Research Letter #17

BURN AND LEARN: FUEL MANAGEMENT IN WEEDY WOODLANDS

The use of low intensity fires for fuel management is an attractive option when areas are large, rocky, steep, forested or densely covered in shrubs. In some cases fire may be the only option (apart from doing nothing!). Also, fuel management using fire can be integrated, in the appropriate circumstances, with fire regimes desirable for ecological reasons.

Near the urban interface in Canberra, hill reserves for conservation and recreation are usually small in area, rocky and clothed by grassy woodlands dominated by eucalypts. Pine plantations, farms and native forests occur in places at the interface but this Letter is about grassy woodlands. These woodlands have had a history of grazing by domestic animals (possibly for 150 years), a history reflected in the abundance of pasture plants and weeds of agriculture.

At the urban interface there are naturally concerns about fuel quantities and fuel condition. In any area, let alone reserves set aside for conservation and recreation (in the case considered here), fuel-reduction methods need to be considered in the light of the management objectives for the area. If there are conflicts with general objectives, a strategic area can be set aside with the specific objective of maintaining low fuel loads.

The small area on which I want to focus was fuel reduced using prescribed fire. The chosen area was listed in a properly constituted, publicly exposed, plan. Burning was done ‘by the book’. The grassy fuel, with a strong component of Wild Oats (Avena sp.), was not fully cured but was completely removed by the fire. A few of the mature eucalypts in the area caught alight during the fire but quickly became the focus of attention of fire crews.

After the fire a number of native plants were emergent but the overwhelming early response was from the weed Patterson’s Curse (Echium plantagineum). The strength of the response seemed to be unexpected; it prompted a spraying with herbicide. Later in the season this area became dominated by Wild Oats. A curiosity evident soon after the fire was that the germination of Patterson’s Curse was greatest in the wheel ruts of the fire-fighting vehicles thereby creating green stripes across the blackened fire ground.

Other observations were:

  1. the fuel-reduction effect lasted one season;
  2. while only a small number of trees died or collapsed as the result of the fire, the proportion affected was high; and,
  3. germination followed by spraying reduced the Patterson’s Curse seed bank and increased the time for the return time for dense populations of this weed.

Fuel-reduction fires in weed-infested areas of conservation reserves offer an opportunity for the enhancement of conservation value. To maximize conservation outcomes in such areas, planning for weed control, and the artificial enhancement of the density of native species, would be prudent. It is perhaps obvious that weeds already present, especially woody ones, can be controlled as they regenerate or germinate. Knowing what other species are going to proliferate after burning would be helpful. However, knowing what is going to proliferate after fire is not always obvious. Clues can be obtained by observing what is already present but such observations may need to be supplemented by a knowledge of which species constitute the soil-seed pool and their abundances. The composition of the soil-seed pool may be gauged by germination of seeds from soil samples or from the burning responses of plants in sample areas treated a year or two in advance of the main event.

These observations are in no way the results of the ‘gilt-edged science’ we might prefer but, none-the-less, they may be useful in view of the general lack of knowledge about fire effects in weedy conservation areas. Whoever we are – scientists, farmers, reserve managers, fire fighters, land carers – we can make every burning experience a learning experience!

Malcolm Gill
13 January 2000