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Landscape fire is a key but poorly understood component of the global carbon cycle. Predicting biomass consumption by fire at large spatial scales is essential to understanding carbon dynamics and hence how fire management can reduce greenhouse gas emissions and increase ecosystem carbon storage. An Australia‐wide field‐based survey (at 113 locations) across large‐scale macroecological gradients (climate, productivity and fire regimes) enabled estimation of how biomass combustion by surface fire directly affects continental‐scale carbon budgets. In terms of biomass consumption, we found clear trade‐offs between the frequency and severity of surface fires. In temperate southern Australia, characterised by less frequent and more severe fires, biomass consumed per fire was typically very high. In contrast, surface fires in the tropical savannas of northern Australia were very frequent but less severe, with much lower consumption of biomass per fire (about a quarter of that in the far south). When biomass consumption was expressed on an annual basis, biomass consumed was far greater in the tropical savannas (>20 times that of the far south). This trade‐off is also apparent in the ratio of annual carbon consumption to net primary production (NPP). Across Australia's naturally vegetated land area, annual carbon consumption by surface fire is equivalent to about 11% of NPP, with a sharp contrast between temperate southern Australia (6%) and tropical northern Australia (46%). Our results emphasise that fire management to reduce greenhouse gas emissions should focus on fire prone tropical savanna landscapes, where the vast bulk of biomass consumption occurs globally. In these landscapes, grass biomass is a key driver of frequency, intensity and combustion completeness of surface fires, and management actions that increase grass biomass are likely to lead to increases in greenhouse gas emissions from savanna fires. Landscape fire is a key but poorly understood component of the global carbon cycle. We undertook an extensive field survey across Australia to measure rates of biomass consumption by fire. We found that in a typical year, fire consumes the equivalent of about 11% of the carbon captured by vegetation across Australia. In the far north, rates of biomass consumption were about 20 times that in the far south. Our results emphasise that fire management to reduce greenhouse gas emissions should focus on fire‐prone tropical savanna landscapes, where the vast majority of fire activity occurs. [ABSTRACT FROM AUTHOR]

Abstract: We studied the effects of fuel type, fuel load and their associated flammability attributes on growth and survival of Callitris intratropica saplings. Callitris intratropica is a fire‐sensitive conifer that is widespread across northern Australia, but its range is contracting because of frequent and intense fires. A small‐scale field experiment was used to compare the effect of three fuel types (grass, eucalypt litter and C. intratropica litter), and a mix of grass and eucalypt litter by varying fuel loads within their naturally occurring bounds, and measuring multiple flammability attributes. Fuel type had the strongest influence on flammability attributes and hence sapling survival. Grass burnt rapidly, producing high temperatures, while duration of flaming was longer for eucalypt litter. Grass–eucalypt litter mixtures had flammability attributes more like grass, while C. intratropica litter was difficult to burn. Fuel load had a secondary effect, with strong interactions between fuel type and load. Differences in sapling survival could be attributed to temperatures at 5 cm height; there was no additional effect of fuel type or canopy temperature. Sapling size variables were also important, and strongly correlated with bark thickness, so we could not identify the protective mechanism. Synthesis. Mortality of Callitris intratropica saplings was consistent with damage to the lower stem, because of the direct relationship with temperatures at 5 cm height. Our results demonstrate the existence of a grass–fire cycle in C. intratropica stands, whereby hot fires damage the stands and allow grass to invade, increasing the stand ignitability and combustibility and promoting further fires. Interrupting this cycle by reducing grass fuel loads and hence the frequency of hot fires should therefore be a management priority to safeguard C. intratropica populations. Our findings also highlight that, under a common climate, vegetation type can shape fire regimes, because fuel type strongly influences flammability attributes, which in turn act as a powerful filter of plant populations. [ABSTRACT FROM AUTHOR]

Aim The impacts of Holocene fires on the genetic architecture of fire-intolerant species have largely been overlooked. Here, we investigate the relative impacts of the last glacial climate versus Holocene fires on the genetic diversity of two co-occurring, fire-intolerant conifers using a comparative population genetic study. Location The palaeoendemic plant-rich montane rain forests and alpine coniferous heath of Tasmania, Australia. Methods The Tasmanian endemic conifers Athrotaxis cupressoides D. Don (461 samples from 20 populations) and Diselma archeri Hook.f. (576 samples from 23 populations, 16 of which were for sites sampled for A. cupressoides), were genotyped using eight and nine EST nuclear microsatellites respectively. Genetic diversity and structure was compared between the two species and the factors underlying genetic patterns in both species were investigated by examining isolation by distance, correlations with Last Glacial Maximum modelled distributions and the fossil record, and a fire history index of the sampled stands. Results The range-wide genetic structure of the two species was similar ( Fst = 0.09 and F'st = 0.21 for A. cupressoides versus D. archeri; Fst = 0.06 and F'st = 0.24), and there were significant correlations between species for population-based expected heterozygosity, allelic richness, private allelic richness and pairwise genetic divergences. Furthermore, genetic diversity metrics decreased significantly with an index of fire history. Given fossil evidence and modelling evidence that both species occurred near their current ranges during the last glaciation and a lack of evidence for isolation by distance in either species, the plausible explanation for the patterns of diversity is genetic decline resulting from repeated Holocene fires. Main conclusions Our study suggests that fire can have substantial impacts on genetic structure and diversity of plant species, particularly those without fire-tolerant traits, and that any increases in fire resulting from climate change may impose substantial threats to such species. In Tasmania, the observed increase in dry lightning in recent years, combined with periods of abnormally dry conditions, may therefore further degrade the range and genetic diversity of fire-intolerant palaeoendemic species. [ABSTRACT FROM AUTHOR]

Aims To (1) identify the trade-offs among flammability attributes within grass and litter fuel types; (2) determine how flammability attributes of grass and litter fuels vary across macro-ecological gradients; and (3) test our hypothesis that inherent flammability attributes of grass and litter fuels scale to satellite-derived proxies for fire frequency and intensity. Location Continent of Australia. Methods Samples of litter and grass fuels collected from 133 sites across Australia were oven dried, then burnt under controlled conditions. Measurements of ignitability, combustibility and sustainability were made. Estimates of fire frequency and fire radiative power (a proxy for intensity) were derived from satellite imagery. Multivariate analyses were used to identify inter-relationships among variables and trends across macro-ecological gradients. Results Flammability was best described by two axes: high rate of combustion versus long duration of burning, and fast rate of spread versus high maximum temperature. As expected, our study confirmed that grass and litter fuel types have inherently differently flammability attributes whereby grass samples burn more quickly, with a higher rate of spread, than litter samples. However, there were also smaller differences in flammability attributes within fuel types, which scaled to rainfall, temperature and soil phosphorus concentrations. In keeping with our hypothesis, we found correlations between inherent fuel flammability attributes and landscape fire activity across the Australian continent. Fire frequency and rate of combustion of grass fuels were both highest in the tropics, and fire intensity and maximum temperature during combustion of litter fuels were highest in temperate areas. Main conclusions At a continental scale, we found landscape fire activity was correlated with inherent flammability of grass and litter fuels. This inherent flammability contributes to observed pyrogeographical patterns that are shaped by climate through its known effects on plant productivity, the abundance of cured grass biomass and fire weather. [ABSTRACT FROM AUTHOR]

At fine spatial scales, savanna-rainforest-grassland boundary dynamics are thought to be mediated by the interplay between fire, vegetation and soil feedbacks. These processes were investigated by quantifying tree species composition, the light environment, quantities and flammability of fuels, bark thickness, and soil conditions across stable and dynamic rainforest boundaries that adjoin grassland and eucalypt savanna in the highlands of the Bunya Mountains, southeast Queensland, Australia. The size class distribution of savanna and rainforest stems was indicative of the encroachment of rainforest species into savanna and grassland. Increasing dominance of rainforest trees corresponds to an increase in woody canopy cover, the dominance of litter fuels (woody debris and leaf), and decline in grass occurrence. There is marked difference in litter and grass fuel flammability and this result is largely an influence of strongly dissimilar fuel bulk densities. Relative bark thickness, a measure of stem fire resistance, was found to be generally greater in savanna species when compared to that of rainforest species, with notable exceptions being the conifers Araucaria bidwillii and Araucaria cunninghamii. A transect study of soil nutrients across one dynamic rainforest -- grassland boundary indicated the mass of carbon and nitrogen, but not phosphorus, increased across the successional gradient. Soil carbon turnover time is shortest in stable rainforest, intermediate in dynamic rainforest and longest in grassland highlighting nutrient cycling differentiation. We conclude that the general absence of fire in the Bunya Mountains, due to a divergence from traditional Aboriginal burning practices, has allowed for the encroachment of fire-sensitive rainforest species into the flammable biomes of this landscape. Rainforest invasion is likely to have reduced fire risk via changes to fuel composition and microclimatic conditions, and this feedback will be reinforced by altered nutrient cycling. The mechanics of the feedbacks here identified are discussed in terms of landscape change theory. [ABSTRACT FROM AUTHOR]

The manipulation of landscape fire to maintain biodiverse, self-sustaining ecosystems in flammable landscapes is rarely considered by restoration ecologists. Fire regimes can interact with ecological processes, food webs, and biodiversity in complex ways (here called pyrodiversity) and understanding these complexities could be used to promote restoration and resilience. We illustrate this using an example from northern Australia. Understanding and using pyrodiversity in ecological restoration programs will be intellectually and financially challenging. In Australia, the considerable technical and financial resources of the mining industry could support such restoration programs, yet redirecting these resources from the current narrow focus on restoring native vegetation cover at the mine-affected site requires overcoming entrenched attitudes among policymakers and restoration ecologists. [ABSTRACT FROM AUTHOR]

Forests that regenerate exclusively from seed following high-severity fire are particularly vulnerable to local extinction if fire frequency leaves insufficient time for regenerating plants to reach sexual maturity. We evaluate the relative importance of extrinsic (such as fire weather and climate cycles) and intrinsic (such as proneness to fire due to stand age and structural development) factors in driving the decline of obligate seeder forests. We illustrate this using obligate seeding alpine ash ( Eucalyptus delegatensis) forests in the montane regions of Victoria, Australia, that were burnt by megafires in 2003 (142,256 ha) or 2007 (79,902 ha), including some twice-burnt areas (11,599 ha). Geospatial analyses showed only a small effect of stand age on the remote sensing estimates of crown defoliation, but a substantial effect of forest fire weather, as measured by forest fire danger index (FFDI). Analysis of meteorological data over the last century showed that 5-year increases in FFDI precede cycle major fires in the E. delegatensis forests. Such strong extrinsic climate/weather driving of high-severity fires is consistent with the 'interval squeeze model' that postulates the vulnerability of obligate seeder forests to landscape-scale demographic collapse in response to worsening fire weather under climate change. [ABSTRACT FROM AUTHOR]