CSIRO and its partners tested the widely held belief that ‘grazing reduces blazing’ in the Alpine environment of south-eastern Australia after the extensive fires of January 2003.
What defines an alpine landscape?
Australian alpine landscapes are tree-less areas in the upper mountainous regions of the south-east. Although these landscapes are rare, covering less than 1 per cent of the continent, they have important soil, water, biodiversity and cultural values.
Prominent examples of alpine landscapes are the Snowy Mountains of New South Wales, the Bogong High Plains in Victoria, and the Central Highlands of Tasmania.
Alpine landscape flammability
The main vegetation communities of alpine landscapes are grasslands, herb fields, heathlands and sphagnum bogs. Closed heathlands are the most flammable parts of the alpine landscape and are found on steeper slopes, where the rate of fire spread is naturally faster. Grasslands, on the other hand, occur on gentle slopes and the grass fuels are less flammable than the shrub fuels.
This history of fire in alpine environments
Fire in alpine environments has been infrequent, with many decades between fires. This is because the combinations of events that are needed for alpine country to burn – an ignition source, prolonged drought, and severe fire weather – occur only several times per century in these regions. Such extensive fires have occurred in alpine country in 1939, 2003 and 2006.
Aboriginal people are known to have used fire in the high country, but the extent, frequency and impact on alpine vegetation is unknown.
Short and long-term impacts of fire on alpine biodiversity values
The immediate impact of fire is to remove the protective blanket of vegetation that covers the delicate alpine soils. The vegetation has a very strong capacity to regenerate, through re-sprouting and reseeding, but it takes time and protection of the soil post-fire is highly dependent upon regeneration.
Complete regeneration and restoration of biodiversity values after fire is likely to take 3–5 years in grasslands, about 10 years in heathlands, and may take many decades in sphagnum bogs.
Cattle grazing and alpine ecology
Cattle prefer to graze the open grassy communities, where there are more palatable plants, and they tend to avoid the closed heath communities. Thus, any fuel reduction effect as a result of cattle grazing is occurring in the least flammable part of the landscape, and not where the propagating fuels (dense shrubs) are located.
Long-term data shows that cattle have very little or no impact on shrub cover (and hence fuel loads) in the heaths. The heaths are therefore likely to burn more severely than the grasslands, and fire severity within heaths – all other things being equal – will be similar whether they are grazed or not.
Does grazing reduce blazing in alpine landscapes?
"Alpine grazing reduces blazing" is a widely and strongly held view, in both rural and urban regions, concerning fire in Australia’s high country. Whether cattle reduce the incidence and intensity of fire by grazing the vegetation, and hence reducing fuel, has been a central question for decades in the debate about land management in the high country. The available bio-physical evidence, based on long-term ecological research and the behaviour and impacts of the wide-spread 2003 fires, suggests it does not.
CSIRO’s study of the 2003 alpine fires
Widespread fires burned tens of thousands of hectares of alpine country in both Victoria and New South Wales in 2003. Not all alpine areas burned, but significant areas of all of the major alpine vegetation types were.
Preliminary surveys of burning patterns were collected on Victoria’s Bogong High Plains soon after the fires, using a variety of indices of fire extent and severity. About 100 km of transect lines were walked, across all the major regions. Measurements on whether country had burned were taken every 50–500 metres, and environmental data on vegetation types, slope and aspect were collected. A measure of fire severity – minimum twig diameter – was recorded on a sample of dominant shrubs in patches that were burned.
Statistical analysis of the data showed that there was no significant difference between grazed and ungrazed country in the proportion of the landscape that burned, in both grassland and heathland. There was no significant effect of grazing on the severity of burning in heathland.
Whatever effects livestock grazing may have on fuels in alpine landscapes, they are likely to be highly localised, with such effects unlikely to translate into landscape-scale modifications of fire behaviour.
Despite their extent and severity, the 2003 fires don't appear to have had disastrous impacts on the plants and animals of the alpine region. Most plant species had regenerated, either by seed or vegetatively, within one year of the fires.
The fires burnt extensive areas of the core habitat (closed heathland) of a number of vulnerable small mammals and some species experienced substantial falls in populations while others experienced substantial increases. Unburnt patches of vegetation are critical to faunal recovery from fire. The flora and fauna of alpine Australia are highly resilient to infrequent, large, intense fires such as those of 1939 and 2003.
These findings support the conclusions of the Esplin Report of the Victorian Government Inquiry into the 2003 bushfires (Chapter 8), that the incidence of fire was not reduced by high country grazing.
Principal scientists involved in the collaborative study
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Dr Henrik Wahren (La Trobe University)
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Professor Ross Bradstock (University of Wollongong)
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Dr John Morgan (La Trobe University)
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Mr Warren Müller (CSIRO)
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Dr Ken Green (NSW National Parks and Wildlife Service)
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Dr Keith McDougall (NSW Department of Environment and Climate Change)
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Mr Dean Heinze (Tasmanian Department of Primary Industries and Water)
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