School of Agriculture, Food and Ecosystem 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.