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Grazing, fire and science

The following Opinion article was published (slightly edited) in Stock and Land on the 12/10/06, in response to a request from Neil Barraclough for information on any studies into the relationship between cattle grazing and fire in the Victorian Alps.

Neil Barraclough asks (S&L 5/10/06) if there is any real science showing that cattle grazing didn't reduce the intensity of the 2003 fires in the alpine area. The answer is "yes".

It's a good question though, because it cuts to the core of what might be the most important issue in conservation management in Victoria over the next few decades: the need for greatly increased research and monitoring.

It seems obvious that because cattle eat grass, and grass burns, then if we have less grass we'll have less fire. But it's the job of scientists to test the obvious (otherwise we'd still think we're on a flat earth instead of spinning, improbably, on a free-floating sphere).

So shortly after the 2003 fire, a group of scientists set about testing the "grazing reduces blazing" theory.

The authors of the study are all scientists with solid reputations: Dick Williams (CSIRO Sustainable Ecosystems), Carl-Henrik Wahren (Centre for Applied Alpine Ecology at La Trobe University), Ross Bradstock (Biodiversity Conservation Science, NSW Dept. of Environment and Conservation), and Warren Mueller (CSIRO Mathematical and Information Sciences).

Measurements were taken in over 400 locations through 100 square kilometres of the Bogong High Plains, in both grazed and ungrazed areas. They surveyed fire occurrence and intensity in alpine heathland (shrubby places) and in open heath (shrubs in grassland), and fire occurrence in grasslands. It wasn't possible to reliably measure fire intensity in grassland after the fire had passed.

The results were interesting.

Heathlands, at 87% burnt, were by far the most flammable, open heaths less at 59%, while only 13% of the grassland areas were burnt. Importantly, there was no significant difference between these results for grazed and ungrazed areas.

So what about severity.

By measuring the size of twigs left on shrubs (small twigs remaining means a less severe burn), it was clear that there was no significant difference between grazed and ungrazed areas of heathland, even in open heathland where cattle had grazed grasses in between and around the shrubs.

Essentially, in alpine areas, fire is mainly spread by flammable shrubs, which cattle don't eat.

In some ways, there are no surprises here.

The 2003 fire blazed through almost every alpine grazing licence area in its path. The notable exception was the Pretty Valley area of the Bogong High Plains, the largest grassy plains area in the Victorian Alps. The only comparable place in Australia is in Kosciuszko National Park, but even larger areas of grassland remained unburnt there, even though they had not been grazed for decades.

And mapping of the fire extent and intensity for the Caledonia fire in the southern section of the park shows that every bit of grazing licence area within the path of the fire went up in flames. That fire stopped at the Avon Wilderness - but mainly because it rained.

Fire behaves differently in different forest types, and areas that have been burnt recover differently in different locations, different altitudes and different soil types. That's why we should be doing more measuring and recording, both before and for many years after control burns, and natural burns. In Justice Stretton's 1946 Royal Commission into forest grazing, he blamed the extent of shrub growth on the cattlemen's habit of burning to promote grasses: "With each burning, the growth of scrub was stimulated so that it successfully contended with the grass for possession of the mountain sides."

It would be very useful to have had reliable and thorough measurements of the effects of the cattlemen's legendary burning, but the idea of carefully recording ecological processes is relatively new. By comparison, our understanding of the way the human body operates, for example, is vast.

With a climate crisis upon us, Victoria's natural areas are going to be placed under unprecedented stress, and our vulnerability to fire will increase. We will need all the knowledge we can muster.

The Victorian National Parks Association is asking for greatly boosted research and monitoring of our natural systems, right across the landscape. That way we, and future generations, might be able to secure safety for those who live near natural areas, and we might also secure the long-term survival of Victoria's remarkable natural heritage.