School of Ecosystem and Forest Sciences - Theses
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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.
Regime resistance and accommodation in sustainable energy transitions
To help accelerate the decarbonisation of electricity generation and meaningfully mitigate climate change, a more nuanced understanding of the power and influence of incumbent electricity firms in government policymaking is required. Building on sustainability transitions literature, concepts from neo-Gramscian political economy and insights from strategic management, this study investigated the ways in which incumbent electricity generators, network operators, retailers, and their industry organisations sought to influence residential solar power policy. The single case study is focused on Victoria, Australia, using data obtained from multiple sources, including: legislation; policy submissions, reports and documents; organisational documents and materials; media releases and articles; and transcripts of in-depth, semi-structured interviews with key informants from electricity utilities and their industry peak bodies. The study examined federal and state government policy instruments that supported the installation of residential solar power before it explored attempts by incumbent electricity firms and their industry organisations to influence the development of Victorian feed-in tariffs, the State Government’s primary policy instrument. The research found that incumbent actors contributed to the (re)production of a socio-technical regime by drawing on material, institutional and discursive forms of power to execute strategies of resistance and accommodation. Incumbent actors resisted feed-in tariffs by discussing them in negative terms, building alliances with opposed civil society organisations, lobbying policymakers and reminding them of their mutually dependent relationship. However, incumbent actors accommodated feed-in tariffs by working with government to implement its policy initiatives. Incumbent firms accommodated renewables more generally by operating renewable energy business units and joining renewable energy industry organisations, although the later served to moderate support for feed-in tariffs. The study also found that a number of external and internal factors shaped the strategic approach of incumbent electricity firms and limited the extent of their resistance. High public support for residential solar power and strong government determination to implement feed-in tariffs were key external factors that discouraged greater resistance from incumbent firms. Key internal factors included the assessment of feed-in tariffs as low risk to the ongoing profitability of incumbent firms, and higher policy priorities, the achievement of which necessitated good relations with government and the sacrifice of lower policy priorities. These findings suggest that a neo-Gramscian approach to understanding politics and power in sustainable energy transitions offers useful insights for policymakers, incumbent and renewable energy firms, and civil society organisations who seek to accelerate the decarbonisation of electricity generation.
Using LiDAR for landscape-scale mapping of potential habitat for the critically endangered Leadbeater's Possum
Leadbeater’s possum (LBP) (Gymnobelideus leadbeateri) is a critically endangered arboreal marsupial located in Victoria’s Central Highlands in southeastern Australia. Populations of hollow-bearing trees, the key nesting habitat resource for Leadbeater’s Possum, are rapidly declining. Disturbances such as bushfires and timber harvesting are believed to be the major causes in the reduction of hollow-bearing trees and thus the extent, quality, and connectivity of LBP habitat. LBP also requires a connected understorey or midstorey for foraging and movement within the forest. Changes in LBP habitat at the landscape-scale are interpolated from plot-level measures and assumed distribution of habitat resources based on forest type and disturbance history. Long-term monitoring at the plot-level has reduced uncertainty around habitat resources required by LBP within the montane ash (Eucalyptus regnans, E. delegatensis, E. nitens) forests of the region; however, it has not addressed uncertainty around the landscape distribution of nesting and foraging habitat resources. Developing effective conservation strategies for LBP requires an understanding of the distribution and quality of available habitat across its potential range. This currently does not exist. I used Light Detection and Ranging (LiDAR) data to develop empirical models that quantify the distribution, quality, and connectivity of LBP habitat in the montane ash forests within a multi-scale framework. LiDAR-derived topographic and vegetation structural metrics were integrated with different habitat analysis approaches to model the distribution of critical LBP habitat features (hollow-bearing trees, foraging and midstorey stratum connectivity) at multiple scales across ~340,000 ha of forest in Victoria’s Central Highlands. In Chapter 2, tree-level individual tree delineation (ITD) algorithms were developed to identify individual trees and analyse tree crown attributes. ITD algorithms for overstorey trees were applied to the whole study area to estimate the abundance and distributions of large live trees with big crowns that have high probability of containing hollows. Based on field surveys in 1939 regrowth mountain ash, the dominant overstorey crowns identified by the ITD algorithms had an 86% success rate in identifying mapped trees in mature forest plots. Our landscape analyses estimated 405,000 large live trees (crown width >15m) and 572,000 (95%CI: 318,000-808,000) potential large live tree with hollows (DBH>150cm), which equate to a mean density of one live large old tree per ha across the Central Highlands. ITD algorithms were also used to map canopies and to calculate the proportion of projection area of midstorey stratum, a surrogate for midstorey coverage, for use in assessments of foraging habitat. Hollow-bearing trees are a key feature of mature forests around the world. They provide critical habitat resources for hollow-dependent animals, many of which are threatened, due to a range of natural and human disturbances. In Chapter 3, to develop more accurate inventories of hollow-bearing trees (both live and dead form classes) across a large landscape, I used LiDAR-based metrics of forest structure and topography, coupled with datasets on environmental conditions to develop statistical models of abundance of hollow-bearing trees using machine learning tools. These provided empirical estimates of HBT density for every hectare of the Central Highlands within the LiDAR footprint. I identified 1,519,000 (95%CI: 1,306,000 – 1,730,000) hollow-bearing trees may occur across the full extent of Victoria’s Central Highlands. This included 833,000 (95%CI: 742,000-923,000) live HBTs and 686,000 (95%CI: 564,000-807,000) dead HBTs. The predictive models provided rigorous, repeatable estimates of tree abundance across a wide range of vegetation classes and forest management zones (with appropriate estimates of uncertainty), as well as a new understanding of the complexity of the structural, topographic, and environmental features associated with abundance of hollow-bearing trees and their spatial variability over large areas. In addition to HBTs for nesting, LBP require a well-connected midstorey stratum to facilitate movement amongst nesting trees and foraging. In Chapter 4, the association between field-assessed multi-storey vegetation connectivity and LiDAR structural metrics was evaluated to develop landscape-scale predictions of connectivity and foraging habitat (density of live wattle) for LBP. Forest structural types with high midstorey connectivity, which are a critical habitat feature for LBP, occupied 17.2% of the study landscape. The landscape-scale predictions of vegetation connectivity provided an understanding of the factors (e.g., topography, fire, logging and interactions among strata) that help shape connectivity and foraging habitat. This understanding is critical for improving the management of the region’s forests and, in particular, ensuring that both key habitat elements, HBTs and dense midstorey vegetation, either co-occur in the same stand or are in close proximity to ensure sufficient high-quality habitat for LBP over space and time. In Chapter 5 I used the landscape-level mapping of habitat resources developed in Chapters 2-4 to predict landscape-scale LBP habitat suitability based on fields records of LBP occurrence. The validated habitat suitability model for LBP had an overall accuracy of 87.3% and an AUC of 0.889. The model predicted that 28,000 ha (95%CI: 17,000ha-40,000ha) of the study landscape (i.e., 9.6%) supported suitable habitat for LBP. Twelve variables were found to have the strongest influence on estimating habitat suitability for LBP. Of these, four related to foraging habitat, three to nesting habitat, three to climatic and topographic factors, and two to disturbance history. Our approach highlights the potential for using high-resolution, spatially explicit data on forest structure at a landscape-scale to map the distribution and abundance of suitable habitat for a critically endangered species. Habitat suitability models generally account for the selection of suitable habitat and their appropriate geographical extents. However, they rarely account for the accessibility of this habitat and connectivity among habitat patches. Effective conservation of species requires that patches of their habitat are connected in space and time. In Chapter 6, graph-theoretic connectivity networks based on resistance surfaces were generated from the LiDAR mapped cover of vertical stratum. The least-cost links between patches from networks were integrated with a kernel density estimator to identify functionally connected regions. The mapping of landscape connectedness identified a potential landscape-scale metapopulation structure for LBP within the Central Highlands. This provides a tool that could be used to expand the existing protected area network to support the metapopulation processes of LBP. The identification of functionally connected regions could enhance the conservation planning for long-term population persistence. The conservation and management of endangered species is major focus of forest and land managers around the world. High-quality data on the distribution and quality of habitat is critical to the development of effective conservation and recovery strategies for species. This thesis developed a set of habitat analysis models for quantifying habitat resources, habitat suitability and connectedness for the critically endangered Leadbeater’s Possum across a range of spatial scales. These analyses highlight the benefits of using high-resolution, spatially explicit LiDAR data from the whole landscape to identify and map (1) the distribution and abundance of hollow-bearing trees, (2) midstorey stratum connectivity, (3) the distribution and abundance of suitable habitat, and (4) metapopulation structures within functionally connected regions. Dynamic modelling, informed by these LiDAR-derived models, can be used to forecast the likely consequences of changing habitat abundance under different management scenarios and evaluate both the short-term and long-term effectiveness of different conservation strategies.
Aspects of the ecology of Astelia australiana, Tall Astelia
The conservation of threatened species requires an understanding of their ecology to identify the factors that are contributing to their decline and to assess their extinction risk. The objective of this thesis was to examine the ecology of Astelia australiana, a threatened herb endemic to Victoria, Australia to inform its conservation management. To achieve this objective, I examined how the distribution and abundance of A. australiana has changed over its entire known range in the 20- year period since its demographic monitoring program began. I also examined its habitat niche and regeneration ecology and response to potential threats including drought, wildfire, disease and low light availability. I then used this new understanding to develop a population viability model to explore the viability of A. australiana to current conditions, threats and limitations. The key findings of my research include a better understanding of the regeneration ecology of A. australiana including that it involves both sexual and asexual reproduction which occur at the same time. This reproduction occurs once in an individual’s lifetime and results in the production of flowers and fruit and three clones. Previously A. australiana had been variously described as dioecious and gynodioecious; however, it is trioecious, having male, female and hermaphrodite flowers on different plants and male and hermaphrodite flowers on the same plants. Various native bird and mammal species are involved in the regeneration ecology of A. australiana as pollinators and dispersers of fruit. Reproduction of A. australiana requires a minimum amount of available light from canopy gaps in the rainforest understorey to occur. A. australiana has declined in abundance by 57% over the 20-year period. Herbivory, and disease have contributed to mortality of A. australiana over this period but do not appear to be the only factors contributing to the observed decline. Although, A. australiana was found to be highly sensitive to drought, multiple lines of evidence including: the pattern of decline and recruitment of A. australiana; comparison of the physiological response of A. australiana to drought in an experimental trial with physiology of individuals in the rainforest; examination of the microclimate of the sites; and assessment of the growth response using dendrochronological techniques, of the dominant tree in the cool temperate rainforest, Nothofagus cunninghamii (Myrtle Beech) to drought periods, all indicate that drought is not driving the observed decline as had been previously concluded by others. Wildfire also resulted in a loss of individuals in one site that was burnt during the study period however, decline from this site was not included in the 57% change in abundance total. Changes in forest structure due to growth in the canopy reduce the light availability in the understory which limits A. australiana recruitment and increases mortality and thus contributes to the species decline. Population viability analysis of A. australiana, predicted that the species populations are at a high risk of large decline (86%) across the species range over the next 50 years under current climate. This research is significant for the conservation management of A. australiana as it highlights new threats to the species and removes some others that were thought to be key threats. It is also significant because the magnitude of the observed decline warrants an up listing of the conservation status of A. australiana from Vulnerable to Endangered at the State and National level. This research has already been used to inform conservation management of the species populations including: fencing, to prevent further decline in one site that had been heavily browsed and disturbed by an introduced herbivore; facilitating targeted surveys for additional sites; increasing its reproductive rate within four sites through manipulation of the light environment; establishing new populations through translocation of individuals; identifying suitable sites for further translocation; establishing the monitoring program at new sites; reviewing the ex situ storage of seed; guiding and prioritising future conservation management actions of A. australiana through modelling and expert advice; and raising the species profile to obtain funding for further research and management of the species.
Between localism and internationalism: multi-level governance, land use decision-making, and REDD+ in Central Kalimantan province, Indonesia
While there has been considerable progress in developing global environmental policies and goals, implementing these at a local level has proven extremely challenging. This study explores how internationally formulated objectives for Reducing Emissions from Deforestation and Forest Degradation (REDD+) are implemented in frontier landscapes undergoing rapid transition. I focus on subnational implementation of REDD+ in relation to land use decision-making in Indonesia. International donors and agencies have actively promoted REDD+ to reduce carbon emissions, improve forest management and broaden livelihood options in developing countries. Indonesia has been a priority country for REDD+ due to high rates of deforestation and continuing land use change. In this thesis, I use multi-level governance (MLG) concepts to investigate how internationally formulated objectives for REDD+ interact with existing systems of land use governance at multiple levels. I incorporate actor-network theory (ANT) within an overall practice orientation to address the following questions: (i) how are land use decisions made, (ii) how is REDD+ being implemented within interacting multi-level governance arrangements, and (iii) how do decision-making processes in these arrangements relate to multiple outcomes? These questions are underscored by a concern with social and environmental justice, and related to this, a concern with ethics in global environmental governance and novel mechanisms such as REDD+. In 2010, Central Kalimantan was selected as the official REDD+ priority province of Indonesia. The province has had a long and complicated history of governance interventions and is currently undergoing rapid land use changes, such as the establishment of large industrial oil palm plantations. I used a case study approach, centring on the southern tropical peatlands of Central Kalimantan, where a variety of REDD+ projects have been implemented. Data was collected during 10 months of field research conducted between 2013 and 2015 and combined ethnographic techniques with document analysis, interviews and field observations. Data collection spread across government levels, actors, and locations. A total of 194 interviews and other field observations and documents were used to explore concepts of negotiation, translation, and learning. The findings show how successive interventions and negotiations over land have transformed the remote forested peat ecosystems into a complex, and contested, mix of land uses. Competing interests and interactions among land use changes are diminishing access to land for villagers and other local people. Processes to translate internationally formulated objectives through multiple layers of governance were difficult to control and lacked flexibility. REDD+ objectives were reinterpreted at each level, and discrepancies and disconnects emerged between higher level objectives and local realities. While learning was mentioned in REDD+ project documents, a reliance on experts, and an emphasis on training and livelihoods to villagers, allowed limited local input into project design. Due to competition for land, REDD+ becomes another powerful force for villagers to contend with. Rather than achieving any desired new status quo, attempts to implement pre-determined plans become entangled in these fluid and messy frontier processes. Overall, this thesis contributes to understanding how interventions for implementing global environmental goals relate to pre-existing, dynamic and emerging land use systems that I conceptualise as ‘frontiers’. It adds new insights into how negotiation, translation, and learning are linked in interactive networked processes and identifies implications for pursuing environmental reforms. I develop a new concept, the entry point, to describe political opportunities and limitations for how those implementing, and being subjected to, global environmental policies can navigate local land allocation systems. The thesis demonstrates the need for social learning in international environmental governance and suggests strategies to move beyond policy design and technical coordination to encourage long-term collaboration and integration of learning at all levels. A focus of REDD+ is carbon rich regions in developing countries that are undergoing rapid changes. Findings from this thesis have implications beyond Indonesia to frontier landscapes in other developing countries where there is competition between large-scale forest conservation and land conversion for local or national economic development.
Impacts of short-interval wildfires on tree demography and forest structure in temperate Australia
Fire is a powerful agent of disturbance in terrestrial ecosystems, and it shapes vegetation composition and patterns globally. This is particularly true in south-eastern Australia where forests are dominated by species of the genus Eucalyptus, many of which have the capacity to recover from high-severity fire by resprouting from epicormic or basal buds. Climate change is predicted to yield more severe fire weather and lengthen fire seasons in temperate Australia, leading to increased wildfire frequency in these forests. While increased fire frequency – resulting in wildfire intervals of under a decade – are known to negatively affect fire-sensitive eucalypts (obligate seeders which have a juvenile period of 10 – 15 years) less is known about how such changes impact fire-tolerant, resprouting eucalypts. This Thesis examines the impacts of recent wildfires in south-eastern Australia, where a series of large wildfires burned over four million hectares of land, leading to the burning of different types of fire-tolerant eucalypt forests (basal resprouters, epicormic resprouters) by high-severity wildfires once, twice, and sometimes three times between 2003 and 2013. In the context of this massive natural experiment in the landscape, my overarching aim was to quantify the impacts of short-interval wildfire on eucalypt tree demography and regeneration, to improve understanding of potential fire-related changes to the structure and resilience of fire-tolerant forests. Short-interval high-severity wildfires significantly increased whole-tree mortality and decreased the abundance of both resprouts and seedlings in basally resprouting eucalypt forests. In these sub-alpine forests, dominated by snow gum (E. pauciflora), more frequent wildfire (two and particularly three short-interval fires) also increased the cover of grasses at the expense of shrubs. In mixed-species eucalypt forests, which occupy extensive tracts of low elevation landscapes in south-eastern Australia, resprouting occurs from both basal and epicormic buds. In these forests, the dynamics of both topkill (i.e. stem, but not whole-tree, mortality) and whole-tree mortality have important ramifications for forest structure. After a single high-severity wildfire, small-diameter stems were typically topkilled; after two short-interval wildfires, the diameter of stems topkilled increased. Additionally, the overall likelihood of either basal or epicormic resprouting decreased after two short-interval wildfires. This decline in resprouting capacity indicated that the size class most vulnerable to ‘resprout failure’ after multiple wildfires was intermediate sized stems (in the vicinity of 20 - 30 cm DBHUB), rather than smaller or larger stems. Seedling regeneration also decreased in these forest types after short-interval wildfires, suggesting that, as for fire-sensitive forests, immaturity risk may be a relevant factor for fire-tolerant forests. Short-interval wildfires reduced the total and aboveground carbon stocks of mixed-species forests, while also increasing the proportion of carbon mass in the dead pool, indicating that resprouter forests might not be perpetually secure carbon stocks under emerging fire regimes. My Thesis highlights that fire-tolerant forests may not be as invulnerable to changes in fire frequency as widely assumed, and that management interventions will likely be required to counteract increasing tree mortality and decreasing tree regeneration if predictions of more frequent and severe wildfires in temperate Australia are realised.
The impact of wood characteristics and properties on the market price of plantation grown teak logs (Tectona grandis Linn.F) in Laos
Teak is considered one of the highest value hardwood species. The Lao wood processing industry has been using teak wood harvested from different ages, ranging from 10 to 35 years, with broadly different prices. However, the current grading rules used for teak logs are unsuitable for development of a fair and transparent pricing market. To date, there has been no regulation of market requirements for wood characteristics and/or wood properties. The key terms of wood characteristics and wood properties used in this study were defined as: a) wood characteristics refer to the visual appearance or features of logs and square logs; for example, heartwood proportion, wood colour, presence of knots, bend, pipe, buttress, decay, end checks and splits; b) wood physical and mechanical properties describe the quantitative characteristics of wood and its behaviour in response to external influences and externally applied forces; for example, wood density, dimensional stability, stiffness, bending strength, compression strength, shear strength, and hardness. The overall aim of this study was to identify the key characteristics and properties of wood that affect the selling price of teak logs grown in Laos. More specifically the objectives of the study were to: 1. define the characteristics and properties of plantation grown teak logs that are valued by wood processors and manufacturers; 2. understand the influences of wood characteristics and properties on the current selling price of plantation grown teak logs used in Lao wood processing and manufacturing industry, and; 3. determine the key characteristics and properties that could be used if a log grading system was to be applied in Laos, and that is based on the results identified from the buyers’ requirements. Both semi-structured interviews of teak buyers and qualitative and quantitative data of wood characteristics and properties of plantation grown teak in Laos that were valued by teak buyers were obtained and analyzed. The results showed that while the harvesting age of plantation teak was reported to be between 10-35-year-old, the dominant harvesting age was between 21-25 years. Three types of teak timber were commonly sold in Laos: 24.7% as standing trees, 39.6% as round logs and 35.7% as square logs. From the marketing supply chain it was found that the end buyers of teak timber were wood sawmillers and wood products manufacturers. The local traders (middlemen) who purchased teak logs from the growers and in turn supply to the end buyers account for 49% of sales. A further 41% was sourced directly from teak growers and the remaining 10% was sourced via local small wood sawmillers and manufacturers. The main wood products produced from plantation teak included joinery products, door and window frames, and furniture (57.9%, 26.3% and 15.8%, respectively). Currently, 83% of teak products produced were consumed on the domestic market. The remaining account for 17% were destined for international markets. The prices of teak showed to be significantly different based on timber types, log sizes, and distance from plantation site to the road in the case of standing trees. However, the price variation was not based on the factors of wood quality and properties. A round log price of US$250/m3, based on both log diameter size (D26-30 cm) and log quality grade (A grade), was much lower than the US$321/m3 amount paid for an ungraded round log of the same size based on log diameter alone. It can be concluded that there is a need to develop a clear system or standard for teak log grading and pricing in Laos. The knot was found to be the major characteristic appearing on all teak wood products, square and round logs. White sapwood, end splits, and buttress were the next most predominant characteristics in teak wood products, square and round logs, respectively. Buyers were found to prefer a larger heartwood proportion and diameter of the logs. On the other hand, decay, pipe, insect holes, bend, and knot holes were found to be the wood defects that the buyers were most concerned about when they bought timbers. Log diameter, bend, buttress and insect holes were only the wood characteristics that have significant impact on log price. Buyers were unwilling to buy any logs containing wood decay or rot. Wood property values were not important for the buyers. Lao teak buyers didn’t offer a different price for teak timbers that have different wood property values. This study concluded that wood properties have no impact on log price. If a grading system is to work, then it must be of use to those who buy logs and square logs, as they would be the main beneficiaries of such a system. Laos already uses a grading scheme; however, the question remains about how well it works. A good grading system can be said to work if the different characteristics; for example, wood characteristics valued by buyers are reflected in the prices for the wood. In a simple test, the following questions could be asked: 1. Is there a significant difference between the prices of graded logs? 2. Do the prices for each grade move independently of one another (thus reflecting the changing nature of how buyers value each characteristic)? and 3. Are the prices of graded logs higher than ungraded logs (at least those that are considered to be of a superior quality). The answers to these questions, when applied to the current grading system, led to the conclusion that such system did not work. All prices tended to move together, and ungraded log prices were found to be greater than graded logs. The next question to address was how a better grading system could be determined. Clearly, any system should reflect the wood characteristics that buyers demand. To that end, it was necessary to survey buyers to determine what they considered to be the most valuable characteristics. These identified characteristics need to be collated into a system that is both clear and usable for the buyers. The following characteristics were found to be important: log diameter, heartwood proportion, presence of insect holes, log bend, presence of knots, end splits, wane/buttress, and wood colour. It should be noted that as the buyers' responses are not universal (for example, some buyers prefer one characteristic, whereas other buyers prefer another), a grading system is preferred. The grading system reflects a set of tolerances within which a range of wood characteristics can be valued by the buyer. In this way, they can pay a price for logs according the characteristics they value and not on the basis of log diameter alone (as they do now). Based on the key finding from the results mentioned above, a guideline for a teak timber grading system was developed. This grading system is a new log grading method, which can be used in Laos and similar developing countries. Implementation of this grading system would benefit both teak buyers and growers. The buyers can minimise timber waste, as buyers can buy only the qualities of timber they want if the timber is graded. Teak growers could also employ practices that result in them growing trees that are more highly valued by buyers because they will have the characteristics buyers pay a premium for. In the long-run, growers would minimise the production of inferior quality logs. The growers will supply only the timber that is required by the industry for specified uses. What should be noted is that in a market where the products are ungraded, average prices for all qualities apply. Thus, it is in the interests of growers to supply the lowest quality product, as this is the one that costs the least to produce and for which they receive the average price as a superior product. On the other hand, a grower who produces a superior product receives the same average price as that of the grower of an inferior product. In a graded product market, the grower receives the price the buyer is willing to pay for the characteristics that are valued by the manufacturers of finished products. Thus, growers are rewarded for improving the quality of the logs that will result in an improved industry.
In defence of flowers: The ecology and biochemistry of a chemical defence, cyanogenesis, in Proteaceae
As sessile organisms, plants produce a remarkable diversity of chemicals to defend their tissues against herbivory. The large body of research into plant defences has primarily focused on plant-herbivore interactions and foliar defences, whereas floral chemical defences have received little attention. This is despite the fact that flowers of many species are known to contain defence metabolites, the sizeable investment of resources in floral structures, the significance of flowers to fitness, and the importance of floral chemistry for both florivores and pollinators. This thesis investigates patterns in floral chemical defence in the Proteaceae, a dominant plant family in Australia characterised by diverse floral traits and a high frequency of floral cyanogenesis - a constitutive nitrogen-based chemical defence involving the release of toxic hydrogen cyanide from endogenous cyanogenic glycosides (CNglycs) upon tissue damage. There were two main aspects to this research, (1) investigations into patterns in the distribution of CNglycs within flowers of different species, and (2) investigations into patterns in whole-plant chemical defence using Telopea speciosissima. In Chapters 2 and 3 I quantified CNglycs in dissected floral tissues and used a new MALDI-MS imaging method to investigate and compare fine-scale patterns in the distribution of CNglycs within flowers of eight congeneric Lomatia species (Chapter 2), and 11 species from different genera from across the family phylogeny (Chapter 3). Together these studies identified: (1) variation in floral CNglyc concentrations over three orders of magnitude across species, (2) unprecedented concentrations of CNglycs in some floral tissues (e.g. Lomatia stigmatic cells and pollen were 11% CNglyc by mass), (3) highly tissue-specific distributions of CNglycs within flowers, (4) substantial interspecific differences in patterns of within-flower CNglyc distribution, and (5) that differences in floral CNglycs across species were not correlated with other traits (e.g. colour, disturbance response) or phylogenetic position. Findings demonstrate the power of MALDI-MSI to reveal dynamic and fine-scale spatial patterns in the distribution of different CNglycs. Data are discussed in relation to defence theories and potential multiple functions of CNglycs in plants. In Chapter 4 I used T. speciosissima, which has CNglycs in all tissues, to compare floral and foliar CNglycs in seven populations from three distinct genetic groups, which also differ in environmental conditions. There was no consistent relationship between floral and foliar cyanogenic capacity within populations; however, mean floral and foliar CNglyc concentrations differed between genetic groups. Correlations between CNglycs and δ13C, N and physical leaf traits suggest these differences reflect both genetic and environmental effects. In Chapter 5, a glasshouse study investigating the effects of N and P supply on above- and below-ground CNglycs in T. speciosissima seedlings identified that root and shoot chemistry responded differently to N and P treatments. The higher CNglyc concentrations in roots may reflect greater importance of root chemical defence in a non-mycorrhizal species that relies on basal resprouting following fire. Together this research provides evidence that foliar chemistry cannot be assumed to reflect whole plant chemistry (floral, root) and that both whole plant and fine-scale tissue-specific studies are required to understand the regulation and roles of CNglycs in plants.
The ecology and evolution of plant-pollinator interactions in Australian Typhonium (Araceae)
Pollination is one of the most important interactions in nature, with the vast majority of flowering plants reliant upon biotic vectors for out-crossing and reproduction. Despite this, the pollination systems of most plants are unknown, limiting our understanding of the evolutionary processes that gave rise to these interactions, dependency on specific pollinators for plant reproduction, and the resilience of interactions in the context of environmental change. The species-rich family Araceae is used worldwide as a model to investigate the ecology and evolution of plant-pollinator interactions, yet detailed studies of pollination in the majority of genera remain scarce. One such sizeable genus is Typhonium Schott, the most diverse genus of Araceae in Australia. Using field studies and a range of analyses (morphological, chemical, molecular), this thesis aimed to investigate the diversity, ecology, and evolution of Typhonium plant-pollinator interactions in Australia. This thesis is divided into four research chapters. Chapter 2 identified significant intra and interspecific variation in floral traits and pollinating insects between allopatric populations of the only species with a broad geographic range, Typhonium brownii, and its geographically restricted sister species T. eliosurum. Both mimic dung, but they are functionally specialised to deceive saprophagous beetle or fly pollinators, respectively. Interspecific trait divergence provided insight into the pollinator-mediated selection of floral traits and the importance of morphological filters. Significant intraspecific variation in T. brownii thermogenesis, anthesis rhythms and scent indicates the occurrence of a T. brownii species complex, comprised of more taxa than currently recognised. The function of floral scent for pollinator attraction was confirmed in field bioassays and is discussed in the context of adaptation to the pre-existing biases of pollinators. Chapter 3 investigated pollination systems of tropical T. angustilobum and T. wilbertii, from north Queensland. T. angustilobum and T. wilbertii were similarly identified as brood-site mimics, share similar thermogenic and anthesis rhythms, but are functionally specialised to beetle and fly pollination, respectively, associated with distinct floral scents and morphological filters. Molecular analyses provide the first evidence of heating via the alternative oxidase (AOX) in Typhonium. Chapter 4 combined pollination data on 14 Typhonium species from across their geographic range to explore trends in plant-pollinator interactions. It presents further evidence for functional specialisation to pollination by saprophagous beetle and fly families in a genus characterised by rewardless brood-site mimicry, floral traps and a high frequency of floral thermogenesis. Differences in pollinator type and climatic region were not related to anthesis rhythms or thermogenic properties. Despite significant scent divergence, some broad differences in scent with pollinator type were identified. Given the prevalence of Staphylinidae-flower interactions in Australian Typhonium, Chapter 5 systematically analysed the worldwide extent of rove beetle floral interactions and pollination. At least 108 staphylinid-plant species interactions were identified across 27 seed plant families, the first assessment of the diverse and complex relationships between staphylinids and plants which were previously overlooked. As concluded in Chapter 6, this thesis develops Typhonium as a new model system to investigate the ecology and evolution of brood-site mimicry, an underappreciated yet widespread form of floral mimicry.