Interval squeeze: altered fire regimes and demographic responses interact to threaten woody species persistence as climate changes

Projected effects of climate change across many ecosystems globally include more frequent disturbance by fire and reduced plant growth due to warmer (and especially drier) conditions. Such changes affect species - particularly fire-intolerant woody plants - by simultaneously reducing recruitment, growth, and survival. Collectively, these mechanisms may narrow the fire interval window compatible with population persistence, driving species to extirpation or extinction. We present a conceptual model of these combined effects, based on synthesis of the known impacts of climate change and altered fire regimes on plant demography, and describe a syndrome we term interval squeeze. This model predicts that interval squeeze will increase woody plant extinction risk and change ecosystem structure, composition, and carbon storage, especially in regions projected to become both warmer and drier. These predicted changes demand new approaches to fire management that will maximize the in situ adaptive capacity of species to respond to climate change and fire regime change

Optimising the spatial planning of prescribed burns to achieve multiple objectives in a fire-dependent ecosystem

1. There is potential for negative consequences for the ecological integrity of fire-dependent ecosystems as a result of inappropriate fire regimes. This can occur when asset (property) protection is prioritised over conservation objectives in burn programs

Biological and geophysical feedbacks with fire in the Earth system

Roughly 3% of the Earth's land surface burns annually, representing a critical exchange of energy and matter between the land and atmosphere via combustion. Fires range from slow smouldering peat fires, to low-intensity surface fires, to intense crown fires, depending on vegetation structure, fuel moisture, prevailing climate, and weather conditions. While the links between biogeochemistry, climate and fire are widely studied within Earth system science, these relationships are also mediated by fuels—namely plants and their litter—that are the product of evolutionary and ecological processes. Fire is a powerful selective force and, over their evolutionary history, plants have evolved traits that both tolerate and promote fire numerous times and across diverse clades. Here we outline a conceptual framework of how plant traits determine the flammability of ecosystems and interact with climate and weather to influence fire regimes. We explore how these evolutionary and ecological processes scale to impact biogeochemical and Earth system processes. Finally, we outline several research challenges that, when resolved, will improve our understanding of the role of plant evolution in mediating the fire feedbacks driving Earth system processes. Understanding current patterns of fire and vegetation, as well as patterns of fire over geological time, requires research that incorporates evolutionary biology, ecology, biogeography, and the biogeosciences

Reducing wildfire risk to urban developments: Simulation of cost-effective fuel treatment solutions in south eastern Australia

Wildfires can result in significant economic and social losses. Prescribed fire is commonly applied to reduce fuel loads and thereby decrease future fire risk to life and property. Fuel treatments can occur in the landscape or adjacent to houses. Location of the prescribed burns can significantly alter the risk of house loss. Furthermore the cost of treating fuels in the landscape is far cheaper than treating fuels adjacent to the houses. Here we develop a Bayesian Network to examine the relative reduction in risk that can be achieved by prescribed burning in the landscape compared with a 500 m interface zone adjacent to houses. We then compare costs of management treatments to determine the most cost-effective method of reducing risk to houses. Burning in the interface zone resulted in the greatest reduction in risk of fires reaching the houses and the intensity of these fires. Fuel treatment in the interface zone allows for a direct transfer of benefits from the fuel treatment. Costs of treating fuels in the interface were significantly higher on a per hectare basis, but the extent of area requiring treatment was considerably lower. Results of this study demonstrate that treatment of fuels at the interface is not only the best means of reducing risk, it is also the most cost-effective

Appraising widespread resprouting but variable levels of postfire seeding in Australian ecosystems: The effect of phylogeny, fire regime and productivity

Postfire resprouting (R+) and recruitment from seed (S+) are common resilience traits in Australian ecosystems. We classified 2696 woody Australian taxa as R+ or not (R−) and as S+ or not (S−). The proportions of these traits in Australian ecosystems were examined in relation to fire regimes and other ecological correlates, and by trait mapping on a phylogeny scaled to time. Resprouting mapped as an ancestral trait. Postfire reseeding recruitment, while ancient, is more taxonomically restricted and has evolved independently several times. Nevertheless, both R+ and S+ are common in most clades, but negatively correlated at the ecosystem level indicating an evolutionary trade-off related to differences in the severity of fire regimes, determined in part by ecosystem productivity. Thus, R+ was associated with persistence in ecosystems characterised by higher productivity and relatively frequent surface fires of moderate to low severity (fire-productivity hypothesis). S+, the fire-stimulated recruitment by seed, occurred in ecosystems characterised by infrequent but intense crown-fire and topkill, reducing competition between postfire survivors and recruits (fire-resource-competition hypothesis). Consistently large proportions of R+ or S+ imply fire has been a pervasive evolutionary selection pressure resulting in highly fire-adapted and fire-resilient flora in most Australian ecosystems

Interactions between climate change, fire regimes and biodiversity in Australia: A preliminary assessment

An assessment of the potential impacts of climate change on fire regimes in Australia, and the consequences of these changed fire regimes for Australia's biodiversity was commissioned by the Australian Government to help increase our understanding of the complex interactions between climate change, fire regimes and biodiversity for future fire management. The report synthesises understanding of the drivers of fire regimes in Australia, identifies changes to fire regimes projected from climate change and identifies the broad implications of these changes for biodiversity. 'Fire regime' is defined as the history of fire events at a point in the landscape. The report finds that fire weather will become more severe in many regions, particularly southern Australia, and that the interactions between biodiversity and fire regimes are complex. It develops a national framework to assess the likely impacts of climate change on fire regimes and biodiversity for different bioregions, using a case study approach. Climate change may affect fire regimes across the Australian landscape through changes to temperature, rainfall, humidity, wind, and the amount of carbon dioxide in the atmosphere. • Modeled climate projections show that much of southern Australia may become warmer and drier. This modeling suggests that, by 2020, extreme fire danger days in south-eastern Australia may occur 5 to 65 per cent more often than at present. • For example, modeling of climate change impacts on the fire regimes of Australian Capital Territory (ACT) landscapes predicts that a 2oC increase in mean annual temperature would increase fire intensity by 25%, increase the area burnt, and halve the mean interval between fires in the ACT. • Climate change is expected to have greater effects on fire regimes in regions where fire weather factors like temperature and wind strength determine fire occurrence and fire intensity. These are regions such as the temperate forests of the south-east and south-west of Australia. Climate change is expected to have less effect on fire regimes in places where fuel levels or ignition sources determine fire occurrence and intensity, such as northern tropical savannas. • Managing fire regimes to reduce risk to property, people and biodiversity under climate change will be increasingly challenging