Ian Mannix
Cosmos newsroom
Australia’s precious Gondwanan forests are drying out. Even the rainforests are burning now.
“Forest flammability,” says Ross Peacock of the NSW National Parks and Wildlife Service (NPWS), “is usually measured in the terms of chemistry, morphology, leaf size, and particularly high moisture content, and shaded understories, so that they were generally assumed to be difficult to ignite.”
But they do.
“In fact, the old timers called them ‘litter fires’ because all they did was burn the litter load, which was maybe 10 centimetres deep.”
But then the temperate rainforest in Victoria’s east Gippsland burnt in the Black Tuesday fires of 2009; the old-growth forests of NSW northern tablelands burnt in the Black Summer of 2019, and that same year fires got into Tasmania’s south-west wilderness.
Peacock and other fire scientists are scrambling now to understand rainforest fires, and, in the face of inevitability, trying to identify the high-value components of a forest and new ways to protect that.
He had been preparing seemingly all his life for forest fires. He’d studied ecology at the University of Tasmania; attended the post-mortem for the 2009 Black Tuesday fires, and knew the signs to look for.
“Someone said as soon as the (water) outputs from those catchment areas hit that critically low level, that was a warning sign that the deep profile fuels had dried to the extent that when the fire ignited, it was going to be incredibly challenging for the Victorian firefighters to contain.”
By November 2019, when bushfires took hold of NSW, Peacock had been in place as chief fire scientist at NPWS for six years. He had acquired more than 60 years of data and since 2013 had been establishing new data collection equipment deep in the forests.
“I was watching, with enormous amount of concern, the line scans showing the fires entering some of my research sites,” he recalls. “As soon as I could get out onto the fire ground (within about a week and a half), we realised the fire had entered these long-term monitoring sites.
“And we started measuring the impacts of those fires. In all cases, we found fire scars in the trees that had burned so there had been previous fires in these stands. We also found counterintuitively, the most susceptible trees to damage and collapse were the large ones. Counterintuitive because generally, the larger trees are considered more robust; they’ve got large buttresses, they’ve got thicker bark.
“But what was happening was very large rainforest trees have significant buttress hollows in them and cavities, and they fill up with dry leaf material, and they ignite.
Peacock says that the loss of these very large old trees is significant, not only because it’s known that a rainforest microclimate is maintained by the canopy, but that for these higher elevation forests, the canopies are a source of substrate for literally hundreds of species of plants that grow on or closer to soil level.
“And when we undertook surveys of those, we were finding species that were undescribed and some that were only thought to be on Lord Howe Island, or New Zealand, and we’re finding them on the mainland.”
“We also found, interestingly, examples of canopies igniting. So in the canopy these large moss beds just completely cover the branches; they’ve become so dry that embers are igniting the canopy. So the fire was being propagated not along the ground, but from spot fires entering the canopy.”
But as NSW was engulfed by wildfires, the rainforests stood proud, says Peacock.
“While there was some ignition in the rainforest, they did incredibly well in not carrying large fires. Most of the fires are very small, 20 to 30 metres or so.”
“But it is also quite significant that if one large tree collapses it will take three to 10 trees down with it. We’ve also been looking at the regeneration process because generally rainforest there’s little or no canopy-stored seed and little or no soil-stored seed available postfire. They largely rely on coppicing from the buttress or surface roots.”
Old trees have also captured the focus of Professor of Pryrogeography at the University of Tasmania, David Bowman, who seems always to be “just returning” from the World Heritage areas. He had four field trips in the first four months of 2023.
Bowman was the lead author of a paper in Ecosystem Collapse and Climate Change outlining the impact of wildfires in the Tasmanian Wilderness World Heritage Area concluding: “Such impacts raise the question of whether the TWWHA should be formally recognised as a world heritage property at risk from climate change-driven fires.”
Bowman’s recent research has culminated in a recommendation to undertake scoping works for a systematic “Monitoring, Evaluation and Reporting” system for all Australia’s Gondwana rainforests to track trends in World Heritage outstanding values or criteria.
In 2022 he had a letter published in Nature on management interventions to protect the world’s giant trees, including those in Tasmania:
Giant eucalypts in Tasmania’s temperate rainforest can be more than 100 metres tall. They are of enormous conservation value, representing just a small fraction of the tree population that existed before 200 years of clearing and logging. Wildfires in 2003, 2010, 2012, 2016 and 2019, mostly ignited by lightning storms under drought conditions, destroyed 17 of the world’s 33 largest eucalypts.
Now he says he’s seen more “alarming” evidence of decline: “You go down the Franklin [River] and pretty well every section there are dead Nothofagus trees.”
“It’s kind of an alarming thing that it’s becoming noticeable, not like an epidemic, but you go down each section there’s a dead tree, a dead tree, dead tree. Like it’s probably one in 10,000. But it means you’re seeing Nothofagus trees dying.”
Nothofagus is a genus of 43 species collectively known as the southern beech; Nothofagus cunninghamii, known in Tasmania as the myrtle beech, is one of the giants and ecological dominants of temperate forests in Tasmania.
“Gondwanan beech tree,” says Bowman. “It’s a keystone rainforest species. Basically, they’re winking out. So we’ve got this whole story of dryness. What you see is dieback. You see, particularly, the Nothofagus trees struggling.
“But the thing that’s most striking, is that under logs, moss beds, they’re dry. Back in the day, you put your hand on the log, and it would be like the biggest sponge in the world. Now they’re dry. You look under logs, the soil is bone dry. And the key thing is, the [watercourses] are low.
“It’s kind of an alarming thing that it’s becoming noticeable, not like an epidemic, but you go down each section there’s a dead tree, a dead tree, dead tree. Like it’s probably one in 10,000. But it means you’re seeing Nothofagus trees dying.”
Professor David Bowman
“Rivers are low, so often what you see, unless it’s raining, is a drying landscape which is receptive to lightning or fire.”
Bowman says Tasmanian weather patterns are being altered by climate change, and the westerlies that bring drenching and frequent rain to the island’s west coast have gone missing.
“When you get a lot of westerlies that’s when the rain-bearing winds come. At the moment the westerlies are massively displaced. Here in Hobart, I don’t think we’ve had a westerly wind, maybe half a day of westerly winds. Back in the olden days the roaring forties would blow for weeks. They were the rain-bearing winds.”
There is no way to avoid the sparks. Attention turns to mitigation: Bowman says everything should be tried to suppress fire in the landscape.
The CSIRO began cloud seeding experiments in South Australia, Victoria and Tasmania in 1947.
The Tasmanian government hydroelectric power authority, ‘The Hydro’, began cloud seeding in 1964, but suspended the operation in June 2016 in the face of concerns from west coast residents that it was creating too much rain. Although The Hydro says cloud seeding is effective and that precipitation is enhanced by up to 8% per ‘seeded’ month in the target areas, the socio-economic impact was worrying residents:
“Frequent rain and cloud cover adds to the need for heating and gives a gloomy atmosphere that can contribute to depression and inactivity. These factors were noted in the Health Needs Assessment report. Perhaps symptomatic of the malaise implied by this is the high concentration of gaming machines. In 2004 there were 75 gaming machines at 7 licensed premises in the West Coast or 14.7 machines per 1000 population. This compares to 4.7 machines per 1000 population in the state as a whole in the same year.”
Steve Leonard, Senior Ecologist and Fire Science Coordinator at the Conservation Science Section of Natural Resources and Environment Tasmania, provides technical advice on fire management to the Tasmanian Parks and Wildlife Service (PWS).
He sees a shift in climatic patterns. “And even the years where we have got kind of average rainfall, the rainfall has tended to be very episodic. So we get a massive downpour – you get 10% of the annual rainfall in a day. Which means you can have several months of below-average rainfall within a year where the annual average is reasonable. So, it’s certainly very apparent to us that western Tasmania has been very dry over the last few years, which is obviously a concern.”
“It’s like a lot of things to do with climate change. It’s panning out more or less exactly how it was predicted.”
Leonard is another who undertakes frequent field trips. “Every time you go out there, it’s like, ‘Wow, it’s really dry’. You know, bushwalking through areas that you would expect to come out with mud up to your knees, you come out with dusty boots. So that’s pretty profound.”
“The rainforest and the palaeo endemic vegetation in western Tasmania is highly fire sensitive. If it’s burnt it can become locally extinct from a single fire. That kind of vegetation typically occurs in places which over evolutionary timeframes fire has been very rare. That’s how it’s managed to hang on – it’s been in fireproof refugia.
“But what we’re seeing now is that those areas are becoming dry enough to burn much more frequently. So in 2016, we saw the fire in the northern part of the Tasmanian World Heritage Area up around Lake Mackenzie, burning fairly substantial areas of pencil pine woodland. It’s kind of a double whammy of more fire, and the fire is more likely to get into the places we really don’t want it to. And that’s kind of the nub of the problem.”
Leonard says the fire management regime is “trying to get more planned burning into the landscape”, guided by detailed values protection plans. How do they define what is high value and what can burn?
“By high value, I mean, the fire-sensitive palaeo endemic vegetation, so pencil pine, King Billy pine, deciduous beech. Some of the other alpine vegetation types which are not well adapted to fire, the things we need to protect.”
Pencil pine (Athrotaxis cupressoides) is endemic to Tasmania and is found at higher elevations in higher rainfall areas. Trees can live for more than 1000 years and are notably slow growing – only about 12mm in diameter a year. King Billy (or King William) pine (Athrotaxis selaginoides) is another long-lived conifer endemic to highland Tasmania.
Leonard says pre-emptive planned burning in the surrounding landscape is one measure taken to reduce the threat. Others include a 500m sprinkler line installed in 2019 to protect King Billy pine forest at Lake Rona and the Denison Range, in western Tasmania.
“And that stopped that King Billy pine forest from being burnt,” Leonard says. “That’s part of the arsenal now.”
He highlights the importance of alternatives to a planned burning regime: “The dilemma of course, with planned burning, is that often you can’t do as much as you want because weather is against you. In a period of drought, it’s really hard to do planned burning.”
Leonard says one of the major improvements in fire management over the past few years is lightning and hotspot detection, which has enabled firefighters to get onto ignitions quickly.
“Kind of in real time [it] pops up on someone’s screen, out in some remote area. And they’ll deploy aircraft to investigate and manage that very quickly. That kind of rapid response has been ramped up significantly over the last few years and appears to be very successful.”
Bowman believes that cultural fire regimes should be investigated, suggesting that Aboriginal people “for 30,000 years” burned the landscape to create paths. Leonard agrees.
“It’s really hard for us to know what burning in the pre-European era was like, in Tasmania,” he says. “I don’t think anyone really has a clear picture of that. Certainly, a lot if not all of Tasmania, was managed intensively using fire by Aboriginal people. We recognise that that is a cultural landscape and the mosaic of vegetation types we see today is at least partly the product of that long history of fire use.
“So that’s certainly part of the picture. And certainly there are moves afoot by [PWS] to bring cultural burning back.
In the face of the climate crisis no-one expects fire will be kept out of the rainforests. So how do they identify critical areas for protection?
“The areas we’ve focused on is where you’ve got a concentration of values – so it might be a stand of several different fire sensitive communities,” Leonard says. “A lot of these areas are also fairly high profile as bushwalking destinations. People care about them.
“The things we really focus on are those communities, where there’s a potential that if they are burned, they’re locally extinct. One fire can mean that they’re gone from that landscape forever. And so those things are really the top of the heap in terms of what we focus on.”