Fire regimes
In our warming, drying world the use of controlled fires to prevent wildfires is a highly contentious topic. There also is a clear inter-dependence between fire management and other threatening processes. Increases in extremely hot days and drought periods through climate change are likely to exacerbate fire impacts. (Williams et al, 2009)
Inappropriate contemporary fire regimes are generally acknowledged as a key threatening process for many Australian plant and animal species that might lead to a substantial number of species’ extinctions. Only the threat of predation by feral cats is regarded as more damaging. (Woinarski et al, 2014)
Even though there is little doubt that fire is one of the major threats to Australian biodiversity, I cannot find any clear descriptions of what constitutes inappropriate fire regimes and how they differ from what we currently employ.
Prescribed burning has been our favourite fire prevention measure, however the obsession with burning our world to the ground in order to prevent it from burning has become a threat in itself.
The dearth of comprehensive field evidence on which to base predictions of benefits or risks of prescribed burning limits the chance of meeting wildfire hazard reduction and conservation goals. (Boer et al, 2009)
Fire management is often implemented with only asset protection in mind, neglecting the possibly negative impacts on other objectives. (Driscoll et al, 2010)
Adopting a target – in the case of the forested part of south-west Western Australia 200,000 hectares per year – can only lead to undesirable outcomes. Burning large remote areas would be the most economical way as it contributes more, faster to reaching the target irrespective of whether such burning will truly protect assets or achieve ecologically desirable outcomes . (Fernandes and Botelho, 2003)
There clearly is a risk of high intensity fires which can result in loss of life and assets and reduction of the commercial values of forests. Low intensity, prescribed fires that reduce fuel loads across extensive areas and therefore potentially decrease the frequency and severity of severe wildfires (Boer et al, 2009, Driscoll et al, 2010, Penman et al, 2011) seem to deliver a solution and more recent bushfires led to more urgent calls for more prescribed burning.
However, extreme weather can influence the spread of a fires in temperate forests and shrub lands to a higher degree than fuel loads (Fernandes and Botelho, 2003, Cary et al, 2009) and some predictions now only attest to negligible asset protection value in widespread prescribed burning (Cary et al, 2009) or claim that funding scenarios will determine the value of the program. (Bradstock et al, 2008)
Biodiversity conservation and asset protection are competing objectives in fire management and there will always be a trade-off to the detriment of biodiversity goals. If biodiversity considerations are included in policy settings at all, outcomes are unlikely to be satisfactory. (Clarke, 2008)
Knowledge is inadequate and research is needed to relate management actions not only to assess management effectiveness in hazard reduction but also in protection of biodiversity.
Some prescribed burns are used as a management tool for biodiversity conservation but assessing the effectiveness of those is obviously difficult while the detrimental impacts of fire on threatened species are fairly obvious.
Mitigating negative impacts looks ineffective at best. (Gibbons et al, 2012)
I am also doubtful how well the outcomes for biodiversity are monitored and reported even though that would be a necessary basis for any improvement.
Long-term collaborative regional-scale fire management with adequate monitoring systems and sufficient financial support seem lacking.
The pattern and characteristics of fires over time such as their frequency, regularity, seasonality, intensity and extent characterise fire regimes in the various regions. The longer-term impacts of those regimes on biodiversity in general and on population viability appear to be at the basis of conservation concerns. (Woinarski et al, 2015)
Fire regimes in some north Australian sanctuaries (AWC) deliver good conservation outcomes but to replicate such programs in other regions seems impossible, particularly as human safety and the protection of economic assets are the major driver of any management in the temperate, heavily populated areas.
Also, historic records regarding the precise nature of traditional Aboriginal burning practices - the scale, frequency, timing and intensity – are scarce. Management plans invoking unspecified Aboriginal burning practices often just seem to deliver justification for widespread burning. (Clarke, 2008)
Large fires in a predominantly wooded landscape in the past posed far less threat to species’ survival than today in fragmented habitat areas. (Woinarski et al, 2005)
Extensive computer modelling using the example of Tasmania tried to find out how large an area we have to burn to provide relative safety from wildfire, returned a highly unrealistic result. 30% of the land area would need to be burned annually – less would be inefficient! (Furlaud and Bowman, 2017)
Research in the Warren region concluded that prescribed burning every 6 years would be effective at reducing the wildfire hazard as fuel accumulation after 6 years increases the probability of wildfire and makes prescribed burns difficult. (Boer et al, 2009)
The long-term impacts on ecosystem functioning for such a fire frequency have however not been researched yet. (Boer et al, 2009)
However, newest research contradicts the assumption that the accumulation of fuel loads will make the forest increasingly flammable. The author even claims that a several decades old forest is a defences against extensive bushfires. (Zylstra, 2018)
The research was conducted in Mountain Ash which will be different to our SW forests, however the principle that fire produces dense regrowth and potentially destroys canopies that maintain a moist micro-climate (Zylstra, 2018) will apply.
Research in western USA found that the extent of an area burnt at high intensity was substantially reduced through thinning and/or prescribed burning. (Schmidt et al, 2008)
Even though this might still hold true, more fire – wild or controlled – also produces a more flammable forest, which then leads to more fires until the ecosystem turns into flammable shrub. (Zylstra, 2018, Taylor et al, 2014)
The strategic placement of fuel treatments reduced the spread and intensity of (simulated) wildfires even under severe weather conditions more effectively than random placement which would require twice the size of area treated to produce the same effect. (Finney et al, 2007)
Strategically locating burns in close proximity to dwellings and other assets may also offer higher levels of risk reduction than burns in the wider landscape. (Ager et al, 2007, Bradstock et al, 2008, Cary et al, 2009)
Buffer burning at the bush–urban interface delivered better outcomes with significantly less area treated. (Cary et al, 2009)
Our ever growing residential sprawl into bush fire prone areas is becoming one of the biggest fire risk factors and clearing large tracts of bush around dwellings to reduce the risk of bushfires can compound the problem as exposed and therefore hotter land surfaces can lead to more severe bushfires. (McAlpine et al, 2009)
Shrinking remnants of habitat at the margins of developments are all that is left for wildlife and the number of threatened species is increasing with the increase in human expansion. (Underwood et al, 2009) Those areas are also those with the need for the most frequent controlled burning. (Driscoll et al, 2010)
In a wildfire, back-burning towards the fire is a commonly used practice to eliminate fuel and to slow if not halt the main fire front. To prevent spot fires downwind of the back-burnt area the back-burnt strip needs to be fairly wide which can potentially lead to huge additionally burnt expanses . The documentation of outcomes like this is rare as are recommendations for an effective width of back- burn. (Driscoll et al, 2010) It is however obvious, that any additionally burnt stretches and in particular those that might have provided refuges have negative implications for survival of wildlife and their post-fire recolonization. (Penman et al, 2007, Robinson et al, 2013)
In a wildfire, forest patches with low-flammability would remain unburnt (Clarke, 2002) and can provide important refuges for surviving wildlife.
We know that the use of fire retardants impacts negatively on aquatic species and waterways but the impacts on terrestrial biodiversity seem not researched. As they can add nutrients such as nitrogen or phosphorus to the environment, they can increase weed invasion post-fire and that way trigger a rapid increase in the next fuel load.
The level of modification of the soil surface's microclimate after any fire and soil temperature during prescribed burns seem to have gained little scientific interest so far, while evidence is available for the decrease in soil moisture and a lowered water infiltration rate. (York et al, 2012)
Severe fires can result in the sterilisation of the upper level of soil and time to complete recovery is highly variable. Even after an only moderately intensive fire in Jarrah Forest in WA recovery of soil and litter-fauna took 3 years. (York et al, 2012)
Fire directly impacts on the habitat structure and floristic of an area and can render a formerly preferred habitat for a species unsuitable (Hopkins and Robinson, 1981), which will have particularly negative impacts on all vertebrate species with highly specific habitat requirements. (Bradshaw and Bradshaw, 2017)
Predictions of animal responses would require good knowledge of their habitat requirements and their adaptability to alternative habitats, which we do not possess for most species. (Clarke, 2008)
Tree foliage will also change after a fire. Leaves may produce more sugars under elevated CO2 levels and carbohydrates may accumulate in the leaves which would result in a down-regulation of photosynthesis. (Carey, 2016) The decrease in nitrogen-containing photosynthetic enzymes in the leaves would thus trigger an increase in the carbon to nitrogen (C:N) ratio of the foliage. (Hovenden and Williams, 2010) This change in plant C:N ratio will have an effect on those animals that use the vegetation as a food source as its nutritional value and the plant toxins will be affected. (Hovenden and Williams, 2010; Reich et al, 2006). The higher level of atmospheric CO2 will therefore potentially change processes for all interconnected elements. (Ellsworth et al, 2004; Kallarackal and Roby, 2012).
We have a good understanding of plant ecology in connection with fire management and how to maintain the diversity of plant communities, however this is lacking for fauna. (Clarke, 2008)
As we rarely have figures for the pre-fire population sizes of the mainly affected species, we cannot estimate fatalities reliably. Surveys of marked individuals pre and post fire are only available for a bird species and a tortoise in Western Australia. (Enright et al, 2012)
Animals mobile enough to escape the direct effect of a fire might disappear shortly after due to a shortage of food and lack of shelter from climatic extremes but the rate of emigration versus the rate of mortality stays unknown. The risk of predation is also heightened due to the opening up of the understorey post-fire. (Sutherland and Dickman, 1999)
In an example of a fire in red-tailed black cockatoo habitat – in this case a prescribed burn of shrubby understorey - eucalyptus seeds were severely reduced for up to 9 years. (Koch, 2005)
As is the declared aim of any controlled burn, understorey will be severely reduced or temporarily completely removed, leaving hardly any shelter for instance for our western ringtail possum. Food is diminished, gaps in the canopy leave no avenues of escape without coming to the ground; competition between the survivors is intensified and re-colonisation of burnt areas is hampered by fragmentation of the habitat and increased isolation of patches if no corridors are left.
Frequent and/or more intense fires also change tree demographic characteristics as large old trees are destroyed which have the best hollows. New hollows take many decades to form in forests regenerating from fire. Even dead and unhealthy trees can be a valuable feature for hollow-dependent animals as they have the deepest hollows that provide the best insulation and protection. (Jones et al, 1994a)
Predation pressure particularly by feral cats increases drastically in recently burnt areas due to the removal of protective ground cover which increases their hunting efficiency.
Recent research (McGregor et al, 2016a) shows that feral cats actively select hunting grounds in recent fire scars. Interestingly they only do this when the fire has not left any pockets of unburnt vegetation. Lower intensity fires at least leave refuges for surviving wildlife.
Both fires and predators are subject to intense management by humans – but we tend to manage them as independent ecosystem drivers instead of simultaneous and interacting threats.
Cats are opportunists and take advantage of the situation while foxes are such extreme habitat generalists that they can survive well even in recently burnt areas.
Python predation also increases as a result of decreased canopy and understorey continuity and increased necessity for ringtail possums to use hollows instead of dreys (lack of building material).
Today’s fire regimes often do not spare riparian strips which could provide refuge areas post-fire. Also, even though predation is known to intensify in the wake of a fire, controlled burns are not in general followed by intensive cat and fox control measures. (Rijksen and Dickman, 2014)
Privately owned land next to conservation estate subjected to a controlled burn will not be included in those measures and often suffers an influx of predators.
There is strong advocacy for a policy of mosaic burning in order to maximise species diversity and create refugia during and after a burn. However, there is no guidance available what patch size is required, how they need to be connected with other patches in the fire mosaic and how close to each other those patches need to be. (Clarke, 2008) Empirical data to identify the desirable characteristics of a mosaic is urgently needed as habitats become increasingly fragmented. (Bradstock et al, 2005, Parr and Andersen, 2006).
If animals are not mobile enough to flee from a fire or get predated upon in the aftermath, extinction at a site is possible. This might only be temporary if re-colonisation through populations within dispersing distance is possible and the habitat values recover in time. A species’ life-history attributes such as their reproductive rate and their dispersal ability will play a major role in whether re-colonisation following fire will be successful or not. (Clarke, 2008) If population numbers were already at very low levels – as western ringtail possum numbers in most bush areas usually are – a burn, no matter whether it is a wildfire or a prescribed burn may cause local extinction of the species. (Clarke, 2008)
Long-term research on the recovery of honey possums after fire showed that even though a fairly quick recovery can follow a first fire incident – after 6 years numbers were at 78% of pre-burn levels – a second fire after 6 years could devastate the population long-term. Modelling showed that a full recovery of the population could take up to 30 years. (Bradshaw and Bradshaw, 2017)
Frequent controlled burns in a wider area may not only lead to species decline and finally extinction (Morrison et al, 1996) but also to an increase in introduced species such as foxes.
Controlled burns should therefore be considerate of the location of threatened species to reduce the threat to biodiversity while protecting assets. (Ager et al, 2007, Cary et al, 2009)
Fire is usually claimed to be a natural component of Australian ecosystems but particularly our fauna is obviously ill-equipped to cope with fire regimes as they are currently implemented.
Also, in extreme heat and winds, tree crowns can catch fire regardless of the amount of leaf litter and surface fuel.
Vegetation biomass that has built up in high rainfall years dries out after the rains have stopped. Planned burning can facilitate weed invasion (Keeley, 2006) and will deliver the fuel for the next intensive fires.
Increased temperatures as projected for Western Australia will a have significant impact on flora and fauna but predictions are very difficult to make as everything is connected. Water availability is reduced, climate-sensitive species will decline and the overall food web will be affected. (Enright et al, 2012)
There will be winners and losers of the changes (Low, 2002) but prediction would require not only good understanding of the impacts of climate change but also of the ecology of those species at risk.
Monitoring and evaluation and adaptive management in the way that future actions are modified in light of any new evidence seem rare. A lack of fauna monitoring is a recurring criticism throughout the literature and usually funding shortcomings are given as the reason.
Planning, implementation, monitoring, evaluation and modification according to findings are the pillars of adaptive management but all emphasis is placed on the first 2 components (Lindenmayer and Burgman, 2005) which limits the chance for insights.
Even an only perceived increase in threat levels will likely lead to an escalation in the use of prescribed burning – in extent and frequency. A level of fire control that could potentially deliver safety for assets would require very frequent removal of ground level fuels over large areas (Morrison et al, 1996) – the equivalent to an ecological disaster.
Also, communities are not only at risk from major fires but also from thick toxic smoke from prescribed burns, resulting in low air quality, pollution and associated health problems (and costs) as well as additional tonnes of carbon dioxide released into the atmosphere and exacerbating climate change.
There is a risk to road users and tourism and industries such as wine can be detrimentally affected.
Fire is a highly emotional topic which polarises the community and environmentalists are even occasionally accused of endangering the public. However, instead of spreading fear and threatening with fines if irrational fuel hazard reduction notices are not followed, we should engage the community in mindful discussions.
We should also remember that the majority of fires in populated areas are caused by humans either deliberately or accidentally. Rates of human ignitions are correlated with population density (Keeley and Fotheringham, 2001) and are expected to increase in step with expected population growth trends. (Cary et al, 2012) There must be more efficient ways to deal with arsonists than to beat them to it.
