Fighting fire with fauna: exploring connections between fire, fuel, and fauna

Abstract

The role of animal-mediated influences on fire is poorly understood from an ecological and fire management perspective. As fire activity is predicted to worsen in fire-prone ecosystems, is it imperative to understand the connections between fire, fuel, and fauna. In this thesis, I examined the drivers of large native herbivore behaviour, and the subsequent impacts on fuel properties, to determine if herbivores can alter fire behaviour. Large herbivores can alter vegetation structure, composition, and function, which are key drivers of fuel properties. However, it is currently unknown if fire management practices in eucalypt forests need to accommodate for large herbivore populations. Quantitative studies are required to measure large herbivore impacts on fuel properties. My study system was a fire-prone National Park in south-eastern Australia in which large herbivores were represented by three macropod species. I first aimed to understand the drivers of macropod occurrence across my study system with respect to fire and vegetation. Analysis incorporated long-term spotlighting surveys; fire history data; and vegetation mapping. I found macropods preferentially selected for recently burnt patches likely due to the green pick available following a fire. Further, macropods were more likely to occur in forest vegetation. Secondly, I constructed exclosure fences to manipulate macropod access to plots in forest vegetation that had been burnt during a wildfire in 2017. My study also incorporated a similar manipulative experiment, comprising smaller exclosure fences, that had been constructed five years prior. Vegetation community metrics and fire behaviour projections were recorded in the experimental plots and compared between fencing treatments. Browsing by macropods reduced measures of species richness, diversity, and evenness in understorey vegetation. This resulted in a depauperate vegetation community in plots exposed to post-fire herbivory compared to fenced plots. The palatability of plant species was the likely driver, as less palatable plants were dominant in browsed plots. I found evidence for large herbivores to affect fire behaviour predictions, but the direction of these effects depended upon the model used and the elements of fuel each model considered. When one fire model that accounts mostly for dead fuel was used, herbivore browsing was predicted to create more moderate fire behaviour, potentially allowing more aggressive firefighting responses. Pronounced trends in other vegetation parameters considered by another fire model indicated that longer-term trends of herbivore browsing would see milder fire behaviour. These findings highlighted the risk of drawing conclusions regarding large herbivore management if the fire model employed accounts for only some of the many vegetation characteristics affected by herbivory. This study demonstrated the capacity for large herbivores to alter fire behaviour with clearer trends likely to become apparent with more time. The final chapter of my thesis aimed to synthesise current literature on large herbivore impacts on vegetation in forest ecosystems in south-eastern Australia. Viewing this research from a fire management perspective, I assessed how large herbivores may be influencing aspects of fuel properties and the likely fire behaviour outcomes of such modifications. I then provided a new framework for the future management of large herbivore populations to utilise large herbivores as a tool for managing bushfire fuel in forests. My research identified some of the relationships between fire, fuel, and fauna within forests of south-eastern Australia. My research highlights the potential for herbivore-mediated changes to future fire regimes in forest ecosystems, an aspect that needs to be addressed in future fire management practices. Show more