School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemPredicting future fire regimes and the implications for biodiversity in temperate forest ecosystems( 2022)Fire regimes are changing around the world. Fire seasons are lengthening, high severity fires are occurring more often and in unexpected places. Relationships among fire, climate, and vegetation are varied, dynamic, and under-examined in many ecosystems. While some studies have explored links between fire, climate, and vegetation such as species distributions or future fire weather under changing climate, relatively few have considered the dynamic interactions among all three simultaneously. In this thesis, I develop and apply modelling approaches to predict future fire regimes in south-eastern Australia and explore the implications for fire-responsive functional plant types. In the first quantitative chapter of my thesis (Chapter 2), I develop a new fuel model for south-eastern Australia. I use edaphic, climatic, and fire variables to build a predictive fuel model that is independent of vegetation classes and their future distributions. In Chapter 3, I use my fuel model in a landscape fire regime simulator, alongside multiple predictions of future climate, to examine the immaturity risk to an obligate seeder tree species (Eucalyptus delegatensis). My simulations indicate that this species will be under increased immaturity risk under future fire regimes, particularly for those stands located on the periphery of the current distribution, closer to roads or surrounded by a drier landscape at lower elevations. In Chapter 4, I expand the application of the above simulation approach to examine the relative importance of future fuel and future climate to changing fire regimes in six case study areas across temperate south-eastern Australia. My results indicate that the direct influence of climate on fire weather will be the principal driver of changes in future fire regimes (most commonly involving increased extent, decreased intervals, and an earlier start to the fire season). The indirect influence of climate on vegetation and therefore fuel was also important, acting synergistically or antagonistically with weather depending on the area and the fire regime attribute. Finally, in my fifth chapter, I consider future climate and fire impacts on plant persistence by combining the landscape fire regime simulator with spatially explicit population viability analyses. Obligate seeder species were at risk of population extinction or reduction in more simulation scenarios than facultative resprouters. However, my approach highlighted that the resilience of facultative resprouters might also be tested by climate related changes in demographic processes and fire regimes. Overall, my research has provided new methods and scientific insights into the changing nature of fire regimes in temperate south-eastern Australia. Some negative impacts on biodiversity from a changing fire regime, particularly on more vulnerable plant functional types like obligate seeders, appear inevitable. Further understanding of the complex interactions among fire, climate, and vegetation will enable improved integration of risks to people, property, and biodiversity into land and fire management planning.
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ItemEdge effects in fire prone landscapes: ecological importance and implications for fauna( 2018)The overarching aim of this thesis was to investigate the ecological importance of fire edges, focusing on the influence of fire-induced edge effects on fauna in forested landscapes. Edges are ubiquitous environmental features, occurring in a wide range of ecosystems and across multiple spatial scales. Edges have been extensively researched in some contexts, particularly agricultural and urban landscapes. Accordingly, much of our understanding about how edges influence animals comes from highly modified ecosystems. Fire is an agent of edge creation and a globally important driver of biome distribution and community composition, yet little is known about how fire edges affect ecological processes in flammable ecosystems. In this thesis I review the literature on fire, fauna and edge effects to summarise current knowledge of faunal response to fire edges and identify knowledge gaps (Chapter 2). I developed a conceptual model for predicting edges effects in fire-prone landscapes, combining several drivers of faunal-fire responses. Fire-generated edge effects were found to differ from edges in modified systems, being temporally dynamic, spatially complex and characterised by the strength of the interaction between components of the disturbance regime and other biophysical factors. In Chapter 3 I investigated the response of ground-dwelling mammals to burnt/unburnt edges created by prescribed burning. I used a space-for-time substitution design to explore how species use of fire edges changes over time as the burnt side of the edge regenerates. I found that understorey complexity was reduced on the burnt side of edges for the first two years after fire. Larger animals with generalist resource requirements were more active at burnt edges immediately after fire, whereas small mammals were generally less active on burnt edges for up to 3 years. Species were not following patterns of temporal change in vegetation structure, with high usage during times of reduced understorey complexity and low usage when complexity was high. This suggests that habitat change is not a good predictor of animal use at fire edges and that other important processes are likely occurring. For example, foxes and cats were using the burnt side of edges immediately after fire, which may have important implications for the long-term persistence of native fauna if changes in habitat structure at fire edges cause predation rates to increase. In Chapter 4 I assessed the trade-off between deploying more detection units or extending the length of the sampling period on two frequently assessed variables in camera trapping studies – species richness and detection probability. The trade-off between these two factors is expected to affect data quality, but there is little information about their relative influence. I examined the trade-off between increasing deployment time or increasing the number of detection units on species richness and detectability (Chapter 4). I found that that increasing the number of cameras deployed per site was an effective method for increasing the detection of ground-dwelling mammals. Multiple cameras and longer deployment times were necessary to detect a high proportion of species present. Increasing the number of cameras or increasing deployment length resulted in high overall detectability for the more detectable species, but multiple cameras were required to achieve high detectability in a reasonable time frame (<50 days) for less detectable species. In Chapter 5 I investigated resource selection of a semi-arboreal mammal eight years after a major wildfire using GPS telemetry. Survival and persistence of animals after fire is largely driven by the abundance and distribution of remaining resources and the rate at which key habitat components regenerate or re-accumulate. I found that resource selection for the mountain brushtail possum (Trichosurus cunninghami) often depended on the sex of the animal and forest type, suggesting that considering spatial changes in resource availability and demographic class may be necessary to accurately determine patterns of resource selection after a major wildfire. This thesis adds to the body of knowledge on the ecological importance of fire edges and their implications for fauna, while providing several important conceptual and methodological advances in the study of ecology. Edges are pervasive and important environmental features that require further attention. Mechanistic approaches based on the strength of habitat associations and resource availability may help to clarify the nature and strength of edge effects in fire-prone landscapes and improve predictive models. A better understanding of fire edges will enable land managers to integrate the needs of biodiversity into future fire management planning.
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ItemThe influence of fire on forest birds at multiple scales( 2014)Improved understanding of the impact of fire on fauna is required because the frequency and severity of fire are predicted to increase under climate change, and the implications for biodiversity are largely unknown. To better understand the characteristics of fire regimes that sustain avian diversity, my thesis tests two overarching hypotheses: (i) that bird diversity increases with fire-mediated landscape heterogeneity; and (ii) that bird diversity increases with fine-scale heterogeneity in vegetation structure and plant species diversity. To test my first hypothesis, I examined bird responses to inter-patch variation in fire age class and vegetation type using landscape sampling units at a large spatial scale (60,000 ha). At a smaller scale (400 ha), I used a before-after control-impact experiment to investigate the effects of intra-patch variation in fire severity on bird diversity and the occurrence of individual species. To test my second hypothesis, I used measurements of vegetation structure and plant diversity to explain patterns in taxonomic diversity, functional diversity and species’ occurrence. Birds were surveyed across a 70-year chronosequence spanning four broad vegetation types, from heathland to wet forest. Results provided some support for both hypotheses. First, bird diversity was positively associated with landscape heterogeneity at the inter- and intra-patch levels. Second, bird functional evenness was positively related to fine-scale structural heterogeneity, and 13 of 15 modelled species responded to elements of habitat structure measured at fine scales. Only four of the 13 species responded to time since fire, indicating that time is unlikely to be a useful surrogate for bird occurrence in systems characterised by variable rates of post-fire structural development. Although I identified positive relationships between bird diversity and fire-mediated heterogeneity at multiple scales, results indicate that older vegetation is of disproportionate importance to the region’s birds, and that the preservation of old vegetation is paramount. Management strategies that use controlled application of patchy, low-severity fire to break up large areas of mature vegetation are likely to enhance avian diversity, ecosystem function and resilience, while conserving species reliant on older vegetation.