Experimental Fire Regimes Research Articles

Dung beetles of an Australian tropical savanna: Species composition, food preferences and responses to experimental fire regimes

AbstractDung beetles are an ecologically important group of insects globally, but the ecology of the Australian fauna is poorly known. Here, we report on the first ecological study of dung beetles in an Australian tropical savanna, documenting species composition, food preferences and responses to fire. Dung beetles were baited using dung from five types of vertebrates as well as mushrooms. We sampled at nine plots subject to experimental fire regimes (three replicates each of high fire severity, moderate fire severity and unburnt over 15 years) at the Territory Wildlife Park near Darwin. Our samples were comprised entirely of nine native species of Onthophagus. Dog dung was the most attractive bait, recording all nine species and nearly 80% of all individuals, whereas no beetles were recorded at either wallaby or magpie‐goose dung. Dung beetle abundance was highest under high fire severity and was negatively correlated with the cover of woody vegetation, a result driven by the two most common species, O. minsiculus and O. nr. quadripunctulatus. Our results indicate that Onthophagus is the dominant genus in dung‐beetle assemblages of monsoonal Australia, as it is in open habitats of the Australian wet tropics. All our species of Onthophagus are relatively small (≤10 mm body length) and are ‘tunnellers’, storing dung and other food resources in tunnels dug immediately below the food source. Such an overwhelming dominance by small tunnellers does not occur in African savannas, reflecting the far lower availability of large mammalian dung in Australia.

Frequent fires prime plant developmental responses to burning.

Coping with temporal variation in fire requires plants to have plasticity in traits that promote persistence, but how plastic responses to current conditions are affected by past fire exposure remains unknown. We investigate phenotypic divergence between populations of four resprouting grasses exposed to differing experimental fire regimes (annually burnt or unburnt for greater than 35 years) and test whether divergence persists after plants are grown in a common environment for 1 year. Traits relating to flowering and biomass allocation were measured before plants were experimentally burnt, and their regrowth was tracked. Genetic differentiation between populations was investigated for a subset of individuals. Historic fire frequency influenced traits relating to flowering and below-ground investment. Previously burnt plants produced more inflorescences and invested proportionally more biomass below ground, suggesting a greater capacity for recruitment and resprouting than unburnt individuals. Tiller-scale regrowth rate did not differ between treatments, but prior fire exposure enhanced total regrown biomass in two species. We found no consistent genetic differences between populations suggesting trait differences arose from developmental plasticity. Grass development is influenced by prior fire exposure, independent of current environmental conditions. This priming response to fire, resulting in adaptive trait changes, may produce communities more resistant to future fire regime changes.

Fine-scale temporal turnover of jarrah forest understory vegetation assemblages is independent of fire regime

BackgroundPrescribed burning is an important management tool in jarrah (Eucalyptus marginata Sm.) forests of southwest Western Australia to reduce the risk of damaging bushfires. In 1986 to 1987, we established long-term study sites in dry (mean annual rainfall ~700 mm) and moist (mean annual rainfall ~1000 mm) jarrah forests to assess the effects of prescribed burning, as well as other fire treatments including fire exclusion, on the composition, richness, and relative abundance of forest understory vegetation.ResultsOver almost 30 years, species assemblages within all fire treatments changed significantly through time, but the changes were independent of treatment. The pattern of change in composition of fire response types over elapsed time was different between sites. At the dry site, changes in species assemblages were initially relatively large in the first decade or so of the study, but slowed thereafter. At the moist site, compositional change driven by obligate seeding shrubs occurred faster and more uniformly with time across all treatments. Species richness was also independent of fire treatment at both sites. Species richness decreased with elapsed time on the moist site but increased with elapsed time on the dry site. The stronger elapsed-time effect rendered the time since fire effect on loss of species richness on the moist site to be insignificant, but there was an inverse relationship with time since fire at the dry site. Within each site, there were clear patterns of changing abundance based on life form and fire response groups, but this was not consistent between sites.ConclusionsAt the scale of the current study, jarrah forest plant communities displayed resilience to imposed experimental fire regimes. Over time, either elapsed time or time since fire, species assemblages across all treatments changed regardless of fire treatment, but changes were mostly associated with specific plant life forms and fire response traits, suggesting that the process is both deterministic and stochastic. While many species changed in abundance over time, no species were lost as a result of the fire treatments. Within the fire frequency and intensity ranges investigated in this study, there was flexibility in the application of prescribed fire to achieve management objectives without loss of plant diversity.

Contingent factors explain average divergence in functional composition over 88 years of old field succession

Abstract “Old fields” are ecosystems that have been previously managed and subsequently abandoned, usually from agricultural use. These systems are classic testing grounds for hypotheses about community assembly. However, old field succession can be difficult to predict: seemingly similar fields often diverge in terms of species composition and environmental conditions. Here, we test the relative roles of contingency and stochasticity in driving vegetative successional dynamics. We draw on three decades of surveys in 24 old fields at the Cedar Creek Ecosystem Science Reserve (Minnesota, USA), and focus on five drivers that are known to shape local plant communities: soil fertility, fire, climate, competition, and demography. These drivers can contribute to contingency when they act consistently across fields and years (e.g., soil nitrogen accumulation, experimental fire regimes, or average climate), or to stochasticity when their effects are variable (e.g., annual variations in weather, or colonization and mortality events). We proceed in two steps. First, we fit regressions estimating abundance, colonization, and mortality for eight major functional groups in relation to these five drivers. We then use these regressions to parameterize a series of metacommunity simulation models, and test whether observed levels of stochasticity and variation in the drivers are sufficient to explain successional divergence. All drivers were significantly associated with plant species abundances, colonization, and mortality. Contingent factors strongly altered predicted successional trajectories. However, replicate simulations with similar conditions followed similar successional trajectories, suggesting that stochastic processes did not lead to divergence. This robustness of successional dynamics may be explained by compensatory trade‐offs. For example, species that were abundant late in succession typically suffered from low colonization rates and high mortality rates early in succession. Synthesis. Average successional dynamics among old fields at Cedar Creek follow largely consistent trends. Though dynamics of individual fields vary, much of this variation can be explained by contingent factors. Stochastic processes appear not to be sufficiently strong to create divergent successional trajectories among fields with similar sets of drivers. Our results therefore suggest that divergence among successional trajectories in chronosequences may be the result of predictable contingent factors, rather than unpredictable stochastic fluctuations.

Burning for biodiversity: highly resilient ant communities respond only to strongly contrasting fire regimes in Australia's seasonal tropics

Summary According to the pyrodiversity paradigm, a wide range of fire regimes is required to maintain biodiversity in fire‐prone landscapes. However, the requisite level of pyrodiversity has seldom been tested and may actually be very low. Here, we examine the sensitivity of tropical savanna ants to variation in fire regimes using results from a long‐term fire experiment near Darwin, Australia. Six experimental fire regimes, with varying fire frequency and seasonality, have been applied to 18 one‐ha plots in three replicated blocks since 2004, with ants sampled prior to experimental burning and then annually after up to 2009. Our primary focus is on the extent to which different patterns of ant richness and composition are associated with each of the six treatment regimes, or whether there is such high overlap that differences only become apparent when experimental treatments are grouped to provide strongly contrasting fire regimes. When treating each of the six fire treatments separately, we were unable to detect a significant influence of fire on any ant community response variable. We were only able to detect significant ant responses when we grouped the experimental treatments into two contrasting fire frequency classes, low (burnt at most once over the 5 years) vs. high (burnt every 1 or 2 years). Even then, these responses were only evident after 3 years of fire treatment. Our findings demonstrate that ant communities have very high resilience in relation to fire, with differences evident only between strongly contrasting regimes. Such resilience appears to be characteristic of savanna ants throughout the world. Synthesis and applications. A large range of finely tuned fire regimes is unlikely to promote regional ant diversity. Rather, only very limited pyrodiversity (a combination of frequently and infrequently burnt areas) would appear to be sufficient for maintaining diversity at a landscape scale. It is important that fire management for biodiversity conservation focuses on the demonstrated requirements of target species, rather than be based on an assumption that ‘pyrodiversity begets biodiversity’.

Aboveground and belowground carbon dynamics in response to fire regimes in the grazed rangelands of northern Australia: initial results from field studies and modelling

The world’s rangelands are often seen as offering considerable potential as a carbon (C) sink, which could contribute to the management of atmospheric C levels, but there are often few data available to assess this potential or to inform the type of management regimes that would be necessary. This paper reports on a review of the literature, a field study and modelling of C stocks under a selection of experimental fire regimes in two plant communities in Australia’s northern rangelands. The field study on an open eucalypt savanna woodland and a savanna grassland-open shrubland suggested that fire regime had no effect or an inconsistent effect on aboveground C stocks. However, modelling using the Century model for the open woodland site showed that increasing fire frequency was associated with reduced aboveground and soil C stocks. Thus, while infrequent fires allowed C stocks to increase (10-yearly fire) or remain stable (6-yearly fire) over a modelled 58-year period, a regime of more frequent fires (4- and 2-yearly fires) reduced C stocks over time. Simulation of C dynamics over 93 years of pastoral settlement suggested that total C stocks had increased by 9.5 t ha–1, largely due to an increase in C in woody vegetation following a reduction in fire frequency associated with pastoral settlement. Frequent burning, as recommended to maintain low woody density and promote pasture production for grazing, will, therefore, reduce aboveground and to a lesser extent soil C stocks where there has been a history of infrequent fire. The opportunities for pastoralists to increase C stocks will depend on the frequency of fire and vegetation type, especially its woodiness or potential woodiness. Reducing fire frequency in woody rangelands will increase C stocks but may have adverse effects on pasture and livestock production. Reducing grazing pressure or destocking might also increase C stocks but may be relevant only when a property is overstocked or where relatively unproductive land could be taken out of livestock production. Any C gains from altering fire and grazing management are likely to be modest.

Does long‐term fire exclusion in an Australian tropical savanna result in a biome shift? A test using the reintroduction of fire

AbstractThe structure of tropical savanna ecosystems is influenced by fire frequency and intensity. There is particular interest in the extent to which long‐term fire exclusion can result in a shift from savanna to forest vegetation that is not easily reversed by the reintroduction of fire. This study examined changes in the structure and composition of a long‐unburnt site within the northern Australian savannas following an extended period of active fire exclusion (>20 years), and the effect of the reintroducing fire through experimental fire regimes, including fires in the early and late dry season at a range of frequencies. After the long period of fire exclusion, the vegetation community was characterized by a well‐developed midstorey and canopy layer, low grass cover, substantially higher densities of woody sprouts and saplings than frequently burnt savanna. The community composition included a high proportion of rainforest‐affiliated species. Three years of experimental fires had no detectable effect on the overall composition of grass layer and woody plants but had an effect on woody vegetation structure. Continued fire exclusion further increased the density of woody stems, particularly in the midstorey (2.0–4.99 m), whereas moderate‐intensity fires (>800 kW m−1) significantly reduced the density of midstorey stems. The reintroduction of higher moderate intensity fire events resulted in the vegetation in some compartments reverting to the open savanna structure typical of frequently burnt sites. Such rapid reversibility suggests that in general, the woody thickening resulting from long‐term fire exclusion did not represent a biome shift to a non‐savanna state. However, there was a small proportion of the site that could not sustain the fires applied to them because grass cover was very low and patchy and therefore appeared to have crossed an ecological threshold towards closed forest.

Effects of experimental fire regimes on the abundance and diversity of cursorial arachnids of Brazilian savannah (cerrado biome)

We investigated the influence of burning frequency and timing on the abundance and diversity of cursorial arachnids in the cerrado (savannah of central Brazil). Five areas were subjected to different burning regimes. In each area, 40 pitfall traps were installed. The arachnids were sampled for three days each month from April 2007 to October 2008. Abundance was higher in the control area than in areas subjected to any fire regime. Species richness was similar in all areas. The evenness was lower in the control area. The areas subject to fires had significantly higher diversity than the control area. Although it was not possible to rank areas according to their diversity, areas burned in the middle of the dry season tended to have higher diversity than areas burned at the beginning or end of this season, indicating that the time at which fire occurs may be more important than the frequency of burning for the diversity of cursorial arachnids in the Brazilian cerrado.

Fire tolerance of perennial grass tussocks in a savanna woodland

AbstractGrass populations in tropical savannas are highly resilient in relation to different fire regimes, but the mechanisms conferring such resilience have been poorly studied. Here we examine one such mechanism, high adult survival during fire, for three perennial grass species in an Australian savanna: Eriachne triseta Nees ex Steud, Eriachne avenacea R.Br and Chrysopogon latifolius S.T.Blake. The study examined survivorship after 3 years, at plots subject to experimental fire regimes (experiencing 0, 1, 2 or 3 fires over the study period) at the Territory Wildlife Park near Darwin in the Northern Territory, Australia. Mean survivorship was 79.9%, 64.3% and 62.0% for E. avenacea, E. triseta and C. latifolius respectively. For the two species of Eriachne, mean survivorship was highest (E. avenacea, 94.6%; E. triseta, 77.1%) in unburnt plots, whereas survivorship of C. latifolius was highest (71.7%) under highest fire frequency. However, variation in survivorship among fire regime treatments was not statistically significant for any of the study species. This negligible difference in survivorship among regimes points to fire tolerance (sprouting ability) as an important mechanism contributing to the resilience and persistence of perennial grasses in these savannas.

No detectable impacts of frequent burning on foliar C and N or insect herbivory in an Australian eucalypt forest

AbstractQuestion: What is the effect of frequent low intensity prescribed fire on foliar nutrients and insect herbivory in an Australian eucalypt forest?Location: Lorne State Forest (Bulls Ground Frequent Burning Study), mid‐north coast, New South Wales, Australia.Methods: Eighteen independent sites were studied representing three experimental fire regimes: fire exclusion (at least 45 years), frequently burnt (every 3 years for 35 years) and fire exclusion followed by the recent introduction of frequent burning (two fires in 6 years). Mature leaves were collected from the canopy of Eucalyptus pilularis trees at each site and analysed for nutrients and damage by invertebrate herbivores.Results: Almost 75% of all leaves showed some signs of leaf damage. The frequency of past fires had no effect on carbon and nitrogen content of canopy leaves. These results were consistent with assessments of herbivore damage where no significant differences were found in the amount of invertebrate herbivory damage to leaves across fire treatments.Conclusions: This eucalypt forest displayed a high degree of resilience to both frequent burning and fire exclusion as determined by foliar nutrients and damage by insect herbivores. Fire frequency had no detectable ecological impact on this aspect of forest health.

Pyromineralization of soil phosphorus in a South African savanna

Savannas are shaped by drought, herbivory, nutrient limitation, and fire. We assessed the interactions between two of these factors—nutrient limitation and fire—across a savanna landscape in Kruger National Park, South Africa, by quantifying increases in plant-available forms of soil phosphorus (P) following experimental or simulated burns. Plant-available pools of P were defined for granitic surface soils subjected to four experimental fire regimes (no fire, triennial fire in the wet season, triennial fire in the dry season, and annual fire in the dry season). To provide context for these results, we also fractionated surface soils from a granitic catena after simulating burning of these soils in a furnace. Burned soils showed comparable pyromineralization rates, with the experimental burn plot soils averaging 0.49 ± 0.04 g labile P m − 2 y − 1 and catena soils averaging 0.63 ± 0.12 g labile P m − 2 y − 1 . Only soils from subplots burned triennially during the wet summer season with moderate fire intensities (∼ 1.1 MW m − 1 ) showed significant increases in labile P relative to control soils. Soils from other burned subplots with greater fire intensities showed smaller gains in labile P, suggesting pyromineralization rates may peak at intermediate fire intensities. We estimated ash contributed up to 33% of pyromineralized P. For catena soils, simulated burning led to significant increases in pyromineralized P for the relatively P-rich footslope soils and smaller increases for sandy crest and midslope soils. These pyromineralization P fluxes are of the same order of magnitude as plant P demand estimated using foliar P levels, and about one-half microbial mineralization rates. In P-limited ecosystems where chemical weathering rates are slow, moderate-intensity fires could play a critical biogeochemical role in the supply of labile P.

Responses of ant communities to experimental fire regimes on rangelands in the Victoria River District of the Northern Territory

Abstract Fire is a significant feature of Australia's savannas. Its use is being encouraged for cattle rangeland management, but there is little knowledge of the ecological effects of prescribed fire regimes on native biodiversity. The responses of ant communities to five experimental fire regimes over 2 years are reported from the Victoria River District in the semi-arid tropics of northern Australia. The experiment was stratified at two levels: soil type (red and black) and fire treatment (unburnt; burnt twice in successive years in early (May) or late (October) dry season and unburnt thereafter; and burnt twice, 3 years apart, in early or late dry season). Ants were sampled twice in April, corresponding with the end of the 1997 and 1998 wet seasons. Ant species richness was not responsive to fire treatment, but reduced with time since fire on black soil. Total ant abundance also reduced with time since fire on the black soil, with significant different abundances in burnt versus unburnt plots in the 1998 sample. Soil type and sampling time had the greatest influence on ant community composition in multivariate analysis than did fire regime, although there were moderate gradients of time since fire with the black soil plots. The abundance of 19 species were significantly different between fire regimes in anova, 13 on red soil and six on black soil. The abundance of eight species (four each on red and black soil) changed significantly with time since fire, with seven promoted by burning. Ant functional group profiles changed little with fire. Total ant abundance and richness had significant relationships with key pasture species and vegetative variables. The responses of ants largely recapitulated those of plants, birds and reptiles on the same plots. It is envisaged that ants will have an important role to play in the sustainable management of Australia's rangelands aiding the off-reserve conservation of biodiversity.

Contrasting fire‐related resilience of ecologically dominant ants in tropical savannas of northern Australia

ABSTRACTThis paper examines the role of fire in mediating the relative abundance of two of the world's major ecologically dominant ant genera, Iridomyrmex and Oecophylla, where they coexist across the tropical savanna landscapes of northern Australia. These taxa have contrasting biogeographical histories, which are predicted to lead to contrasting responses to fire. Iridomyrmex is an autochthonous Australian genus that has radiated primarily in the arid zone; as such, its abundance is predicted to be promoted by frequent fire because this maintains an open habitat. In contrast, Oecophylla is a genus of leaf‐nesting ants occurring in the canopies of Old World tropical rainforest, and is a recent arrival to Australia in geological time; the abundance of these ants is predicted to decline under frequent fire. We test these predictions using results from a landscape‐scale fire experiment, where three experimental fire regimes (including no fire) were applied to replicated subcatchments over a 5‐year period. Using sweep nets, ants were sampled in the grass layer (the habitat layer of greatest overlap between Iridomyrmex and Oecophylla) in eucalypt woodland (canopy cover < 30%) and open eucalypt forest (canopy cover about 50%) habitats. A total of 27 species from 11 genera were collected during the study; eight were common enough for statistical analysis, and the abundances of four of these were significantly affected by fire treatment. As predicted, the abundance of Iridomyrmex was promoted by fire, whereas that of Oecophylla declined. These changes occurred only under late‐season (relatively high intensity) fires, and for Oecophylla occurred only in open forest (not woodland) habitat. This fire‐mediated relationship between Iridomyrmex and Oecophylla mirrors the much broader, ecosystem‐wide dynamic between eucalypt‐dominated savanna and rainforest in tropical Australia, with savannas dominated by fire‐resistant sclerophyll elements of Australian origin, and rainforest dominated by fire‐sensitive mesophyll elements of South‐East Asian origin.

Fire frequency and biodiversity conservation in Australian tropical savannas: implications from the Kapalga fire experiment

Abstract Every year large proportions of northern Australia's tropical savanna landscapes are burnt, resulting in high fire frequencies and short intervals between fires. The dominant fire management paradigm in these regions is the use of low‐intensity prescribed fire early in the dry season, to reduce the incidence of higher‐intensity, more extensive wildfire later in the year. This use of frequent prescribed fire to mitigate against high‐intensity wildfire has parallels with fire management in temperate forests of southern Australia. However, unlike in southern Australia, the ecological implications of high fire frequency have received little attention in the north. CSIRO and collaborators recently completed a landscape‐scale fire experiment at Kapalga in Kakadu National Park, Northern Territory, Australia, and here we provide a synthesis of the effects of experimental fire regimes on biodiversity, with particular consideration of fire frequency and, more specifically, time‐since‐fire. Two recurring themes emerged from Kapalga. First, much of the savanna biota is remarkably resilient to fire, even of high intensity. Over the 5‐year experimental period, the abundance of most invertebrate groups remained unaffected by fire treatment, as did the abundance of most vertebrate species, and we were unable to detect any effect of fire on floristic composition of the grass‐layer. Riparian vegetation and associated stream biota, as well as small mammals, were notable exceptions to this general resilience. Second, the occurrence of fire, independent of its intensity, was often the major factor influencing fire‐sensitive species. This was especially the case for extinction‐prone small mammals, which have suffered serious population declines across northern Australia in recent decades. Results from Kapalga indicate that key components of the savanna biota of northern Australia favour habitat that has remained unburnt for at least several years. This raises a serious conservation concern, given that very little relatively long unburnt habitat currently occurs in conservation reserves, with most sites being burnt at least once every 2 years. We propose a conservation objective of increasing the area that remains relatively long unburnt. This could be achieved either by reducing the proportion of the landscape burnt each year, or by setting prescribed fires more strategically. The provision of appropriately long unburnt habitat is a conservation challenge for Australia's tropical savanna landscapes, just as it is for its temperate forests.

POPULATION VIABILITY ANALYSES OF CHAMAECRISTA KEYENSIS: EFFECTS OF FIRE SEASON AND FREQUENCY

Conservation of species of concern in fire-dependent ecosystems requires restoring the historical fire regime that has shaped the species' life history. The historical fire regime of the endangered pine rockland ecosystem is controversial. In this study, we attempted to infer the historical fire regime of this ecosystem by studying the effects of contrasting experimental fire regimes on Chamaecrista keyensis, a narrowly endemic species of the pine rocklands of the Lower Florida Keys, USA. We constructed multiple matrix population models for C. keyensis using demographic data from replicated wet- and dry-season burns, 1–30 years since fire, and seed bank dynamics derived from extensive field seed bank experiments. We then carried out deterministic analyses and stochastic simulations. Recently burned sites (1–2 years postfire) had the highest finite population growth rates of all sites. Differences in finite population growth rate between winter and summer fires were more pronounced during the year of burn than in subsequent years. Stochastic simulations show that dry-season (winter) burns generated lower extinction risks and population decline probabilities than a wet-season (summer) fire regime. Fire return intervals of 5–7 years generated the lowest extinction and population decline probabilities for both seasons. C. keyensis may have evolved under a fire regime that consisted of both anthropogenic dry-season fires along with lightning-caused wet-season fires. If phenology is also a key to fire responses in other pine rockland species, a diverse fire regime including a wide range of fire seasons may be critical to maintaining the diversity of the pine rockland ecosystem.

Responses of ant communities to experimental fire regimes on rangelands in the Victoria River District of the Northern Territory

Abstract Fire is a significant feature of Australia's savannas. Its use is being encouraged for cattle rangeland management, but there is little knowledge of the ecological effects of prescribed fire regimes on native biodiversity. The responses of ant communities to five experimental fire regimes over 2 years are reported from the Victoria River District in the semi‐arid tropics of northern Australia. The experiment was stratified at two levels: soil type (red and black) and fire treatment (unburnt; burnt twice in successive years in early (May) or late (October) dry season and unburnt thereafter; and burnt twice, 3 years apart, in early or late dry season). Ants were sampled twice in April, corresponding with the end of the 1997 and 1998 wet seasons. Ant species richness was not responsive to fire treatment, but reduced with time since fire on black soil. Total ant abundance also reduced with time since fire on the black soil, with significant different abundances in burnt versus unburnt plots in the 1998 sample. Soil type and sampling time had the greatest influence on ant community composition in multivariate analysis than did fire regime, although there were moderate gradients of time since fire with the black soil plots. The abundance of 19 species were significantly different between fire regimes in anova, 13 on red soil and six on black soil. The abundance of eight species (four each on red and black soil) changed significantly with time since fire, with seven promoted by burning. Ant functional group profiles changed little with fire. Total ant abundance and richness had significant relationships with key pasture species and vegetative variables. The responses of ants largely recapitulated those of plants, birds and reptiles on the same plots. It is envisaged that ants will have an important role to play in the sustainable management of Australia's rangelands aiding the off‐reserve conservation of biodiversity.

Determinants of survival for the northern brown bandicoot under a landscape‐scale fire experiment

Summary More than half of all Australian bandicoot species (family Peramelidae) are listed by the IUCN as extinct or threatened and changed fire regimes in arid and semi‐arid Australia have been identified as an important agent in their decline. The northern brown bandicoot is currently one of Australia's most common bandicoots, but their continued persistence in the tropical savannas cannot be taken for granted. Previous studies in Kakadu National Park, Northern Territory have shown this species to be prone to sudden declines in abundance, possibly linked to the occurrence of intense fires. Here we examine the impact of four experimental fire management regimes (fire prevention, early dry season burning, late dry season burning and progressive burning several times through the dry season) on survival of the northern brown bandicoot. The analysis is based on capture–mark–recapture data obtained during a landscape‐scale fire experiment conducted at Kapalga, in Kakadu National Park from 1989 to 1995. All experimental fire treatments (including total fire exclusion) were associated with decline in survival rates over time, indicating that none of the tested approaches were appropriate for this species. Burning in the late dry season or progressively throughout the dry season produced substantially more severe declines in survival than did early dry season fires or fire exclusion. Fire regime was found to be the most important determinant of bandicoot survival, far exceeding other factors such as gender, age, vegetation type, rainfall and season, all of which had comparatively little influence. The results demonstrate the importance of the frequency and seasonal timing of fires in determining the survival of bandicoots and suggest that spatially uniform and temporally invariant fire regimes are inappropriate for bandicoot conservation in the north Australian savannas.

RAINFALL-CONTINGENT DETECTION OF FIRE IMPACTS: RESPONSES OF BEETLES TO EXPERIMENTAL FIRE REGIMES

Fire is a valuable tool for maintaining biodiversity in many ecosystems throughout the world, particularly tropical savannas. An understanding of the impact of different fire management regimes is essential if desired outcomes are to be achieved. Numerous studies have shown patchy and inconsistent responses of insects to fire. This may be because detection of responses to fire was contingent upon environmental conditions such as rainfall. Here we examine how ground-active beetles respond to savanna fires and how detection of these responses is contingent upon the amount of rain occurring prior to sampling. We also test the extent to which family-level responses are “taxonomically sufficient” to reveal responses detected at the species level. Our study was part of a landscape-scale, replicated field experiment at Kapalga Research Station, Kakadu National Park, in the wet–dry tropics of northern Australia. Over a 7-yr period (1988–1994), ground-active beetles were monitored using pitfall traps. In 1988 and 1989 fires were excluded from all of the 15–20-km2 experimental compartments. From 1990 to 1994, three experimental fire regimes were applied: burning annually early in the dry season (May/June), burning annually toward the end of the dry season (September/October), and exclusion of fire. Each treatment was replicated three times. Pitfall trapping began at the start of the wet season in 1988 and continued twice a year, in the middle of the dry season (July/August) and early in the wet season (November/December), until the conclusion of the study at the end of 1994. Beetle abundance in dry-season samples was too low and variable for any meaningful statistical analyses. For wet-season samples, repeated-measures analysis of variance revealed that fires late in the dry season significantly reduced the number of ground-active beetle individuals, families, and species. However, detecting this decline was contingent upon substantial amounts of rain falling prior to sampling. In addition, canonical correspondence analysis (CCA) showed that fire intensity and amount of rainfall prior to sampling interacted to change abundance of several common beetle families and species. Fires late in the dry season appeared to disadvantage some common wet-adapted taxa, while favoring other common groups that were dry-adapted. A Mantel test, comparing dissimilarity matrices based on abundances of common families and species, confirmed that analysis at the family level was taxonomically sufficient to reveal most responses found by analysis at the species level. The strong influence of rainfall on detection of beetle responses to fire poses a challenge to managers using such insects to monitor fire-prone ecosystems. Unless monitoring strategies include rainfall in the sampling design, burning prescriptions may not appear to produce desired or consistent outcomes; fire impacts may be there, but go undetected.

Rainfall-Contingent Detection of Fire Impacts: Responses of Beetles to Experimental Fire Regimes

Fire is a valuable tool for maintaining biodiversity in many ecosystems throughout the world, particularly tropical savannas. An understanding of the impact of different fire management regimes is essential if desired outcomes are to be achieved. Numerous studies have shown patchy and inconsistent responses of insects to fire. This may be because detection of responses to fire was contingent upon environmental conditions such as rainfall. Here we examine how ground-active beetles respond to savanna fires and how detection of these responses is contingent upon the amount of rain occurring prior to sampling. We also test the extent to which family-level responses are “taxonomically sufficient” to reveal responses detected at the species level. Our study was part of a landscape-scale, replicated field experiment at Kapalga Research Station, Kakadu National Park, in the wet–dry tropics of northern Australia. Over a 7-yr period (1988–1994), ground-active beetles were monitored using pitfall traps. In 1988 and 1989 fires were excluded from all of the 15–20-km2 experimental compartments. From 1990 to 1994, three experimental fire regimes were applied: burning annually early in the dry season (May/June), burning annually toward the end of the dry season (September/October), and exclusion of fire. Each treatment was replicated three times. Pitfall trapping began at the start of the wet season in 1988 and continued twice a year, in the middle of the dry season (July/August) and early in the wet season (November/December), until the conclusion of the study at the end of 1994. Beetle abundance in dry-season samples was too low and variable for any meaningful statistical analyses. For wet-season samples, repeated-measures analysis of variance revealed that fires late in the dry season significantly reduced the number of ground-active beetle individuals, families, and species. However, detecting this decline was contingent upon substantial amounts of rain falling prior to sampling. In addition, canonical correspondence analysis (CCA) showed that fire intensity and amount of rainfall prior to sampling interacted to change abundance of several common beetle families and species. Fires late in the dry season appeared to disadvantage some common wet-adapted taxa, while favoring other common groups that were dry-adapted. A Mantel test, comparing dissimilarity matrices based on abundances of common families and species, confirmed that analysis at the family level was taxonomically sufficient to reveal most responses found by analysis at the species level. The strong influence of rainfall on detection of beetle responses to fire poses a challenge to managers using such insects to monitor fire-prone ecosystems. Unless monitoring strategies include rainfall in the sampling design, burning prescriptions may not appear to produce desired or consistent outcomes; fire impacts may be there, but go undetected.

Fire and biodiversity: responses of grass‐layer beetles to experimental fire regimes in an Australian tropical savanna

Summary Up to 50% or more of the savanna landscapes of northern Australia are burnt each year, but the effects of these fires on savanna faunas are poorly known, especially for arthropods. We investigated the responses of grass‐layer beetles to three fire regimes (unburnt – fires excluded; early – annual fires lit early during the dry season; late – annual fires lit late during the dry season) as part of a landscape‐scale fire experiment at Kapalga in Australia’s Northern Territory, where replicated fire regimes were applied to 15–20‐km2 landscape units over a 5‐year period. We also sought to identify beetle species that might act as indicators of particular fire regimes, and examined the extent to which analysis at the family level is sufficient to reveal patterns evident from species‐level analysis. Beetles were sampled using sweep nets during February (mid‐wet season) and May (end of wet season) each year, from 1989 (18 months prior to the imposition of fire treatments) to 1995 (after 5 years of treatments). A total of 3865 beetles from 233 species was recorded, with the dominant families Chrysomelidae (leaf beetles) and Curculionidae (weevils) contributing 91% of all beetles and 57% of total species. Total beetle abundance, species richness, family richness and the abundances of one of the 10 most common species were significantly affected by fire treatment according to anova. In all cases, beetle abundance and richness were similar in the two burning treatments, but greater than in the unburnt treatment. These differences were only apparent during the second half of the experiment. The responses were mirrored by changes in composition at species, family and guild levels, according to multivariate analysis. According to indicator analysis, five beetle species were significant indicators of late fires, and one of early fires. All these species were infrequently recorded and therefore of limited use for management. However, two common species were indicative of burnt habitats if early and late treatments are considered together. Family richness was highly correlated (r2 = 0·615) with species richness, and multivariate analysis of family‐level abundances revealed the compositional changes in relation to fire that were evident in species‐level analysis. Family was therefore a reliable surrogate of species for detecting beetle responses. Although we found significant effects of our experimental treatments, in the broader context of overall beetle dynamics the assemblages appeared to be remarkably resilient to fire. This reflects a long history of association with frequent fire, and is consistent with many other components of the northern Australian fauna, where fire appears to be of secondary importance to variation in rainfall and soil type. The lack of effect of fire timing on grass‐layer beetles calls into question a management paradigm that focuses largely on fire intensity, and suggests that fire management needs to be more mindful of fire frequency.