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The influence of plant traits on forest fire behaviour has evolutionary, ecological and management implications, but is poorly understood and frequently discounted. We use a process model to quantify that influence and provide validation in a diverse range of eucalypt forests burnt under varying conditions. Measured height of consumption was compared to heights predicted using a surface fuel fire behaviour model, then key aspects of our model were sequentially added to this with and without species-specific information. Our fully specified model had a mean absolute error 3.8 times smaller than the otherwise identical surface fuel model (p < 0.01), and correctly predicted the height of larger (≥1 m) flames 12 times more often (p < 0.001). We conclude that the primary endogenous drivers of fire severity are the species of plants present rather than the surface fuel load, and demonstrate the accuracy and versatility of the model for quantifying this.

Forests of the Australian Alps (SE Australia) are considered some of the most vulnerable to climate change in the country, with ecosystem collapse considered likely for some due to frequent fire. It is not yet known, however, whether increasing fire frequency may stabilize due to reductions in flammability related to reduced time for fuel accumulation, show no trend, or increase due to positive feedbacks related to vegetation changes. To determine what these trends have been historically, dynamics were measured for 58 years of mapped fire history. The 1.4 million ha forested area was divided into broad formations based on structure and dominant canopy trees, and dynamics were measured for each using flammability ratio, a modification of probability of ignition at a point. Crown fire likelihood was measured for each formation, based on satellite-derived measurements of the 2003 fire effects across a large part of the area. Contrary to popular perception but consistent with mechanistic expectations, all forests exhibited pronounced positive feedbacks. The strongest response was observed in tall, wet forests dominated by Ash-type eucalypts, where, despite a short period of low flammability following fire, post-disturbance stands have been more than eight times as likely to burn than have mature stands. The weakest feedbacks occurred in open forest, although post-disturbance forests were still 1.5 times as likely to burn as mature forests. Apart from low, dry open woodland where there was insufficient data to detect a trend, all forests were most likely to experience crown fire during their period of regeneration. The implications of this are significant for the Alps, as increasing fire frequency has the potential to accelerate by producing an increasingly flammable landscape. These effects may be semi-permanent in tall, wet forest, where frequent fire promotes ecosystem collapse into either the more flammable open forest formation, or to heathland.

Globally, collapse of ecosystems—potentially irreversible change to ecosystem structure, composition and function—imperils biodiversity, human health and well‐being. We examine the current state and recent trajectories of 19 ecosystems, spanning 58° of latitude across 7.7 M km2, from Australia's coral reefs to terrestrial Antarctica. Pressures from global climate change and regional human impacts, occurring as chronic ‘presses’ and/or acute ‘pulses’, drive ecosystem collapse. Ecosystem responses to 5–17 pressures were categorised as four collapse profiles—abrupt, smooth, stepped and fluctuating. The manifestation of widespread ecosystem collapse is a stark warning of the necessity to take action. We present a three‐step assessment and management framework (3As Pathway Awareness, Anticipation and Action) to aid strategic and effective mitigation to alleviate further degradation to help secure our future.

Summary'Flammability' means different things to different people. Scientifically, it can be defined through three component variables that describe how well the fuel ignites (ignitibility), how well it burns (combustibility) and how long it burns (sustainability). The 'fuel' may be a plant organ, a whole plant or a plant community. While the terms ignitibility, combustibility and sustainability have been developed for laboratory studies, there are conceptual equivalents suited to the field; these are rate of spread, intensity and residence times. Another variable is added for field circumstances -probability of burning at a point. Eucalypt forests can be highly 'flammable' even considering all criteria and scales, while Australian forests in general show the whole range of variation from low ('closed forests' or 'rainforests') to high (e.g. relatively short stringy-barked open forests of Eucalyptus with abundant wiregrass). The expression of flammability depends on the local circumstances. In the field this can be summarised in terms of weather, terrain and ignition. Predicting how much potential forest fuel, and the attributes of that fuel, will be involved at any particular time, and under extreme weather conditions, remains a challenge. How social, climatic and fuel-species' changes will affect flammability, directly and indirectly, in the next 50-100 y is uncertain but potentially very significant.

As climatic changes continue to drive increases in the frequency and severity of forest fires, it is critical to understand all of the factors influencing the risk of forest fire. Using a spatial dataset of areas burnt over a 58-year period in a 528,343-ha study area, we examined three possible drivers of flammability dynamics. These were: that forests became more flammable as fine biomass (fuel) returned following disturbance (H1), that disturbance increased flammability by initiating dense understorey growth that later self-thinned (H2), and that climatic effects were more important than either of these internal dynamics (H3). We found that forests were unlikely to burn for a short ‘young’ period (5-7 years) following fire, very likely to burn as the regrowing understorey became taller and denser (regrowth period), then after a total post-disturbance period of 43-56 years (young + regrowth periods), fire became unlikely and continued to decrease in likelihood (mature period). This trend did not change as the climate warmed, although increases in synoptic variability (mean changes in synoptic systems per season) had a pronounced effect on wildfire likelihood overall. Young forest and regrowth forest became increasingly likely to burn in years of greater synoptic variability and the time taken for forests to mature increased, but in years with the most severe synoptic variability, mature forests were the least likely to burn. Our findings offer an explanation for fire behaviour in numerous long-term studies in diverse forest types globally and indicate that, even in the face of a warming climate, ‘ecologically-cooperative’ approaches may be employed that reinforce rather than disrupt natural ecological controls on forest fire. These range from traditional indigenous fire knowledge, to modern targeting of suppression resources to capitalise on the benefits of self-thinning, and minimise the extent of dense regrowth in the landscape.

1. Floral fire ecology incorporates a feedback loop in which plants influence fire behaviour and fire behaviour influences the flora. Recent advances in fire behaviour modelling have quantified many plant-based drivers of fire behaviour, but the consequent ecological effects of this have not yet been adequately modelled mechanistically.2. Here, I introduce the Fire Research and Modelling Environment (FRaME) as the open-source R package frame on GitHub. FRaME calculates the influence of plants on fire behaviour using a biophysical, mechanistic model of fire behaviour, building this into complex simulations. From these, it models heat transfer from flames into surrounding surfaces, calculating its ecological effects on plants and soils. I demonstrate the application of the central analysis functions using a detailed case study, in which I validate predictions of fire behaviour and ecological effects, and derive quantitative measures for the efficacy of different management treatments to mitigate fire risk to a vulnerable ecosystem.3. FRaME modelling predicted ecological effects such as the breaking of seed dormancy, scorch and the girdling of different tree strata, consistent with observed effects and providing insights into treatment efficacy that were not captured by existing assumptions. FRaME analyses were able to identify treatments that both increased the likelihood of success in containing fires and minimised fire impacts on a fire-sensitive ecosystem.4. FRaME provides a platform to examine the full role of fire in an ecosystem, from the ways that biota drive flammability to the influence of that flammability on the ecosystem. By mechanistically incorporating the effect of biophysical drivers throughout this feedback, FRaME can provide novel insights and solutions for complex problems, quantify risk and guide effective mitigation measures. The model is extensible, providing a conceptual framework into which emerging work on flammability and fire effects can be incorporated.

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