Effects of the fire regime on mammal occurrence after wildfire: Site effects vs landscape context in fire-prone forests
Introduction
Fire has an important role in determining the distribution and abundance of species in fire-prone regions globally (Bond et al., 2005, Bowman et al., 2013). Multiple components of the fire regime (sensu Gill, 1975), including fire frequency, intensity, season and type of fire, can influence biodiversity (Gill, 1975, Gill and Allan, 2008). The intensity of a large wildfire, for example, influences the composition and spatial pattern of plant communities (Pausas et al., 2008, Roman-Cuesta et al., 2009, Turner et al., 1994). While knowledge of the relationship between fire regimes and plant communities is growing (Driscoll et al., 2010, Whelan et al., 2002), much less is known about the components of the fire regime and their influence on fauna and ecosystems (Clarke, 2008, Fontaine and Kennedy, 2012). Fire regimes are expected to change in future decades as a consequence of climate change (Krawchuk et al., 2009, Moritz et al., 2012); wildfires are predicted to increase in size, occurrence and frequency over a longer fire season in some fire-prone areas (Clarke et al., 2011, McKenzie et al., 2004, Wotton et al., 2010). Fire regimes are also altered by changes in land management practices, including the use of planned burning for ecological or fuel reduction purposes (Moritz et al., 2012, Parks et al., 2015).
The fire regime can influence the occurrence of animal species at two spatial scales: (a) at the site-level via its influence on the suitability of habitat at a particular location; and (b) at the landscape-level via its influence on the landscape context of a site. At the site-level, fire intensity and the time between fires are important components of the fire regime. Fire intensity relates to the amount of energy emitted during the fire, whilst fire severity relates to the amount of vegetation or organic matter lost after a fire event (Keeley, 2009). Here, we refer to fire severity. A high severity fire may result in complete incineration of ground and canopy vegetation; whereas in a low severity fire the understorey may burn in a patchy manner and the canopy remains largely unburnt. Consequently, fire severity will have marked effects on the availability of resources such as shelter, foraging substrates and food for animal species post-fire (Fontaine et al., 2009, Keith et al., 2002, Smucker et al., 2005). The effect of fire severity on fauna after wildfire has rarely been quantified (but see Lindenmayer et al., 2013). Fire history (including the time between fire events), can also influence the suitability of a site by affecting vegetation successional stage and associated habitat structure (Bradstock et al., 2005). Sequential fires at short or longer intervals can have differing outcomes for structural features that provide habitat resources for animal species (Haslem et al., 2011). For instance, in semi-arid mallee vegetation in Australia, long fire intervals (at least >40 years) are required for tree hollows to develop and be suitable for hollow-nesting animals, whereas leaf litter can accumulate quickly within shorter fire intervals to provide habitat for other species (Haslem et al., 2011).
At the landscape-level, spatial variation in components of the fire regime contribute to landscape heterogeneity. Large fires vary spatially in their intensity, leading to a post-fire landscape of vegetation patches of differing fire severity (Leonard et al., 2014, Roman-Cuesta et al., 2009, Schoennagel et al., 2008). Animal populations potentially are influenced by the way in which such fire-induced heterogeneity determines the landscape context at a particular site. For instance, a patchy mosaic of burnt and unburnt vegetation may benefit species that move between fire age-classes to obtain different resources (e.g. shelter, food) (Buchalski et al., 2013, Doumas and Koprowski, 2013b). Unburnt patches within the landscape may act as refuges for species which otherwise are eliminated from, or are scarce in, severely burnt areas (Robinson et al., 2013). The extent and proximity of refuges may influence the rate of population recovery at severely burned sites (Bradstock et al., 2005, Robinson et al., 2013).
Environmental attributes, such as topographic variation in soils and moisture, also influence landscape heterogeneity and may mitigate the effects of fire by enabling survival of animals during or after a fire event (Bradstock et al., 2010, Garvey et al., 2010, Leonard et al., 2014). Understanding the effects of the fire regime and environmental attributes on mammal species at multiple scales can improve ecological knowledge of species responses, and is valuable for applied management.
Here, we examine the effects of an extensive wildfire on the occurrence of native terrestrial mammals in foothill eucalypt forests of south-eastern Australia. These are some of the most fire-prone forests worldwide (Adams and Attiwill, 2011). We surveyed the mammal assemblage 2–3 years after wildfire, at sites stratified in relation to two components of the fire regime, fire severity and fire history (interval since last fire). The overall aim was to test the relative influence on native mammals of components of the fire regime operating: (a) at the site-level (i.e. site specific wildfire severity and fire history); and (b) at the landscape-level (i.e. amount of unburnt forest and heterogeneity of fire severity within the surrounding landscape). We predicted that site level effects, particularly wildfire severity, would be the primary influence on the distribution of mammal species; but that landscape context would also influence the occurrence of species, in particular via unburnt forest functioning as a refuge and providing a source of colonising individuals for nearby burnt sites.
Section snippets
Study area
The study was based in the foothills of the central highlands of Victoria, Australia (Fig. 1), where elevation ranges from ∼150 to 1000 m. The climate is temperate with cool winters (mean monthly minimum 4 °C) and mild summers (mean monthly maximum 23 °C), and a mean annual rainfall of ∼1200 mm (BOM, 2013). From 1997 to 2009, a severe drought occurred in south-eastern Australia (van Dijk et al., 2013). The drought broke in 2010, with above-average annual rainfall recorded in both 2010 and 2011 (
Species recorded and detection probability
From January–August 2011 we surveyed a total of 6084 camera trap-nights. From this effort, 13 species of native mammals were detected, eight of these were examined further (Table 2). Five species (mostly arboreal) were detected at fewer than seven sites (<9%) and were excluded from analyses. These included the common brushtail possum (Trichosurus vulpecula) recorded at 6 sites (8%), the koala (Phascolarctos cinereus) detected at 2 sites (3%), whilst the remaining three species were rare and
Discussion
Understanding how fire regimes influence fauna at different scales can improve ecological knowledge for fire management (Driscoll et al., 2010, Di Stefano et al., 2011). In the aftermath of a severe wildfire, we had a unique opportunity to investigate how native terrestrial mammals were influenced by fire-regime components at multiple scales, in one of the most fire-prone forests in the world. At 2–3 years post-fire, fire effects at the site-level exerted more influence on the occurrence of
Acknowledgements
This study is part of the Faunal Fire Refuges Project, funded by the Department of Environment, Land, Water and Planning (DEWLP), Victoria. We thank DELWP, Parks Victoria, Victorian State Forests, and associated staff. Natasha Robinson provided valuable contributions to the overall project design and site selection. We appreciate the help of numerous staff and volunteers for field assistance; and Dale Nimmo for advice on statistical models. Comments from Dan Lunney improved the final version of
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- 1
Present address: Department of Ecology, Environment and Evolution, La Trobe University, Melbourne, Victoria 3086, Australia.
- 2
Present address: Arthur Rylah Institute for Environmental Research, DELWP, Heidelberg, Victoria 3081, Australia.