Landscape analysis of Aboriginal fire management in Central Arnhem Land, north Australia

Aim To describe the spatial and temporal pattern of landscape burning with increasing distance from Aboriginal settlements. Location Central Arnhem Land, a stronghold of traditional Aboriginal culture, in the Australian monsoon tropics. Methods Geographical information system and global positioning system technologies were used to measure spatial and temporal changes in fire patterns over a one decade period in a 100 × 80 km area that included a cluster of Aboriginal settlements and a large uninhabited area. The major vegetation types were mapped and fire activity was assessed by systematic visual interpretation of sequences of cloud‐free Landsat satellite images acquired in the first (May to July) and second (August to October) halves of the 7‐month dry season. Fire activity in the middle and end of one dry season near an Aboriginal settlement was mapped along a 90‐km field traverse. Canopy scorch height was determined by sampling burnt areas beside vehicle tracks. Results Satellite fire mapping was 90% accurate if the satellite pass followed shortly after a fire event, but the reliability decayed dramatically with increasing time since the fire. Thus the satellite mapping provided a conservative index of fire activity that was unable to provide reliable estimates of the spatial extent of individual fires. There was little landscape fire activity in the first half of the dry season, that was mostly restricted to areas immediately surrounding Aboriginal settlements, with burning of both inhabited and uninhabited landscapes concentrated in the second half of the dry season. The mean decadal fire indices for the three dominant vegetation types in the study area were three in the plateau savanna, two in the sandstone and five in the wet savanna. The spatial and temporal variability of Aboriginal burning apparent in the satellite analyses were verified by field traverse surrounding a single settlement. Fires set by Aborigines had low scorch height of tree crowns reflecting low intensity, despite generally occurring late in the dry season. Conclusions Our findings support the idea that Aboriginal burning created a fine‐scale mosaic of burnt and unburnt areas but do not support the widely held view that Aboriginal burning was focused primarily in the first half of the dry season (before July). The frequency and scale of burning by Aborigines appears to be lower compared with European fire regimes characterized by fires of annual or biennial frequencies that burn large areas. The European fire regime appears to have triggered a positive feedback cycle between fire frequency and flammable grass fuels. The widely advocated management objective of burning in the first half of the dry season burning provides one of the few options to control fires once heavy grass fuel loads have become established, however we suggest it is erroneous to characterize such a regime as reflecting traditional Aboriginal burning practices. The preservation of Aboriginal fire management regimes should be a high management priority given the difficulty in breaking the grass‐fire cycle once it has been initiated.     

Cultural legacies,fire ecology,and environmental change in the Stone Country of Arnhem Land and Kakadu National Park,Australia

We use the fire ecology and biogeographical patterns of Callitris intratropica, a fire‐sensitive conifer, and the Asian water buffalo (Bubalus bubalis), an introduced mega‐herbivore, to examine the hypothesis that the continuation of Aboriginal burning and cultural integration of buffalo contribute to greater savanna heterogeneity and diversity in central Arnhem Land (CAL) than Kakadu National Park (KNP). The ‘Stone Country’ of the Arnhem Plateau, extending from KNP to CAL, is a globally renowned social–ecological system, managed for millennia by Bininj‐Kunwok Aboriginal clans. Regional species declines have been attributed to the cessation of patchy burning by Aborigines. Whereas the KNP Stone Country is a modern wilderness, managed through prescribed burning and buffalo eradication, CAL remains a stronghold for Aboriginal management where buffalo have been culturally integrated. We surveyed the plant community and the presence of buffalo tracks among intact and fire‐damaged C. intratropica groves and the savanna matrix in KNP and CAL. Aerial surveys of C. intratropica grove condition were used to examine the composition of savanna vegetation across the Stone Country. The plant community in intact C. intratropica groves had higher stem counts of shrubs and small trees and higher proportions of fire‐sensitive plant species than degraded groves and the savanna matrix. A higher proportion of intact C. intratropica groves in CAL therefore indicated greater gamma diversity and habitat heterogeneity than the KNP Stone Country. Interactions among buffalo, fire, and C. intratropica suggested that buffalo also contributed to these patterns. Our results suggest linkages between ecological and cultural integrity at broad spatial scales across a complex landscape. Buffalo may provide a tool for mitigating destructive fires; however, their interactions require further study. Sustainability in the Stone Country depends upon adaptive management that rehabilitates the coupling of indigenous culture, disturbance, and natural resources.     

Seasonal patterns in biomass smoke pollution and the mid 20th-century transition from Aboriginal to European fire management in northern Australia

Aim Globally, most landscape burning occurs in the tropical savanna biome, where fire is a characteristic of the annual dry season. In northern Australia there is uncertainty about how the frequency and timing of dry season fires have changed in the transition from Aboriginal to European fire management. Location In the tropical eucalypt savannas that surround the city of Darwin in the northwest of the Northern Territory of Australia. Methods Our study had three parts: (1) we developed a predictive statistical model of mean mass (µg) of particulates 10 µm or less per cubic metre of air (PM₁₀) using visibility and other meteorological data in Darwin during the dry seasons of 2000 and 2004; (2) we tested the model and its application to the broader air shed by (a) matching the prediction of this model to PM₁₀ measurements made in Darwin in 2005, (b) matching the predictions to independent measurements at two locations 20 km to the north and south of Darwin and (c) matching peaks in PM₁₀ to known major fire events in the region (2000–01 dry seasons); and (3) we used the model to explore changes in air quality over the last 50 years, a period that spans the transition from Aboriginal to European land management. Results We demonstrated that visibility data can be used reliably as a proxy for biomass burning across the largely uncleared tropical savannas inland of Darwin. Validations using independent measurements demonstrated that our predictive model was robust, and geographically and temporally representative of the regional airshed. We used the model to hindcast and found that seasonal air quality has changed since 1955, with a trend to increasing PM₁₀ concentrations in the early dry season. Main conclusions The results suggest that the transition from Aboriginal to European land management has been associated with an increase in fire activity in the early months of the dry season.     

Differing impact of a major biogeographic barrier on genetic structure in two large kangaroos from the monsoon tropics of Northern Australia

Tropical savannas cover 20–30% of the world's land surface and exhibit high levels of regional endemism, but the evolutionary histories of their biota remain poorly studied. The most extensive and unmodified tropical savannas occur in Northern Australia, and recent studies suggest this region supports high levels of previously undetected genetic diversity. To examine the importance of barriers to gene flow and the environmental history of Northern Australia in influencing patterns of diversity, we investigated the phylogeography of two closely related, large, vagile macropodid marsupials, the antilopine wallaroo (Macropus antilopinus; n = 78), and the common wallaroo (Macropus robustus; n = 21). Both species are widespread across the tropical savannas of Australia except across the Carpentarian Barrier (CB) where there is a break in the distribution of M. antilopinus. We determined sequence variation in the hypervariable Domain I of the mitochondrial DNA control region and genotyped individuals at 12 polymorphic microsatellite loci to assess the historical and contemporary influence of the CB on these species. Surprisingly, we detected only limited differentiation between the disjunct Northern Territory and Queensland M. antilopinus populations. In contrast, the continuously distributed M. robustus was highly divergent across the CB. Although unexpected, these contrasting responses appear related to minor differences in species biology. Our results suggest that vicariance may not explain well the phylogeographic patterns in Australia's dynamic monsoonal environments. This is because Quaternary environmental changes in this region have been complex, and diverse individual species’ biologies have resulted in less predictable and idiosyncratic responses.     

Aboriginal Resource Utilization and Fire Management Practice in Western Arnhem Land, Monsoonal Northern Australia: Notes for Prehistory, Lessons for the Future

This paper considers traditional resources and fire management practices of Aboriginal people living in a near-coastal region of western Arnhem Land, monsoonal northern Australia. The data illustrate that before the arrival of Europeans freshwater floodplains and riverine habitats provided the major proportion of food resources over much of the seasonal cycle. By contrast, the extensive lowland woodlands and open forests, the sparser vegetation of the Arnhem Land escarpment and plateau, and the generally small patches of rain forest (jungle), provided relatively few resources, although jungle yams were of critical importance through the relatively lean wet season. The paper then considers burning as a management tool through the seasonal cycle. In broad terms, burning commenced in the early dry season and was applied systematically and purposefully over the landscape. Burning in the late dry season was undertaken with care, and resumed in earnest with the onset of the first storms of the new wet season, particularly on floodplains. These general patterns of resource use and fire management are shown to have applied widely over much of near-coastal northern Australia. The implications of these data for prehistory and for contemporary land management practices in the region, are considered. It is suggested that pre-European patterns of fire management in the region are likely to have been practiced only over the past few thousand years, given the development of abundant food resources in the late Holocene. It is shown that traditional burning practice offers a generally useful, conservative model for living in and managing a highly fire-prone savanna environment.     

Munmarlary revisited: Response of a north Australian Eucalyptus tetrodonta savanna protected from fire for 20 years

Abstract A comparison was made between the total density of tree species recorded on three 1 ha plots that have been protected from fire for 20 years, and from three surrounding sites that have been subjected to the ambient fire regime. Both unburnt plots and ambient sites were in a lowland coastal Eucalyptus tetrodonta savanna in Kakadu National Park. Fire protection resulted in a substantial increase in the number of saplings (16 times more than ambient), poles (five times more than ambient) and trees (2. 5 times more than ambient), but slightly fewer (7%) sprouts than ambient. Of the 32 species recorded in the six 0. 2 ha samples, only nine species could legitimately be analysed using Chi-squared analysis to test for differences in the density of sprouts and saplings between unburnt and ambient samples; eight of these species had significantly different distributions. Typically the unburnt samples had a greater number of saplings compared to ambient conditions, but fewer sprouts. Eucalyptus miniata showed no significant difference in the density of sprouts and saplings between the unburnt and ambient samples. Chi-squared analyses of the frequency distribution among four size classes (sprouts, saplings, poles and trees) was possible for six species. The results for five of these species mirrored the findings of the comparison between sprouts and saplings. However, the fan palm Livistona humilus, which typically forms a component of the mid-layer in E. tetrodonta savannas, was found to have a large number of sprouts on the unburnt samples and a complete absence of stems in any of the other size classes. Dead L. humilus stems attested to the former occurrence of larger size classes of this species on the unburnt plots. No rainforest species were recorded in the unburnt samples. Minor differences in species composition between unburnt and ambient samples are thought to reflect sampling effects. The results of this study are consistent with the conclusions of an earlier study at the same site which also concluded that rainforest tree species do not readily colonize unburnt Eucalyptus savanna.     

Frequent fires reduce tree growth in northern Australian savannas: implications for tree demography and carbon sequestration

Tropical savannas are typically highly productive yet fire‐prone ecosystems, and it has been suggested that reducing fire frequency in savannas could substantially increase the size of the global carbon sink. However, the long‐term demographic consequences of modifying fire regimes in savannas are difficult to predict, with the effects of fire on many parameters, such as tree growth rates, poorly understood. Over 10 years, we examined the effects of fire frequency on the growth rates (annual increment of diameter at breast height) of 3075 tagged trees, at 137 locations throughout the mesic savannas of Kakadu, Nitmiluk and Litchfield National Parks, in northern Australia. Frequent fires substantially reduced tree growth rates, with the magnitude of the effect markedly increasing with fire severity. The highest observed frequencies of mild, moderate and severe fires (1.0, 0.8 and 0.4 fires yr^?1, respectively) reduced tree growth by 24%, 40% and 66% respectively, relative to unburnt areas. These reductions in tree growth imply reductions in the net primary productivity of trees by between 0.19 t C ha^?1 yr^?1, in the case of mild fires, and 0.51 t C ha^?1 yr^?1, in the case of severe fires. Such reductions are relatively large, given that net biome productivity (carbon sequestration potential) of these savannas is estimated to be just 1–2 t C ha^?1 yr^?1. Our results suggest that current models of savanna tree demography, that do not account for a relationship between severe fire frequency and tree growth rate, are likely to underestimate the long‐term negative effects of frequent severe fires on tree populations. Additionally, the negative impact of frequent severe fires on carbon sequestration rates may have been underestimated; reducing fire frequencies in savannas may increase carbon sequestration to a greater extent than previously thought.     

Predicting savanna vegetation structure on the basis of plant available moisture (PAM) and plant available nutrients (PAN): a case study from Australia

The use of the plant available moisture (PAM)/plant available nutrients (PAN) concept to compare savanna structure was examined using data from twenty Australian sites. Above-ground biomass was regressed on various combinations of seventeen different estimates of PAM (plant available moisture) and two estimates of PAN (plant available nutrients). The ratios of actual transpirational loss from the subsoil to potential evapotranspiration (PET), and total annual rainfall to PET, were most highly correlated with total biomass. Grass biomass is poorly predicted by PAM on its own, and requires inclusion of woody leaf biomass in the regression. PAN had little effect on total biomass, although it is likely to be important for other, functional aspects of vegetation. The woody : grass ratio is best predicted by an index involving the ratio of subsoil : topsoil moisture. For biomass comparisons the use of a detailed water-balance model to estimate PAM is not warranted.     

The responses of small mammals to patches regenerating after fire and rainfall in the Simpson Desert,central Australia

Abstract Patch‐burning is frequently advocated as a management tool to enhance the biodiversity and pasture values of spinifex (Triodia) grasslands. In this study we compare the capture rates of small mammals in habitats regenerating shortly after fire (aged 1–5 years) and in long‐unburnt habitats (aged >25 years). To unravel the effects of temporally and spatially variable rainfall on capture rates, the study was replicated at three locations spaced over 50 km apart that experience different rainfall regimes. Ten species of small mammals were captured over the course of the study, between October 1999 and June 2001. Pseudomys desertor showed a strong preference for long‐unburnt habitats. Notomys alexis, Sminthopsis youngsoni and Sminthopsis hirtipes showed some preferences for regenerating habitats, but these were not consistent throughout the study. Factors indicative of temporal and spatial variation in rainfall, time and site had important effects on capture rates. High rainfalls associated with the La Niña phase of the El Niño/Southern Oscillation in 2000 increased seed production and prompted eruptions of rodent species and the carnivorous Dasycercus cristicauda. The greatest numbers of captures were made at the sites that received the highest rainfalls. We conclude that patch‐burning regimes do not benefit small mammals directly, but are likely to increase the resilience of ‘fire‐sensitive’ species that are dependent on dense spinifex by reducing the extent of wildfires.     

Contemporary landscape burning patterns in the far North Kimberley region of north-west Australia: human influences and environmental determinants

Aim This study of contemporary landscape burning patterns in the North Kimberley aims to determine the relative influences of environmental factors and compare the management regimes occurring on Aboriginal lands, pastoral leases, national park and crown land. Location The study area is defined at the largest scale by Landsat Scene 108–70 that covers a total land area of 23,134 km² in the North Kimberley Bioregion of north‐west Australia, including the settlement of Kalumburu, coastline between Vansittart Bay in the west and the mouth of the Berkeley River in the east, and stretching approximately 200 km inland. Methods Two approaches are applied. First, a 10‐year fire history (1990–1999) derived from previous study of satellite (Landsat‐MSS) remote sensing imagery is analysed for broad regional patterns. And secondly, a 2‐year ground‐based survey of burning along major access roads leading to an Aboriginal community is used to show fine‐scale burning patterns. anova and multiple regression analyses are used to determine the influence of year, season, geology, tenure, distance from road and distance from settlement on fire patterns. Results Satellite data indicated that an average of 30.8% (±4.4% SEM) of the study area was burnt each year with considerable variability between years. Approximately 56% of the study area was burnt on three or more occasions over the 10‐year period. A slightly higher proportion of burning occurred on average in the late dry season (17.2 ± 3.6%), compared with the early dry season (13.6 ± 3.3%). The highest fire frequency occurred on basalt substrates, on pastoral tenures, and at distances 5–25 km from roads. Three‐way anova demonstrated that geological substrate and land use were the most significant factors influencing fire history, however a range of smaller interactions were also significant. Analysis of road transects, originating from an Aboriginal settlement, showed that the timing of fire and geology type were the most significant factors affecting the pattern of area burnt. Of the total transect area, 28.3 ± 2.9% was burnt annually with peaks in burning occurring into the dry season months of June, August and September. Basalt uplands (81.2%) and lowlands (30.1%) had greater areas burnt than sandstone (12.3%) and sands (17.7%). Main conclusions Anthropogenic firing is constrained by two major environmental determinants; climate and substrate. Seasonal peaks in burning activity in both the early and late dry season relate to periods of optimal fire‐weather conditions. Substrate factors (geology, soils and physiognomy) influence vegetation‐fuel characteristics and the movement of fire in the landscape. Basalt hills overwhelmingly supported the most frequent wildfire regime in the study region because of their undulating topography and relatively fertile soils that support perennial grasslands. Within these spatial and temporal constraints people significantly influenced the frequency and extent of fire in the North Kimberley thus tenure type and associated land uses had a significant influence on fire patterning. Burning activity is high on pastoral lands and along roads and tracks on some tenure types. While the state government uses aerial control burning and legislation to try to restrict burning to the early dry season across all geology types, in practice burning is being conducted across the full duration of the dry season with early dry season burning focused on sandstone and sand substrates and late dry season burning focused on basalt substrates. There is greater seasonal and spatial variation in burning patterns on landscapes managed by Aboriginal people.     

Contrasting demographics of tropical savanna and temperate forest eucalypts provide insight into how savannas and forests function. A case study using Corymbia clarksoniana from north‐eastern Australia

Eucalypts (Eucalyptus spp. and Corymbia spp.) dominate many communities across Australia, including frequently burnt tropical savannas and temperate forests, which receive less frequent but more intense fires. Understanding the demographic characteristics that allow related trees to persist in tropical savannas and temperate forest ecosystems can provide insight into how savannas and forests function, including grass–tree coexistence. This study reviews differences in critical stages in the life cycle of savanna and temperate forest eucalypts, especially in relation to fire. It adds to the limited data on tropical eucalypts, by evaluating the effect of fire regimes on the population biology of Corymbia clarksoniana, a tree that dominates some tropical savannas of north‐eastern Australia. Corymbia clarksoniana displays similar demographic characteristics to other tropical savanna species, except that seedling emergence is enhanced when seed falls onto recently burnt ground during a high rainfall period. In contrast to many temperate forest eucalypts, tropical savanna eucalypts lack canopy‐stored seed banks; time annual seed fall to coincide with the onset of predictable wet season rain; have very rare seedling emergence events, including a lack of mass germination after each fire; possess an abundant sapling bank; and every tropical eucalypt species has the ability to maintain canopy structure by epicormically resprouting after all but the most intense fires. The combination of poor seedling recruitment strategies, coupled with characteristics allowing long‐term persistence of established plants, indicate tropical savanna eucalypts function through the persistence niche rather than the regeneration niche. The high rainfall‐promoted seedling emergence of C. clarksoniana and the reduction of seedling survival and sapling growth by fire, support the predictions that grass–tree coexistence in savannas is governed by rainfall limiting tree seedling recruitment and regular fires limiting the growth of juvenile trees to the canopy.     

Ecology and biogeography in 3D: The case of the Australian Proteaceae

The key biophysical pressures shaping the ecology and evolution of species can be broadly aggregated into three dimensions: environmental conditions, disturbance regimes and biotic interactions. The relative importance of each dimension varies over time and space, and in most cases multiple dimensions need to be addressed to adequately understand the habitat and functional traits of species at broad spatial and phylogenetic scales. However, it is currently common to consider only one or two selective pressures even when studying large clades. We illustrate the importance of the all‐inclusive multidimensional approach with reference to the large and iconic plant family, Proteaceae: we review life‐history traits related to these three dimensions for the 46 genera occurring in Australia and show that this family can be considered the product of a long history of harsh environments, recurrent fires and strong faunal interactions. Because most Proteaceae species occur in fire‐prone ecosystems and possess fire‐adaptive traits that are both ancient and essential for their survival, disturbance by fire is likely to explain much of this family's ecology, evolution and distribution. Approaches that only examine prevailing environmental variables may fail to identify the mechanisms that drive a taxon's biogeography; they need to consider the likely mechanisms of adaptation and accept or reject plausible alternative hypotheses as the evidence allows. As multidisciplinary teams that consider all aspects of a taxon's ecology are assembled, and databases and numerical tools become increasingly available, studies on the ecology, biogeography and diversity of organisms at broader spatial and phylogenetic scales will arrive at more realistic conclusions.     

Holocene boundary dynamics of a northern Australian monsoon rainforest patch inferred from isotopic analysis of carbon, (14C and δ13C) and nitrogen (δ15N) in soil organic matter

Abstract Soil organic matter (SOM) was sampled from lateritic soil profiles across an abrupt eucalypt savanna–monsoon rainforest boundary on the north coast of Croker Island, northern Australia. Accelerator mass spectrometry dating revealed that SOM that had accumulated at the base of these 1.5 m profiles had a radiocarbon age of about 5000 years. The mean carbon and nitrogen stable isotope composition of SOM from 10 cm deep layers from the surface, middle and base of three monsoon rainforest soil profiles was significantly different from the means for these layers in three adjacent savanna soil profiles, suggesting the isotopic ‘footprint’ of the vegetation boundary has been stable since the mid Holocene. Although there were no obvious environmental discontinuities associated with the boundary, the monsoon rainforest was found to occur on significantly more clay rich soils than the surrounding savanna. Tiny fragments of monsoon rainforest and abandoned ‘nests’ (large earthen mounds) of the orange‐footed scrubfowl, an obligate monsoon rainforest species, occurred in the savanna, signalling that the rainforest was once more extensive. Despite episodic disturbances, such as tropical storm damage and fires, the stability of the boundary is probably maintained because clay rich soils enable monsoon rainforest tree species to grow rapidly and achieve canopy closure, thereby excluding grass and reducing the risk of fire. Conversely, slower tree growth rates, grass competition and fire on the savanna soils would impede the expansion of the rainforest although high rainfall periods with shorter dry seasons may enable rainforest trees to grow sufficiently quickly to colonize the savanna successfully.     

Distribution and abundance of large herbivores in a northern Australian tropical savanna: A multi‐scale approach

Australian mammals have exhibited exceptionally high rates of decline since European settlement 230 years ago with much focus on small mammals in northern tropical savannas. In these systems, little scientific attention has been given to the suite of grazing macropods, family Macropodidae, (common wallaroo (Osphranter robustus), antilopine wallaroo (O. antilopinus) and agile wallaby (Notamacropus agilis)). These species may be impacted by feral herbivores and contemporary fire regimes, two threats linked to small mammal declines. A multi‐scale approach using aerial surveys, road surveys and camera trapping was utilised to determine the effects of feral cattle and fire on the distribution and abundance of large macropods in the North Kimberley bioregion. Feral cattle density and biomass exceeded that of macropods regardless of survey technique. Density estimates for cattle were up to 125 times higher (0.3–10.0 km^?2) than estimates for macropods (0.08–0.49 km^?2). Cattle biomass, based on the aerial survey estimates (corrected for perception bias), were 15 and 95 times higher than macropods for infertile (279 vs. 19 kg km^?2) and fertile savannas (518 vs. 5 kg km^?2), respectively. Proximity to the nearest pastoral station was a significant predictor of the aerial sightings of feral cattle (P ≤ 0.05). Abundance and foraging activity of cattle were positively associated (P ≤ 0.05) with recently burnt areas. In contrast, camera trapping showed agile wallaby and wallaroo occurrence and foraging were associated with longer unburnt areas (P ≤ 0.05). Agile wallaby and wallaroo were negatively associated with cattle (P ≤ 0.05) and showed substantial diurnal and seasonal separation consistent with an antagonistic interspecific interaction. Results also suggest that the agile wallaby is the primary prey of the dingo, not wallaroo. Collectively, this study suggests that recent landscape changes such as altered fire regimes and introduced herbivores have negatively impacted large grazing macropod species.     

Spatial subdivision among assemblages of Spanish mackerel, Scomberomorus commerson (Pisces: Scombridae) across northern Australia: implications for fisheries management

Aim This study investigated the use of stable δ¹³C and δ¹⁸O isotopes in the sagittal otolith carbonate of narrow‐barred Spanish mackerel, Scomberomorus commerson, as indicators of population structure across Australia. Location Samples were collected from 25 locations extending from the lower west coast of Western Australia (30°), across northern Australian waters, and to the east coast of Australia (18°) covering a coastline length of approximately 9500 km, including samples from Indonesia. Methods The stable δ¹³C and δ¹⁸O isotopes in the sagittal otolith carbonate of S. commerson were analysed using standard mass spectrometric techniques. The isotope ratios across northern Australian subregions were subjected to an agglomerative hierarchical cluster analysis to define subregions. Isotope ratios within each of the subregions were compared to assess population structure across Australia. Results Cluster analysis separated samples into four subregions: central Western Australia, north Western Australia, northern Australia and the Gulf of Carpentaria and eastern Australia. Isotope signatures for fish from a number of sampling sites from across Australia and Indonesia were significantly different, indicating population separation. No significant differences were found in otolith isotope ratios between sampling times (no temporal variation). Main conclusions Significant differences in the isotopic signatures of S. commerson demonstrate that there is unlikely to be any substantial movement of fish among these spatially discrete adult assemblages. The lack of temporal variation among otolith isotope ratios indicates that S. commerson populations do not undergo longshore spatial shifts in distribution during their life history. The temporal persistence of spatially explicit stable isotopic signatures indicates that, at these spatial scales, the population units sampled comprise functionally distinct management units or separate ‘stocks’ for many of the purposes of fisheries management. The spatial subdivision evident among populations of S. commerson across northern and western Australia indicates that it may be advantageous to consider S. commerson population dynamics and fisheries management from a metapopulation perspective (at least at the regional level).     

Corticolous lichens as potential bioindicators of fire history: a study in the cerrado of the Distrito Federal, central Brazil

Abstract. The aim of this study was to investigate the potential use of epiphytic corticolous lichens as indicators of fire history in the cerrado (savannas) of central Brazil. Work was carried out at the Reserva Ecológica do IBGE and the Jardim Botânico de Brasilia, 33 km outside Brasilia D.F., in ten plots of cerrado denso within the ‘Fire Project’ area. Each plot was subjected to a specific prescribed burning regime, with study sites varying from a plot protected from fire for over 20 years to a plot burned every 2 years. Research was carried out in two stages: (1) a preliminary survey of plots with different fire histories, measuring variables about the lichen habitat and the lichen communities present in the habitats; (2) lichen sampling in plots with different fire histories, where collection and identification of lichen species took place. Field techniques used included plotless sampling, and identification of lichens was carried out using taxonomic keys, both in the field and in the laboratory. The results show that fire is a major determinant of epiphytic corticolous lichen communities in cerrado denso vegetation. The abundance, distribution and recolonization of lichen communities can clearly be correlated with the frequency and behaviour, in terms of homogeneity and flame heights, of the fires that have occurred in each of the plots surveyed. Particular lichen species also show differential sensitivities to fire frequency and behaviour. This study shows that responses of corticolous lichens, at both the community and species level, can be used as bioindicators of fire history in areas of cerrado denso vegetation in central Brazil.