The Spatial Ecology of Fire Refuges in the Victorian Central Highlands

Abstract

The spatial and temporal pattern of fire occurrence within landscapes is a principal factor influencing species distributions and a core driver of biodiversity. However, climate change, land use change, invasive species and detrimental land management practices are altering the distribution, frequency, scale and intensity of large wildfires globally. This poses a major challenge to biodiversity management as ecosystems adapt to novel patterns of fire occurrence. Within fire-affected landscapes, areas which experience unique disturbance regimes may act as refuges for biota, reducing the impacts of fire on species and increasing their likelihood of survival. However, very few studies have attempted to quantify the desirable spatial attributes of such areas within fire mosaics for faunal conservation. This thesis aimed to quantify the ecological role of fire refuges by examining the factors responsible for refuge establishment, how the spatial properties of refuges influence their use by fauna, and the mechanisms underpinning faunal responses.

To investigate the factors responsible for the spatial distribution of fire refuges in montane forests I tested the operational validity of a pre-constructed fire simulation model with actual fire severity patterns produced following a large fire in the modelled landscapes. I found that for fires which occurred in extreme fire conditions, severity patterns were largely determined by stochastic factors, such as weather. When fire conditions were moderate, physical landscape properties appeared to mediate fire severity distribution. The study highlighted that fire refuges are a potentially ecologically important outcome of large wildfires. I recommend that detrimental land management practices are minimized to enable the ecological processes relevant to the establishment and subsequent use of fire refuges to be maintained.

In recently burnt Mountain Ash forests in south-eastern Australia, I examined how fire severity, patch size and landscape context influenced the abundance of arboreal marsupials. We aimed to determine if fire refuges are an important mechanism for facilitating the survival within extensively burnt landscapes. I found the mountain brushtail possum had a positive response to a particular kind of topographic refuge (unburnt peninsulas connected to larger areas of unburnt forest), whereas the greater glider had a negative response to fire in the landscape. The study highlighted the need for a more developed understanding of how post-fire habitat patterns facilitate species survival within burnt landscapes.

In a correlative landscape-scale study, I examined how bird use of potential refuges was influenced by 1) the size and connectivity of each refuge, 2) the extent of fire severities at different scales in the surrounding landscape, and 3) the interaction between severity patterns, vegetation structure and environmental gradients. I found that unburnt mesic gullies facilitated the retention of forest birds within extensively burnt montane forest landscapes. The study presented a key advance, in that the effects of fire-induced habitat patterns on the distribution of fauna varied between areas depending on their spatial relationships with key biotic and abiotic landscape patterns. I demonstrated that developing contingent theory by examining ecological interactions between fire induced habitat patterns and biotic and abiotic gradients is essential to understanding complex faunal responses to fire.

Using GPS telemetry within a replicated landscape scale study design, I examined how the spatial patterns of fire severity created by a large wildfire influenced the spatio temporal movement patterns of an arboreal marsupial, the Mountain Brushtail Possum, Trichosurus cunninghammi. I found a difference in temporal movement dynamics, habitat selection and spatial movement patters between forested landscapes which were burnt to differing extents. Forest systems recently burnt at high severity may provide suitable habitat for some species, if protected from subsequent disturbance such as salvage logging. However, spatial and temporal patterns of habitat selection and use differed considerably between burnt and undisturbed landscapes. The spatial outcomes of ecological disturbances such as wildfires have the potential to alter the behaviour and functional roles of fauna across large areas.

Employing a qualitative research approach, I identified the barriers and enablers to spatially managing fire for biodiversity. I then developed a conceptual framework and set of key steps to achieve the integration of spatial approaches to fire into management. I identified that spatial approaches to fire management must co-exist within a complex system of social and ecological feedbacks between landscapes, academic research, socio-political land management systems, and environmental pressures. I suggest that the integration of spatial approaches to fire can be achieved by developing community understanding of fire science, improving the relevance of fire research outputs to land management, amending existing government policy approaches and refining management tools, structures, scales and monitoring to meet biodiversity and fire risk objectives. The insights into fire refuge ecology provided by the papers in this thesis are highly relevant to faunal conservation. Collectively, this thesis constitutes an important contribution to global forest fire ecology and management and has implications for both understanding the impacts of ecosystem disturbances on faunal persistence and distributions, and for developing effective future research and conservation strategies. Show more