Fire and weeds

Weed encroachment

Some grasses that have been introduced into native pastures in northern Australia, such as mission grass and gamba grass have the potential to cause problems as weeds in the tropical savannas. They increase the risk of intense late-season fires because they dry out later in the year than native grasses and are more productive, thus increasing the fire fuel loads.

Lack of regular burning on cattle properties in the tropical savannas has also probably been a key factor in the establishment of introduced shrubs—notably rubber vine, prickly acacia, mesquite and chinee apple—over wide areas. It has also allowed the widespread development of thickets of some native shrubs. These exotic and native woody weeds displace pasture and make mustering increasingly difficult and expensive, presenting a major challenge to the pastoral industry in some regions.

Burning rubber vine: an effective control Photo: CSIRO

Fire to manage weeds

Fire offers the best hope for managing the problem. Research in the Victoria River District of the Northern Territory shows that burning, with a frequency determined by seasonal and local factors, can be effective in managing the native woody weeds there. While fires seldom kill the plants, they can burn away most of the wood and suppress sucker development. In Queensland, research has shown that one or two fires in a 10-year period may be sufficient to reduce rubber vine populations, keep the plant at tolerable densities, and reduce the probability of it spreading further.