School of Ecosystem and Forest Sciences - Theses
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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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ItemMaking the connection between history, agricultural diversity and place: the story of Victorian apples( 2016)Apple growing practices are embedded in a productivist mentality aiming for ever higher efficiency and productivity. And while the climate change impacts are to a large extent known, there is little attention given to the coupling of the social and the ecological effects. I use apple growing as a case study to explore the relationship between place, biodiversity and rural change in Victoria. My research is based on historical research; including an analysis of the Museum Victoria’s collection of wax apple models, and in-depth interviews with orchardists. By drawing on environmental history, social-ecological systems thinking and Bourdieu's theory of practice, I highlight the importance of a systems perspective and inform it by emphasis on the critical role of underlying power structures and individual dispositions, or the habitus, of the growers. These dispositions have been shaped and internalised by the growers’ histories and their physical surroundings. Orchardists have been able to respond to intensifying production requirements by utilizing technologies and scientific nous to keep up with the continuous aim for efficiency. Growers are caught up in a self-reinforcing cycle of satisfying the demand for perfect apples by adopting expensive techno-scientific approaches to enable ever more intensive production. The symbolic violence and amplified biophysical pressure orchardists experience has driven many to despair; resulting in a significant decline in small scale apple growing businesses over the last decade. I offer some suggestions for government policy and support measures and argue that any services or support programs need to be tailored to the appropriate level and need of each orchard business and the individuals who are involved. My analysis shows that those growers, who engage more closely with their biophysical place as well as their history and identity as apple growers in that place are (re-)creating another version of what it means to be an apple grower. In some cases this is resulting in resistance to the vortex of agricultural productivism that has been the basis of their existence for many generations.
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ItemHabitat complexity impacts soil biodiversity and ecological processes in urban ecosystems( 2015)In urban ecosystems human management alters the structural complexity of vegetation, litter and soil creating novel habitat combinations not observed in natural and semi-natural ecosystems. This provides a unique opportunity to investigate how habitat complexity affects soil biodiversity, soil biogeochemical and hydrological processes using novel field experimental settings. In this PhD thesis, I tested whether urban habitat complexity operates as a trait-based environmental filter able to shape the diversity of ant assemblages. I found a higher habitat complexity to be detrimental for ant species richness. Nonetheless, habitat complexity did not operate as an environmental filter for ant species acting upon their morphological traits, suggesting the presence of other more complex ecological mechanisms structuring urban ant assemblages. The second aim of the project was to investigate the effects of urban habitat complexity upon macrofauna detritivores, litter and soil microbes, relating their diversity and community composition to organic matter comminution and decomposition processes. A strong positive relationship between habitat complexity and decomposition and comminution processes was found. Organic matter comminution was significantly enhanced by macrofauna detritivore species richness and abundance. Nonetheless, while habitat complexity did not affect soil and litter microbial functional diversity, it did affect litter microbial community composition. Litter microbial community composition was also correlated to the decomposition status of organic matter, but not microbial functional diversity. A final component of this study evaluated effects of the complexity of the habitat components, vegetation, litter and soil upon urban hydrological processes. Canopy stormwater interception, litter water storage and soil water infiltration were higher under more complex urban habitats. This research suggests that urban habitat complexity can exert significant effects on soil biodiversity, biogeochemical and hydrological processes as previously observed in natural and semi-natural ecosystems. Management practices targeting urban habitat complexity through the modification of vegetation, litter and soil components can be designed to promote soil biodiversity and key ecological processes sustained by soil organisms.
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ItemEcological benefits of termite soil interaction and microbial symbiosis in the soil ecosystem in two climatic regions of Australia( 2015)Termite soil interaction is a multidimensional process, the interphase between the surface and subsurface being the most prominent location termitaria and other termite structures usually occupy. Genetic and environmental conditions, including soil type and moisture content, in different climatic regions affect this interaction. There is scant information on termite preferences, foraging behavior within these conditions and impact on soil profile and associated symbiont microorganisms. Foraging activity of termites (Coptotermes frenchi), depth and changes in soil profile with layers of top soil, fine sand, coarse sand and gravel, was studied using a test tank in a laboratory. Termite activities were intensive in only the longest foraging galleries via which they reached and foraged up to the edge of the tank. Wood stakes inserted vertically at three different depth level intervals (0-100, 100-200, and 200-300 mm), visual observations of soil profile samples taken using auger and excavated cross sections of the soil profile all confirmed presence of termite activity, transport and mixing of soil up to the lowest horizon in the otherwise uniform sandy or gravely lower horizons. However, termite activity did not result in complete mixing of soil horizons within the study period. Termites (Coptotermes acinaciformis) were tested for their preference topsoil, fine sand, potting mix and peat, in a laboratory condition at soil moisture contents of 0, 5, 10, 15 and 20% for 30 days. The experimental apparatus involved termite colonies foraging from nesting jars connected to four sets of standing perspex tubes filled with each soil type and moisture content combination attached to the jar lid on top. Soil type had a significant effect on termite preference whereas soil moisture content did not. At lower moisture levels of 0 and 5%, termites preferred fine sand while topsoil was preferred at 10, 15 and 20%. Soil heterogeneity and textural variability with respect to particle size distribution due to termite activity was investigated in two climatic regions of Australia. Mound and surrounding soils of Coptotermes lacteus in Boola Boola State Forest, Victoria, and Amitermes laurensis and Nasutitermes eucalypti in Gove, Northern Territory were studied. The residual effects on bacteria and fungi counts were also investigated in the former. For C. lacteus and A. laurensis mounds the very fine particles sizes (< 0.045 mm) were significantly higher than that of the surrounding soil while the reverse was true for the 2 - 1 mm particle size ranges. For the Nasutitermes mound, however, they recorded significantly higher 2 - 1 mm particle sizes and significantly lower < 0.045 mm particle size ranges than the surrounding soils. For the other particle size ranges in both sites no significant difference was observed between the mound and surrounding soils except for the 0.5 – 0.2 and 0.20.063 mm ranges in the A. laurensis mound which were significantly higher than surrounding soil. Average moisture content of the surrounding soils was significantly higher than that of the mound surfaces which could have resulted in the higher bacteria and fungi counts (cfu/ml) in the surrounding soils.
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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 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.
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ItemEcosystem goods and services in production landscapes in south-eastern Australia( 2013)Ecosystem goods and services (EGS), the benefits that humans obtain from ecosystems, are vital for human well-being. As human populations increase so do demands for almost all EGS. Managing changing landscapes for multiple EGS is therefore a key challenge for resource planners and decision makers. However, in many cases the supply of different types of goods and services can conflict. For example, the enhancement of provisioning services can lead to declines in regulating and cultural services, but there are few tools available for analysing these trade-offs in a spatially-explicit way. This thesis developed approaches and tools for spatially explicit measurement and management of multiple EGS provided by production landscapes. These were used to assess the impacts of land-use change and to provide a basis for managing these trade-offs using case studies in two contrasting production landscapes in south-eastern Australia. Both landscapes have been subject to extensive clearing of native vegetation, which is now present in remnant patches. One study landscape had a concentration of commercially-valuable hardwood and softwood plantations, and the other was dominated by land traditionally focused on agricultural production that is currently being re-configured to provide for more sustainable farming practices and to increase provision of multiple ecosystem services. The study involved five components: (i) development of a novel, qualitative approach for rapid assessment of EGS in changing landscapes that was used to assess observed and potential changes in land use and land cover and their impact on the production of different EGS (Chapter 2); (ii) development and testing of an approach for assessing multiple EGS across space and time using a case study of six key EGS in a sub-catchment in Lower Glenelg Basin, south-western Victoria that demonstrated landscape-scale trade-offs between provisioning and many regulating services (Chapter 3); (iii) an economic valuation of EGS using market and non-market techniques to produce spatial economic value maps (Chapter 4); (iv) spatial assessment of the biodiversity values that underpin provision of many ecosystem services utilising a variety of readily available data and tools (Chapter 5); and (v) assessment of trade-offs and synergies among multiple EGS under current land use and realistic future land-use scenarios (Chapter 6). Results indicate that EGS can be assessed and mapped in a variety of ways depending on the availability of data, time, and funding as well as level of detail and accuracy required. A qualitative assessment can be useful for an initial investigation (Chapter 2) while quantitative and monetary assessments may be required for detailed landscape-scale planning (Chapters 3, 4). In addition, the provision of EGS by production landscapes can vary considerably depending on land use and land cover, and management choices. The study demonstrates that landscapes dedicated mostly to agricultural production have limited capacity to produce the range of ecosystem services required for human health and well-being, while landscapes with a mosaic of land uses can produce a wide range of services, although these are often subject to trade-offs between multiple EGS (Chapters 2, 3). Furthermore, the study demonstrated that spatial assessment and mapping of biodiversity value plays a vital role in identifying key areas for conservation and establishing conservation priorities to allocate limited resources (Chapter 5). There is potential for an improved balance of the multiple EGS required for human health and well-being at the landscape scale, although the economic incentive to adopt more sustainable land use practices that produce a wide range of services are compromised due to the lack of economic valuation of public ecosystem services (Chapter 6). High hopes have been placed by researchers on spatial assessment, mapping and economic valuations of ecosystem goods and services to influence policy makers for coping with the accelerating degradation of natural capital. The approaches and tools used in this thesis can potentially enhance our collective choices regarding the management of landscapes for multiple values and can help policy makers and land managers to enhance the total benefits that landscapes provide to societies through the provision of an optimal mix of goods and services.
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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.