The Burning Planet: Changing fire regimes across the world

By Kate Bongiovanni

Both natural and human-instigated fires have long been part of Australia’s landscape and climate, particularly during the Holocene, an era of about 10,000 years defined by mild, stable climatic conditions favourable to the rise of a global human civilisation.

However, many assert we are now living in a new era, the Anthropocene, where human activities are the prevailing influence on Earth’s climate and have impacted the geologic record. No species has ever caused such rapid climatic changes.

Fire patterns are linked to climate conditions, and thus have been undergoing changes in recent times. It is imperative to understand these changes in order to more effectively forecast fires and manage them for both human safety and the preservation of biodiversity.

The rapid climatic changes of the Anthropocene are widely discussed and debated in the scientific community, and in the media. However, research on the effects of fire on Earth’s climate is still developing. Studies on pyrodiversity, the varying effects of fire on our environment and local ecologies, are still in their early stages. Dr Luke Kelly, Senior Lecturer and Centenary Research Fellow from the School of Ecosystem and Forest Sciences at the University of Melbourne, works with a group of colleagues to change this picture. Luke is conducting field research on animal and plant responses to fire and climate change.

Scientific research from field studies such as Luke’s are just one source of Australia’s store of wisdom on fire; the knowledge base of Australia's First Nations' peoples extends back many thousands of years. Many other Australians also have first-hand, intergenerational experience of bush fires. Over the last hundred years or so, government agencies, community organisations, private industries and traditional custodians have added to our trove of knowledge about fire, how the use of fire is changing and strategies to manage fire cycles.

While many ecosystems in Australia depend on fire to flourish, they require specific kinds of fires, differing in intensity and timing with local germination and breeding cycles. Therefore, changes to fire regimes can lead to the demise of species and ecosystems. For example, the Alpine Ash forests of south-east Australia’s central highlands are experiencing increasedfrequency of fire, resulting in the trees being unable to sow their seeds as they are incinerated prior to maturity. If this continues unabated, the alpine ash is likely to be wiped out of the region entirely and threatened with extinction.

This is not an exclusively Australian story. Similar transformations and threats to the persistence of forests are in evidence in the western USA, where bigger, hotter fires are devastating tree species in iconic areas such as Yellowstone National Park. The devastating fires in the Amazon Rainforest over recent months presents an alarming example of changing conditions. In the last year, there have been over 50,000 outbreaks of fire, causing severe environmental degradation and loss of ecological value, unlike in the Australian bush landscape where fire is a normal and necessary element for the survival of an adapted ecosystem. The Amazon rainforest environments do not require fire and do not traditionally burn. Instead, these fires have been deliberately lit to speed land clearing for large-scale farming, and have been exacerbated by hotter, drier climate conditions.

Meanwhile, Spain’s reforestation projects have been in motion in Pont de la Train since the mid-1900s. These schemes promote tree growth and provide habitat for various animals; however, they also cause a higher risk of fire outbreak, particularly with fewer people located in rural areas to monitor and manage the forests. In addition to researching Australian flora and fauna, Luke is part of a fellowship at the Fire Research Centre in Catalonia, Spain, where he collected data in the area and analysed it to investigate the effect of different variables, such as wetness and temperature, on fire probability. Luke found that many of these factors were simply overridden by climate influences; extreme, sustained high temperatures are the dominant condition for wildfires.

Yet the increase in fires and extension of fire seasons (the number of hot, windy days conducive to starting and maintaining fires) is not a ubiquitous global phenomenon. Where forests are cleared to make way for farmland, fire fuel is reduced along with the likelihood of fires, along with the destruction of habitats for plant and animal communities, which is clearly a poor outcome for biodiversity.

Other negative impacts on biodiversity from changing fire regimes are found in the vulnerable periods after fires, when introduced animals prey on native animals. Luke’s research surveys the effects of fire in Australian ecosystems by examining the ningaui species in the Murray-Mallee region. Ningaui are small, native marsupials, first discovered by scientists in Victoria in 1977. Luke and his team use bucket traps to safely catch various ningaui species at about 300 sites in arid areas in order to investigate what the marsupials require from their habitats. The data is used to create models, incorporating climatic influences, soil composition and other land use changes to discover the kind of pyrodiversity ningaui require and, from this, determine which locations they will most likely thrive in. This research can be used to devise a management plan for the persistence of ningaui and similar small species to prevent their extinction. This research is important, as changes to fire regimes has thus far led to the extinction of thirteen Australian marsupial species.

However, the size of the fire, duration, intensity and time interval between fires all have important implications for the conservation of biodiversity, and can be factored in as a management response to counter the degree to which wildfires can devastate forest ecologies. The importance of fire severity is demonstrated by the black-backed woodpecker of North America. Following a big hot fire, the burnt forest hosts a prevalence of worms which the woodpecker relies on for food. Changing fire severity is challenging the woodpecker’s survival. In Australia, the survival of the Hooker banksia tree has been tested by variations in the time interval between fires. This banksia is very sensitive to fire time intervals, requiring fires every 10-30 years to avoid expiry.

This knowledge helps us set objectives for the desired pyrodiversity in different forest ecologies. Different fire regimes can support a range of different species at different times. For instance, a forest recovering from a fire in the last decade can encourage the coexistence of multiple species through a more diverse expression of tree size, species and expression, whereas a mature forest can facilitate the persistence of a narrower, and different, range of species. Essentially, biodiversity requires a fire regime to manage forest and habitat diversity in ecologies adapted to fire. As we take action on pyrodiversity we need to consider the kind of burning we want to promote “mosaic” forests.

Once we have set our objectives, we then need to think about how we can achieve them. For example, could we target our fire suppression priorities during wildfires to include threatened ecological assets? Should we have planned burnings? And if so, how should these be carried out, and by whom? Careful planning and research needs to be done when performing prescribed burning to prevent risks to human safety, forests and extinction of species in the burned region. The Royal Commission into bushfires following Black Saturday in 2009 examined the effects of fire on human safety and biodiversity, and the influence of preventative measures such as prescribed burning.New research models simulating different kinds of burning can help us figure out the “optimal” burning. The model simulations can factor in different scales and different shapes (like strip burning) of fires and allow us to examine their effects on landscapes and biodiversity. The Murray Sunset National Park is one such area where large strips of forest are burnt to reduce fire fuel in the area and hence prevent future fires from spreading.

As well as prescribed burning, there are many other ways to mitigate disruptions to ecosystems from fire. The efforts of “ecological engineers” could play a role in reducing fire activity. When small animals such as bilbies and bandicoots make their burrows, they modify the ground and water flow in a way that potentially reduces fire fuel and limits the spread of fire. An additional way of inhibiting the span of a fire is by using “green firebreaks,” strips of low flammability vegetation with limited fire risk that can act as barriers between species with higher flammability while still providing vital habitat support.

The disruption to the long-standing, traditional management of forests and fire by Indigenous communities following European colonisation have led to a lack of small, recurrent, low-intensity burns. This is causing an increase in the large, climate-driven fires that inhibit pyrodiversity. However, the re-emergence of traditional management of fire could alleviate this effect. Similarly, in the USA, too much fire suppression has led to uncontrollable “mega fires”. Perhaps simply allowing bushfires to burn in moderate conditions could be beneficial in preventing larger, more destructive fires in peak conditions. It’s a difficult proposition.

Another area of investigation is the adaptation of species in zones with high fire occurrence versus zones with low occurrence. It raises the question of how fast plants can evolve and how we can use evolutionary knowledge strategically in order to aid translocations and adaptations.²

^‍Fire science is helping us understand changing fire regimes and our changing climate. This understanding is imperative in an increasingly warmer world with elevated green-house gas emissions. We must aim to reduce these emissions to mitigate climate change and further changes in pyrodiversity. However, the climate is not the only thing changing in our world today. People are becoming more disconnected from landscapes and each other. In order to adapt and survive, we, as individuals, need to come together in our local communities, with governments and researchers, to share our knowledge and learn from each other. Collaboration and research will continue to expand the number of actions available to promote the optimal pyrodiversity.

‍References:

1. Kelly, L. T., et al. (2020). Fire and biodiversity in the Anthropocene. Science, 370(6519). doi.org/10.1126/science.abb0355
2. Gomez-Gonzalez, S., et al. (2011). Anthropogenic fire drives the evolution of seed traits. Proceedings of the National Academy of Sciences, 108(46), 18743–18747. doi.org/10.1073/pnas.1108863108

Video

Luke Kelly's prsented to the Royal Society of Victoria on 26 September, 2019 with a presentation titled "Pyrodiversity: Fire and Wildlife in the Anthropocene," which can be viewed on Facebook at https://www.facebook.com/share/v/6xdvGvMjDSiJEX2w/ .