Direct and indirect effects of fire on microbial communities in a pyrodiverse dry-sclerophyll forest

Fire is one of the predominant drivers of the structural and functional dynamics of forest ecosystems. In recent years, novel fire regimes have posed a major challenge to the management of pyrodiverse forests. While previous research efforts have focused on quantifying the impacts of fire on above-ground forest biodiversity, how microbial communities respond to fire is less understood, despite their functional significance. Here, we describe the effects of time since fire, fire frequency and their interaction on soil and leaf litter fungal and bacterial communities from the pyrodiverse, Eucalyptus pilularis forests of south-eastern Australia. Using structural equation models, we also elucidate how fire can influence these communities both directly and indirectly through biotic-abiotic interactions. Our results demonstrate that fire is a key driver of litter and soil bacterial and fungal communities, with effects most pronounced for soil fungal communities. Notably, recently burnt forest hosted lower abundances of symbiotic ectomycorrhizal fungi and Acidobacteria in the soil, and basidiomycetous fungi and Actinobacteriota in the litter. Compared with low fire frequencies, high fire frequency increased soil fungal plant pathogens, but reduced Actinobacteriota. The majority of fire effects on microbial communities were mediated by fire-induced changes in litter and soil abiotic properties. For instance, recent and more frequent fire was associated with reduced soil sulphur, which led to an increase in soil fungal plant pathogens and saprotrophic fungi in these sites. Pathogenic fungi also increased in recently burnt forests that had a low fire frequency, mediated by a decline in litter carbon and an increase in soil pH in these sites. Synthesis. Our findings indicate that predicted increases in the frequency of fire may select for specific microbial communities directly and indirectly through ecological interactions, which may have functional implications for plants (increase in pathogens, decrease in symbionts), decomposition rates (declines in Actinobacteriota and Acidobacteriota) and carbon storage (decrease in ectomycorrhizal fungi). In the face of predicted shifts in wildfire regimes, which may exacerbate fire-induced changes in microbial communities, adaptive fire management and monitoring is required to address the potential functional implications of fire-altered microbial communities

Effects of altered fire intervals on critical timber production and conservation values

Forests exhibit thresholds in disturbance intervals that influence sustainability of production and natural values including sawlog production, species existence and habitat attributes. Fire is a key disturbance agent in temperate forests and frequency of fire is increasing, threatening sustainability of these forest values. We used mechanistically diverse, theoretical fire interval distributions for mountain ash forest in Victoria, Australia, in the recent past and future to estimate the probability of realising: (i) minimum sawlog harvesting rotation time; (ii) canopy species maturation; and (iii) adequate habitat hollows for fauna. The likelihood of realising fire intervals exceeding these key stand age thresholds diminishes markedly for the future fire regime compared with the recent past. For example, we estimate that only one in five future fire intervals will be sufficiently long (∼80 years) to grow sawlogs in this forest type, and that the probability of forests developing adequate habitat hollows (∼180 years) could be as low as 0.03 (3% of fire intervals). Therefore, there is a need to rethink where sawlogs can be sourced sustainably, such as from fast-growing plantations that can be harvested and then regrown rapidly, and to reserve large areas of existing 80-year-old forest from timber harvesting.DBL received funding from the Threatened Species Recovery Hub of the Australian Government’s National Environmental Science Program. CNF was supported by a Linkage Grant from the Australian Research Counci

Forest fire management, climate change, and the risk of catastrophic carbon losses

Approaches to management of fireprone forests are undergoing rapid change, driven by recognition that technological attempts to subdue fire at large scales (fire suppression) are ecologically and economically unsustainable. However, our current framework for intervention excludes the full scope of the fire management problem within the broader context of fire−vegetation−climate interactions. Climate change may already be causing unprecedented fire activity, and even if current fires are within the historical range of variability, models predict that current fire management problems will be compounded by more frequent extreme fire-conducive weather conditions (eg Fried et al. 2004)

The Proximal Drivers of Large Fires: A Pyrogeographic Study

Variations in global patterns of burning and fire regimes are relatively well measured, however, the degree of influence of the complex suite of biophysical and human drivers of fire remains controversial and incompletely understood. Such an understanding is required in order to support current fire management and to predict the future trajectory of global fire patterns in response to changes in these determinants. In this study we explore and compare the effects of four fundamental controls on fire, namely the production of biomass, its drying, the influence of weather on the spread of fire and sources of ignition. Our study area is southern Australia, where fire is currently limited by either fuel production or fuel dryness. As in most fire-prone environments, the majority of annual burned area is due to a raelatively small number of large fires. We train and test an Artificial Neural Networks ability to predict spatial patterns in the probability of large fires (>1,250 ha) in forests and grasslands as a function of proxies of the four major controls on fire activity. Fuel load is represented by predicted forested biomass and remotely sensed grass biomass, drying is represented by fraction of the time monthly potential evapotranspiration exceeds precipitation, weather is represented by the frequency of severe fire weather conditions and ignitions are represented by the average annual density of reported ignitions. The response of fire to these drivers is often non-linear. Our results suggest that fuel management will have limited capacity to alter future fire occurrence unless it yields landscape-scale changes in fuel amount, and that shifts between, rather than within, vegetation community types may be more important. We also find that increased frequency of severe fire weather could increase the likelihood of large fires in forests but decrease it in grasslands. These results have the potential to support long-term strategic planning and risk assessment by fire management agencies.OP’s salary was provided by the NSW Rural Fire Service. MB was partly financially supported by the Bushfires and Natural Hazards Cooperative Research Centre

Fire regimes and carbon in Australian vegetation

Fires regularly affect many of the world\u27s terrestrial ecosystems, and, as a result, fires mediate the exchange of greenhouse gases (GHG) between the land and the atmosphere at a global scale and affect the capacity of terrestrial ecosystems to store carbon (Bowman et al. 2009). Variations in fire -regimes can therefore potentially affect the global, regional and local carbon balance and, potentially, climate change itself (Bonan 2008). Here we examine how variation in fire regimes (Gill 1975; Bradstock et al. 2002) will potentially affect carbon in fire-prone Australian ecosystems via interactions with the stocks and transfers of carbon that are inherent to all terrestrial ecosystems. There are two key reasons why an appreciation of fire regimes is needed to comprehend the fate of terrestrial carbon. First, the status of terrestrial carbon over time will be a function of the balance between losses (emissions) from individual fires (of differing type, season and intensity), which occur as a result of immediate combustion as well as mortality and longerterm decomposition of dead biomass, and carbon that accumulates during regeneration in the intervals between fires. The length of the interval between fires will determine the amount of biomass that accumulates. Second, fire regimes influence the composition and structure of ecosystems and key processes such as plant mortality and recruitment. Hence, alternative trajectories of vegetation composition and structure that result from differing fire regimes will affect carbon dynamics. We explore these themes and summarise the dynamic aspects of carbon stocks and transfers in relation to fire, present conceptual models of carbon dynamics and fire regimes, and review how variation in fire regimes may affect overall storage potential as a function of fireinduced losses and post-fire uptake in two widespread Australian vegetation types. We then appraise future trends under global change and the likely potential for managing fire regimes for carbon \u27benefits\u27, especially with respect to emissions

Stand boundary effects on obligate seeding Eucalyptus delegatensis regeneration and fuel dynamics following high and low severity fire: Implications for species resilience to recurrent fire

Increased fire frequency can result in a decline of obligate seeding plants, which rely on re-seeding for population persistence following canopy scorching fire. The resilience of obligate seeding plants to fire at any point in time depends on plant maturity and the size of plants in relation to potential fire scorch height. We investigated variation in the resilience of post-fire regenerating Eucalyptus delegatensis subsp. delegatensis (alpine ash) to a short inter-fire interval at its boundaries with E. fastigata (brown barrel) stands. The resilience of postfire E. delegatensis regeneration was modelled across these stand boundaries as a function of the height of the plants, their reproductive maturity and predicted fire behaviour derived from local fuel characteristics. We measured these attributes 14 years following the Canberra 2003 wildfires and stratified study sites by fire severity. The height and reproductive maturity of post-fire E. delegatensis saplings decreased at stand boundaries with E. fastigata, while fuel was uniformly abundant and capable of supporting canopy scorching fire under mild fire weather conditions. This suggests that E. delegatensis is less resilient to frequent fire in the presence of interspecific competition and other environmental conditions that occur at stand boundaries, which represent the edge of the species’ realised niche. With forecasts for increased fire frequency in south eastern Australia, persistence of E. delegatensis may be greatest in pure stands corresponding to the core of the species’ realised niche, and in moist and sheltered topographic areas that are less prone to frequent canopy scorching fire. Our findings suggest the importance of considering fine-scale spatial variation in important obligate seeding plant traits when predicting and managing the response of obligate seeding species to frequent fire.This research was funded by project scholarshipsprovided by the National Parks Association of theACT and the Dr Robert Lesslie Memorial Founda-tion

Global change and fire regimes in Australia

Global change can be defined strictly in terms of changes in atmospheric composition, climate and land use (Walker and Steffen 1996), although broader definitions also include human population, economy and urbanisation (Steffen et al. 2004). In Australia, global change significantly affects the drivers of fire activity and there is potential for considerable changes in fire regimes. It is widely accepted that carbon dioxide (C02) concentration in the atmosphere is steadily increasing (see Steele et al. 2007), as is nitrous oxide (Forster et al. 2007). Atmospheric methane concentration has also risen significantly, but is now relatively constant (Beer et al. 2006). Given the increase in these greenhouse gases, an increase in the energy trapped by the atmosphere is expected, resulting in atmospheric warming (Arrhenius 1896; IPCC 2007). Therefore, Australia\u27s climate is changing. Average temperatures are expected to increase by between 0.6 and 4°C, depending on emission scenario, timeframe and locality (CSIRO and Australian Bureau of Meteorology 2007) (Figure 7.1). Patterns of precipitation are projected to shift by the end of this century, with higher precipitation in the continent\u27s north and east and declines in the south and west - a pattern generally mimicked by evaporation (Lim and Roderick 2009) (Figure 7.2). Average relative humidity could decline by up to 4% in central and eastern Australia by 2070, while average wind speed may increase by 10% in similar areas (see CSIRO and Australian Bureau of Meteorology 2007). The frequency of extreme frontal events may double or more by the end of this century (Hasson et al. 2009), yet outcomes for circulation patterns associated with El Nifio and the Southern Oscillation (ENSO) (Philander 1990) are uncertain (Collins et al. 2010). Importantly, uncertainty arising from choice of emission scenarios and climate sensitivity, and from differences among models, is common (CSIRO and Australian Bureau of Meteorology 2007; Lim and Roderick 2009)

Relationships between mature trees and fire fuel hazard in Australian forest

Increasing density of mid-storey vegetation since European settlement has been observed in forests and woodlands in several parts of the world and may result in greater fire fuel hazard. This phenomenon is often attributed to a longer interval between fires since European settlement, but may also be influenced by tree removal during the same period. We hypothesised that the number of mature trees in a stand reduces mid-storey vegetation cover and the associated fire fuel hazard through competition. To test this hypothesis, we examined associations between mid-storey cover and fire fuel hazard and the mean diameter of trees within stands of open forest and woodland in south-eastern Australia, a region prone to wildfires. We found that vegetation cover between 2 and 4 m and 4 and 6 m above the ground and two measures of fire fuel hazard were negatively associated with the quadratic mean tree diameter. Our results suggested that the removal of mature trees since European settlement may have triggered tree and shrub regeneration, resulting in higher mid-storey cover and fire fuel hazard. Thus, managing stands for the persistence and replacement of mature trees may contribute to long-term fuel reduction in Australian forests and woodlands

When can refuges mediate the genetic effects of fire regimes? A simulation study of the effects of topography and weather on neutral and adaptive genetic diversity in fire-prone landscapes

Understanding how landscape heterogeneity mediates the effects of fire on biodiversity is increasingly important under global changes in fire regimes. We used a simulation experiment to investigate how fire regimes interact with topography and weather to shape neutral and selection-driven genetic diversity under alternative dispersal scenarios, and to explore the conditions under which microrefuges can maintain genetic diversity of populations exposed to recurrent fire. Spatial heterogeneity in simulated fire frequency occurred in topographically complex landscapes, with fire refuges and fire-prone “hotspots” apparent. Interannual weather variability reduced the effect of topography on fire patterns, with refuges less apparent under high weather variability. Neutral genetic diversity was correlated with long-term fire frequency under spatially heterogeneous fire regimes, being higher in fire refuges than fire-prone areas, except under high dispersal or low fire severity (low mortality). This generated different spatial genetic structures in fire-prone and fire-refuge components of the landscape, despite similar dispersal. In contrast, genetic diversity was only associated with time since the most recent fire in flat landscapes without predictable refuges and hotspots. Genetic effects of selection driven by fire-related conditions depended on selection pressure, migration distance and spatial heterogeneity in fire regimes. Allele frequencies at a locus conferring higher fitness under successional environmental conditions followed a pattern of “temporal adaptation” to contemporary conditions under strong selection pressure and high migration. However, selected allele frequencies were correlated with spatial variation in long-term mean fire frequency (relating to environmental predictability) under weak dispersal, low selection pressure and strong spatial heterogeneity in fire regimes.Sam Banks was funded by Australian Research Council Future Fellowship FT130100043