Fire in grassy places 2

While many Aussie grasslands and grassy woodlands occur where their presence could be predicted by climate and landscape characteristics, this is not always the case. Some grassy patches are found in environments that can grow rainforest. In these patches, it is likely that Aboriginal people used fire, over thousands of years, to keep closed forest at bay.

Places where these grassy patches have been formally documented by western science include the Bunya Mountains north of Toowooomba in south-east Queensland (where they’re called ‘balds’), inside the Big Scrub rainforest in north-eastern NSW (‘grasses’), and in north-west Tasmania. Similar patches occurred around Dorrigo (eg Killungoodie Grassland Plain).

The disappearing balds of the Bunya Mountains, south-east Queensland. The photos of the bush were taken in 1993 (top) and 2013 (bottom). In each you can see woody plants encroaching into the grassy 'bald'. The Queensland Parks and Wildlife sign explains the origins and conservation value of the balds, and the importance of managing them with fire. There were once over 100 balds in the Bunya Mountains, which were a gathering-place for Aboriginal clans.

In the ranges of northern NSW and south-east Queensland, grassy forests occur in a matrix with rainforest. Without frequent fire in the grassy understorey, rainforest rapidly takes over. This is a story I know very well, as I have been part of a recovery team trying to save grassy habitat for the Eastern Bristlebird. Read about it here.

In eastern Australia, most of these fabulous grassy places adjacent to rainforest are no more. As with other grasslands, settlers rapidly took over. In some places, such as the Big Scrub, the surrounding rainforest has been cleared, leaving a profoundly altered landscape. Elsewhere, including in the Bunya Mountains, north-west Tasmania, and the Border Ranges, grassy patches have been, or are being, overwhelmed by rainforest.

Still, while there’s life there’s hope, and in some places people are working to save remaining grassy patches, including Dorrobbee Grass in northern NSW, the Bunya balds in Queensland, and montane grassland in Tasmania.

Woody plant expansion into grassy vegetation is also happening in other parts of Australia eg in tall grassy forests adjacent to rainforest to the west of the Great Divide in North Queensland, in North Queensland’s Iron Range, near Ocean Grove in Victoria, and on other continents (Africa, North America, South America).

Two views from Dorrobbee Grass, Dunoon, northern NSW. This was one of many 'grasses' located on hilltops in the Big Scrub rainforest. Local indigenous people are once again using fire to care for this patch.

The transition from grassland to rainforest represents one end of a spectrum in terms of potential for change in the absence of fire. Some grasslands and grassy woodlands, while not being prone to a complete biome shift, can change from grassy to shrubby. I encountered this in the grassy woodland I studied for my PhD, Western Sydney’s Cumberland Plain Woodland. Here, a single native shrub species (Blackthorn) dominated long-unburnt sites to the detriment of the primary grass species (Kangaroo Grass), other shrub species, and some herbs. A similar scenario has been documented in once-grassy places in other parts of Australia and around the world (see box above). These over-abundant native species aren’t bad, in some (but not all) cases they are an integral part of the landscape. However it is possible to have too much of a good thing, particularly when the whole character of an ecosystem is changed, and other ecosystem elements are affected. Aboriginal fire practitioner Victor Steffensen talks about using fire to encourage these species to move ‘back to their own country’, and that makes sense to me.

The potential for grassy ecosystems to 'shrub up' in the absence of regular burns is greater in places that are wetter, warmer, and where soils are more fertile. Other factors that may hasten the process include increased CO2, which may ‘fertilise’ woody plants, allowing them to more readily outcompete grasses. Overgrazing can weaken grasses, allowing woody species to establish more easily. In grassy forests, logging of old growth eucalypts may advantage shrubs (eg lantana), particularly if machinery disturbs the soil.

All the more reason to get the right fire happening in grassy places, I reckon. In the woodlands I studied for my PhD, frequent fire maintained a healthy Kangaroo Grass understorey, despite all my study sites having been exposed to logging, grazing and of course, increased CO2.

Two sides of the road, in hilly country north of Woodenbong, NSW. The grassy forest is lightly grazed farmland, burnt regularly to produce 'green pick' for cattle. The shrubby forest is managed for timber, and has been without fire for a long time. Its eucalypts are suffering from die-back. Whether lack of appropriate fire is a cause of dieback is hotly debated - personally I think it is. The smooth-barked eucalypt is probably Sydney Blue Gum (Eucalyptus saligna).

While we’re on controversial topics, might climate-change-fueled intense fires reverse this trend, pushing ‘shrubbed-up’ forest back to open grassy forest, or even creating open grassy ecosystems where rainforest stood under Aboriginal management? I think it’s highly unlikely. Reasons include the surprising resilience of rainforest species to fire, and a lack of persistent seedbanks amongst native grasses (so once they're gone, they won't come back without help). And as outlined on this page, the trend both in Australia and worldwide is in the opposite direction.

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