School of Ecosystem and Forest Sciences - Theses

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    Using field experiments to test associations between plant traits and fire regimes
    Kreger, Isaac Daniel ( 2021)
    Conservation of biodiversity in fire-prone landscapes requires a thorough understanding of how plants are impacted by fire regimes. Altered fire regimes, due to changes in climate and land use, will likely impact many plant species in arid and semi-arid ecosystems. The study of functional traits – including fire-related traits that help plants to persist in areas subject to recurrent fire - provides a way to understand how plants respond to contemporary and future fire regimes. In my first chapter I studied the influence of a large-scale fire and climate gradient on variation of functional traits of a serotinous tree species, Callitris verrucosa. I measure intraspecific variation in fire-related traits including level of serotiny, bark thickness and tree size on C. verrucosa populations along a 340 km north-south gradient in semi-arid southeastern Australia. Level of serotiny was strongly associated with fire frequency: tree-level of serotiny increased at stands estimated to experience higher fire frequency, while the variation in level of serotiny at standsincreased with lower fire frequency. After accounting for tree size, relative bark thickness was also strongly associated with fire frequency and average annual rainfall. Thicker bark is allocated to smaller stems in areas that experience more frequent fire. In my second chapter, I used a field experiment to explore topkill of resprouting eucalypts after a planned burn in a semi-arid mallee woodland. I measured fire-related traits of eucalypt trees and stems including bark thickness, basal diameter, and canopy height, as well as elements of fuels including litter depth, ground cover, and vertical strata. The probability of topkill declined with taller stems (>3 m): taller mallee eucalypts appear to ‘escape’ low intensity fire. Fuels were also important, with topkill higher in areas with increased cover of hummock grass. Overall, my research demonstrates clear relationships between plant functional traits -including serotiny, 3 height and bark thickness - and fire regimes. This knowledge can be used to inform manipulations of fuels, habitat structure and plants through planned burning, to achieve a wide range of social and environmental objectives. Moreover, the demonstrated variation in C. verrucosa fire-related traits could be used to guide restoration efforts. For example, seeds sourced from southern locations, where populations have higher levels of serotiny, may promote resilience under a scenario of more frequent fire. While the extent to which fire regimes will change is uncertain, field experiments help us learn about contemporary processes and forecast future changes.
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    Multi-scale drivers of vertebrate communities in flammable landscapes
    Dorph, Annalie Joan ( 2021)
    For successful biodiversity conservation, knowledge of the patterns and processes acting in the landscape to influence faunal species diversity is essential. One hypothesis developed to explain how spatial variation affects species diversity is the environmental heterogeneity hypothesis. This hypothesis postulates that increased spatial variability in resources will lead to greater niche availability and subsequent increases in faunal diversity. Environmental heterogeneity is created by two key sources (1) biophysical factors (e.g. topography, climate) and (2) stochastic or anthropogenic disturbances (e.g. fire, land clearing). Species and communities respond to this environmental heterogeneity at both the local- (<1 ha) and landscape-levels (10-1000s ha). Understanding the multi-level effects of different sources of environmental heterogeneity on faunal communities will help land managers to successfully implement management programs and conservation activities. In this thesis, I examined how environmental heterogeneity measured at multiple levels influenced faunal communities in flammable landscapes. I used two case studies from separate landscapes to understand the effects of biophysical factors, disturbances and habitat structure on species and community responses. In the first case study, I examined a mammal community in a topographically-complex, unfragmented landscape. In the second case study, I examined a reptile community in a highly-modified landscape. In both cases I measured environmental drivers at multiple scales using novel approaches, such as gradient modelling to account for spatial pattern created by continuous environmental variables. Local-level measures were better for predicting mammal species richness, while reptile richness was not influenced by any of the local-level measures tested. Specifically, habitat structural complexity and biophysical factors were the strongest drivers of mammal richness at the local-level. Disturbance from fire had no local-level effect on the mammal or reptile community. Landscape-level measures of environmental heterogeneity were stronger predictors of species richness for disturbance from fire and changes to land use in both the mammal and reptile community. Mammal richness was most strongly driven by landscape-level measures of vegetation productivity, time since fire, elevation and habitat complexity. Reptile richness was most strongly driven by landscape-level measures of land use and habitat complexity. Time since fire had no effect on reptile richness at the landscape-level, however individual species were driven by spatial fire patterns at the landscape-level. Studies of the response of species and communities to local- and landscape-level measures of their environment are still limited in many areas of ecology. In this thesis, I advance our understanding of how faunal communities respond to two key sources of environmental heterogeneity in landscapes affected by different processes. From a management perspective, I found that the impact of disturbances on fauna are better assessed at the landscape-level rather than local-level. Additionally, I re-emphasise the importance of retaining native vegetation in modified landscapes for maintaining species diversity. In future, more work is needed to understand how species resource selection and faunal community response are determined by the relative influence of local- and landscape-level measures of different processes acting in both fragmented and unfragmented landscapes