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Fire and Australian alpine environments
The Issue
Australian alpine landscapes are the treeless areas at and above treeline in the mountainous regions of the southeast. Prominent examples are the Snowy Mountains of NSW, the Bogong High Plains in Victoria, and the Central Highlands of Tasmania. These landscapes are rare, occupying less than 1% of the area of the continent. Despite this rarity, alpine landscapes have important soil, water, biodiversity and cultural values.
How did the 2003 fires affect alpine landscapes? What has happened in the past?
The 2003 fires burnt large tracts (tens of thousands of hectares) of alpine country in both Victoria and NSW. Not all alpine areas burnt, but significant areas of all of the major alpine vegetation types - grasslands, herbfields, heathlands and sphagnum bogs - burnt.
Historically, 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. The last time such extensive fire occurred in alpine country was 1939. Aboriginal people are known to have used the high country, but the extent, frequency and impact of Aboriginal burning on alpine vegetation is unknown.
Short and long term impacts of the fires on alpine biodiversity values
The immediate impact of fire is to remove the protective blanket of vegetation that covers the delicate alpine soils, and protection of the soil post-fire is highly dependent upon the natural processes of regeneration. The vegetation has a very strong capacity to regenerate, through resprouting and reseeding, but it takes time. Regeneration to pre-fire state is likely to take 3-5 years in grasslands, about 10 years in heathlands, and may take many decades in sphagnum bogs.
CSIRO Research
Does alpine grazing reduce blazing?
The available bio-physical evidence suggests it does not. Indeed, the recent Esplin Report of the Victorian Government Inquiry into the 2003 bushfires (Chapter 8) concluded that the incidence of fire was not reduced by high country grazing.
All landscapes, and the various components of landscapes, are differentially flammable; alpine landscapes are no exception. The most flammable parts of the alpine landscape are the closed heathlands on the steeper slopes, where 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. Cattle prefer to graze the open grassy communities, where there are the most 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 show 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 that are grazed or not.
Preliminary surveys of burning patterns, collected on the Bogong High Plains soon after the 2003 fires, using a variety of indices of fire extent and severity, support these predictions. About 80 km of transect lines were walked, across all the major regions of the Bogong High Plains, and measurements taken every 50-500 m on whether country had burnt, and environmental data such as vegetation type, slope and aspect. Twig diameter (a measure of fire severity) was recorded on a sample of the dominant shrubs in patches that were burnt. Statistical analysis of the data showed that there was no significant difference between grazed and ungrazed country in the proportion of the landscape burnt, or in the severity of burning in those areas that were burnt.
Alpine grazing reduces blazing: A landscape test of a widely held hypothesis
Richard J. WilliamsA,E, Carl-Henrik WahrenB, Ross A. BradstockC and Warren J. MüllerD
"Alpine grazing reduces blazing" is a widely and strongly held view, in both rural and urban settings, concerning the effects of livestock grazing on fuels, and therefore fire behaviour and impact, in Australia’s high country landscapes. As a test of this hypothesis, we examined the patterns of burning across the alpine (treeless) landscapes of the Bogong High Plains in Victoria, following the extensive fires of January 2003. Data were collected from multiple transects, each 3-5 km long, with survey points located randomly at either 50, 200 or 500 m intervals along each transect. The transects traversed the major regions of the Bogong High Plains, both grazed and ungrazed. At each point, we recorded whether the point was burnt or unburnt, the vegetation type (closed heathland, open heathland, grassland or herbfield), the estimated pre-fire shrub cover, slope, aspect, and a GPS location. At burnt heathland sites, we recorded the minimum twig diameter (an aposteriori measure of fire severity) in a sample of common shrubs. In total, there were approximately 80 km of transect lines, 360 survey points and 3700 twig measurements, with sample points equally distributed across grazed and ungrazed country. The occurrence of fire (i.e. burnt or unburnt) in grazed and ungrazed areas was analysed by logistic regression; the variation in twig diameters by ANOVA. Fire occurrence was determined primarily by vegetation type and pre-fire shrub cover. The deceasing order of flammability of plant communities, as measured by the percentage of country burnt, was closed heath (87% burnt) open heath (59% burnt), grassland (12% burnt) and snow patch herbfield (unburnt). With respect to both fire occurrence and severity, there was no detectable effect of grazing; p-values of the grazing effect and associated 2-way grazing interactions (e.g. grazing x vegetation type; grazing x slope) were invariably >0.2. The lack of a detectable grazing effect is consistent with previous research on shrub dynamics (little or no grazing effect on long term- abundance of taller shrubs), diet and behaviour of cattle (herbs and dwarf shrubs preferred to tall shrubs; closed heath vegetation generally avoided), and fuel flammability (shrubs more flammable than grass). 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.
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