweden, Estonia, Lithuania and Latvia. During the LGM, however, the δ18O values in these regions were similar, while Germany was around 2.2‰ higher than Hungary. Records of oxygen isotopic oscillations at sub-annual scale were also obtained. The isotopic oscillations are in regular cycles with regional peaks and troughs representing summer and winter seasons respectively. The δ18O values during summers were approximately 9.3 – 14.6 ‰ higher than those during winters. Seasonal differences, indicated by the difference between mean δ18O values of summer and winter, were most enhanced during around 50ka, while LGM seasonality was intermediate between those in 50ka and 40ka intervals. We also analyzed the paleo-ecology of M. primigenius on their diets and tooth growth. The mean δ13C values for all of our mammoths were around -12.0‰ and -12.5‰, indicating that they primarily consumed C3 plants. This matched with the studies from mammoth feces, as well as pollen records, which indicated that Germany was dominated by semi-desert steppe landscapes from 50 – 23ka. There was a trend towards more positive δ13C values from MIS 3 to the LGM, which may be caused by the C4 plant expansion due to reduced aridity or reduced water availability in a C3 dominated landscape. Mammoth enamel growth rates were also estimated using the seasonal variation of stable isotopes. The mean growth rate was estimated to be around 15mm/year, with a general trend of decreasing speed of growth through time. Finally, our study has shown the utility of using high resolution stable isotope analyses for reconstructing past environmental and palaeo-ecological changes from mammoth teeth. This method has great potential for expanding our knowledge of both seasonal and millennial scale paleo-environmental changes across the geographic range where mammoth remains are found.
Investigations into the transcriptional regulation of wood formation
Xylogenesis (wood formation) is one of the planet’s most crucial biological processes. It is characterised by the complex, multi-stage development of cells commencing with periclinal divisions of cambial initials which subsequently undergo a series of dynamic, differentiation stages including further cell division, xylem cell expansion, secondary cell wall deposition and programmed cell death. Each of these stages is orchestrated by molecular controllers which are strictly regulated by an underlying network of transcription factors, the central regulators of wood formation. These transcription factors determine the morphology, chemical composition and physical properties of xylogenic cells as well as the overall dynamics of the wood formation process including its responsiveness to biotic and abiotic stresses including distinct responses to gravitational stress. This thesis used wood formed in response to gravitational stress (reaction wood) to dissect the transcriptional regulation of xylogenesis in order to gain detailed insights into the molecular control of wood formation in woody perennials. It does this by examining the current literature on transcriptional regulation of wood and reaction wood formation with specific focus on the roles played by transcription factors. Using this information, nine candidate transcription factors were chosen for subsequent experimentation to add to our current sketchy understanding of their specific functions during wood formation. Selected genes from Eucalyptus included INDOLE-3-ACETIC ACID INDUCIBLE 13 (EgIAA13), KNOTTED-LIKE HOMEODOMAIN 7 (EgKNAT7), MYELOBLASTOSIS 103 (EgMYB103), SECONDARY WALL NAC DOMAIN 2 and 3 (EgSND2 and EgSND3), BELL1-LIKE HOMEODOMAIN 6 (EgBLH6), EgWRKY2 and EgWLIM1. Aiding these functional investigations, also a suite of contemporary microanalytical techniques was reviewed assessing their suitability for phenotyping wood cell morphology and cell wall chemical composition in instances where available wood samples amount to as little as a only a few micrograms, as was the case for the induced somatic sector analysis (ISSA) derived samples analysed in this thesis. In these in vivo transformation experiments, up- and down-regulation constructs of candidate transcription factors were used to perturb wood formation in the ecologically and economically important forest tree species Eucalyptus and Populus. Our investigations revealed that EgIAA13 significantly alters xylem fibre and vessel morphology as well as xylem cell division rates, identifying EgIAA13 as a novel regulator of cambium dynamics and xylem formation. Subsequent protein-protein interaction analyses revealed that EgIAA13-EgARF (2, 5, 6 and 19) modules are presumably involved in mediating this dual regulatory role of EgIAA13. Our results also demonstrate that EgKNAT7 and EgMYB103 significantly alter xylem fibre morphology in terms of secondary cell wall thickness and fibre size, confirming their regulatory involvement in mediating secondary cell wall deposition and xylem expansion, respectively.
Complex Sociotechnical Problems: Insights from the Investigation of the Maintenance of Stormwater Control Measures in Melbourne
The expansion of urban development across the globe has brought with it significant environmental impacts. Prominent amongst these impacts is the degradation of marine and freshwater environments caused by conventional approaches to stormwater management infrastructure that facilitate the rapid conveyance of untreated stormwater to waterways. Stormwater control measures (SCMs) are a sustainability innovation developed to redress these environmental impacts. However, there are growing concerns that SCMs are not receiving sufficient maintenance and that, consequently, their long-term performance may be compromised. By taking a mixed methods approach, this study sought to gauge the veracity of these concerns and ascertain the barriers and challenges to the maintenance of SCMs. Nine local councils in Melbourne, Australia were engaged to provide condition data for their SCMs and access to their professional staff to collect perspectives on the barriers and challenges to SCM maintenance. Condition data analysis triangulated against survey data and similar studies from other jurisdictions indicate that concerns about insufficient maintenance have merit. Grounded Theory informed analysis identified 55 inter-dependent barriers and challenges across nine sociotechnical categories, confirming SCM maintenance as a complex multi-causal sociotechnical problem, and one potentially symptomatic of a loss of momentum towards mainstream adoption. Termed Failure to Thrive, this loss of momentum is considered a function of three over-arching issues: An under-developed stormwater industry, government policy inertia and, importantly, the invisibility of SCMs in the community. Using sociotechnical systems thinking and theory, three ‘intervention pathways’ are postulated to redress shortcomings in the maintenance of SCMs by Victorian local government and, likewise, address the Failure to Thrive scenario. In doing so, this study provides an example of how explorative, inductive research and sociotechnical systems theory can be used to decipher complex sociotechnical problems. Based on the findings of this study, an alternative transition pathway for Sustainability Transitions is proposed that accounts for the complex path-dependencies involved in the transition of sustainable innovations like SCMs and the need for pro-active institutional work accordingly to minimise the risk of partial or total failed transitions.
The role of tubulins in secondary cell wall deposition in woody tree species
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.
Effects of vegetation structure, fire and habitat amount on microbat functional diversity
Human modification of land cover and disturbance regimes is occurring at unprecedented rates globally, and often results in significant biodiversity loss. However, it is often unclear how the loss of species affects ecosystem function. The relationship between ecosystem function and biodiversity depends on the functional traits and niches filled by organisms, as these traits respond to and drive ecosystem processes. Functional diversity describes the range, value and distribution of traits and is a better predictor of ecosystem function than species richness. This study investigated the effects of vegetation structure, fire and habitat amount on microbat functional diversity. Using passive acoustic monitoring, we surveyed microbats at 140 sites over two years. Four bat functional traits were used to calculate four functional diversity indices (richness, evenness, divergence and dispersion). The influence of vegetation structural complexity, time since fire and habitat amount on bat functional diversity and species richness was examined using generalised linear models. With the exception of one measure of functional diversity, time since fire did not influence any of the response variables. In contrast, vegetation structural complexity was a much stronger predictor of functional diversity than time since fire, with functional diversity increased in more structurally open environments. Both functional evenness and functional dispersion of bats were both positively associated with habitat amount, indicating that increased habitat amount results in reduced environmental filtering and an increased breadth of functional roles performed by the bat community. Finally, FD responses often depended on the survey year, indicating that responses were influenced by temporal variability in background conditions. These findings suggest that management for biodiversity should be focused on optimising vegetation structure through the use of fire, rather than focusing on fire regime alone. Further, management actions that protect and increase habitat amount should, therefore, increase overall bat functional diversity arising from the increased abundance of foraging and roosting resources available. Lastly, long-term monitoring programs measure species responses across a variety of conditions, thereby providing more representative evidence to develop well informed management decisions.
Improving species distribution models using extreme value theory and climate dataset ensembles
The development of climate datasets at fine spatial and temporal scales has commonly been driven by the need to better understand vegetation distributions and ecological systems. While a wide range of global, national and regional climate datasets have been developed over the last two decades, they are rarely compared directly in the ecological literature. This thesis evaluates a range of climate interpolation techniques and investigates how the spatial and temporal characteristics of climate datasets may be utilised to improve the predictive performance of plant species distribution models (SDM). A series of spline-based and geostatistical methods for interpolating temperature variables are first compared across Victoria, southeast Australia. Secondary predictors (thermal remote sensing data and local topographic indices) which indirectly capture mesoscale microclimate and cold air drainage regimes were found to improve monthly mean minimum temperature interpolations by up to 39%. Thermal remote sensing data only reduced root mean square error (RMSE) by up to 6% for maximum temperature across Victoria and was most effective during the summer months. The interpolation methods used in southeast Australia were subsequently transferred to the Royal Himalayan Kingdom of Bhutan to validate their effectiveness in a novel climate. In Bhutan, the predictive performance of minimum temperature interpolations was also improved considerably (up to 23% reduction in RMSE) when using thermal remote sensing data and local topographic indices as spatial covariates. Thermal remote sensing data also reduced the RMSE for maximum temperature interpolations by up to 16% in Bhutan. Interannual variability of climate extremes were used to evaluate how the temporal characteristics of climate may be used to improve the predictive performance of SDMs. Generalised Extreme Value (GEV) distributions were fitted to monthly climate data to generate variables which account for the skewed distribution of extremes. Models incorporating interannual variability (drawn from a range of expected return intervals) improved predictive performance compared to models using seasonal extremes only for 28 of 37 species assessed. Iteratively fitting models using alternate expected return intervals typically acted on the leading and trailing edges of current distributions, indicating that such methods may be useful for model calibration and characterising climate-driven source-sink population dynamics. The impact of spatial disparities in climate on the predictive performance of plant SDMs was evaluated using three distinct datasets developed for Victoria as part of this research, in addition to two global datasets (WorldClim v1 and v2). Individual models were compared against one another and as ensembles to explore the potential for alternate predictions to complement one another. The Victorian datasets demonstrated a significant improvement over the original WorldClim dataset (up to 17.3% mean increase in D2) and trended towards an improvement relative to WorldClim v2; however, no significant differences were found when comparing the alternate Victorian datasets. Multi-model ensembles achieved a mean increase of up to 13.8% and 29.2% in D2 relative to individual models when using regional and global datasets, respectively. Ensembles provide a pragmatic method to improve the predictive performance of SDMs and allow a trade-off between the uncertainties and potential biases embedded in competing climate datasets.
The potential for flow restoration in urban streams
Flow regimes in urban waterways are degraded by urbanization and hydraulically efficient stormwater drainage systems. To return more natural flow regimes, urban stormwater management has, in recent times, increasingly focused on source-control approaches – use of Stormwater Control Measures (SCMs). However, experimental evidence of the success of such approaches at the catchment scale is limited, which is a key impediment to the widespread implementation of SCMs. The overarching aim of this Ph.D. thesis is to evaluate the effects of SCMs on flow regimes in urban waterways. This research includes literature reviews and experimental analyses. The literature reviews identified the challenges in the design and analysis of catchment-scale experiments and outlined a series of considerations to address these challenges, which provided practical guidance for future experimental studies and prepared for the methodological development for the experimental part. The experimental analyses were based on an ambitious long-term catchment-scale experiment in Melbourne, Australia, including four Impact catchments (urban with intervention), two Control catchments (urban without intervention), and three Reference catchments (forested, non-urban). Over 700 SCMs were implemented across the four Impact catchments during the study period (October 2009 – September 2017). A suite of flow metrics at different temporal scales and SCM implementation metrics integrating imperviousness and hydrological information were selected, based on literature review and statistical analysis, to facilitate the assessment. An investigation on the hydrological effects of urbanization, using a space-for-time approach, found that quickflow and variability metrics were the most affected by urbanization levels as measured by effective imperviousness (EI). Total flow and slowflow metrics were also affected by urbanization but to a lesser extent. This analysis was used to hypothesize the likely effects of SCM implementation on the flow metrics. The hydrological effects of SCMs were investigated using sophisticated statistical models, to identify to what extent have SCMs changed the flow regime over time. In general, SCMs reduced the negative effects of urbanization, by reducing quickflow, total flow, and absolute variability. However, there were negligible changes in slowflow and inconsistent changes in relative variability metrics, requiring further research. The SCMs have more impacts on short-term flow regime characteristics that better capture the immediate effects of SCMs. The differing relationships between each of the SCM implementation metrics and the flow metrics helped to identify and interpret the likely mechanisms driving SCM impacts on flows. These findings also helped prioritize future work in both practice and research. This novel study makes a significant contribution to the understanding of the effects of the catchment-wide implementation of SCMs on flow regime restoration. It revealed that the SCMs returned most aspects of the flow regime towards the natural condition, but more work is required to restore the full flow regime. This study will also serve as a model for future studies, informing the selection of metrics and statistical methods, and the requirements for future such experiments.