Fire research for conservation management in tropical savannas: Introducing the Kapalga fire experiment

Abstract Fire is a dominant feature of tropical savannas throughout the world, and provides a unique opportunity for habitat management at the landscape scale. We provide the background and methodology for a landscape-scale savanna fire experiment at Kapalga, located in Kakadu National Park in the seasonal tropics of northern Australia. The experiment addresses the limitations of previous savanna fire experiments, including inappropriately small sizes of experimental units, lack of replication, consideration of a narrow range of ecological responses and an absence of detailed measurement of fire behaviour. In contrast to those elsewhere in the world, Australia's savannas are sparsely populated and largely uncleared, with fires lit primarily in a conservation, rather than pastoral, context. Fire management has played an integral role in the traditional lifestyles of Aboriginal people, who have occupied the land for perhaps 50 000 years or more. Currently the dominant fire management paradigm is one of extensive prescribed burning early in the dry season (May-June), in order to limit the extent and severity of fires occurring later in the year. The ecological effects of different fire regimes are hotly debated, but we identify geo-chemical cycling, tree demography, faunal diversity and composition, phenology, and the relative importance of fire intensity, timing and frequency, as critical issues. Experimental units (‘compartments’) at Kapalga are 15–20km² catchments, centred on seasonal creeks that drain into major rivers. Each compartment has been burnt according to one of four treatments, each replicated at least three times: ‘Early’- fires lit early in the dry season, which is the predominant management regime in the region; ‘Late’- fires lit late in the dry season, as occurs extensively in the region as unmanaged ‘wildfires’; ‘Progressive’- fires lit progressively throughout the dry season, such that different parts of the landscape are burnt as they progressively dry out (believed to approximate traditional Aboriginal burning practices); and ‘Unburnt’- no fires lit, and wildfires excluded. All burning treatments have been applied annually for 5 years, from 1990 to 1994. Six core projects have been conducted within the experimental framework, focusing on nutrients and atmospheric chemistry, temporary streams, vegetation, insects, small mammals, and vertebrate predators. Detailed measurements of fire intensity have been taken to help interpret ecological responses. The Kapalga fire experiment is multidisciplinary, treatments have been applied at a landscape scale with replication, and ecological responses can be related directly to measurements of fire intensity. We are confident that this experiment will yield important insights into the fire ecology of tropical savannas, and will make a valuable contribution to their conservation management.     

The impact of experimental fire regimes on seed production in two tropical eucalypt species in northern Australia

Abstract This study investigated the effect of three experimental fire regimes on the fecundity, ovule development and seedfall of two common wet-dry tropical savanna eucalypts, Eucalyptus minima and Eucalyptus tetrodonta, in northern Australia. Both species flower early in the dry season and ovule development occurs during the dry season. This coincides with a period of frequent fires. The three fire regimes considered were applied for four years between 1990 and 1994. These regimes were (i) Unburnt, (ii) Early, fires lit early in the dry season, and (iii) Late, fires lit late in the dry season. The treatments were applied to nine catchments (15–20 km²) with each fire regime replicated three times. Fire intensity typically increases as the dry season proceeds. Therefore, early dry season fires generally differ from late dry season fires in both their intensity and their timing in relation to the reproductive phenology of the eucalypts. Late dry season burning significantly reduced the fecundity of both species, whereas Early burning had no significant effect. Ovule success was significantly reduced by the Early burning for both species. The Late burning significantly reduced ovule success in E. tetrodonta, but not in E. miniata. The results suggest that fire intensity and fire timing may both be important determinants of seed supply. Fire intensity may be a determinant of fecundity, whereas fire timing in relation to the reproduction phenology may have a significant impact on ovule survival. Both fire regimes resulted in a substantial reduction in seed supply compared with the Unburnt treatment. This may have a significant impact on seedling regeneration of these tropical savanna eucalypts.     

Anomalies in grasstree fire history reconstructions for south‐western Australian vegetation

Abstract A new fire history for south‐western Australian sclerophyll forests was proposed recently based on grasstree (Xanthorrhoea preissii ) records that were interpreted to show a high frequency (3–5 years) ‘pre‐European burning regime’. Such a fire regime appears incompatible with the long‐term survival of many fire‐killed woody taxa. We investigated the local fire history in a small area of the northern sand‐plain shrub‐lands of south‐western Australia using 15 grasstrees, examining individual grasstree records in detail and comparing this with the decadal or averaged approach used in the original research, and with fire histories reconstructed from satellite images for the period since 1975. Results lead us to question the utility of the proposed grasstree fire history record as a tool for understanding past fire regimes for two reasons: First, inconsistencies in fire histories among individual grasstrees were considerable – some individuals were not burnt by known fires, while some apparently were burned many times during periods when others were not burned at all. Second, the grasstree record indicates a possible increase in patchiness of fires since 1930, while contemporary evidence and interpretations of the nature of Aboriginal (pre‐European) fire regimes would suggest the opposite. We believe that further research is needed to identify to what extent the grasstree method for reconstruction of fire histories can be used to re‐interpret how fire operated in many highly diverse ecosystems prior to European settlement of Australia.     

A biogeographic model of fire regimes in Australia: current and future implications

Aim Patterns of fire regimes across Australia exhibit biogeographic variation in response to four processes. Variations in area burned and fire frequency result from differences in the rates of ‘switching’ of biomass growth, availability to burn, fire weather and ignition. Therefore differing processes limit fire (i.e. the lowest rate of switching) in differing ecosystems. Current and future trends in fire frequency were explored on this basis. Location Case studies of forests (cool temperate to tropical) and woodlands (temperate to arid) were examined. These represent a broad range of Australian biomes and current fire regimes. Methods Information on the four processes was applied to each case study and the potential minimum length of interfire interval was predicted and compared to current trends. The potential effects of global change on the processes were then assessed and future trends in fire regimes were predicted. Results Variations in fire regimes are primarily related to fluctuations in available moisture and dominance by either woody or herbaceous plant cover. Fire in woodland communities (dry climates) is limited by growth of herbaceous fuels (biomass), whereas in forests (wet climates) limitation is by fuel moisture (availability to burn) and fire weather. Increasing dryness in woodland communities will decrease potential fire frequency, while the opposite applies in forests. In the tropics, both forms of limitation are weak due to the annual wet/dry climate. Future change may therefore be constrained. Main conclusions Increasing dryness may diminish fire activity over much of Australia (dominance of dry woodlands), though increases may occur in temperate forests. Elevated CO₂ effects may confound or reinforce these trends. The prognosis for the future fire regime in Australia is therefore uncertain.     

Ngadju kala: Australian Aboriginal fire knowledge in the Great Western Woodlands

Indigenous fire knowledge offers significant benefits for ecosystem management and human livelihoods, but is threatened worldwide because of disruption of customary practices. In Australia, the historical prevalence and characteristics of Aboriginal burning are intensely debated, including arguments that Aboriginal burning was frequent across the continent. Frequent burning is supported by contemporary Aboriginal knowledge and practice in some regions, but in southern Australia evidence is typically limited to historical and ecological records. Towards characterizing Aboriginal fire regimes in southern Australia, we collaborated with Ngadju people from the globally significant Great Western Woodlands in south‐western Australia to document their fire knowledge. We used workshops, site visits, interviews and occupation mapping to aid knowledge sharing. Consistent with the established significance of Aboriginal fire in Australia, planned fires were important in Ngadju daily life and land management. However, Ngadju use of fire was characterized by its selectivity rather than its ubiquity. Specifically, Ngadju described only highly targeted planned burning across extensive eucalypt woodlands and sandplain shrublands. By contrast, frequent planned burning was described for resource‐rich landscape elements of more restricted extent (granite outcrop vegetation, grasslands and coastal scrub). Overall, Ngadju fires are likely to have resulted in subtle but purposeful direct effects on the vegetation and biota. However the extent to which they collectively constrained large, intense wildfires remains unclear. Ngadju demonstrated a predictive knowledge of the ecological consequences of burning, including attention to fine‐scale needs of target organisms, and application of diverse fire regimes. These are consistent with the recently proposed concept that Aboriginal burning was guided by ‘templates’ targeting different resources, although diverse regimes predominantly reflect edaphically driven vegetation patterns rather than template‐driven use of fire to create resource diversity. We conclude that Ngadju fire knowledge fills an important gap in understanding Aboriginal fire regimes in southern Australia, highlighting a novel balance between frequent and constrained use of fire.     

Simplifying the savanna: the trajectory of fire‐sensitive vegetation mosaics in northern Australia

Aim Fire is a key agent in savanna systems, yet the capacity to predict fine‐grained population phenomena under variable fire regime conditions at landscape scales is a daunting challenge. Given mounting evidence for significant impacts of fire on vulnerable biodiversity elements in north Australian savannas over recent decades, we assess: (1) the trajectory of fire‐sensitive vegetation elements within a particularly biodiverse savanna mosaic based on long‐term monitoring and spatial modelling; (2) the broader implications for northern Australia; and (3) the applicability of the methodological approach to other fire‐prone settings. Location Arnhem Plateau, northern Australia. Methods We apply data from long‐term vegetation monitoring plots included within Kakadu National Park to derive statistical models describing the responses of structure and floristic attributes to 15 years of ambient (non‐experimental) fire regime treatments. For a broader 28,000 km² region, we apply significant models to spatial assessment of the effects of modern fire regimes (1995–2009) on diagnostic closed forest, savanna and shrubland heath attributes. Results Significant models included the effects of severe fires on large stems of the closed forest dominant Allosyncarpia ternata, stem densities of the widespread savanna coniferous obligate seeder Callitris intratropica, and fire frequency and related fire interval parameters on numbers of obligate seeder taxa characteristic of shrubland heaths. No significant relationships were observed between fire regime and eucalypt and non‐eucalypt adult tree components of savanna. Spatial application of significant models illustrates that more than half of the regional closed forest perimeters, savanna and shrubland habitats experienced deleterious fire regimes over the study period, except in very dissected terrain. Main conclusions While north Australia’s relatively unmodified mesic savannas may appear structurally intact and healthy, this study provides compelling evidence that fire‐sensitive vegetation elements embedded within the savanna mosaic are in decline under present‐day fire regimes. These observations have broader implications for analogous savanna mosaics across northern Australia, and support complementary findings of the contributory role of fire regimes in the demise of small mammal fauna. The methodological approach has application in other fire‐prone settings, but is reliant on significant long‐term infrastructure resourcing.     

Californian mixed-conifer forests under unmanaged fire regimes in the Sierra San Pedro Mártir, Baja California, Mexico

Aim This study appraises historical fire regimes for Californian mixed‐conifer forests of the Sierra San Pedro Mártir (SSPM). The SSPM represents the last remaining mixed‐conifer forest along the Pacific coast still subject to uncontrolled, periodic ground fire. Location The SSPM is a north–south trending fault bound range, centred on 31°N latitude, 100 km SE of Ensenada, Baja California. Methods We surveyed forests for composition, population structure, and historical dynamics both spatially and temporally over the past 65 years using repeat aerial photographs and ground sampling. Fire perimeter history was reconstructed based on time‐series aerial photographs dating from 1942 to 1991 and interpretable back to 1925. A total of 256 1‐ha sites randomly selected from aerial photographs were examined along a chronosequence for density and cover of canopy trees, density of snags and downed logs, and cover of non‐conifer trees and shrubs. Twenty‐four stands were sampled on‐the‐ground by a point‐centred quarter method which yielded data on tree density, basal area, frequency, importance value, and shrub and herb cover. Results Forests experience moderately intense understory fires that range in size to 6400 ha, as well as numerous smaller, low intensity burns with low cumulative spatial extent. SSPM forests average 25–45% cover and 65–145 trees per ha. Sapling densities were two to three times that of overstory trees. Size‐age distributions of trees ≥ 4 cm dbh indicate multi‐age stands with steady‐state dynamics. Stands are similar to Californian mixed conifer forests prior to the imposition of fire suppression policy. Livestock grazing does not appear to be suppressing conifer regeneration. Main conclusions Our spatially‐based reconstruction shows the open forest structure in SSPM to be a product of infrequent, intense surface fires with fire rotation periods of 52 years, rather than frequent, low intensity fires at intervals of 4–20 years proposed from California fire‐scar dendrochronology (FSD) studies. Ground fires in SSPM were intense enough to kill pole‐size trees and a significant number of overstory trees. We attribute long fire intervals to the gradual build‐up of subcontinuous shrub cover, conifer recruitment and litter accumulation. Differences from photo interpretation and FSD estimates are due to assumptions made with respect to site‐based (point) sampling of fire, and nonfractal fire intensities along fire size frequency distributions. Fire return intervals determined by FSD give undue importance to local burns which collectively use up little fuel, cover little area, and have little demographic impact on forests.     

Detecting invertebrate responses to fire depends on sampling method and taxonomic resolution

New knowledge about the responses of species to fire is needed to plan for biodiversity conservation in the face of changing fire regimes. However, the knowledge that is acquired may be influenced by the sampling method and the taxonomic resolution of a study. To investigate these potential sampling biases, we examined invertebrate responses to time since fire in mallee woodlands of southern Australia. Using a large‐scale replicated study system, we sampled over 60 000 invertebrates with large pitfall traps, wet pitfall traps and sweep nets, and undertook analyses at morphospecies and order level. Large pitfalls and sweep nets detected several strong fire effects, whereas wet pitfall traps detected few effects. Invertebrate abundance in sweep nets was highest shortly after fire because of grasshopper outbreaks. Several additional morphospecies showed strong preferences for different stages in the post‐fire succession. In contrast with morphospecies effects, analyses at order level either failed to detect fire effects or were driven by the most abundant species. For fire research to produce credible results with the potential to guide management, it must use a range of sampling techniques and undertake analyses at (morpho)species level. Homogeneous fire management, such as fire suppression in fragmented landscapes or widespread frequent burning for asset protection, is likely to cause declines in fire‐affected invertebrates.     

A conceptual model of vegetation dynamics for the unique obligate‐seeder eucalypt woodlands of south‐western Australia

Models of vegetation dynamics framed as testable hypotheses provide powerful tools for predicting vegetation change in response to contemporary disturbances or climate change. Synthesizing existing information and applying new data, we develop a conceptual model of vegetation states and transitions for the previously overlooked woodlands dominated by obligate‐seeder eucalypts of dry to semi‐arid south‐western Australia. These comprise the largest extant temperate woodland globally, are uniquely dominated by a high diversity of obligate‐seeder eucalypts (55 taxa), but are under threat from wildfire. Our conceptual model incorporates four critical ecological processes that also distinguish obligate‐seeder woodlands from temperate woodlands dominated by resprouting eucalypts: (i) a lack of well‐protected epicormic buds results in major disturbances (prominently fire) being stand‐replacing. The pre‐disturbance tree cohort is killed, followed by dense post‐disturbance recruitment from seed shed from a serotinous seed bank; (ii) competition between saplings leads to self‐thinning over a multi‐century timeframe, with surviving individuals having great longevity (regularly >400 years); (iii) multiple processes limit recruitment in the absence of stand‐replacement disturbances, leading to frequent single‐cohort stands. However, unlike the few other obligate‐seeder eucalypt communities, trickle recruitment in very long‐unburnt stands can facilitate indefinite community persistence in the absence of stand‐replacement disturbances; and (iv) discontinuous fuels, relatively low understorey flammability (low grass and often high chenopod cover) and topographic barriers to fire (salt lakes) allow mature woodlands to persist for centuries without burning. Notably though, evidence suggests that flammability peaks at intermediate times since fire, establishing a ‘flammability bottleneck’ (or landscape fire trap) through which regenerating woodlands must pass. Our model provides a framework to support management to conserve obligate‐seeder eucalypt woodlands. Research into reasons for exceptional tree heights relative to ecosystem productivity, the evolution of diverse and dominant obligate‐seeder eucalypts, the paucity of grass, and the recent spatial distribution of fires, will further inform conservation management.     

Anthropogenic modifications to fire regimes in the wider Serengeti‐Mara ecosystem

Fire is a key driver in savannah systems and widely used as a land management tool. Intensifying human land uses are leading to rapid changes in the fire regimes, with consequences for ecosystem functioning and composition. We undertake a novel analysis describing spatial patterns in the fire regime of the Serengeti‐Mara ecosystem, document multidecadal temporal changes and investigate the factors underlying these patterns. We used MODIS active fire and burned area products from 2001 to 2014 to identify individual fires; summarizing four characteristics for each detected fire: size, ignition date, time since last fire and radiative power. Using satellite imagery, we estimated the rate of change in the density of livestock bomas as a proxy for livestock density. We used these metrics to model drivers of variation in the four fire characteristics, as well as total number of fires and total area burned. Fires in the Serengeti‐Mara show high spatial variability—with number of fires and ignition date mirroring mean annual precipitation. The short‐term effect of rainfall decreases fire size and intensity but cumulative rainfall over several years leads to increased standing grass biomass and fuel loads, and, therefore, in larger and hotter fires. Our study reveals dramatic changes over time, with a reduction in total number of fires and total area burned, to the point where some areas now experience virtually no fire. We suggest that increasing livestock numbers are driving this decline, presumably by inhibiting fire spread. These temporal patterns are part of a global decline in total area burned, especially in savannahs, and we caution that ecosystem functioning may have been compromised. Land managers and policy formulators need to factor in rapid fire regime modifications to achieve management objectives and maintain the ecological function of savannah ecosystems.     

Post‐fire regeneration in alpine heathland: Does fire severity matter?

Fire severity is thought to be an important determinant of landscape patterns of post‐fire regeneration, yet there have been few studies of the effects of variation in fire severity at landscape scales on floristic diversity and composition, and none within alpine vegetation. Understanding how fire severity affects alpine vegetation is important because fire is relatively infrequent in alpine environments. Globally, alpine ecosystems are at risk from climate change, which, in addition to warming, is likely to increase the severity and frequency of fire in south‐eastern Australia. Here we examine the effects of variation in fire severity on plant diversity and vegetation composition, 5 years after the widespread fires of 2003. We used floristic data from two wide‐spread vegetation types on the Bogong High Plains: open heathland and closed heathland. Three alternative models were tested relating variation in plant community attributes (e.g. diversity, ground cover of dominant species, amount of bare ground) to variation in fire severity. The models were (i) ‘linear’, attributes vary linearly with fire severity; (ii) ‘intermediate disturbance’, attributes are highest at intermediate fire severity and lowest at both low‐ and high‐severity; and (iii) ‘null’, attributes are unaffected by fire severity. In both heathlands, there were few differences in floristic diversity, cover of dominant species and community composition, across the strong fire severity gradient. The null model was most supported in the vast majority of cases, with only limited support for either the linear and intermediate disturbance models. Our data indicate that in both heathlands, vegetation attributes in burnt vegetation were converging towards that of the unburnt state. We conclude that fire severity had little impact on post‐fire regeneration, and that both closed and open alpine heathlands are resilient to variation in fire severity during landscape scale fires.     

Post‐fire development of faunal habitat depends on plant regeneration traits

The concept that vegetation structure (and faunal habitat) develops predictably with time since fire has been central to understanding the relationship between fire and fauna. However, because plants regenerate after fire in different ways (e.g. resprouting from above‐ground stems vs. underground lignotubers), use of simple categories based on time since fire might not adequately represent post‐fire habitat development in all ecosystems. We tested the hypothesis that the post‐fire development of faunal habitat structure differs between ecosystems, depending on fire regeneration traits of the dominant canopy trees. We measured 12 habitat components at sites in foothill forests (n = 38), heathy woodlands (n = 38) and mallee woodlands (n = 98) in Victoria, Australia, and used generalised additive models to predict changes in each variable with time since fire. A greater percentage of faunal habitat variables responded significantly to time since fire in mallee woodlands, where fires typically are stand‐replacing, than in foothill forests and heathy woodlands, where canopy tree stems generally persist through fire. In the ecosystem with the highest proportion of epicormic resprouters (foothill forests), only ground cover and understorey vegetation responded significantly to time since fire, compared with all but one variable in the ecosystem dominated by basal resprouters (mallee woodlands). These differences between ecosystems in the post‐fire development of key habitat components suggest there may also be fundamental differences in the role of fire in shaping the distribution of fauna. If so, this challenges the way in which many fire‐prone ecosystems currently are categorised and managed, especially the level of dependence on time since fire and other temporal surrogates such as age‐classes and successional states. Where time since fire is a poor surrogate for habitat structural development, additional complexity (e.g. fire severity, topography and prior land‐use history) could better capture processes that determine faunal occurrence in fire‐prone ecosystems.     

Forest‐fire regimes affect thermoregulatory opportunities for terrestrial ectotherms

Fire‐induced changes in canopy openness may affect sunlight penetration to the forest floor, and thus the operative temperatures available to terrestrial ectotherms. We examined thermal regimes for two types of ectotherms: diurnally active species that utilize sun‐exposed patches to regulate their body temperatures, and nocturnally active species that depend upon solar radiation striking the rocks under which they shelter. We measured canopy openness, shrub height, radiation transmission and operative environmental temperatures in the open and inside reptile retreat‐sites, at 24 study sites in eucalypt forests in two regions (Gosford and Yengo) in south‐eastern Australia. All sites were last burnt in 2000–2001, but had experienced different fire frequencies (1–4 fires over the previous 37 years). In Gosford, higher fire frequencies reduced canopy openness and radiation transmission at ground and shrub level, and thus reduced environmental temperatures and the thermal quality of reptile habitats. Our modelling based on thermal preferenda of an endangered snake species (the broad‐headed snake Hoplocephalus bungaroides) suggests that increased fire frequency at Gosford halved the amount of time an animal could spend within its preferred (set‐point) range, regardless of whether it thermoregulated beneath rocks or basked out in the open. At Yengo, however, fire frequency did not affect the thermal quality of reptile habitats. Thus, the effects of fire frequency on forest structure and the thermal environment at ground level differed between adjacent areas, and relatively small changes in canopy openness translated into major effects on thermoregulatory opportunities for reptiles. Although fire is a useful management tool for creating open habitats, we need to understand more about the effects of fire frequency on vegetation structure and thermal environment before we can use fire to manage habitats for reptiles.     

Cattle grazing does not reduce fire severity in eucalypt forests and woodlands of the Australian Alps

Large grazing herbivores can change fire regimes by altering fuel types and abundance, particularly in savanna biomes where the dominant fuel is grass. The use of herbivores as a fire management tool is receiving increasing consideration globally, but this intervention has a limited evidence‐base and is controversial because of potential deleterious ecological effects. These issues are well illustrated by the political and scientific debate about the capacity of cattle grazing to reduce fire hazard in the Victorian Alps of Australia; there have been remarkably few scientific studies to illuminate this issue. Here we use remote sensing and geographic information system analysis to determine the effect of active grazing licences on fire severity (crown scorch) in eucalypt forests and woodlands following large fires in the Alps during the summers of 2002/2003 and 2006/2007. Our statistical analyses, which controlled for spatial autocorrelation, found crown scorch was strongly related to vegetation type but there was no evidence that cattle grazing reduced fire severity. There was some evidence that grazing could increase fire severity by possibly changing fuel arrays. Such landscape analyses are a critical approach given that large‐scale grazing × fire trials are prohibitively expensive and impractical to conduct.     

Substrate controls growth rates of the woody pioneer Leptospermum lanigerum colonizing montane grasslands in northern Tasmania

Woody encroachment into grasslands is occurring across the world and is of concern to land managers. Studies of forest–grassland boundaries have informed models describing factors that govern tree establishment and the maintenance and origin of grassland ecosystems. Central to these models is the role of fire relative to ‘bottom up’ resources such as soil and the geological substrate in determining the extent of grassland and forest in the landscape. The view that human lit fires have shaped vegetation across the Australian continent has been bolstered by early 19th century observations of Aboriginal‐set fires in Tasmanian montane grasslands and the documented encroachment of trees into these grasslands in the 20th century. We examined the pattern of lateral encroachment of woolly tea‐tree (Leptospermum lanigerum (Sol. ex Aiton) Sm.) into these grasslands and used tree ring chronologies to investigate (i) past fire activity and (ii) how the geological substrate mediates growth rates of L. lanigerum. Changes in fire regimes inferred from L. lanigerum recruitment were corroborated by historical records. Encroachment (and increases in woody cover) of trees into grasslands was highest on granitic substances, although L. lanigerum growth rates were highest on basalt substrates, followed by conglomerate, granite and Mathinna sediments. Frequent burning up to the 1980s may have stymied the encroachment of trees in grasslands underlain by basalt. Growth rates decreased with increasing distance from the forest edge. This may be due to incremental changes in soil resources, grass competition and/or microclimate. The dynamics between grasslands and forests in montane Tasmania are consistent with tree growth–fire interaction models that highlight the interplay of edaphic factors, growth rates and fire history. Such complexity cautions against generalizations concerning the direct effects of landscape fire in shaping vegetation distribution across Australia.     

Do we know enough about vegetation dynamics to manage fire regimes in central Australia?

Ecologists have long been concerned that contemporary fire regimes of central Australia have poor consequences for some plant species, vegetation communities and the native animals they support. Fire frequency, size and intensity (the ‘fire regime’) have all been implicated in the decline of native biota and in vegetation changes that potentially constitute ecological drift. However, not all perceived declines and changes are quantified or proven. The fire regimes themselves defy quantification and are arguably unknowable. We examine the relationships between fire, vegetation and the physical landscape and consider the adequacy of available knowledge for guiding fire management. Devising targeted ‘fire management regimes’, which take into account vegetation type and management objectives such as pastoral production, conservation and cultural observance, and which actively use fire to achieve those objectives, is a more realistic goal than controlling unquantifiable fire regimes in spatially diverse landscapes.     

Long‐term fire exclusion and ant community structure in an Australian tropical savanna: congruence with vegetation succession

Aim To examine the extent to which succession from tropical savanna to rain forest in the long‐term absence of fire is matched by successional changes in ant communities. This is done by describing ant community responses to 23 years of fire exclusion in a northern Australian tropical savanna, with a particular focus on the extent of colonization by specialist rain forest taxa. Location Solar Village, near Darwin in Australia's Northern Territory. Methods Ants were sampled within 12 plots located inside (‘unburnt’– protected from fire for 23 years) and outside (burnt every 1–2 years) Solar Village in ridge and slope habitat dominated by Eucalyptus spp. The litter, ground‐foraging and arboreal faunas were sampled separately, using Berlese funnels, unbaited pitfall traps and baited pitfall traps attached to tree trunks, respectively. Each species was assigned a forest‐association score ranging from 0 (open savanna species) to 3 (specialist forest species) based on their known habitat preferences in the region. Results A total of 85 ant species from 35 genera were recorded, with multivariate analysis demonstrating distinct litter, ground and arboreal communities. Ant communities also varied substantially with topographic position, which interacted strongly with fire exclusion. A total of 72 species were recorded in burnt habitat, compared with only 45 in unburnt, and the number of ant species records was also about twice as high in burnt compared with unburnt habitat. Fire exclusion has resulted in a dramatic increase in forest‐associated taxa (those occurring in forest and denser, but rarely open, savanna), with such species representing 51% of species records in unburnt habitat compared with 19% in burnt. However, only five specialist forest species were recorded, representing < 1% of total ant records. Main conclusions Fire exclusion at Solar Village has markedly increased the prevalence of forest‐associated ant species, but has led to only very minor incursions by specialist rain forest ant taxa. These responses match very closely those of the vegetation.     

Fire regime shifts affect bird species distributions

Aim Fire is a major driver of ecosystem structure and process, and shifts in fire regimes are implicated in the decline of many species. Shifting fire regimes have been documented around the world, and fire frequency and extent is predicted to increase in many areas because of changes in both climate and land management. Here, we evaluate how predicted increases in fire frequency are likely to impact on species distributions. Location The tropical savannas of northern Australia. Methods We developed distribution models for 44 bird species using the modelling algorithm Maxent. Our models incorporated bird locality records and environmental variables including climate, total fire frequency and the subset of fire frequency occurring late in the dry season. We investigated the effect of increasing total fire frequency and increasing fire late in the dry season, on species distributions by projecting species model algorithms onto scenarios of incrementally increased total fire frequency. Results The probability of presence for most species was higher when fire frequency late in the dry season was low. Species showed a mixed response to an overall increase in total fire frequency, with one‐third predicted to increase in distribution. However, almost all species (98%) showed a decrease in predicted range with increased late‐dry season fire, and species distribution area was generally negatively correlated with an increase in late‐dry season fire. Main conclusions Our study highlighted the array of responses of species to increasing fire frequency and suggested that increased fire frequency late in the dry season is detrimental to most savanna‐restricted bird species. The understanding of individual species’ preferences for particular fire frequencies is important for informed conservation planning.     

Tropical and north Pacific teleconnections influence fire regimes in pine-dominated forests of north-eastern California, USA

Aim To assess the importance of drought and teleconnections from the tropical and north Pacific Ocean on historical fire regimes and vegetation dynamics in north‐eastern California. Location The 700 km² study area was on the leeward slope of the southern Cascade Mountains in north‐eastern California. Open forests of ponderosa pine (Pinus ponderosa var. ponderosa Laws.) and Jeffrey pine (P. jeffreyi Grev. & Balf) surround a network of grass and shrub‐dominated meadows that range in elevation from 1650 to 1750 m. Methods Fire regime characteristics (return interval, season and extent) were determined from crossdated fire scars and were compared with tree‐ring based reconstructions of precipitation and temperature and teleconnections for the period 1700–1849. The effect of drought on fire regimes was determined using a tree‐ring based proxy of climate from five published chronologies. The number of forest‐meadow units that burned was compared with published reconstructions of the El Niño/Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO). Results Landscape scale fires burned every 7–49 years in meadow‐edge forests and were influenced by variation in drought, the PDO and ENSO. These widespread fires burned during years that were dryer and warmer than normal that followed wetter and cooler years. Less widespread fires were not associated with this wet, then dry climate pattern. Widespread fires occurred during El Niño years, but fire extent was mediated by the phase of the PDO. Fires were most widespread when the PDO was in a warm or normal phase. Fire return intervals, season and extent varied at decadal to multi‐decadal time scales. In particular, an anomalously cool, wet period during the early 1800s resulted in widespread fires that occurred earlier in the year than fires before or after. Main conclusions Fire regimes in north‐eastern California were strongly influenced by regional and hemispheric‐scale climate variation. Fire regimes responded to variation that occurred in both the north and tropical Pacific. Near normal modes of the PDO may influence fire regimes more than extreme conditions. The prevalence of widespread teleconnection‐driven fires in the historic record suggests that variation in the Pacific Ocean was a key regulator of fire regimes through its influence on local fuel production and successional dynamics in north‐eastern California.     

Fire history of Araucaria–Nothofagus forests in Villarrica National Park, Chile

Aim In this study we examine fire history (i.e. c. 500 yr bp to present) of Araucaria–Nothofagus forests in the Andes cordillera of Chile. This is the first fire history developed from tree rings for an Araucaria–Nothofagus forest landscape. Location The fire history was determined for the Quillelhue watershed on the north side of Lanin volcano in Villarrica National Park, Chile. The long‐lived Araucaria araucana was commonly associated with Nothofagus pumilio and N. antarctica in more mesic and drier sites respectively. Methods Based on a combination of fire‐scar proxy records and forest stand ages, we reconstructed fire frequency, severity, and the spatial extent of burned areas for an c. 4000 ha study area. We used a composite fire chronology for the purpose of determining centennial‐scale changes in fire regimes and comparing the pre‐settlement (pre‐1883) and post‐settlement fire regimes. In addition, we contrasted Araucaria and Nothofagus species as fire‐scar recorders. Results In the study area, we dated a total of 144 fire‐scarred trees, representing 46 fire years from ad 1446 to the present. For the period from ad 1696 to 2000, using fire dates from Araucaria and Nothofagus species, the composite mean fire interval varied from 7 years for all fires to 62 years for widespread events (i.e. years in which ≥ 25% of recorder trees were scarred). Sensitivity to fire was different for Araucaria and Nothofagus species. More than 98% of the fires recorded by Nothofagus species occurred during the 1900s. The lack of evidence for older fire dates (pre‐1900) in Nothofagus species was due to their shorter longevity and greater susceptibility to being killed by more severe fires. Whereas the thin‐barked N. pumilio and N. antarctica are often destroyed in catastrophic fire events, large and thick‐barked Araucaria trees typically survive. The spatial extent of fires ranged from small patchy events to those that burned more than 40% of the entire landscape (c. > 1500 ha). Main conclusions Fire is the most important disturbance shaping the Araucaria–Nothofagus landscape in the Araucarian region. The forest landscape has been shaped by a mixed‐severity fire regime that includes surface and crown fires. High‐severity widespread events were relatively infrequent (e.g. 1827, 1909 and 1944) and primarily affected tall Araucaria–N. pumilio forests and woodlands dominated by Araucaria–N. antarctica. Although there is abundant evidence of the impact of Euro‐Chilean settlers on the area, the relative influence of this settlement on the temporal pattern of fire could only be tentatively established due to the relatively small number of pre‐1900 fire dates. An apparent increase in fire occurrence is evident in the fire record during Euro‐Chilean settlement (post‐1880s) compared with the Native American era, but it may also be the result of the destruction of evidence of older fires by more recent stand‐devastating fires (e.g. 1909 and 1944). Overall, the severe and widespread fires that burned in Araucaria–Nothofagus forests of this region in 2002, previously interpreted as an ecological novelty, are within the range of the historic fire regimes that have shaped this forested landscape.