School of Ecosystem and Forest Sciences - Theses
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ItemExploring the indirect effects of climate change on fire activity in Australian wet Eucalypt forests( 2022)Understanding the impacts of climate change on future fire activity is critical for assessing the risks posed to biodiversity and communities. However, the mechanisms through which climate change may influence fire activity are varied. In temperate forests, climate change is expected to directly increase fire activity through elevated temperatures and more variable rainfall, resulting in weather conditions conducive to large fire events. However, climate change may indirectly influence fire activity through effects on forest structure and composition. While the direct effects of climate change are well studied, indirect mechanisms are poorly understood. These mechanisms are important because changes to vegetation structure and composition have the potential to amplify or dampen the direct effects of climate change on fire activity through their effects on fuels, particularly dead fuel moisture content (FMC). Forest structure and composition moderate microclimate conditions compared to the open, which is an important factor affecting the moisture content of understorey fuels. FMC is a key determinant of fire activity, particularly in wet Eucalypt forests with high biomass loads. However, our understanding of the magnitude of forest structure and composition effects on microclimate and subsequently FMC dynamics, is a critical knowledge gap in our understanding of climate change effects on future fire activity more broadly. In this thesis, I aimed to quantify the potential for indirect effects of climate change to influence fire activity, through their influence on dead FMC in the wet Eucalypt forests of south-eastern (SE) Australia. In these forests, recurrent high-intensity fire has altered vegetation structure and composition, resulting in a range of alternative forest states to the dominant wet Eucalypt system. To quantify the magnitude of these on potential fire activity, seven alternative forest states and two adjacent open weather stations were instrumented with automated fuel moisture sticks and micrometeorological sensors. FMC and microclimate were measured over a 2-year observation period, and lidar data were used to evaluate the role of forest structure in FMC dynamics. I used a process-based fuel moisture stick model to quantify the relative importance of forest structure effects on microclimate to FMC variability. This model was then used in conjunction with new methods to estimate microclimate from open conditions, and a 48-year climate dataset to model FMC at alternative forest states across the range of climate conditions characteristic to the region. I also evaluated the potential contribution of live species to changes in fuel moisture in a conifer forest and related this to the potential impacts of forest conversion to alternative states. Overall, I found significant differences in dead FMC across alternative forest states, with potentially meaningful implications for fire activity. The sensitivity of FMC to forest structure was examined, with longwave radiation and vapor pressure deficit emerging as key drivers of FMC variability related to structural change. These findings informed the modelling process, where results indicated that differences in FMC related to alternative forest state were greater than the direct effects of climate change (modelled at an open reference site), indicating strong positive and negative feedback processes in this system. Overall, my results suggest that the indirect effects of climate change on potential fire activity are meaningful for fire management, exceeding the role of direct effects in the context of FMC. Consequently, the potential for forests to convert to alternative states is a key issue for land and fire managers.
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ItemDynamics of woody vegetation in fire prone temperate forests of south-eastern Australia( 2017)An improved understanding of the dynamics and response of vegetation to environmental variability and perturbation will assist in the sustainable management and conservation of ecosystems in the face of anticipated changes to climate and fire regimes. Using time since last fire (TSLF) as a measure of ecosystem development I investigate broad to fine scale community and population processes and dynamics of woody vegetation in fire prone temperate forests of south-eastern Australia. This thesis aims to provide a clearer understanding of the dynamics and fire-related processes at play in these temperate forests with the primary objective of providing tangible and applicable outcomes for forest fire management. In chapter 2 I show that relative to stand structure, TSLF and dispersal mediated processes, environmental heterogeneity, explains the greatest portion of beta diversity of woody species within understorey, mid-storey and canopy strata, although the relative importance of edaphic and climatic variables differ among strata. I also show that TSLF has a limited capacity to explain beta diversity regardless of strata. Forest management based on broad-scale TSLF classification – such as focusing solely on growth stage - are therefore unlikely to capture the suite of factors that influence biodiversity in these temperate forests. Rather, landscape-scale conservation and management of these forests will require metrics that more fully capture environmental heterogeneity and disturbance histories. A comparison of above and below ground vegetation dynamics (Chapter 3) shows that the standing vegetation provides limited insight into the soil seed bank. For example, a number of species maintain a presence below ground despite declines in the standing vegetation. Employing differences in temporal dynamics in above and belowground vegetation, I provide a new framework for classifying species according to their fire response which could facilitate improved selection of key fire response species to help determine appropriate tolerable fire intervals for informing fire management of these forests. Shifting my focus to the species level, I explore population dynamics of a ubiquitous understorey species in relation to TSLF using dendroecology (Chapter 4). I find that Pomaderris aspera can be used to determine TSLF with confidence. I also investigate release and suppression events of this understorey species. This chapter also sheds light on the role of the canopy in understorey development. I conclude my examination of the dynamics of woody vegetation in temperate fire prone forests of south-eastern Australia by comparing the multivariate structure of vegetation communities with pre-defined fire management classifications (ecological vegetation divisions – EVD). I find that the current management approach does not recognize the diversity of site or species associations found within the sampled woody vegetation. I highlight the disjunction between the a priori and a posteriori classifications and the potential vulnerability of individual species and communities to the application of inappropriate tolerable fire intervals. In support of the findings from examination of the soil seed bank dynamics (Chapter 3), this re-iterates the importance of base-line autoecological information for determining ecologically based fire management. The outcomes of this research show that woody vegetation of fire prone temperate forests in south-eastern Australia demonstrate a variety of responses to environmental variability and TSLF and importantly; the response varies for different strata. The paucity of autoecological information available for many woody understorey species highlights the potential vulnerability of species to inappropriately managed fire regimes. The framework developed as part of this work that incorporates the temporal dynamics of both standing vegetation and the soil seed bank, combined with the targeted application of dendroecology provides much scope for improvements in ecologically-based fire management strategies.
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ItemSavanna dynamics in seasonal tropical forests: how fire, grass, and drought shape deciduous dipterocarp forests in continental Southeast Asia( 2017)Savanna is defined by the co-occurrence of a continuous C4 grass layer and a discontinuous tree layer. The deciduous dipterocarp forests (DDF) of continental Southeast Asia share the defining feature of savannas, yet have been historically considered a seasonally dry tropical forest. I studied DDF at YokDon National Park (YDNP) in the Central Highlands of Vietnam using a range of empirical experiments that examined the effects of fire, grass, and drought on the four dominant tree species of southeast Asian DDF. My studies provide new insights into the roles these factors play in shaping the DDF and place the DDF into the broader context of global savannas. I first quantified the variation in structure and species composition of the DDF on 70 20 x 20 m plots across YDNP. Four deciduous dipterocarp species dominated the plots in the tree density and basal area. However, all four species rarely co-occur. Instead one or two of the four species dominate the density and basal area within a plot, forming distinct and readily identifiable communities. The most striking structural feature of the DDF is the absence of saplings. My experiments demonstrated that the observed demographic bottleneck is driven primarily by fire and to a lesser extent by grasses and drought in the dry season. The mechanisms by which fire, grasses, and drought prevent recruitment of saplings in the DDF are relatively similar (i.e., seedlings are topkilled preventing the transitions into later life-history stages). In the absence of fire, seedlings in the DDF gained up to 50% of the sizes in the previous growth season, suggesting a high chance of transition to the sapling size class. In the longer term, this may even lead to a shift to closed forest if fire is suppressed for long enough. The burning and drought experiments that I conducted revealed that seedlings of the four dominant species in DDF are highly vulnerable to fire and drought, but that their vigorous resprouting ability allowed them to persist in the environment. One novel result of my study is the quantification of post-fire recovery of >6500 seedlings and juveniles on a bi-weekly basis. These detailed measurements revealed that up to 95% of the pre-burnt sizes was regained within ~10 weeks after the fire, that but further growth over 22 weeks later were negligible. The grass removal experiment, which included measurements on the growth of >3500 seedlings and juveniles suggested that one limitation to seedling growth (particularly diameter) over these 22 weeks was suppression by competing grasses. I found no evidence of soil nutrients and canopy cover (and unlikely water availability) limiting seedling growth during this period. The slow growth of the seedlings during the wet season suggests that further studies should focus on the dynamics of carbohydrate mobilization and accumulation to understand more about the dynamics of this ecosystem. My experiments also revealed how species-specific differences in responses to fire, grass suppression, and drought shape community assembly patterns in the DDF. Dipterocarpus tuberculatus had greater survival, growth, and fire escape rates than S. siamensis, S. obtusa and D. obtusifolius, which is consistent with the observed dominance of D. tuberculatus across the YDNP landscape. My study demonstrated that the structure of, and processes driving, the DDF are the same as those that define savannas globally. Consequently, to better understand and conserve the DDF, it is necessary to understand the role that these drivers—fire, grass, and drought—have on the dynamics of the DDF and how they might be managed now and in the future.
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ItemFire effects on pollinators and pollination( 2016)One of the most important knowledge gaps currently inhibiting biodiversity conservation in fire-prone landscapes concerns the interactions between fire and other ecosystem processes. Animal-mediated pollination, whereby animals transport pollen between the male and female parts of flowers, is an important ecosystem processes as it is required for approximately 80-90% of the Earth’s flowering plants to reproduce sexually. The aim of my thesis is to better understand fire effects on pollinators and pollination and their role in fire management. First I synthesise the literature to develop a conceptual model, and then describe my empirical work exploring the ideas underlying this model. The central idea is that fire can influence plant-pollinator interactions through multiple processes operating over different spatial scales, and this was supported by my empirical work (and a study (Ponisio et al. 2016) from North America published as I was finalising my thesis). I collected data from the Mediterranean climate zone of south-eastern Australia, employing a space-for-time substitution design with spatially independent sites along a 75 year post-fire successional gradient. I monitored pollinator visitation to the sexually-deceptive orchid Caladenia tentaculata, capsule set of the food-deceptive orchid Diuris maculata sensu lato, and sampled aerial invertebrate assemblages (focusing on known fly and wasp pollinator groups) across these sites. I found that visitation to C. tentaculata was greatest when the site was recently burnt but the surrounding landscape was long-unburnt. Diuris maculata s.l. capsule set was influenced mostly by rainfall in the growing and flowering season (winter and spring). Flies and wasps exhibited only moderate or weak responses to post-fire age. Interestingly, though, species richness was positively related to fire age diversity within 800 m of sample locations but negatively related to fire age diversity within 200 m. My model could form the basis for simulations of plant and pollinator population dynamics in fire-prone landscapes, parameterised with spatially-explicit empirical data as presented in my thesis.
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ItemAridity as a predictor of the hydrogeomorphic response of burnt landscapes( 2016)Wildfire is an important disturbance in natural systems which can lead to changes in runoff and erosion processes. Increased runoff and erosion, including extreme erosion events such as debris flows, pose a hazard to soil and water resources, habitats, infrastructure, and lives. Natural resource managers require information about potential post-fire response in order to plan prevention, mitigation, or recovery activities which deal with the impacts of runoff and erosion events. Changes in hydrogeomorphic processes due to fire may also have important implications for long-term sediment budgets and landscape development. However, post-fire responses vary widely due to the landscape, fire, and post-fire rainfall properties, making it important to identify and understand mechanisms which control response variation. Previous studies, anecdotal evidence, and soil development theory suggest that moisture availability may influence post-fire runoff and erosion response. Therefore, this study aimed to investigate and quantify the relationship between moisture availability (characterised by an aridity index) and hydrogeomorphic response following high severity wildfire in the upper reaches of forested water catchments in central Victoria, Australia. This aim was addressed by examining the relationships between aridity index (AI) and soil infiltration capacity, runoff generation, and debris flow occurrence. In the first year following fire, infiltration rates and patterns, soil moisture, and soil water repellency were measured in the field. Saturated hydraulic conductivity (Ksat), soil porosity, texture, and density as well as water repellency of air-dried soils and the change in repellency with soil moisture were measured in the laboratory. To quantify the relationship between AI and surface runoff, total (all events) and real-time (within events) surface runoff and rainfall were monitored over 10 months. Aerial photography and spatial datasets were used to model (logistic regression) the relationship between the AI and the probability of post-fire debris flow occurrence. Overall the results suggest aridity exerts control over both long-term (decades to centuries) and short-term (daily to annual) system properties which result in a strong, quantifiable relationship between AI and post-fire soil infiltration capacity, runoff generation, and debris flow occurrence in the forested catchments of Victorian uplands. Increased AI resulted in reduced saturated hydraulic conductivity, suggesting a long-term control of aridity on soil structure. This, coupled with long- and short-term control of aridity on soil water repellency, led to field infiltration rates three times higher and over twice the proportion of the soil actively contributing to infiltration at the lowest AI site (AI 1.1) compared with the highest AI site (AI 2.4). Higher AI sites were consistently drier (had lower soil moisture content) leading to increased actual water repellency (measured in situ), as well as having an increased level of potential (air dry) water repellency. The reduction in infiltration capacity resulted in higher AI sites producing a greater percentage of runoff and higher peak discharge, for longer timeframes than lower AI sites. Average runoff ratio of the highest AI site (33.6%) was an order of magnitude higher than the lowest AI site (0.3%). Peak discharge during rainfall events also increased with increasing AI, with up to a thousand fold difference observed during one event. Undergrowth on the lower AI sites (AI 1.2 and 1.4) recovered more quickly (> 30% projected foliage cover within the first 6 months) than higher AI sites (AI 1.9 and 2.4) (< 5%), suggesting increased AI increases the window of disturbance. At the single headwater catchment scale, increased AI was empirically related to increased probability of post-fire debris flows. Post-fire debris flow producing catchments had significantly higher minimum, mean, and maximum AI values than non-debris flow producing catchments on average. Results indicated debris flows only occurred in catchments which contained pixels with an AI of 2.2 or higher. Logistic regression modelling results showed the probability of debris flows was highly sensitive to changes in maximum AI (sensitivity 0.95 and elasticity 2.05). This study supports the theory that aridity is a dominant first order control of hydrogeomorphic sensitivity to wildfire in this environment. Over geomorphic timescales, aridity-driven variation in runoff and erosion could have significant implications for landscape and ecosystem development. The effect of aridity is likely to become even more pronounced as climate change alters current rainfall regimes, and as the frequency and intensity of fires subsequently increases. This is the first study to quantify the relationship between AI and runoff and erosion processes following wildfire in this environment. The results of the study are a first step in using AI to predict and map soil hydrologic properties, runoff potential, and debris flow risk across burnt landscapes. As these properties and post-fire processes are resource intensive to determine in the field, AI provides an alternative spatial predictor variable which can be used to estimate these factors. Results of the study suggest AI could be a useful environmental indicator for management, capable of identifying areas of post-fire runoff and erosion risk in S.E. Australia.
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ItemFire, resources and behavioural responses of ground-dwelling mammals( 2015)Planned fire is commonly used to reduce adverse effects of bushfire to human life and property, but may also be used to conserve biodiversity. However, there is a dearth of information regarding the effect of these fires on fauna. I investigated the response of ground-dwelling mammals to a planned fire event in the Otway Ranges, south-eastern Australia. Bush rats (Rattus fuscipes) and swamp wallabies (Wallabia bicolor) were chosen as study species given that they are expected to be affected by a change in vegetation resources due to fire. The differences in body size of the two species provided the scenario to study fire effects at two different spatial scales. At a small scale, I studied changes in abundance of bush rats as a consequence of fire, plus the role of unburnt areas as refuges. I used microsatellite markers to study movement of individuals between slopes and gullies. At a larger scale, I used GPS technology to track swamp wallabies before, during and after fire, to study changes in home range and habitat selection, as well as behaviour during fire. The studies included different temporal levels as well, the study on abundance and movement of bush rats, and on habitat selection of swamp wallabies, compared data from two months before with two months after fire. Home range data of swamp wallabies compared data two months before fire with data from up to eight months after the fire. Finally, the study on movement of wallabies during the fire, included data from 36 hours when the fire was burning compared to pre-fire data. The study on bush rats corresponded to a Before-After Control-Impact (BACI) design using a paired catchment approach, while the study on wallabies corresponded to an Impact Analysis (IA) design, comparing responses not only before and after, but also during fire. There was no strong relationship between the different responses that were quantified and the amount of area that was burnt within transects and home ranges, possibly because there were enough unburnt areas available in the post-fire landscape, emphasizing the importance of keeping areas of unburnt vegetation when applying planned fires. Yet, the impact of fire was presumably larger on bush rats; this was reflected in the reduction of abundance of individuals, while all swamp wallabies survived. The impact of fire varied between the two study species, reflecting the importance of investigating the effect of planned burns at different spatial and temporal scales. The strategy used in the fire event that I studied, i.e. of low intensity, progressively and in patches across the targeted area did not have major effects on the study species. The information provided in this thesis intends to improve the capacity for land managers to consider the ecological effects of planned fire by adding to current knowledge linking fire, resources and behavioural responses. Further assessment involving more intense fire would be necessary to assess the response of bush rats and swamp wallabies, and to predict the possible consequences that a wildfire could have on these species.
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ItemMethane oxidation in soil from the Bogong High Plains, Victoria: controlling factors and fire effects( 2014)Fire rapidly changes terrestrial ecosystems by removing vegetation and exposing mineral soil. Methane (CH4) is an important greenhouse gas but little is known about the effects of fire on its production or consumption. Aerobic soils, such as those found in temperate forests and woodlands are important sinks of CH4, consuming 15-45 Tg y-1 of global atmospheric CH4. The composition and activity of the methanotrophic bacteria responsible for this sink are affected by disturbances such as fire. In this study, sub-alpine sites in the Bogong High Plains, Victoria, were used to examine interacting effects of climate and abiotic soil properties on CH4 consumption. Two predominant vegetation types, Alpine Ash (Eucalyptus delegatensis) forest and Snow Gum (E. pauciflora) woodland, were selected to encompass a range of recent fire histories. Methane oxidation followed first-order enzyme kinetics in Alpine Ash soil so that rates were exponentially proportional to the concentration of available CH4. Methane concentrations decreased exponentially down the soil profile indicating that the sole source of CH4 for oxidation was diffusion from the atmosphere. Soil at depths 5 to 20 cm had the greatest capacity to oxidise CH4. The Michaelis-Menten model was used to describe the kinetics of the enzyme rate reaction of CH4 oxidation, and the model parameters indicated that the bacteria responsible were high-affinity methanotrophs (Type II). Soils were confirmed as CH4 sinks with oxidation rates averaging 76.9 ± 5.3 µg CH4 m-2 h-1 in Alpine Ash forest, and 84.2 ± 4.9 µg CH4 m-2 h-1 in Snow Gum woodland. The effects of key abiotic properties such as CH4 diffusion, soil moisture, temperature, bulk density, inorganic nitrogen and pH were examined in relation to potential variation in CH4 oxidation associated with climate change and fire. Soil moisture influenced CH4 oxidation such that at high moisture content, CH4 oxidation was limited by diffusion, and at low soil moisture content methanotroph activity was limited by physiological water stress. Temperature had a relatively small effect with marginal linear increases in CH4 oxidation in the temperature range of 5 to 30 C°C. Methane oxidation was exponentially limited by increasing soil ammonium concentrations, which had a greater effect on CH4 oxidation than temperature and pH. This indicated a potential impact of fire, as soil ammonium concentrations increased in the first year after fire. The relationship between soil pH and CH4 oxidation was quadratic, with CH4 oxidation decreasing with changes in pH either side of an optimum. Soil pH increased after fire although sites that were more recently or severely burnt were still below the optimum pH for CH4 oxidation. This study provided an understanding of the variation of CH4 oxidation in soil from sub-alpine vegetation in the Bogong High Plains. Further research is required to estimate the magnitude of the soil CH4 sink in the Bogong High Plains, and to predict net changes in CH4 fluxes under future fire and climate scenarios, including improved understanding of the composition of methanotroph populations responsible for this important CH4 sink.
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ItemInteractions between fire, environmental heterogeneity and ground-dwelling mammals( 2014)Environmental heterogeneity is known to influence a range of ecological processes at various spatial scales, from individual habitat selection and interspecific interactions, to species’ distributions and diversity. Fire regimes can influence environmental heterogeneity by altering the spatial and temporal distribution of resources. In this thesis I used the ground-dwelling mammals of south-eastern Australia as a focal group to explore the role of fire-mediated heterogeneity in driving individual species distributions, abundance and species diversity. I focussed on two aspects of fire regimes as drivers of environmental heterogeneity at different spatial scales; time since fire at a landscape scale and spatial extent of fire within an individual planned burn. As a secondary objective I also evaluated techniques used to detect ground-dwelling mammals. I investigated relationships between fire-mediated heterogeneity and species diversity at the landscape scale. I compared heterogeneity defined by spatial pattern metrics based on fire age and vegetation type, versus heterogeneity derived from site-based habitat structural measurements. I used two complementary diversity metrics, species richness and beta diversity as response variables. Heterogeneity defined by habitat structural contrasts was positively correlated with beta diversity, however heterogeneity defined by mapped post-fire age classes and vegetation types did not influence beta diversity, and neither measure of heterogeneity was related to species richness. The mammal communities in our study area were influenced by environmental heterogeneity but only if it was present in specific structural attributes of the environment. This suggests that relationships between heterogeneity and diversity depend on how variables representing these properties are quantified. The spatial pattern metrics based on fire age and vegetation type did not reflect physical contrasts that are important for maintaining ground-dwelling mammal diversity. Building on the knowledge at the mammal community level, I investigated individual species responses to time since fire at the landscape scale. Specifically, I used a space for time substitution to investigate interrelationships between the occurrence of eight ground-dwelling mammals, time since fire, and structural resources. Individual species distributions were not well predicted by time since fire. Time since fire was moderately correlated with habitat structure yet was a poor surrogate of mammal occurrence. Variables representing habitat structure were better predictors of mammal occurrence than time since fire for all species considered. These results suggest that time since fire is unlikely to be a useful surrogate for ground-dwelling mammals in heterogeneous landscapes. At a smaller spatial scale, I used a before-after-control-impact experiment, focussed on a planned fire, to investigate the role of unburnt patches in providing post-fire refugia for Agile Antechinus Antechinus agilis and Bush Rats Rattus fuscipes. The two species responded differently to the presence of unburnt patches associated with wet gullies in the burnt landscape. Relative to controls, fire had little effect on Bush Rat abundance in unburnt gullies. In contrast, the fire caused Agile Antechinus abundance to increase in gullies, indicating a shift of individuals from burnt parts of the landscape. Bush Rats that previously occupied burnt parts of the landscape most likely perished in the aftermath of the fire. These differences are likely driven by differences in habitat use and intraspecific competition between these species. I evaluated the three techniques used to detect mammals, live trapping, camera trapping and hair detection. The camera traps detected more species than the other two techniques but live trapping consistently complemented the cameras by detecting unique species. Furthermore the effectiveness of the different techniques varied across the landscape, with live trapping detecting more unique species in wetter, more productive vegetation types, whereas in dry vegetation types the camera trapping alone detected all species present in the sample. I also evaluated two different camera trap models. I found that Reconyx cameras consistently detected more species than Scoutguard camera, mostly because they detected small and medium species more frequently. The results showed that the use of Scoutguard cameras in isolation would have led to erroneous conclusions about the main drivers of species distributions across the landscape.
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ItemThe effects of fire on bark habitats and associated beetle assemblages( 2013)Structurally complex habitats can often support more diverse animal assemblages than simpler habitats. Additionally, changes in habitat structure can alter assemblage composition. Structural changes can occur due to fire, and over time since last fire (TSLF), which may have implications for biodiversity management in fire-prone environments. The bark of Eucalyptus trees is readily modified by fire, but also provides habitat for a diverse fauna, including beetles (order Coleoptera). In a fire-prone forest type in south-east Australia, hypothesised relationships between TSLF, bark complexity and bark-associated beetle assemblages were investigated on two bark types: fibrous bark (typified by Eucalyptus obliqua) and ribbon bark (smooth bark that peels to form loose ‘ribbons’, typified by E. cypellocarpa). The research involved both a long-term (chronosequence ranging from 1 to 72 years postfire) and a short-term component (treatment-control study, comparing sites < 1 year post-fire with sites that had not been burnt for 27 years). Based on ecological theory it was expected that habitat complexity would change with TSLF, and that biodiversity would respond to complexity. The chronosequence study investigated whether bark complexity increased with TSLF; whether beetle richness and Simpson’s diversity relates to bark complexity and/or TSLF; whether TSLF affects assemblage composition; and whether assemblage responses to complexity were stronger than to TSLF. Bark-associated beetles were collected and a range of bark variables were assessed from study trees (of both bark types) at sites belonging four TSLF categories (1- 5 years; 27 – 29 years; 43 – 49 years; 72 years). Several aspects of bark complexity on fibrous-barked trees related to TSLF, but none on ribbon-barked trees. On fibrous-barked trees, Simpson’s diversity (but not richness) correlated modestly with the one element of bark complexity (surface cover of loose bark flaps), but with no others, nor with TSLF. On ribbon-barked trees, richness (but not Simpson’s diversity) was modestly related to the surface cover of loose ‘ribbons’. No other relationships with bark complexity or TSLF were found. On neither bark type was a TSLF effect on assemblage composition apparent; with many common morphospecies detectable throughout the chronosequence. Composition did not differ between the two bark types, and many morphospecies used both, suggesting that many beetles in this system can tolerate substantial differences in bark structure. The short-term comparative study was adopted in order to clarify the effects of very recent fire on bark complexity, and because some fire effects on beetle assemblages were anticipated to be short-lived (< 1 year). Burnt sites were found to have less complex bark than unburnt sites, and differences in assemblage composition (but not richness or Simpson’s diversity) were detected. Despite the detection of short-term compositional differences, the lack of longer term differences, and paucity of strong relationships with complexity, suggested that these assemblages were resilient, rather than responsive, to fire-related habitat change. This was contrary to hypothesised relationships between structural complexity and biodiversity, but consistent with suggestions that assemblages in fire-prone regions will exhibit a degree of resilience to fire impacts.
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ItemEffects of prescribed burning on surface runoff and erosion( 2012)Prescribed burning – the deliberate use of fire to achieve management objectives – is used extensively in fire-prone vegetation for reducing fuel hazards and enhancing ecological values. As governments set ambitious targets for more prescribed burning, it is important to understand and manage the potential negative impacts, such as increased erosion. While globally there are many studies that consider the effects of prescribed burning on surface runoff and erosion, there are critical knowledge gaps for particular forest types (e.g. dry eucalypt forests) and in relation to understanding the factors controlling particular post-fire hydrologic and erosion responses, the likelihood of large impacts, the effects of spatial scale on the magnitude of an impact and the long-term risks of repeated burning. Therefore, the aim of thesis was to quantify the effects of prescribed burning on soil hydrologic properties, surface runoff and erosion in dry eucalypt forests in Victoria, Australia. This aim was addressed by examining the effects of two potentially important aspects of fire regimes – fire severity and burn patchiness – on soil hydrologic properties, surface runoff and erosion. Measurements were conducted in unburnt, low fire severity (scorched understorey and intact canopy) and high fire severity (burnt understorey and scorched canopy) areas at three dry eucalypt forest sites. Soil water repellency (using the critical surface tension test) and infiltration capacity (using ponded and tension infiltrometers) were measured at the point-scale for all sites immediately post-burn and then at six-month intervals. Rainfall simulations were used to measure runoff and erosion at the plot-scale (3 m2) six-weeks and 11-months post-burn at one site. Additionally, at one site runoff samplers (116 unbounded plots, 10 cm wide and approximately 100 m from the catchment divide) were used to measure runoff and erosion downslope of six burn categories: (1) high severity, (2) low severity, (3) unburnt, and low severity above (4) 1 m, (5) 5 m, and (6) 10 m wide unburnt patches. Prescribed burning resulted in higher runoff and erosion rates. Cumulative hillslope runoff volumes (over16-months) were approximately two orders of magnitude higher on burnt hillslopes and cumulative sediment loads were approximately three orders of magnitude higher. Water repellency increased following burning at two sites, but loss of vegetation cover appeared to be the primary driver for increased runoff and erosion in burnt areas, as fire-induced water repellency did not affect point-scale infiltration capacities. Fire severity differences had relatively little effect on runoff and erosion, presumably because surface vegetation cover was similar in the high and low fire severities. Unburnt patches were highly effective at reducing the connectivity of runoff and erosion from upslope burnt areas, with reductions in overall sediment loads of 96.6% and 99.8% for the 5 m and 10 m wide patches, respectively. The effectiveness of the unburnt patches at reducing runoff and erosion connectivity varied with patch width and rainfall intensity. For example, the 1 m wide unburnt patch reduced the overall sediment load by 92% for rainfall events with average recurrence intervals of < 10 years but was ineffective during a 10-year storm. Overall, the results suggested that despite higher plot-scale runoff and erosion rates post-burn, prescribed burns are unlikely to substantially affect runoff and erosion at the catchment-scale for most rainfall events given their inherent patchiness. Only during particularly intense storms, when unburnt patches become less effective at intersecting runoff and erosion, might severe erosion occur. From a management perceptive, the results suggest that to minimise runoff and erosion connectivity and potential water quality impacts following prescribed burning, there should be a fine-grained mosaic of burnt and unburnt patches throughout a burn (e.g. > 50% unburnt and patches 5-10 m wide) and unburnt streamside buffers. Such burn patterns may be achieved by the ignition pattern, and burning under mild conditions when there are moisture differentials throughout the burn area. While fire severity was found to be a less significant factor in relation to post-burn runoff and erosion rates, it is likely that lower fire severities are associated with more patchy burns and therefore it would be reasonable to aim for low severity burn outcomes.