Shrubland an woodland communities, typically dominated by a range of Eucalyptus species, are widespread throughout the 300 to 500 mm rainfall zone of southern Western Australia; this area lies to the east of the main belt of Jarrah (Eucalyptus marginata) forest. The region experiences a Mediterranean climate with a protracted summer drought, and dry lightning storms are common during the summer months. The annual fire season extends from October to April, but fires may even occur in the winter months during drought years.
The Western Australian Department of Conservation and Land Management (CALM) is responsible for the management of extensive tracts of shrubland and woodland, mostly contained in national parks and nature reserves. Nature conservation and low-impact recreation are the predominant activities within these reserves. Considerable areas also remain as state-owned lands not yet vested in a land management agency. Most reserves are remnants surrounded by land cleared for agriculture, principally cereal cropping and sheep grazing. There are a number of large reserves ranging in size from 100,000 ha to over 500,000 ha, together with many smaller areas.
Fire management is a key issue in shrubland and woodland reserves. Uncontrolled fires may pose a threat to life, property and community assets in more densely settled areas, and may also be incompatible with some nature conservation objectives, where retention of sizeable areas of long unburned vegetation is considered important for the conservation of species with restricted occurrence. One of the key objectives for fire management, therefore, is to minimize the likelihood of entire reserves being burnt at the one time. Important constraints on fire management include the remote and often inaccessible nature of the terrain, the scarcity of surface water, and the limited resources available for use in fire suppression. Organisations involved in planning and implementing fire management on these lands include CALM, the Western Australian Bush Fires Board and bush fire brigades comprised of volunteers from local communities.
Fire behaviour is also an important consideration. The discontinuous nature of many of the fuel types results in a situation where fires behave erratically, with sudden changes in spread rate and intensity. During dry summer conditions, fires may spread at up to 8 km/h with associated fireline intensities of 20,000 kW/m, making direct attack impossible.
Extensive lightning-caused fires have been a feature of the past two summers. In December 1989, three simultaneous lightning-caused fires burnt 123,000 ha in the Fitzgerald River National Park. Most of this area was burnt during the initial ten hour period of fire activity which was characterized by extreme fire danger conditions. During the summer of 1990/91 fires started by a series of lightning strikes burnt some 750,000 ha of woodland over a period of several months, in some cases affecting areas burnt by previous lightning fires only eight years before. Fortunately, these fires burnt in remote locations and did not cause any significant property damage.
CALM is undertaking research to improve the understanding of fire behaviour and ecological effects in shrubland and woodland communities . A major study has been established in shrubland at the Stirling Range National Park, and to date sixteen experimental fires have been conducted on plots (4 ha each) over a range of weather conditions. Litter fuel moisture content appears to be a key factor determining threshold conditions for sustained fire spread. Case studies from significant wildfires have provided valuable fire behaviour data for more extreme weather conditions where conventional experimentation has not been possible. Ecological studies are focussing on the response of plants and small vertebrates to fires in spring and autumn seasons.
Patch burning to create a mosaic of fuel ages within large reserves has considerable potential to achieve both fuel reduction and habitat management objectives, and reduce the opportunity for extensive uncontrolled fires. Recent trials have confirmed that mosaic of burnt and unburned strips can be achieved using ignition from fixed-wing aircraft. Information from research studies is being used to develop reliable prescriptions for burning, and as a basis for determining fire regimes appropriate for meet particular management objectives.
From: Lachlan McCaw Address: Department of Conservation and Land Management Research Centre AUS-Manjimup, Western Australia 6258