Fire as a weed and pasture management tool

Fire can be used effectively in rangeland livestock systems to control woody regrowth, promote desirable pasture species, suppress weeds and unpalatable species and maintain pasture health and quality - improving feed conversion efficiency.  

Fire encourages desirable plant species by:

• reducing the competitive advantage of undesirable species (eg wiregrass)
• encouraging some desirable species (eg black speargrass)
• suppressing and reducing weed species (eg rubbervine and lantana)
• removing rank or decaying pasture, especially in under-utilised areas

Use fire to spread grazing pressure across a paddock and minimise the effects of patch grazing. 

Animals prefer to patch-graze fresh nutritious regrowth from previously grazed patches, rather than old rank material. If patch grazing persists, desirable species and ground cover levels decline. 

Regular burning can spread grazing pressure, reducing the likelihood of overgrazed patches forming.

Key principles

• Burning during the dry season when pasture is dormant has little impact on pastures.
• Perennial grass tussocks regenerate from protected buds near or below the soil surface, so are sensitive to heavy grazing immediately after being burnt.
• Burning during the growing season can harm some grasses.
• Annual grasses regenerate from seed buried and protected in the soil.

Fire and tree management

A planned burning regime can be used to manage the composition (species mix) and structure (density and height) of trees and shrubs across grazing land. 

Prescribed burning suppresses the growth of new plants (or regrowth), and controls woodland thickening.

The effectiveness of using fire to manage trees and shrubs depends on the species present. Fire can soften hard seed and stimulate huge germinations of wattles, while other species can be completely killed.

The frequency, timing and intensity of fires determine the effect on plants and woodland structure. Use fire to manage the structure of tree regrowth and shrubs less than 2 metres high. If regrowth is greater than 2m, top-kill and subsequent regrowth control is difficult.

A grass fuel load of at least 1500 kg DM/ha is needed to carry an effective fire. Fuel loads of 2000 kg DM/ha or more are recommended to suppress woody regrowth.

Is there enough grass to burn?

The optimum fire frequency for controlling tree and shrub species in regions with 500-600 mm of annual rainfall is 3–5 years. 

In these areas less frequent burning allows the plants to grow more than 2m in height, making them more resistant to fire control. Many tree species, including most eucalypts, survive by regrowing from the base of the plant. Control of regrowth with fire is higher when plants are smaller.