Fire Mosaics Research Articles

The influence of fire mosaics on mammal occurrence in north-western Australia

BackgroundUnderstanding the relationship between fire and species habitat preferences is critical in an era of rapid environmental change. In northern Australia, large, intense, and frequent fires are thought to be a primary cause of mammal population declines, particularly through their influence on habitat suitability. Here, we used a large species presence database in combination with satellite-derived fire history data to assess the influence of fire attributes, including burn extent, frequency, and pyrodiversity, on the likelihood of occurrence of eight mammal species in north-west Western Australia.ResultsThe likelihood of occurrence declined for some species with an increasing proportion of recently burnt habitat and increased for most species with an increasing proportion of long unburnt habitat. The occurrence of six species was negatively correlated with increasing fire frequency, while the occurrence of four species was positively correlated with increasing pyrodiversity.ConclusionsOur results indicate that fire likely plays an important role in influencing mammal occurrence in the Pilbara and support previous research indicating that frequent large-scale burns have a mostly negative impact on small to medium-sized mammals in northern Australia. To improve mammal habitat suitability, land managers should aim to reduce the extent of large late dry season burns and increase the availability of mature spinifex grasslands.

Promoting Optimal Habitat Availability by Maintaining Fine-Grained Burn Mosaics: A Modelling Study in an Australian Semi-Arid Temperate Woodland

The pyrodiversity–biodiversity (P–B) hypothesis posits that spatiotemporally variable fire regimes increase wildlife habitat diversity, and that the fine-grained mosaics resulting from small patchy fires enhance biodiversity. This logic underpins the patch mosaic burning (PMB) paradigm and reinforces the benefits of Indigenous fire management, which tends to promote pyrodiversity. However, tests of the P–B hypothesis and PMB paradigm are few. One of the most comprehensive field evaluations—a snapshot study of pre-existing fire mosaics in south-east Australian semi-arid mallee eucalypt woodlands—found little support. To explore the longer-term effects of fire mosaic grain size on habitat availability and biodiversity, we combined published data from the mallee study with a simple fire simulation. We simulated 500 years of landscape burning under different fire sizes. In the resulting mosaics, we assessed the proportional mixture and patch configuration of successional habitat states, then summarised habitat availability through time using a composite index based on the published fire history responses of 22 vertebrate taxa from the mallee study. Small fires formed fine-grained mosaics with a stable habitat mixture and with habitat diversity occurring at fine scales. Large fires formed coarse-grained mosaics with the opposite properties. The fine-grained mosaics maintained optimal habitat availability for vertebrate diversity over 500 years, while the fluctuating habitat mixture in the coarse-grained mosaics was unlikely to maintain maximum vertebrate diversity. Broadly, our results support the P–B hypothesis and justify further field-testing and evaluation of PMB programs to manage both pyrodiversity and biodiversity in the mallee and other flammable landscapes.

Species-Specific Responses of Medium and Large Mammals to Fire Regime Attributes in a Fire-Prone Neotropical Savanna

Fire occurrence affects the distribution of key resources for fauna in natural ecosystems worldwide. For fire management strategies adequate for biodiversity conservation, the understanding of how species respond to fire-induced changes is essential. In this study, we investigated the role of fire regimes on spaces used by medium and large mammals at multiple spatial scales (0.8 ha to 78.5 ha) in a fire-prone savanna ecosystem (Brazilian Cerrado). We sampled mammals using 60 camera traps distributed in 30 sampling units located in grassland and typical savanna formations. We applied single-species occupancy models and AIC-based model selection to assess how mammals use the space in response to pyrodiversity (both diversity of fire frequencies and diversity of fire ages), the proportion of recently burned area, and the proportion of long-unburned area while accounting for detectability. Our results showed that fire regime variables affected the study species differently. Deer species used the space regardless of mosaic pyrodiversity and the proportion of specific fire ages. Fire-related variables, however, affected space use by tapirs and maned wolves. Tapirs preferred to use fire mosaics with lower diversity of fire frequencies, whereas maned wolves more intensively used mosaics with high fire age diversity and a high proportion of recently burned areas. Based on our findings, we recommend that fire management targeting specific mammal species should not necessarily focus on maximum pyrodiversity. Instead, we suggest a management strategy combining “patch mosaic burning” with the maintenance of specific fire-age patches suitable for different species’ requirements.

The threatened Gouldian finch preferentially forages in prescribed burnt savannas

Background The granivorous finches of Australia’s tropical savannas heavily rely on a sequence of perennial and annual grass seed production to feed throughout the year. An increase in late dry season wildfires has been suggested to detrimentally effect seed production sequence and has been attributed to poor physiological condition and a reduction in fitness of granivorous finches. Early dry season prescribed burning is an asset protection management strategy often implemented to reduce the incidence of late dry season wildfire, but has also been shown to improve the abundance and nutritional quality of grass seed Aims To assess whether the Gouldian finch (Chloebia gouldiae) preferentially used areas that were subject to early dry season prescribed burning over areas that were not burnt. Methods The creation of a landscape mosaic across the landscape with varying fire histories. Then the assessment of individual finch movement and site utilisation using VHF-radio telemetry transmitters, detected by an array of static receivers deployed across the landscape. Key results Finches significantly preferred to forage in areas burnt in the early season every 2–3 years. Conclusions The study demonstrates that early dry season prescribed burning creates preferred foraging habitat patches for Gouldian finches within savanna fire mosaics.

Double-Differenced dNBR: Combining MODIS and Landsat Imagery to Map Fine-Grained Fire MOSAICS in Lowland Eucalyptus Savanna in Kakadu National Park, Northern Australia

A neglected dimension of the fire regime concept is fire patchiness. Habitat mosaics that emerge from the grain of burned and unburned patches (pyrodiversity) are critical for the persistence of a diverse range of plant and animal species. This issue is of particular importance in frequently burned tropical Eucalyptus savannas, where coarse fire mosaics have been hypothesized to have caused the recent drastic population declines of small mammals. Satellites routinely used for fire mapping in these systems are unable to accurately map fine-grained fire mosaics, frustrating our ability to determine whether declines in biodiversity are associated with local pyrodiversity. To advance this problem, we have developed a novel method (we call ‘double-differenced dNBR’) that combines the infrequent (c. 16 days) detailed spatial resolution Landsat with daily coarse scale coverage of MODIS and VIIRS to map pyrodiversity in the savannas of Kakadu National Park. We used seasonal Landsat mosaics and differenced normalized burn ratio (dNBR) to define burned areas, with a modification to dNBR that subtracts long-term average dNBR to increase contrast. Our results show this approach is effective in mapping fine-scale fire mosaics in the homogenous lowland savannas, although inappropriate for nearby heterogenous landscapes. Comparison of this methods to other fire metrics (e.g., area burned, seasonality) based on Landsat and MODIS imagery suggest this method is likely accurate and better at quantifying fine-scale patchiness of fire, albeit it demands detailed field validation.

Contrasting responses of native and introduced mammal communities to fire mosaics in a modified landscape.

Planned fire is increasingly recognized as an important tool in conservation, but other factors such as land-use change may hinder the ability of land managers to use fire for the benefit of biodiversity. The mosaic of past fires in native vegetation may interact with the mosaic of other land-cover types in human-modified landscapes, yet the effects of these interactions on mammal communities are unknown. We investigated the responses of ground-dwelling mammal community composition and species richness to interactions between land cover and post-fire vegetation growth-stage mosaics in southern Australia. This fire-prone, human-modified landscape features a fine-scale fire mosaic in native vegetation patches surrounded by pasture, horticulture, and peri-urban environments. We measured the composition of land-cover types and fire mosaics (landscape structure) at multiple scales of up to 1257 ha surrounding 129 study sites, and considered native and introduced species together and separately. Land-cover composition was the primary driver of community composition: native species favored areas with a greater proportion of native heathy woodland, whereas introduced species were associated with landscapes comprising more cleared land. The fire mosaic also influenced community composition and species richness: greater growth-stage diversity was associated with native habitat-specialist communities and fewer introduced species. In areas with more cleared land, native species richness increased when there was a greater proportion of mid-successional vegetation, demonstrating that the effect of fire mosaics on mammal diversity depended on land-cover composition. The positive relationship between introduced species richness and cleared land extent was also stronger in recently burned sites than in other growth stages, suggesting that introduced species are well suited to more modified areas of the landscape. Land managers need to consider the underlying land-cover composition and the potential interactions it may have with fire mosaics and species composition. In this landscape a greater diversity of growth stages may disadvantage introduced species yet an increase in mid-successional vegetation in more modified areas would be likely to benefit native mammal communities. Our study highlights that fire management may need to be tailored depending on the context of land use and the species of interest.

Landscape-Scale Effects of Fire, Cats, and Feral Livestock on Threatened Savanna Mammals: Unburnt Habitat Matters More Than Pyrodiversity

Northern Australia has undergone significant declines among threatened small and medium-sized mammals in recent decades. Conceptual models postulate that predation by feral cats is the primary driver, with changed disturbance regimes from fire and feral livestock in recent decades reducing habitat cover and exacerbating declines. However, there is little guidance on what scale habitat and disturbance attributes are most important for threatened mammals, and what elements and scale of fire mosaics actually support mammals. In this study, we test a series of hypotheses regarding the influence of site-scale (50 × 50 m) habitat and disturbance attributes, as well as local-scale (1 km radius), meta-local scale (3 km), landscape-scale (5 km) and meta-landscape scale (10 km) fire mosaic attributes on mammal abundance and richness. We found that habitat cover (rock, perennial grass, and shrub cover) at the site-scale had a positive effect, and disturbance factors (feral cats, fire, feral livestock) had a negative influence on mammal abundance and richness. Models supported site-scale habitat and disturbance factors as more important for mammals than broader-scale (local up to meta-landscape scale) fire mosaic attributes. Finally, we found that increasing the extent of ≥ 4 year unburnt habitat, and having an intermediate percentage (ca. 25%) of recently burnt (1-year burnt) habitat within the mosaic, were the most important functional elements of the fire mosaic at broad scales for mammals. Contrary to expectations, diversity of post-fire ages (‘pyrodiversity’) was negatively associated with mammal abundance and richness. These results highlight the need for management to promote retention of longer unburnt vegetation in sufficient patches across savanna landscapes (particularly of shrub and fruiting trees), maintain low-intensity patchy fire regimes, reduce the extent of intense late dry season wildfires, and to reduce the impact of feral livestock. This study provides further evidence for the role of feral cats in northern Australian mammal declines, and highlights the need for increased research into the efficacy of cat control methodologies in reducing biodiversity impacts in these extensive landscapes.

Indigenous burning shapes the structure of visible and invisible fire mosaics

Indigenous burning shapes the structure of visible and invisible fire mosaics

Fire mosaics in south-west Australian forest landscapes

In fire-prone environments, prescribed burning is important for achieving many public land management objectives including protecting communities and the environment from damaging bushfires. There is evidence that in some biomes, reducing the size of burnt patches and creating a fine-scale mosaic of vegetation at different times since last fire (seral stages) may benefit biodiversity. However, planning and implementing an ongoing burning program to achieve this is problematic. To advance an understanding of the factors affecting burn patch size and seral diversity metrics, a novel experimental management trial that aimed to create and quantify a fine-scale fire mosaic was implemented in a south-west Australian forest landscape. The 10-year trial demonstrated that the fire mosaic characteristics, including diversity of seral stages, burnt patch size, patch distribution and patch connectedness, can be managed to a large extent by ignition frequency, which affects landscape fuel flammability, and the timing of the introduction of fire with respect to weather conditions. In this trial, the frequent introduction of fire under low to moderate Forest Fire Danger Indices resulted in a landscape comprising a quantifiably higher diversity of seral stages and smaller burnt patches than adjacent areas treated by fuel reduction prescribed burns and by a high intensity bushfire.

Fire mosaics and habitat choice in nomadic foragers

In the mid-1950s Western Desert of Australia, Aboriginal populations were in decline as families left for ration depots, cattle stations, and mission settlements. In the context of reduced population density, an ideal free-distribution model predicts landscape use should contract to the most productive habitats, and people should avoid areas that show more signs of extensive prior use. However, ecological or social facilitation due to Allee effects (positive density dependence) would predict that the intensity of past habitat use should correlate positively with habitat use. We analyzed fire footprints and fire mosaics from the accumulation of several years of landscape use visible on a 35,300-km2 mosaic of aerial photographs covering much of contemporary Indigenous Martu Native Title Lands imaged between May and August 1953. Structural equation modeling revealed that, consistent with an Allee ideal free distribution, there was a positive relationship between the extent of fire mosaics and the intensity of recent use, and this was consistent across habitats regardless of their quality. Fire mosaics build up in regions with low cost of access to water, high intrinsic food availability, and good access to trade opportunities; these mosaics (constrained by water access during the winter) then draw people back in subsequent years or seasons, largely independent of intrinsic habitat quality. Our results suggest that the positive feedback effects of landscape burning can substantially change the way people value landscapes, affecting mobility and settlement by increasing sedentism and local population density.

Integrating functional connectivity and fire management for better conservation outcomes.

Globally, the mean abundance of terrestrial animals has fallen by 50% since 1970, and populations face ongoing threats associated with habitat loss, fragmentation, climate change, and disturbance. Climate change can influence the quality of remaining habitat directly and indirectly by precipitating increases in the extent, frequency, and severity of natural disturbances, such as fire. Species face the combined threats of habitat clearance, changing climates, and altered disturbance regimes, each of which may interact and have cascading impacts on animal populations. Typically, conservation agencies are limited in their capacity to mitigate rates of habitat clearance, habitat fragmentation, or climate change, yet fire management is increasingly used worldwide to reduce wildfire risk and achieve conservation outcomes. A popular approach to ecological fire management involves the creation of fire mosaics to promote animal diversity. However, this strategy has 2 fundamental limitations: the effect of fire on animal movement within or among habitat patches is not considered and the implications of the current fire regime for long-term population persistence are overlooked. Spatial and temporal patterns in fire history can influence animal movement, which is essential to the survival of individual animals, maintenance of genetic diversity, and persistence of populations, species, and ecosystems. We argue that there is rich potential for fire managers to manipulate animal movement patterns; enhance functional connectivity, gene flow, and genetic diversity; and increase the capacity of populations to persist under shifting environmental conditions. Recent methodological advances, such as spatiotemporal connectivity modeling, spatially explicit individual-based simulation, and fire-regime modeling can be integrated to achieve better outcomes for biodiversity in human-modified, fire-prone landscapes. Article impact statement: Land managers may conserve populations by using fire to sustain or enhance functional connectivity.

Bridging the Divide: Integrating Animal and Plant Paradigms to Secure the Future of Biodiversity in Fire-Prone Ecosystems

Conserving animals and plants in fire-prone landscapes requires evidence of how fires affect modified ecosystems. Despite progress on this front, fire ecology is restricted by a dissonance between two dominant paradigms: ‘fire mosaics’ and ‘functional types’. The fire mosaic paradigm focuses on animal responses to fire events and spatial variation, whereas the functional type paradigm focuses on plant responses to recurrent fires and temporal variation. Fire management for biodiversity conservation requires input from each paradigm because animals and plants are interdependent and influenced by spatial and temporal dimensions of fire regimes. We propose that better integration of animal-based and plant-based approaches can be achieved by identifying common metrics that describe changes in multiple taxa; linking multiple components of the fire regime with animal and plant data; understanding plant-animal interactions; and incorporating spatial and temporal characteristics of fires into conservation management. Our vision for a more integrated fire ecology could be implemented via a collaborative and global network of research and monitoring sites, where measures of animals and plants are linked to real-time data on fire regimes.

Effects of a large wildfire on vegetation structure in a variable fire mosaic.

Management guidelines for many fire-prone ecosystems highlight the importance of maintaining a variable mosaic of fire histories for biodiversity conservation. Managers are encouraged to aim for fire mosaics that are temporally and spatially dynamic, include all successional states of vegetation, and also include variation in the underlying "invisible mosaic" of past fire frequencies, severities, and fire return intervals. However, establishing and maintaining variable mosaics in contemporary landscapes is subject to many challenges, one of which is deciding how the fire mosaic should be managed following the occurrence of large, unplanned wildfires. A key consideration for this decision is the extent to which the effects of previous fire history on vegetation and habitats persist after major wildfires, but this topic has rarely been investigated empirically. In this study, we tested to what extent a large wildfire interacted with previous fire history to affect the structure of forest, woodland, and heath vegetation in Booderee National Park in southeastern Australia. In 2003, a summer wildfire burned 49.5% of the park, increasing the extent of recently burned vegetation (<10yr post-fire) to more than 72% of the park area. We tracked the recovery of vegetation structure for nine years following the wildfire and found that the strength and persistence of fire effects differed substantially between vegetation types. Vegetation structure was modified by wildfire in forest, woodland, and heath vegetation, but among-site variability in vegetation structure was reduced only by severe fire in woodland vegetation. There also were persistent legacy effects of the previous fire regime on some attributes of vegetation structure including forest ground and understorey cover, and woodland midstorey and overstorey cover. For example, woodland midstorey cover was greater on sites with higher fire frequency, irrespective of the severity of the 2003 wildfire. Our results show that even after a large, severe wildfire, underlying fire histories can contribute substantially to variation in vegetation structure. This highlights the importance of ensuring that efforts to reinstate variation in vegetation fire age after large wildfires do not inadvertently reduce variation in vegetation structure generated by the underlying invisible mosaic.

Mosaics of fire and water: the co-emergence of anthropogenic landscapes and intensive seed exploitation in the Australian arid zone

In arid Australia, the antiquity, role and ecological contexts of ‘firestick’ farming in seed-based foraging economies remain unclear. We use Landsat imagery to analyse effects of contemporary Martu hunting fires on seed-bearing grasses and forbs. Today, Martu rarely harvest wild seeds but inadvertently foster patches of grass when they burn to hunt burrowing monitor lizards. Therefore, anthropogenic seed patches need only be by-products of fires set to achieve other goals rather than the intended crop of firestick farming. Nonetheless, sustained burning over the long-term creates and maintains closely juxtaposed mosaics of seed and small game patches. We use the marginal value theorem (MVT) to model how pre-contact foragers may have used seed patches within such mosaics in response to climate change and population growth. We show that seeds would have been reliably available to foragers in anthropogenic patches whenever small game hunting returns were low and travel distances to new hunting patches long. Such circumstances probably occurred during the middle to late Holocene when population growth filled better-watered habitats of arid Australia, and climatic variability associated with the El Niño/Southern Oscillation (ENSO) reduced the number of water sources that could support foraging. Prolonged occupation around the water sources that remained triggered the emergence of fine-grained, anthropogenic fire mosaics. If so, the late Holocene proliferation of formalised seed milling equipment closely followed the emergence of firestick farming and signalled the consequent development of seed-based foraging economies, further fuelling population growth and social complexity when more mesic climatic conditions returned. Earlier milling technology during the Pleistocene and early Holocene probably accommodated seed distributions created in fire regimes other than the mosaic burning conducted by Martu today.

Fly and wasp diversity responds to elements of both the visible and invisible fire mosaic

It is increasingly recognised that fire management for biodiversity conservation must account for two kinds of landscape mosaics: 1) the ‘visible’ mosaic of post-fire age classes as it relates to organism responses to the most recent fire events; and 2) the ‘invisible’ mosaic of inter-fire intervals, frequencies and other components of the fire regime as they relate to the cumulative effects of multiple fires. Patch mosaic burning (PMB) aims to create landscape mosaics of fire ages to cater for the needs of a diversity of species differing in their age class preferences, but empirical studies often fail to detect a link between species richness and the visible mosaic. Empirical studies of cumulative effects have so far related species richness to the fire regimes of sample locations rather than the invisible mosaic, within which sample locations are embedded. Invertebrate responses to landscape fire mosaics are particularly poorly understood, so we investigated relationships between fire history heterogeneity and fly and wasp species richness. We find support for the PMB paradigm and the notion the invisible mosaic influences species richness. To the best of our knowledge, this is the first empirical test of the invisible mosaic’s influence on animal communities.

Analysing patterns of spatial and niche overlap among species at multiple resolutions

AbstractAimAnalyses of spatial overlap in species distributions are frequently used to test a range of ecological and evolutionary hypotheses, from the role of competition in community assembly to the geography of speciation. Most studies quantify overlap at one spatial resolution. Here we explore the effects of measuring spatial and niche overlap patterns for the same clade (Banksia) at multiple resolutions.LocationAustralia.MethodsWe quantify overlap among species using broad overlap of species range polygons, proximity of occurrence points and co‐occurrence within small survey plots. We compare overlap patterns with null models using age–range correlations and the frequency of sympatric sister species. We then use similar methods to examine patterns of overlap in environmental niche dimensions.ResultsBanksia species show a wide range of overlap values based on range polygons and point proximities, but very low levels of co‐occurrence at the local scale. Intercepts of age–range correlations point to higher levels of overlap among recently diverged species than expected. However, comparing the frequency of sympatric sister species with an evolutionary null model supports a prevailing allopatric mode of speciation. In many cases, niche overlap between species exceeds that expected from phylogenetic relatedness or spatial overlap alone.Main conclusionsPatterns of broad geographical overlap among Banksia species support a predominantly allopatric mode of speciation, combined with post‐speciation range drift. There is more evidence for niche conservatism than for rapid niche divergence among closely related species. This pattern is consistent with broad‐scale geomorphic and landscape complexity as a driver of plant speciation in south‐west Australia. It is less consistent with finer‐scale mechanisms of species divergence such as fire mosaics, or with ecological divergence in sympatry. Analysis of species overlap patterns at different resolutions is a useful approach for revealing the multiple ecological and historical factors that influence species distributions.

Influence of Fire Mosaics, Habitat Characteristics and Cattle Disturbance on Mammals in Fire-Prone Savanna Landscapes of the Northern Kimberley.

Patch mosaic burning, in which fire is used to produce a mosaic of habitat patches representative of a range of fire histories (‘pyrodiversity’), has been widely advocated to promote greater biodiversity. However, the details of desired fire mosaics for prescribed burning programs are often unspecified. Threatened small to medium-sized mammals (35 g to 5.5 kg) in the fire-prone tropical savannas of Australia appear to be particularly fire-sensitive. Consequently, a clear understanding of which properties of fire mosaics are most instrumental in influencing savanna mammal populations is critical. Here we use mammal capture data, remotely sensed fire information (i.e. time since last fire, fire frequency, frequency of late dry season fires, diversity of post-fire ages in 3 km radius, and spatial extent of recently burnt, intermediate and long unburnt habitat) and structural habitat attributes (including an index of cattle disturbance) to examine which characteristics of fire mosaics most influence mammals in the north-west Kimberley. We used general linear models to examine the relationship between fire mosaic and habitat attributes on total mammal abundance and richness, and the abundance of the most commonly detected species. Strong negative associations of mammal abundance and richness with frequency of late dry season fires, the spatial extent of recently burnt habitat (post-fire age <1 year within 3 km radius) and level of cattle disturbance were observed. Shrub cover was positively related to both mammal abundance and richness, and availability of rock crevices, ground vegetation cover and spatial extent of ≥4 years unburnt habitat were all positively associated with at least some of the mammal species modelled. We found little support for diversity of post-fire age classes in the models. Our results indicate that both a high frequency of intense late dry season fires and extensive, recently burnt vegetation are likely to be detrimental to mammals in the north Kimberley. A managed fire mosaic that reduces large scale and intense fires, including the retention of ≥4 years unburnt patches, will clearly benefit savanna mammals. We also highlighted the importance of fire mosaics that retain sufficient shelter for mammals. Along with fire, it is clear that grazing by introduced herbivores also needs to be reduced so that habitat quality is maintained.

Life history influences how fire affects genetic diversity in two lizard species.

'Fire mosaics' are often maintained in landscapes to promote successional diversity in vegetation with little understanding of how this will affect ecological processes in animal populations such as dispersal, social organization and re-establishment. To investigate these processes, we conducted a replicated, spatiotemporal landscape genetics study of two Australian woodland lizard species [Amphibolurus norrisi (Agamidae) and Ctenotus atlas (Scincidae)]. Agamids have a more complex social and territory structure than skinks, so fire might have a greater impact on their population structure and thus genetic diversity. Genetic diversity increased with time since fire in C. atlas and decreased with time since fire in A. norrisi. For C. atlas, this might reflect its increasing population size after fire, but we could not detect increased gene flow that would reduce the loss of genetic diversity through genetic drift. Using landscape resistance analyses, we found no evidence that postfire habitat succession or topography affected gene flow in either species and we were unable to distinguish between survival and immigration as modes of postfire re-establishment. In A. norrisi, we detected female-biased dispersal, likely reflecting its territorial social structure and polygynous mating system. The increased genetic diversity in A. norrisi in recently burnt habitat might reflect a temporary disruption of its territoriality and increased male dispersal, a hypothesis that was supported with a simulation experiment. Our results suggest that the effects of disturbance on genetic diversity will be stronger for species with territorial social organization.

Does pyrodiversity beget alpha, beta or gamma diversity? A case study using reptiles from semi‐arid Australia

AbstractAimA common assumption in fire ecology and management is that landscapes with a greater diversity of fire‐ages will support a greater diversity of animal species (i.e. ‘pyrodiversity begets biodiversity’). This assumption is based on the idea that landscapes with a more diverse fire history provide a greater array of post‐fire habitats, leading to a greater number of species within the landscape. We assessed the hypothesis that pyrodiversity begets biodiversity by enhancing community differentiation (β diversity), resulting in increased landscape‐scale richness (γ‐diversity). We used reptiles as a case‐study.LocationThe Mallee region of south‐eastern Australia.MethodsWe used a study design in which ‘whole’ fire mosaics (12.6 km2) were the unit of replication. Study landscapes (n = 28) were selected to represent a gradient in the diversity and extent of fire‐age classes. We surveyed reptiles by using pitfall traps at 10 sites within each landscape (280 sites in total). Reptile data were used to characterize reptile assemblages at the landscape‐scale in three ways: alpha (average within‐site diversity), beta (between‐site diversity) and gamma diversity (total diversity).ResultsThe diversity of fire‐age classes had little influence on the alpha, beta or gamma diversity of reptile assemblages. The properties of fire mosaics that most influenced assemblages were the extent of structurally important fire‐age classes. The extent of long‐unburned vegetation increased beta diversity but reduced alpha diversity of the total reptile assemblage, essentially cancelling each other out at the landscape scale.Main conclusionsThis study highlights the importance of considering multiple measures of diversity when exploring the influence of landscape properties on biodiversity, as ‘null’ results at the landscape scale (gamma diversity) can result from contrasting patterns in alpha and beta diversity. Using fire to create habitat mosaics, at the scale of this study, is unlikely to enhance the status of reptiles in the region.

Defining vegetation age class distributions for multispecies conservation in fire-prone landscapes

The generation of heterogeneous fire mosaics is commonly advocated as a strategy for biodiversity conservation in flammable ecosystems, but it is usually unclear how mosaic properties link to biodiversity outcomes. Here we define a formal relationship between these elements and outline a method for determining the composition of fire mosaics defined by vegetation age classes that maximise species diversity. The method involves 1. quantifying species abundance in each of several previously defined vegetation age classes, and 2. using optimisation to determine the age class distribution that maximises species diversity. We applied the method to 135 species from four taxa in a southeastern Australian heathy woodland. In addition, we quantified the degree to which each taxa could act as a surrogate for others, and assessed how our chosen diversity metric changed with departures from the optimal distribution. Optimal age class distributions differed among taxa, and surrogacy relationships between most groups were poor. Departure from the optimal distribution resulted in an estimated decline in species diversity, a measure that may be used to quantify the biodiversity cost of alternative management strategies. Our measure of departure, relative entropy, was a strong predictor of diversity decline for some taxa but not for others. In cases where predictive capacity was strong, the rate of decline differed among groups. In flammable ecosystems our method can help determine fire management strategies empirically linked to a landscape-scale conservation objective.