“This is the Giant Stinger tree – avoid it”. Work place health and safety now out of the way, I could then get on with introducing my students to Australia’s forests.
In Queensland’s O’Reilly’s/Lamington Park I began my student classes with a walk down the road. There happened to be a convenient juvenile ‘Giant stinger’ tree growing a few minutes along the way. Roads are light-gaps, which are just the places that stingers usually start their life in. Although they can grow to be forest giants, it’s the young ones – with leaves at body/face-height, that you have to watch out for. They are covered in hairs which can inject a truly horrific neurotoxin. Touch wood (so to say), I’ve never had that particular pleasure, but my tutors had and vividly recalled it.
From the road we turned off down one of the several National Park trails towards Python Rock. A few hundred metres in there was a nice place to stop, where I would ask the students to look about and see how many distinct types of tree trunk they could distinguish. We could easily see the twisted dark trunks of ebony wood, the fluted pale trunks of yellow hollywood, the reddish trunks of rosewood looking like cracked old mosaic, the buttressed booyongs, and of course the strangler figs. This is ‘core’ Australian rainforest – the real McCoy. It’s a vegetation that does not require fire to survive, is typically killed by it and indeed, actively seems to keep it out by being cool and moist which quickly decomposes leaves and branches (aka ‘fire fuel’). The plants here can grow in the shade, or the small light gaps of fallen trees. They don’t need the light of the open canopy formed by fires in the way that other Australian forests do – the ‘flame-forests’ (see Bowman 2000a for details). The object of this first exercise was for the students to feel a little more at home in the forest. To see that the forest wasn’t just ‘trees’, but a community with ‘individuals’ that they could get familiar with.
We would walk further along the track on until we came across an enormous tree – one with obvious black fire damage (see the featured image). Stopping for a look around, we could see that we were standing on a forest boundary, that within a few paces, we had crossed over. Behind us was the rainforest we had just walked through, but off to our right, it was typical aussi ‘flame-forest’ (in the parlance of David Bowman, 2000b), with eucalypt trees over fine-leaved shrubs and grass. Directly behind the burnt tree, was a solid wall of green rainforest. We had seen these sharp forest boundaries before – on the bus trip up from Brisbane. For the most part, along the highway, then winding up the mountain, its that open flame-forest. Then there was a point where our bus instantly seemed to pass into a dark tunnel – the first bit of rainforest. We quickly exited that, back into open eucalypt trees over grass, then finally, back into dark rainforest. These sharp boundaries are maintained by fire. It burns repeatedly in the flame-forest, but stops (except in extreme circumstances) at the rainforest.
The location of these boundaries across a landscape is a long-term equilibrium, set by the interaction of several agents. Topography, which can channel or deflect fire, is a super important one. In the O’Reilly’s/Lamington area, topography tends to reflect the underlying geology. Nutrient-rich basalt tends to favour rainforest and gives rise to smoother topography, whereas lower-nutrient rhyolite tend to favour flame-forest and can create steep cliffs. The fires themselves reinforce the boundaries. Flammable plants will tend to regenerate quickly after a fire, and the fires burn off accumulated nutrients favouring flame forest over rainforest. And that’s a problem with ‘hazard reduction burning’. It works – by reducing undergrowth and ground cover, under normal circumstances, it can reduce the risk of big, canopy fires. But it’s also a treadmill, locking in the status-quo.
From that fire boundary, the track turned back into what certainly looked like genuine rainforest. However, as we walked along it, the alert would notice huge trees, but often having large scars at the base of their trunks. These were obviously old fire scars – the result of fires repeatedly burning against them. What was going on here? We thought we were in a rainforest – which don’t burn. The answer is that these fire scars are clearly old, and that the trees that they are present on, called ‘box-brushes’, are no longer regenerating. These trees clearly once existed in, and were totally at home within, a much more open forest – one with a grassy understory and fine-leaved shrubs, through which small fires regularly burnt – just like what we had seen back at the boundary. But at some time, those fires had stopped burning, the boundary had stepped back a few hundred meters, and rainforest was taking over what had been flame-forest. Under the shadier rainforest canopy, the seed of those box brushes would quickly die and eventually, the giants themselves would die of old-age, and crash to the rainforest floor. From then on, there would be no evidence that this had ever been a flame-forest. There was a certainly a boundary where my class stood – just not a horizontal boundary, but a vertical one. The place of these giant trees in the ecosystem has even led to questions about how we define rainforest (Tng et al. 2012).
So what might have caused the fires to stop burning in here and when did the rainforest start to take over? Whenever I’ve walked the trails in this area I’ve always kept an eye out for the sawn-logs that National Parks leave when they clear up a fallen tree. I’ve looked at them for growth rings to get an idea of how old the rainforest trees are. Unfortunately, the rings in these forests are too vague to use as an annual record. They are probably responding more to periods of dry and wet. However, it’s a fair guess that the relict ‘giant’ trees date back several centuries. Putting a date to when the fires stopped and the rainforest began to grow around them is shaky ground, but I’d tell my classes that a century or two seemed reasonable.
At this point I would ask what was the big event in Australia around that long ago? Perhaps with some thoroughly shameless coaching, we would get to the answer that I was looking for – European arrival, dispossession of the Aborigines and the disruption of their ‘cultural’ burning (It is argued that this is a more gentle form of deliberate burning than ‘hazard reduction burning). If fire became less frequent, it is possible that seedling rainforest trees around the fringes of the rainforest had a chance to grow, rather than be periodically burnt, and could eventually decrease the local flammability, forcing the fire-boundary back to a new location. Disruption of Aboriginal burning practices sounds like a reasonable hypothesis, and has been proposed by earlier observers for south-eastern Australia (e.g. Fraser and Vickery, 1939). However, there might be other explanations. A slight increase in rainfall might also decrease fires and give the edge to rainforests.
However, in northern, tropical Australia, rainforest is also clearly expanding into fire-forest (e.g. Russell-Smith et al, 2004). In fact, so much so that in some places, it’s regarded as a problem. In the monsoonal tropics there has been more cultural continuity with the present, and consequently, it’s less likely that a let-up in Aboriginal cultural burning lies behind this. Some researchers studying the phenomena in this region also discount changes in rainfall and argue that the cause is fertilisation from increasing amounts of atmospheric carbon dioxide (Bowman et al. 2010). Whether the same explanation applies to O’Reillys/Lamington, is currently unknown.
Eventually the path would lead us to the edge of a huge scarp and a spectacular view. It’s one of those dramatic bits of landscape which owes its existence to the rhyolite. We were back into ‘flame-forests here, with plenty of evidence of recent fires, including several tall ‘grass trees’, whose trunks recorded a long history of fires. The fire boundary in this area was beautifully illustrated one year when a fire began on the slopes a few kilometers below Python Rock. National Parks closed access to the region, but it was just a typical quietly-burning bush fire and (for educational purposes of course) we could still get to see it in the private O’Reilly areas. However, that night, it was was predicted to overrun the end of Castle Crag, directly opposite Python Rock.
I wanted to see if I could take a night photograph of the fire burning its way up the valley from the high vantage point of Castle Crag. So after dark, I stole away, and made the clandestine walk entirely by moonlight. Directly below O’Reillys I passed the hollow ‘Wishing Tree’ (damned spooky in the dead of night) – another relict of flame-forest being overtaken by rainforest.
From there I climbed the far valley and entered the National Park, passing a sign to the effect that because the area was closed, anyone caught past here would get a four-figure fine. Keeping my torch off, I headed out along the narrow ridge, and finally arrived at Castle Crag. Standing at this point always gives me the feeling of being in the cockpit of a jet aircraft. On this evening, I found myself looking directly down into the bush-fire, the hot air rising up into my face. I set up my tripod with my brand new digital camera. It was the first such camera I had ever had (primitive by today’s standards and with a far lower resolution than my 35 mm film camera), and I was still getting used to its knobs, dials and buttons. When the shot looked right – I pressed the ‘shutter’ … and the bloody flash went off. Whereupon I high-tailed it back to O’Reillys before someone appeared to fine me. Unfortunately the fantastic shot that I would have got with my ‘normal’ camera, loaded with slow transparency film, was forever lost. That night the fire burned slowly over the ridge where I had been and near Python Rock, it burnt up to the old boundary, and, as predicted, stopped there.
My student classes would also involve a day hike up to the ‘Crater Rim’ (a tale of another adventure up in that region can be found here). A few kilometers up from the National Park headquarters there are some truly giant Box Brushes. Once again, many of them have fire scars and judging from the apparent age of the rainforest which they are now within -the fires may well have been from ‘cultural burning’. The box brushes are associated with a group of truly ancient ‘Antarctic Beech’ – far outside their normal range of the ridge tops. This patch of beeches, somewhat paradoxically, probably also result from long—ago fires. So in at least three places, it seems clear the flame-forest boundary has ‘stepped back’ some tens or hundred of meters from the core rainforest at O’Reillys/Lamington. It may have done this in several leaps in different places, but the end result is the same.
These events of long-ago seem to have helped extend the ‘buffer’ of fire-retarding rainforest around the Lamington National Park and O’Reillys Guest House areas. As far as I know, there wasn’t such a buffer around the Binnaburra Lodge (feel free to correct me on this), which burnt in the September 2019 fires. Trying to exclude fire from the wetter Australian fire-forests until they eventually turn in to rainforests would seem like a smart thing to do. There are plenty of places where the climate would allow them to become rainforest. However, on such a broad scale, this generally seems to be a chimera. Between the monsoon tropics, where the process seems to be happening of its own accord, and perhaps places like wettest Tasmania, where there may be a realistic hope of excluding fire long enough, there are big areas where eventually, one way or another, the fire will come. On the other hand, if you insist on living in Eucalyptus forest, or even, as it seems, anywhere in critical parts of south-eastern Australia, it makes really good sense to try and grow a fire-retarding buffer of rainforest trees around your home.
Just a few students (guys) would take the warning about the Giant Stinger tree as a challenge (there were gals about). Now I’ve been told that it is possible that by taking a firm grasp of a stinger leaf, you might get away, unscathed. But I’ve never had the nerve to test this tale. The one time I did very firmly grasp the giant stingers slightly less toxic relative (I didn’t recognise it), I spent the night with my hand outside my sleeping bag. But hey, here’s a video (thanks Robbie, for alerting me to this) of a …. considered, deliberate encounter with a Giant Stinger tree. Skip to 4:28 if you want to get an idea of how bad they can be….. (Despite the title, it’s in English)
Bowman, D.M.J.S. 2000a. Australian Rainforests: Islands of Green in a Land of Fire. Cambridge University Press, Cambridge.
Bowman, D.M.J.S. 2000b. Rainforests and flame forests: the Great Australian forest dichotomy. Australian Geographical Studies, 38:327-331.
Bowman, D.M.J.S., Murphy, B.P., and Banfai, D.S. 2010. Has global environmental change caused monsoon rainforests to expand in the Australian monsoon tropics? Landscape Ecology 25:1247-1260 DOI: 10.1007/s10980-010-9496-8.
Fraser, L., and Vickery, J.W. 1939. The ecology of the upper Williams River and Barrington Tops District. III. The eucalypt forests and general discussion. Proceedings of the Linnean Society of New South Wales, 64:1-33.
Russell-Smith J, Stanton PJ, Whitehead PJ, Edwards A. 2004.Rain forest invasion of eucalypt-dominated woodland savanna, Iron Range, north-eastern Australia I. Successional processes.Journal of Biogeography, 31: 1293–1303.
Tng, D.Y.P., Williamson, G.J., Jordan, G.J., and Bowman, D.M.J.S. 2012. Giant eucalypts–globally unique fire-adapted rain-forest trees? New Phytologist, 196:1001–1014 doi: 10.1111/j.1469-8137.2012.04359.