Search

Over the Austral spring and summer of 2019/20 > 7 million ha of Eucalyptus forest and woodland, including some of Australia's most carbon dense ecosystems, were burnt on the east coast of Australia. We estimated bootstrapped mean CO2 emissions of c. 0.67 Pg, with other available estimates ranging from 0.55 to 0.85 Pg. Eucalyptus forests are renowned for their ability to resist and recover from wildfire so it would be expected that emitted CO2 will be reabsorbed. The combination of drought and frequent fires is likely reducing the capacity to recover from the fire so future Australian forests may store less carbon. Broadscale prescribed burning is a widely promoted approach to reduce uncontrolled wildfires, yet the benefits for the management of carbon stores are controversial. Prescribed burning can reduce carbon losses from subsequent wildfire, yet the "carbon costs" of it may equal or outweigh the "carbon benefits" in reduced wildfire emissions. Likewise, mechanical thinning of vegetation to reduce fuel loads also carries heavy carbon costs with uncertain carbon benefits. Research involving empirical measurements, modelling and a mix of large‐scale management intervention is urgently required to determine what interventions can maximise carbon storage in the face of climate change‐driven fires. In this Invited Review, we briefly describe the geographic scale of the 2019/20 Australian Black Summer Fires and undertake a quasi‐estimate of CO2 emissions from these fires. Although it is assumed the CO2 will be reabsorbed by post‐fire regrowth, we review evidence that this may not be the case because of climate change. We consider possible management interventions to reduce carbon losses from fires and reflect on the carbon costs and benefits of these management approaches. We conclude by highlighting the need for a much better understanding of fire‐driven carbon dynamics in Australian Eucalyptus forests to underpin future management. [ABSTRACT FROM AUTHOR]

Australian savannas lack native megaherbivores (>500 kg body mass), but since the commencement of European colonisation in the 19th century bovine livestock, such as cattle (Bos sp.) and water buffalo (Bubalus bubalis), have established large feral populations that continue to geographically expand. The largest extant native herbivores are marsupials in the family Macropodidae (henceforth 'macropods': common wallaroo, Osphranter robustus [c. 40 kg]; antilopine wallaroo, O. antilopinus [c. 35 kg] and agile wallaby, Notamacropus agilis [c. 20 kg]). These species occur at low densities, with evidence that some species are in decline, the cause of which remains uncertain. We tested the hypothesis that bovines and macropods compete for nutritious forage in the North Kimberley, Western Australia by using carbon isotope analysis of feral cattle and native macropod dung (as a proxy for the relative contribution of C4 grass to their diet) and nutrient analysis of standing herbaceous biomass. Grass consumption varied between macropod species and was highest in larger wallaroo species and lowest in the smaller agile wallaby reflecting its broader diet. Grass consumption by wallaroos was maximal on fertile sites. The relative abundance of grass in the diet of cattle was lowest in the middle of the dry season with an interaction between fire and substrate fertility where grass consumption was highest on fertile sites, particularly those recently burnt. Grass consumption by cattle and wallaroos was negatively correlated with fibre content of live biomass, which was lowest on fertile and burnt sites. Introduced bovines shift their diets to non‐grasses as quality of herbaceous biomass declines with increasing fibre content, and by contrast, the largest macropod herbivores do not have this dietary flexibility. We conclude a plausible mechanism for the success of bovines and the decline of large macropods in Australian savannas is competition for nutritious grass that is abundant immediately after fire. [ABSTRACT FROM AUTHOR]

Aims To detect changes in area and vegetation dynamics of monsoon rain forests in relation to disturbance and an observed wetting trend. Location The Mitchell Plateau and the Bougainville Peninsula (north Kimberley, Australia). Methods Geo-rectified aerial photographs acquired in 1949 and 1969 and a pre-existing map from 2005 were used to detect changes in rain forest boundaries. To ground-truth rain forest expansion, we established 20 transects running across rain forest-savanna boundaries and recorded plant species, stand basal area, grass and rock cover, cattle impact, and canopy cover. Generalised linear models and Akaike's information criterion were used to detect differences in these variables between locations. Results On the Bougainville Peninsula average fire frequency was low (0.11 per year) and cattle entirely absent, while on the Mitchell Plateau average fire frequency was high (0.58 per year), and cattle were common and associated with lower seedling density in savannas. Rain forests expanded more on the Bougainville Peninsula (69%), where patches were bigger and more convoluted, than on the Mitchell Plateau (9%). Rain forest expansion was positively associated with rainfall and topographic complexity, and on level terrain it occurred only on the Bougainville Peninsula. Rain forests were floristically and structurally similar in the two locations, while savannas on the Bougainville Peninsula had denser vegetation and more abundant rain forest elements. The frequency distribution of canopy cover was bimodal on the Mitchell Plateau, signalling the presence of two distinct vegetation states, and unimodal on the Bougainville Peninsula, consistent with the blending of the two states. Main conclusions Wetting trends are likely strong drivers of rain forest expansion, but at a landscape scale their effect is probably modulated by fire activity and the presence of mega-herbivores, which may also be pivotal in maintaining sharp floristic and structural distinctions between rain forests and savannas. [ABSTRACT FROM AUTHOR]

Alternative stable-state theory (ASS) is widely accepted as explaining landscape-level vegetation dynamics, such as switches between forest and grassland. This theory argues that webs of feedbacks stabilise vegetation composition and structure, and that abrupt state shifts can occur if stabilising feedbacks are weakened. However, it is difficult to identify stabilising feedback loops and the disturbance thresholds beyond which state changes occur. Here, we argue that doing this requires a synthetic approach blending observation, experimentation, simulation, conceptual models, and narratives. Using forest boundaries and large mammal extinctions, we illustrate how a multifaceted research program can advance understanding of feedback-driven ecosystem change. Our integrative approach has applicability to other complex macroecological systems controlled by numerous feedbacks where controlled experimentation is impossible. [ABSTRACT FROM AUTHOR]

Fire is an ancient influence on the Earth system, affecting biogeochemical cycles and ecosystems. Humans have had a profound influence on global fire activity through setting and controlling fires, modifying the flammability of landscapes, and, more recently, changing the climate through the combustion of fossil fuels. We review this web of complex direct and indirect effects of fire on Earth using the framework provided by the emerging discipline of pyrogeography that unites biological, atmospheric, and social perspectives on fire. We describe the transition from fire activity before humans evolved, through the hunter-gatherer and agricultural phases, to the current period in Earth history dominated by industrialization (Anthropocene). We illustrate how pyrogeography provides the necessary framework to understand fire in the Anthropocene, including the management of pyrogenic emissions, protection of human life, conservation of biodiversity, and provision of ecosystem services. [ABSTRACT FROM AUTHOR]

Abstract: Pricing greenhouse gas emissions is a burgeoning and possibly lucrative financial means for climate change mitigation. Emissions pricing is being used to fund emissions-abatement technologies and to modify land management to improve carbon sequestration and retention. Here we discuss the principal land-management options under existing and realistic future emissions-price legislation in Australia, and examine them with respect to their anticipated direct and indirect effects on biodiversity. The main ways in which emissions price-driven changes to land management can affect biodiversity are through policies and practices for (1) environmental plantings for carbon sequestration, (2) native regrowth, (3) fire management, (4) forestry, (5) agricultural practices (including cropping and grazing), and (6) feral animal control. While most land-management options available to reduce net greenhouse gas emissions offer clear advantages to increase the viability of native biodiversity, we describe several caveats regarding potentially negative outcomes, and outline components that need to be considered if biodiversity is also to benefit from the new carbon economy. Carbon plantings will only have real biodiversity value if they comprise appropriate native tree species and provide suitable habitats and resources for valued fauna. Such plantings also risk severely altering local hydrology and reducing water availability. Management of regrowth post-agricultural abandonment requires setting appropriate baselines and allowing for thinning in certain circumstances, and improvements to forestry rotation lengths would likely increase carbon-retention capacity and biodiversity value. Prescribed burning to reduce the frequency of high-intensity wildfires in northern Australia is being used as a tool to increase carbon retention. Fire management in southern Australia is not readily amenable for maximising carbon storage potential, but will become increasingly important for biodiversity conservation as the climate warms. Carbon price-based modifications to agriculture that would benefit biodiversity include reductions in tillage frequency and livestock densities, reductions in fertiliser use, and retention and regeneration of native shrubs; however, anticipated shifts to exotic perennial grass species such as buffel grass and kikuyu could have net negative implications for native biodiversity. Finally, it is unlikely that major reductions in greenhouse gas emissions arising from feral animal control are possible, even though reduced densities of feral herbivores will benefit Australian biodiversity greatly. [Copyright &y& Elsevier]

Ecology Letters (2012) 15: 748-758 Abstract Forest and savanna biomes dominate the tropics, yet factors controlling their distribution remain poorly understood. Climate is clearly important, but extensive savannas in some high rainfall areas suggest a decoupling of climate and vegetation. In some situations edaphic factors are important, with forest often associated with high nutrient availability. Fire also plays a key role in limiting forest, with fire exclusion often causing a switch from savanna to forest. These observations can be captured by a broad conceptual model with two components: (1) forest and savanna are alternative stable states, maintained by tree cover-fire feedbacks, (2) the interaction between tree growth rates and fire frequency limits forest development; any factor that increases growth (e.g. elevated availability of water, nutrients, CO2), or decreases fire frequency, will favour canopy closure. This model is consistent with the range of environmental variables correlated with forest distribution, and with the current trend of forest expansion, likely driven by increasing CO2 concentrations. Resolving the drivers of forest and savanna distribution has moved beyond simple correlative studies that are unlikely to establish ultimate causation. Experiments using Dynamic Global Vegetation Models, parameterised with measurements from each continent, provide an important tool for understanding the controls of these systems. [ABSTRACT FROM AUTHOR]

Abstract: Massive environmental changes have occurred since European settlement of Australia more than 200 years ago. We examined the demographics of Callitris columellaris F. Muell. (Cupressaceae) across Australia as a potential bio-indicator of environmental change. This species is a widespread obligate seeder with large reproductive potential but is sensitive to fire and herbivory. We measured variation in tree size, stem density, basal area, and seedling recruitment among 90 sites that encompassed a wide range of climates and landscape settings across Australia. Soils from each site were analysed for pH, %C, % N and %P. We also noted evidence of fire and herbivory. Climate at each site was classified as tropical, temperate or arid. Case studies and published literature are used to illustrate the contrasting effects of disturbance in the three climate zones. Climate had a strong influence on stand basal area, density of juveniles and proportions of seedlings and saplings in a population, as well as on prevailing disturbance regimes. Structure of Callitris populations was not strongly associated with soil fertility. In the arid zone overall, and in many individual populations, there were relatively few juveniles and evidence of a chronic recruitment deficit during the last 100–200 years, consistent with reported adverse effects of introduced herbivores on Callitris regeneration. By contrast, most tropical and temperate populations conformed to a negative exponential distribution, consistent with frequent regeneration. Many temperate sites showed extremely dense juvenile populations. In the tropics, juvenile density is lower, probably because of frequent, relatively mild fires that kill many juveniles but few adult trees. We conclude that C. columellaris is a sensitive bio-indicator, and is in decline across much of arid Australia, reflecting the inherent vulnerability of ecosystems in regions with low productivity. [Copyright &y& Elsevier]

Georeferenced digital aerial photographs were used to assess changes in overstorey vegetation cover since 1948 in the Victoria River District, Northern Territory, Australia, across a range of lowland tropical savanna habitats and with explicit consideration of known and variable site-specific grazing and fire management histories. Vegetation surveys at corresponding locations on the ground identified five distinct woody vegetation communities defined primarily by water drainage and secondarily by soil characteristics. Air-photo analyses revealed that, contrary to popular perceptions and in contrast to results from other habitats, there has been no generalized net increase in overstorey woody vegetation cover across the full range of lowland savanna habitats. Rather, different habitats exhibited distinctly different vegetation change mechanisms: low-lying seasonally inundated‘wet’ habitats have experienced woody vegetation increase since 1948, whereas well-drained‘dry’ habitats have experienced overstorey vegetation stability or loss. In almost every instance woody vegetation increase could be attributed to the invasion or proliferation of a single species,Melaleuca minutifoliaF.Muell. The extent ofM. minutifoliaincrease was unrelated to historical grazing/fire regime. Demographic analyses for this species revealed that recruitment was often episodic and that synchronized recruitment events occurred uniformly across the full range of historical management treatments, most likely as a consequence of favourable climatic conditions in years with an extended wet season. Heavy grazing facilitated juvenile survival and/or recruitment, most likely by reducing grassy fuel loads and eliminating landscape fire. We conclude that while there has been no generalized net increase in overstorey woody vegetation cover in lowland environments, savanna dynamics are complex, and multiple change mechanisms have occurred simultaneously in different habitats, some of which have been significantly transformed since 1948. Where net woody vegetation increase has occurred it is primarily a natural consequence of episodicM. minutifoliaestablishment in climatically favourable years, but the extent and magnitude of this effect is likely mediated by fire/grazing regime. [ABSTRACT FROM AUTHOR]

• Tasmanian subspecies of E. delegatensis recovers from fire by epicormic resprouts. • By contrast, the mainland Australian subspecies is a post-fire obligate seeder. • Tasmanian subspecies has greater resilience to fire than mainland subspecies. • Stems < 20-cm diameter of the Tasmanian subspecies are vulnerable to fire kill. • Risk of regeneration failure for several decades in clear-felled Tasmanian forests. Eucalyptus delegatensis is native to the Australian Alps (subsp. delegatensis) and montane Tasmania (subsp. tasmaniensis). Post-fire regeneration mechanisms of the obligate-seeder subspecies on the Australian mainland are well-known, but less is known about the resprouter Tasmanian subspecies. In January 2016, large tracts of Eucalyptus delegatensis forests in central Tasmania, logged at different intensities, were burnt by low- and high-severity fire. We used statistical modelling to understand how tree survival, vegetative regeneration and seedling recruitment differed according to understorey type, fire severity, logging intensity and tree size (DBH). Fire severity, defined as unburnt, low-severity (fire scarring on the stem and/or lower canopy burnt) and high-severity (full canopy burnt), affected tree survival: 84% of trees were alive in unburnt transects, compared with 43% in low-severity transects and 36% in high-severity transects. Epicormic resprouting was the dominant mode of vegetative recovery, with < 1% of total trees recovering solely by basal resprouting. Fire severity significantly affected epicormic resprouting, with 70% of live stems resprouting post-fire in low-severity transects and 99% in high-severity transects, compared with 4% in unburnt transects. Tree survival was strongly influenced by tree size: in high-severity transects, 24% of trees with DBH < 20 cm were alive, compared with 88% of trees with DBH ≥ 20 cm. These differences in survival were primarily because large trees were more likely to resprout epicormically, with epicormic shoots present on 24% of live trees with DBH < 20 cm, compared with 79% of live trees with DBH ≥ 80 cm. The strong effect of tree size renders clear-felled forests especially vulnerable to fire during the several decades when all the regenerating trees are small (DBH < 20 cm). Seedling recruitment was uncommon, independent of understorey type and logging intensity, but with higher occurrence on high-severity (54%) than low-severity (19%) or unburnt (15%) transects. When present, seedling densities were typically low: median = 400 and maximum = 4·104 seedlings ha−1. This study highlights that mature forests of Eucalyptus delegatensis in Tasmania are more resilient (able to return to pre-disturbance conditions) to single high-severity fires than their mainland counterparts, because they can recover more quickly through epicormic resprouting. However, clear-felling reduces this resilience for several decades because it decreases median tree size and, hence, leads to higher post-fire mortality. It is difficult to predict how the Tasmanian subspecies will respond to an increased frequency of high-severity fires associated with a projected warmer and drier climate. [ABSTRACT FROM AUTHOR]

Maximising the spatiotemporal variability of prescribed fire (i.e. pyrodiversity) is often thought to benefit biodiversity. However, given mixed empirical support, the generality of the pyrodiversity hypothesis remains questionable. Here, we use a simulation experiment to explore the effects of spatiotemporal fire patterns on the population trajectories of four mammal species in a northern Australian savanna: northern brown bandicoot (Isoodon macrourus), northern brushtail possum (Trichosurus vulpecula arnhemensis), grassland melomys (Melomys burtoni), and northern quoll (Dasyurus hallucatus). Underpinned by data from a landscape-scale fire experiment, we simulated mammal population trajectories under three scenarios of fire size (ambient, small/dispersed fires, large/clumped fires) and three levels of dispersal ability (low, moderate, high) over a 21-year period across the Kapalga area of Kakadu National Park. The simulated population size of all four species declined markedly, regardless of fire spatial pattern and dispersal ability. However, the predicted final population size (i.e. number of individuals in the final timestep of the simulation) for the northern brown bandicoot, northern brushtail possum and grassland melomys were significantly influenced by fire size, with declines most severe under the small/dispersed fire scenario. Our results suggest that maximising the dispersion of small fires at the expense of disturbance refugia (such as less-frequently burnt areas) may exacerbate the severity of mammal decline. This highlights the importance of considering trade-offs between spatial (i.e. fire dispersion) and temporal (i.e. fire frequency) aspects of pyrodiversity, and the potential risks when applying fire management for biodiversity conservation without a firm understanding of the requirements of the target species. [ABSTRACT FROM AUTHOR]