Bushfires flicker at the edges of the Australian dream; they are the scourge and spectacle of the summertime. One fire ecologist argues that as the planet warms, we’re likely to see more frequent and more persistent fires than ever before.

Bushfires enjoy an ambiguous standing in the Australian psyche. They are respected as part of the natural order of things in our tinder-box landscapes, yet they are also a scourge, chasing people from their homes, swallowing property and lives. One scientist believes we’re going to have to be much smarter about this animate element. He says that in addition to warmer days, rising waters and parched earth, climate change will also lead to many more bushfires than we’ve experienced in the past.

Dr Geoff Cary is a fire ecologist at the Fenner School of Environment and Society at ANU. When explaining what it is that he does, one term crops up with regularity: fire regime. This describes the frequency and intensity of bushfires in a particular area over a period of time.
The concept of fire regimes was pioneered by Dr Malcolm Gill – now a visiting fellow at the Fenner School – in the mid-1970s. Gill pointed out the importance of understanding the interval between fires, the intensity of the blazes and the seasons in which those fires occur. Since then, some researchers have sought out patterns of vegetation change in areas routinely burned. Other scientists have attempted manipulative experiments, studying the effects of deliberately ignited blazes in a controlled area over long periods of time. Both of these efforts have tended to concentrate on the ecological effects of bushfires.

Cary says there has been much less study about what drives fire regime patterns in the first place. “We have a good understanding at the continental scale, but we don’t have a long history of mapped fires to draw on. That’s something we’d love to have, and it’s led on to a lot of the work we’ve done here at the Fenner School.”

The desire to learn more about the patterns and causes of fire regimes led Cary and his colleagues to develop FIRESCAPE. This process-based computer model allows users to test the relationships between factors including fuel loads, fire behaviour, weather, ignition likelihood, and suppression capacity. This last term refers to the ability of humans to extinguish fires where and when desired. From out of these equations it’s possible to build up a picture of fire regimes across complex landscapes. The model has since been tested with data from the Sydney basin, the ACT, southwestern Tasmania, Central Australia, and Montana. Leaving the US case study aside, Cary said the work builds up a picture of patterns in fire regime over a continuum of terrains and vegetation types, and over periods up to 100 years in length.
“The way that we would test the model would be to run it in those landscapes with the current climate – and our current understanding of fuel and vegetation dynamics and the relationship to fire spread – and compare to the number of different-sized fires that you would get over a period.

“You can highlight areas of the landscape that are likely to have shorter intervals between fires. They are the ones that have a higher probability of having fires in the next few years. But whether it happens or not largely depends on the weather. What we’re averaging is the results over much longer simulations.”

The results achieved with FIRESCAPE are based on probabilities, which means it’s not yet possible to point to any given point on the map and say with certainty that there will be a fire there next January, for example. But the model can provide some future insights in the longer term, which means Cary and his colleagues have been able to look at what might happen to fire regimes as the planet’s temperature rises. The outlook is alarming.

“As the globe warms, the interval between fires is likely to become shorter, the intensity of fires is likely to increase,” Cary says. “But I think it’s not the intensity of fires that you see at the very high intensity end of the spectrum – the type of thing you see on the news reports – it’s the other end: how often does it go out, or how easy is it to put out when it’s small. A fire that is not put out when it’s small, or one that doesn’t extinguish overnight, really becomes an ignition point for the next day. If that continues, you’re more and more likely to run into severe weather that will occur under current weather or climate change.”

He’s not painting a picture of massive fires burning with demonic intensity, but Cary is pointing to the likelihood of more frequent and more persistent bushfires. He and his colleagues estimate that there could be up to a 50 per cent reduction in the interval between fires, with a significant climate change in the ACT region by about 2070. And it’s not just FIRESCAPE that predicts this. In order to test the accuracy of the model, the researchers took tools of similar intent from the US, Canada, Europe and Australia. They then systematically studied the effects of climate change on fire regimes in diverse settings.

“We introduced a three and a half degree increase in temperature, which is about the middle of what we might expect,” Cary says. “We also increased rainfall by a fifth, and we decreased rainfall by a fifth, as it’s uncertain how global warming will influence precipitation. The interesting thing was that four out of five of those models responded in the same way: with increased areas burned in the study areas irrespective of whether they were wetter or drier. That gave us consensus across the models.” In other words, Cary is confident that a warmer planet will lead to more persistent and intense bushfires in forested systems around the world.
According to Cary, variations in the fire regime can have far-reaching consequences for plant species and the animals that depend on them. Take Banksia ericifolia, or Heath-leaved Banksia, which is killed by fire. It doesn’t resprout like many eucalypts do. It also doesn’t have a soil-stored seed bank, so all of the individuals in the species exist as seedlings after a fire. It takes in the order of five to seven years to produce enough seeds to guarantee the survival of the next generation. If the interval between fires is repeatedly shorter than five to seven years, the species faces local extinction.

“B. ericifolia is what we’d call a dominant canopy species. The loss of that species, and three or four others that respond in the same way to fires, results in a very different vegetation community, which has implications for habitat and productivity for the birds and small mammals who rely on the production of nectar.”

Cary says that, on average, just under a third of plant species in forested plant communities are obligate-seeding species, plants like the Heath-leaved Banksia that can’t resprout but instead rely on seedling regeneration after a fire. Some of these do have stored seed banks, which means they can survive with shorter intervals between fires over a longer period. But even the most resilient plant species will eventually rely on seedlings for generational change, so the frequency and intensity of fires are very important factors.

As fires occur more and more often, it’s going to become much more difficult to extinguish the lower intensity fires. If they’re not dealt with quickly, the likelihood is that the blazes will remain in the landscape for longer periods, which increases the chances that they will still be burning when severe weather occurs. Faced with this prospect, Cary argues that emergency services and other fire management personnel would be best to focus on rapid responses, extinguishing hot spots while they are still relatively small. The fire ecologist says he does not dismiss other forms of fire control, such as prescribed burning and the creation of containment lines around large fires. Rather, he sees these as part of a coordinated strategy that has early and rapid response as its major component. But none of these measures will prevent fires altogether, which means people will need to think more about where they want to live.
“There is no doubt that fires, particularly high intensity ones, are scary,” Cary says. “The noise, the lack of visibility and the potential damage to people and property is no doubt a scary phenomenon.

“Fire is a part of the natural ecosystem in Australia and it has been for a long time. We’re afraid of fires destroying our property, and that has occurred ever since we started building in the path of fires that have been occurring for a long time.

“Australians are becoming and need to become more thoughtful about how they interact with the landscape. For example, thinking about where we position our assets in the landscape. This is becoming more common. An example is in NSW, where the Rural Fire Service has a say about where you can place a building on any property in bushfire prone land.

“That’s starting to recognise the fact that fires will occur: they’re not going to be prevented by fire management agencies. We see that time and time again. We need to be more thoughtful about where we build our assets, how we maintain our properties during fire seasons.
“Ultimately it’s a risk trade off. We like to live at the edge of places like Canberra, adjacent to very fire prone areas. People are making a choice, because the benefits of living there outweigh the fear factor.”

^^

ANU Reporter 
Spring 2007